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Thread: Front brake upgrade - Planning process

  1. #1
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    Front brake upgrade - Planning process

    Fellas,

    Im in the process of nutting out a brake upgrade for the Gemini and for fairly obvious reasons, I want to ensure I get this right, both from a component mix-and-match perspective, and in terms of the basic engineering behind it. At the moment I’m just concentrating on the front brake setup; the rear disc upgrade is a pretty well travelled path so I don’t really need to re-invent the wheel in this area, and its pointless discussing brake master cylinders and required pedal ratios until the disc/caliper side of the equation is finalized. I would appreciate input and or suggestions as effectively, being able to stop is kind of a life-or-death sort of deal. Apologies for the wall of text and numbers.

    For those wondering why I haven’t taken the readily available options, there are a few draw backs to these existing upgrades which make them unsuitable for my application, which ill go into below.
    First, as a comparision, the standard Gemini setup:



    Fixed rotor bolted to back of cast iron hub, cast iron twin piston caliper. Non vented rotor with pcd of 4 x 88 drilled into it to bolt onto hub, disc mounted hub-centric. Dimensions as follows:

    Disc DBA006
    Diam: 240mm
    Thickness: 10mm
    Hat height: 47mm
    Centre bore: 68mm

    The first is the more common/off the shelf VT upgrade first done by Hoppers Stoppers and then copied by a billion other parts manufacturers. Gemini stub axle is retained, alloy hub bolted to it. VT disc then becomes full-floating, VT twin piston calipers are used. Ive ruled this particular swap out for the following reasons: Its ridiculously heavy, requires the caliper mounts be slotted to bolt to the Gemini stub axle which is a bit dodge in my eyes, the calipers themselves are ordinary, it reduces turning circle [lock-stop required to be welded to control arm] and it increases offset by 10mm PER SIDE. All of these are compromises I am not willing to accept.

    The second more commonly done conversion is to use either a Magna disc DBA425 with the Volvo Girling 4pot or an Audi disc [I believe its DBA806] with the same caliper. The issue I have with this swap is as follows: The Magna disc is close to ideal dimensionally, but differs in hat height by -2mm and centrebore by +1mm – essentially requiring a spacer to go between hub and disc to maintain disc position, and either requiring the disc to be non-hubcentric OR machining to hub/disc to allow a spigot ring/centering ring to be inserted. Audi disc has correct centre bore but is every so slightly off on hat height [-.8mm – probably not enough to worry about?]. My biggest concern is if using the Magna disc, the spacer between hub and disc, and the caliper choice – the Volvos weigh a fucking ton.
    Ive spent some time trawling the DBA online catalog to try and find a couple of discs that are as close as possible to the standard Gemini disc in hat height and centre bore, and have come up with a few possible alternatives. Ive then tried to match these to corresponding calipers. So….a few questions:

    -How critical is the hat height, keeping in mind its not a floating hub arrangement? I understand that a higher hat height would effectively put the disc OVER the steering knuckles etc and wouldnt work, and this could be solved by machining the hub mounting face to bring the disc further forward, but what about SHORTER hat heights? For eg, the Magna disc being 2mm shorter – Can this be left as is, with the +2mm added to the caliper bracket/adaptor to centre the caliper instead? Im thinking +/- 5mm would be the maximum here.

    -What is the concern/train of thought regarding multiple PCDs in a disc? Given the PCD of the hub [4 x 88] required to bolt the disc to hub, and the models that the potential donor discs are from, I don’t like my chances of being able to acquire said disc in a blank format. There would be no over-lap on stud holes given the PCD of the hub, so in the event of an originally 4stud PCD disc id be having it drilled at 45deg to the original pattern so that the holes are spaced central to original PCD. Bit trickier in 5stud obviously; is there a minimum distance between holes that should be aimed for? Im assuming that the concern is regarding cracking between holes drilled, but surely if the original PCD was plugged and the new PCD had more than 10mm between it and original holes, it should be ok?

    -How important is it that the disc remains hub-centric? A few of the possible discs have larger centre bores; definitely hub ring territory? And if so, what should the minimum thickness on this be – 2mm? Minimum measurement is kinda critical – if the recommended thickness for a hub ring is, say for arguments sake 4mm, implication is that either the hub or disc will need to get opened up if the c/b difference is 1mm [Magna is a good example again]

    -For discs with c/b smaller than hub, is it recommended to machine the hub OR the disc or a bit of both? For eg, DBA488 has a c/b of 64 – would I remove 4mm from disc c/b to slide over 68mm hub, or would I be best to remove 4mm from hub to fit 64mm disc?

    -Regarding calipers, there are a few Im considering dependant on disc dimensions. Id prefer to use an alloy 4pot, so in terms of OEM calipers that leaves Nissan Z32/Skyline, and FD/FC RX7 – did I miss any? Consdering WRX calipers also but they are cast iron and could be a bit heavy

    -The Wilwoods are getting popular in other conversions but how good are they in a predominantly street car application? Getting conflicting info about which calipers are actually available in dust booted applications – Wilwood website says not many, but strangely the images of their radial calipers appear to have dust boots despite not being listed as having them?

    -Is anyone aware of a single or twin piston alloy caliper for use on rear disc [listed a bit below? Wilwood has a few but refer to comments about lack of dustbooting [or at least, not being able to confirm dust boot application]. Rear disc setup is VN– VS disc and caliper – DBA016, 279mm diam and 10.5 thick. Calipers pretty chunky/heavy so if I could replace that with something lighter, itd be good.
    What im currently thinking is that given the cars relatively light weight [sub 1000kg] and intended use [mainly fast road/occasional track] I don’t need to overkill the brake setup. Its naturally aspirated so its not like its capable of ridiculous acceleration and speed so the disc doesn’t need to be too big. Any benefits of brake torque from going a larger disc would be lost given the relatively narrow rubber [195/50/R15] and lack of weight transfer. Im thinking 270-280mm disc is optimum for application – thoughts?

    That’s it…for now I guess.

    Cheers

    N-
    Last edited by F3ARED; 10-07-17 at 10:57 AM.

  2. #2
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    Quote Originally Posted by F3ARED View Post
    Fellas,

    Im in the process of nutting out a brake upgrade for the Gemini and for fairly obvious reasons, I want to ensure I get this right, both from a component mix-and-match perspective, and in terms of the basic engineering behind it. At the moment I’m just concentrating on the front brake setup; the rear disc upgrade is a pretty well travelled path so I don’t really need to re-invent the wheel in this area, and its pointless discussing brake master cylinders and required pedal ratios until the disc/caliper side of the equation is finalized. I would appreciate input and or suggestions as effectively, being able to stop is kind of a life-or-death sort of deal. Apologies for the wall of text and numbers.

    For those wondering why I haven’t taken the readily available options, there are a few draw backs to these existing upgrades which make them unsuitable for my application, which ill go into below.
    First, as a comparision, the standard Gemini setup:

    Your photo doesn't work, thanks photobucket you cunts.

    Quote Originally Posted by F3ARED View Post
    Fixed rotor bolted to back of cast iron hub, cast iron twin piston caliper. Non vented rotor with pcd of 4 x 88 drilled into it to bolt onto hub, disc mounted hub-centric. Dimensions as follows:

    Disc DBA006
    Diam: 240mm
    Thickness: 10mm
    Hat height: 47mm
    Centre bore: 68mm

    The first is the more common/off the shelf VT upgrade first done by Hoppers Stoppers and then copied by a billion other parts manufacturers. Gemini stub axle is retained, alloy hub bolted to it. VT disc then becomes full-floating, VT twin piston calipers are used. Ive ruled this particular swap out for the following reasons: Its ridiculously heavy, requires the caliper mounts be slotted to bolt to the Gemini stub axle which is a bit dodge in my eyes, the calipers themselves are ordinary, it reduces turning circle [lock-stop required to be welded to control arm] and it increases offset by 10mm PER SIDE. All of these are compromises I am not willing to accept.

    The second more commonly done conversion is to use either a Magna disc DBA425 with the Volvo Girling 4pot or an Audi disc [I believe its DBA806] with the same caliper. The issue I have with this swap is as follows: The Magna disc is close to ideal dimensionally, but differs in hat height by -2mm and centrebore by +1mm – essentially requiring a spacer to go between hub and disc to maintain disc position, and either requiring the disc to be non-hubcentric OR machining to hub/disc to allow a spigot ring/centering ring to be inserted. Audi disc has correct centre bore but is every so slightly off on hat height [-.8mm – probably not enough to worry about?]. My biggest concern is if using the Magna disc, the spacer between hub and disc, and the caliper choice – the Volvos weigh a fucking ton.
    Ive spent some time trawling the DBA online catalog to try and find a couple of discs that are as close as possible to the standard Gemini disc in hat height and centre bore, and have come up with a few possible alternatives. Ive then tried to match these to corresponding calipers. So….a few questions:

    -How critical is the hat height, keeping in mind its not a floating hub arrangement? I understand that a higher hat height would effectively put the disc OVER the steering knuckles etc and wouldnt work, and this could be solved by machining the hub mounting face to bring the disc further forward, but what about SHORTER hat heights? For eg, the Magna disc being 2mm shorter – Can this be left as is, with the +2mm added to the caliper bracket/adaptor to centre the caliper instead? Im thinking +/- 5mm would be the maximum here.
    Floating calipers by design give you a little more wiggle room with rotor location. You can also deal with hat heights that are a couple of mm too tall by skimmin the rotor mounting face.
    There's an aluminium version of the volvo caliper that was fitted to some BMW 7 series - they're around, but not common. Also look at Austin Princess calipers.
    Only issue you'll run into with shorter hat heights is clearance between the caliper and the wheel spokes.

    Quote Originally Posted by F3ARED View Post
    -What is the concern/train of thought regarding multiple PCDs in a disc? Given the PCD of the hub [4 x 88] required to bolt the disc to hub, and the models that the potential donor discs are from, I don’t like my chances of being able to acquire said disc in a blank format. There would be no over-lap on stud holes given the PCD of the hub, so in the event of an originally 4stud PCD disc id be having it drilled at 45deg to the original pattern so that the holes are spaced central to original PCD. Bit trickier in 5stud obviously; is there a minimum distance between holes that should be aimed for? Im assuming that the concern is regarding cracking between holes drilled, but surely if the original PCD was plugged and the new PCD had more than 10mm between it and original holes, it should be ok?
    No issue drilling a 4 bolt. Drilling a 5 bolt rotor for 4 bolt can get a bit ropey.

    Quote Originally Posted by F3ARED View Post
    -How important is it that the disc remains hub-centric? A few of the possible discs have larger centre bores; definitely hub ring territory? And if so, what should the minimum thickness on this be – 2mm? Minimum measurement is kinda critical – if the recommended thickness for a hub ring is, say for arguments sake 4mm, implication is that either the hub or disc will need to get opened up if the c/b difference is 1mm [Magna is a good example again]

    -For discs with c/b smaller than hub, is it recommended to machine the hub OR the disc or a bit of both? For eg, DBA488 has a c/b of 64 – would I remove 4mm from disc c/b to slide over 68mm hub, or would I be best to remove 4mm from hub to fit 64mm disc?
    I'd keep it hubcentric.
    Machine the discs to fit the hub. If you need to use a spacer, machine a chamfer on the disc and a lip on the spacer so it's held captive by the disc.

    Quote Originally Posted by F3ARED View Post
    -Regarding calipers, there are a few Im considering dependant on disc dimensions. Id prefer to use an alloy 4pot, so in terms of OEM calipers that leaves Nissan Z32/Skyline, and FD/FC RX7 – did I miss any? Consdering WRX calipers also but they are cast iron and could be a bit heavy

    -The Wilwoods are getting popular in other conversions but how good are they in a predominantly street car application? Getting conflicting info about which calipers are actually available in dust booted applications – Wilwood website says not many, but strangely the images of their radial calipers appear to have dust boots despite not being listed as having them?

    -Is anyone aware of a single or twin piston alloy caliper for use on rear disc [listed a bit below? Wilwood has a few but refer to comments about lack of dustbooting [or at least, not being able to confirm dust boot application]. Rear disc setup is VN– VS disc and caliper – DBA016, 279mm diam and 10.5 thick. Calipers pretty chunky/heavy so if I could replace that with something lighter, itd be good.
    What im currently thinking is that given the cars relatively light weight [sub 1000kg] and intended use [mainly fast road/occasional track] I don’t need to overkill the brake setup. Its naturally aspirated so its not like its capable of ridiculous acceleration and speed so the disc doesn’t need to be too big. Any benefits of brake torque from going a larger disc would be lost given the relatively narrow rubber [195/50/R15] and lack of weight transfer. Im thinking 270-280mm disc is optimum for application – thoughts?

    That’s it…for now I guess.

    Cheers

    N-
    Evo rear Brembo calipers are a twin piston opposed, use the same forging as the Brembo opposed caliper on the front of Alfa GTV6s/75s/90s. Doesn't have a handbrake mech incorporated in it though.
    There's a Willwood superlite fitment that's an almost exact swap for a Volvo 4 pot caliper (Or there used to be!) - not sure about dust seals though.
    "Where can we get hold of a Vincent Black Shadow?" "Whats that?" "A fantastic bike," I said. "The new model is something like two thousand cubic inches, developing two hundred brake-horsepower at four thousand revolutions per minute on a magnesium frame with two styrofoam seats and a total curb weight of exactly two hundred pounds."

  3. #3
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    RX7 caliper
    Biggest disc you can fit in the wheel to suit (slotted)
    Decent pads
    Machine hub to fit disc ... so when you need one to fit in a hurry a STD disc will without finding a machine shop to machine disc in a hurry on a Sunday before a track day.
    R32 rear caliper. DBA020 rear disc if your thinking 016's were a thing. Either way you're going to struggle with handbrake.
    Location Perth Western Australia

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    A few more thoughts:

    With increasing hat height, the rotor is moving inboard so make sure it's not going to foul on the end of the LCA or any other components under full bump.

    When selecting a replacement caliper, make sure you can get your desired pad compound to suit it.

    Are you going for looks or stopping power? You will get greatly improved stopping power just with a good pad compound and a vented rotor with good airflow.

    270 - 280mm diameter for a sub 1000kg car with not heaps of power will be fine, that's the spec of our track car ATM and it stops just fine. I'm not sure you will get much more rotor than that under a 15 inch wheel anyway.

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    Quote Originally Posted by dattoman1000 View Post
    RX7 caliper
    Biggest disc you can fit in the wheel to suit (slotted)
    Decent pads
    Machine hub to fit disc ... so when you need one to fit in a hurry a STD disc will without finding a machine shop to machine disc in a hurry on a Sunday before a track day.
    R32 rear caliper. DBA020 rear disc if your thinking 016's were a thing. Either way you're going to struggle with handbrake.
    ^ Just do this. I can't recall which disc we used but the RX7 calipers are light, easy to get and have a reasonable pad selection.
    Willwoods don't have dust boots and in my opinion the cheaper models aren't particularly good at the best of times. I'd say that for a street car you'd be better off looking at OEM brakes than aftermarket.
    Nissan R32/Z32/R33/R34 rears are hard to beat, the only downside is the internal handbrake issue.

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    Quote Originally Posted by dattoman1000 View Post
    Machine hub to fit disc ... so when you need one to fit in a hurry a STD disc will without finding a machine shop to machine disc in a hurry on a Sunday before a track day.
    Yeah, nah. Machining meat off the outside of the bearing carrier has the potential to end very poorly. He has to redrill the rotors anyway, so smashing a std disc on on a sunday isn't going to be a thing.

    Just remembered a mate used to use the RX7 calipers, and has done a couple of sets that are in use by others - they're a good thing.
    "Where can we get hold of a Vincent Black Shadow?" "Whats that?" "A fantastic bike," I said. "The new model is something like two thousand cubic inches, developing two hundred brake-horsepower at four thousand revolutions per minute on a magnesium frame with two styrofoam seats and a total curb weight of exactly two hundred pounds."

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    Quote Originally Posted by Gammaboy View Post
    Your photo doesn't work, thanks photobucket you cunts.


    Floating calipers by design give you a little more wiggle room with rotor location. You can also deal with hat heights that are a couple of mm too tall by skimmin the rotor mounting face.
    There's an aluminium version of the volvo caliper that was fitted to some BMW 7 series - they're around, but not common. Also look at Austin Princess calipers.
    Only issue you'll run into with shorter hat heights is clearance between the caliper and the wheel spokes.


    No issue drilling a 4 bolt. Drilling a 5 bolt rotor for 4 bolt can get a bit ropey.


    I'd keep it hubcentric.
    Machine the discs to fit the hub. If you need to use a spacer, machine a chamfer on the disc and a lip on the spacer so it's held captive by the disc.


    Evo rear Brembo calipers are a twin piston opposed, use the same forging as the Brembo opposed caliper on the front of Alfa GTV6s/75s/90s. Doesn't have a handbrake mech incorporated in it though.
    There's a Willwood superlite fitment that's an almost exact swap for a Volvo 4 pot caliper (Or there used to be!) - not sure about dust seals though.
    Should work now, sorted alternative hosting. Now to upload all my other photos and fix links….thanks Photobucket you bunch of cunts!

    Didn’t think to machine the face of the disc, ill keep that one in mind. Id like to avoid having to run a spacer between disc and hub but this is entirely dependent on disc selection. The problem is most of the discs that are close dimensionally are 5 x 114.3 or 5 x 112. Quick sketch on cad and I end up with ~4mm between 1 set of holes, the rest clear pretty decently if you rotate the PCDs the correct way. Surely that’s not enough to just leave the holes? Im hoping its ok with an interference plug in it.

    Any reason why to avoid machining the hub? Or is it just from a disc-needs-doing-anyway perspective and may as well do it all to disc?

    Had a quick look this morning, funnily enough I think the Evo calipers may actually be cheaper! Had a search for the Volvo/Wilwood but couldn’t find anything. Their website is a clusterfuck to search through unless you know EXACTLY what disc you want to use. Radial calipers look good/look like they have the dust seals….but don’t come up as an option for dust booted etc. Pain in the arse.

    Quote Originally Posted by dattoman1000 View Post
    RX7 caliper
    Biggest disc you can fit in the wheel to suit (slotted)
    Decent pads
    Machine hub to fit disc ... so when you need one to fit in a hurry a STD disc will without finding a machine shop to machine disc in a hurry on a Sunday before a track day.
    R32 rear caliper. DBA020 rear disc if your thinking 016's were a thing. Either way you're going to struggle with handbrake.
    Is there a difference between the FC and FD calipers? From what I can see they share the same pad, discs are same thickness but different diameter so one meant for an FD should work on a 280mm disc. Outside face of caliper body is different – FC is finned and has a knob/bump in middle of body where as FD just has MAZDA. Any reason to use one over the other?

    Like Gamma touched on lower down, unfortunately being able to swap discs easily is not an option given the fact that I will need to have a PCD drilled into the disc anyway. Im a bit concerned over just how much I can remove from which bit.

    Intention was to use DBA016; I had heard there was a vented Commodore rear rotor but couldn’t find it [admittedly ive mainly been searching for fronts] so part number helps immensely, thanks. Only .6 difference in hat height which wont matter/can be removed from face like Gamma suggested earlier.


    Quote Originally Posted by Sprinkles View Post
    A few more thoughts:

    With increasing hat height, the rotor is moving inboard so make sure it's not going to foul on the end of the LCA or any other components under full bump.

    When selecting a replacement caliper, make sure you can get your desired pad compound to suit it.

    Are you going for looks or stopping power? You will get greatly improved stopping power just with a good pad compound and a vented rotor with good airflow.

    270 - 280mm diameter for a sub 1000kg car with not heaps of power will be fine, that's the spec of our track car ATM and it stops just fine. I'm not sure you will get much more rotor than that under a 15 inch wheel anyway.
    Im conscious of moving the disc in/outboard, which is why Im trying so hard find a disc that will keep the standard hat height. Objective is to basically put together a brake package with good stopping power and good modulation. I realize the stopping power part of the equation is limited by tyre size/choice and modulation has more to do with the brake master setup [which ive gone nowhere near yet]. Looks aren’t a factor – the wheels I have make them almost entirely invisible anyway.
    What are you running on yours/what car is it if you don’t mind me asking? Ive been looking at MX5s and what they use as upgrades to hopefully give me a somewhat comparable baseline.


    Quote Originally Posted by Komdotkom View Post
    ^ Just do this. I can't recall which disc we used but the RX7 calipers are light, easy to get and have a reasonable pad selection.
    Willwoods don't have dust boots and in my opinion the cheaper models aren't particularly good at the best of times. I'd say that for a street car you'd be better off looking at OEM brakes than aftermarket.
    Nissan R32/Z32/R33/R34 rears are hard to beat, the only downside is the internal handbrake issue.
    Preference is to use OEM stuff, if primarily only because the R&D budgets they have mean everything is done properly plus parts are easier to come by. Whats the story with the handbrake though, am I missing something? The commodore backing plates go straight on to Gemini diff, can use the internal handbrake on that. No its not the greatest from a rallying or motorsport perspective but ill be mainly using it for parking.

    The RX7 Calipers sound like a go and are easily available, question is can they be used on a 23mm disc? This would open up my choices massively, however if they HAVE to be 22mm discs then my choices are as follows:

    -DBA2812 ex Audi A3, MK7 Golf etc – 280mm, 49 height, 65 C/B
    -DBA806 ex Audi A4 B5 – 280mm, 46.2 height, 68 C/B
    -DBA542 ex Mini Cooper – 276mm, 44 height [will need spacer], 64 C/B
    -DBA2586 ex Suzuki SX4 – 280mm, 47 height, 62 C/B
    -DBA919 ex Nissan S13 – 280mm, 49 height, 68 c/b

    Theres a few other Nissan discs which are close inc one that’s perfect but its meant for the R31 GTS and theres only a few sets left [basically, im thinking long term and don’t want to have to redo this because discs are NLA].

    Leaning towards DBA919 as an option but not sure about long term availability given that SR20 S13’s are getting a bit long in the tooth. Plus is its 4 stud so the comments regarding the PCD drilling dont apply. DBA2812 is also an option but its 5 x 112 which is fucking tight between holes.

    OR

    The other option is to use DBA582X which is Toyota MR2; 275mm w/ 47 hat height and 62 centre bore, and use it with a Nissan 4 pot. Again though, disc availability in future is a bit of a concern.

    Am I over thinking it?

    Thanks heaps for the replies gents. Appreciate it.

    N-

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    Quote Originally Posted by F3ARED View Post
    What are you running on yours/what car is it if you don’t mind me asking? Ive been looking at MX5s and what they use as upgrades to hopefully give me a somewhat comparable baseline.
    N-
    Suzuki Swift, stock rotors (270 x 23mm) and stock single piston calipers, Penrite Racing brake fluid, stone guards removed, and Project Mu Club Racer pads. The pads are the key to the car stopping so well.

    Re your question about the RX7 calipers, I used to run them back in the day on the turbo Datto, they worked great, ran them with Skyline rotors which from memory were 30mm thick, and you could get any pad you wanted for them. If you want to run them with 23mm rotors, you could use an old set of backing plates to pack the pads out to make up for the thinner rotor. Probably pretty noisy though.

    You might want to check the piston surface area of your current calipers vs the RX7s, you may need a bigger master cylinder if the RX7s have more piston area.

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    Yep so similar deal to me - relatively light underpowered car. Im not sure what to do about pad compound given that its predominantly a street car - needs to not squeel and do my face in from bone cold, but not melt at the first sign of a bit of hard work. Suggestions?

    You sure you ran them on 30mm rotors? The reason i was asking about the disc thickness is RX7 discs are 22mm; theres a Civic Sport/S2000 rotor thats got good dimensions [and also good availability] but its 23mm.

    Piston surface area will require change but im planning on redoing the whole system, not just the brakes on all four corners. Doing a booster delete and will require the pedal to be modified - cant run the calculations though until i establish what calipers are going on the corners.

    Cheers

    N-

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    Quote Originally Posted by F3ARED View Post
    Should work now, sorted alternative hosting. Now to upload all my other photos and fix links….thanks Photobucket you bunch of cunts!

    Didn’t think to machine the face of the disc, ill keep that one in mind. Id like to avoid having to run a spacer between disc and hub but this is entirely dependent on disc selection. The problem is most of the discs that are close dimensionally are 5 x 114.3 or 5 x 112. Quick sketch on cad and I end up with ~4mm between 1 set of holes, the rest clear pretty decently if you rotate the PCDs the correct way. Surely that’s not enough to just leave the holes? Im hoping its ok with an interference plug in it.

    Any reason why to avoid machining the hub? Or is it just from a disc-needs-doing-anyway perspective and may as well do it all to disc?
    The 4mm is probably fine with a pressed in bung in the empty hole. Remember, the bolt holes technically aren't taking any load unless the bolts are loose - the bolts are just clamping the disc, and friction is transferring the load across the hub/disc interface.

    The issue with carving chunks off the hub to ease disc fitment is a couple of things - 2 of them are structural concerns, and the other is convenience. The structural concerns are you're carving into material that (in this case) is carrying the load from the inner wheel bearing to the wheel mounting flange - I'd be wary of reducing the diameter of the hub in that area, and the other issue is there's likely a large radius in the OEM machining, which is reflected in a chamfer on the leading edge of the OEM disc centre bore. That radius is there to help prevent crack initiation that will see the wheel mounting flange separate from the rest of the hub - if you machine the hub down and replicate the radius, you have to machine a matching chamfer in the disc, which is likely not there on the slip over discs (or on the wrong side of the disc). Hence, it's easier just to chuck the disc up in a lathe and sort it.
    Eyballing the hub now the picture is up, I wouldn't have thought there's a huge amount of excess meat on that hub to go carving material off of.
    Last edited by Gammaboy; 10-07-17 at 03:08 PM.
    "Where can we get hold of a Vincent Black Shadow?" "Whats that?" "A fantastic bike," I said. "The new model is something like two thousand cubic inches, developing two hundred brake-horsepower at four thousand revolutions per minute on a magnesium frame with two styrofoam seats and a total curb weight of exactly two hundred pounds."

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    Quote Originally Posted by F3ARED View Post
    Yep so similar deal to me - relatively light underpowered car. Im not sure what to do about pad compound given that its predominantly a street car - needs to not squeel and do my face in from bone cold, but not melt at the first sign of a bit of hard work. Suggestions?
    Have a read of the "Track day pad for S15" thread in this section. In spite of all the bagging in that thread, the QFM A1RMs work fine, it seems that the guys who had issues with them were driving heavy, powerful cars. If you are not on a tight budget, it might be good to spend a little more money and try something with a bit more bite. You could also consider getting a set of dedicated track day pads, and just swap them over when you get to the track, it's a very simple job with an open backed caliper like the RX7. Then you could run just a normal street pad for the street. Best of both worlds.

    Quote Originally Posted by F3ARED View Post
    You sure you ran them on 30mm rotors? The reason i was asking about the disc thickness is RX7 discs are 22mm;
    No, I'm not sure, it was 20 years ago! I would have thought if you were within 1mm that would be OK.

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    Quote Originally Posted by Gammaboy View Post
    The 4mm is probably fine with a pressed in bung in the empty hole. Remember, the bolt holes technically aren't taking any load unless the bolts are loose - the bolts are just clamping the disc, and friction is transferring the load across the hub/disc interface.

    The issue with carving chunks off the hub to ease disc fitment is a couple of things - 2 of them are structural concerns, and the other is convenience. The structural concerns are you're carving into material that (in this case) is carrying the load from the inner wheel bearing to the wheel mounting flange - I'd be wary of reducing the diameter of the hub in that area, and the other issue is there's likely a large radius in the OEM machining, which is reflected in a chamfer on the leading edge of the OEM disc centre bore. That radius is there to help prevent crack initiation that will see the wheel mounting flange separate from the rest of the hub - if you machine the hub down and replicate the radius, you have to machine a matching chamfer in the disc, which is likely not there on the slip over discs (or on the wrong side of the disc). Hence, it's easier just to chuck the disc up in a lathe and sort it.
    Eyballing the hub now the picture is up, I wouldn't have thought there's a huge amount of excess meat on that hub to go carving material off of.
    Thanks for the explanation mate, appreciated. Found this earlier, this is a snap of an already-machined hub to suit i *think* a Honda disc; note the hub to disc face has had a bit removed [few mm from memory] and its been spun down to suit the Honda C/B which is 64. It looks like the hub has a shoulder for the disc to sit on - do your comments still then apply to this given the already-extra material in this area? I think judging by this blokes photos [using Volvos] im going to have to watch caliper to wheel clearance. Man i hope i dont need new wheels....ive gone through about 5 sets on this car





    Quote Originally Posted by Sprinkles View Post
    Have a read of the "Track day pad for S15" thread in this section. In spite of all the bagging in that thread, the QFM A1RMs work fine, it seems that the guys who had issues with them were driving heavy, powerful cars. If you are not on a tight budget, it might be good to spend a little more money and try something with a bit more bite. You could also consider getting a set of dedicated track day pads, and just swap them over when you get to the track, it's a very simple job with an open backed caliper like the RX7. Then you could run just a normal street pad for the street. Best of both worlds.



    No, I'm not sure, it was 20 years ago! I would have thought if you were within 1mm that would be OK.
    Ill have a read now, cheers.

    N-

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    I'm not a fan of the small radius at the base of the flange there I have to say!

    Re: Pads - I beat the living fuck out of Ferodo DS2500s - similar-ish power, similar weight, smaller pads, yet I've had the same set of pads in the car for near on 6 years of driving now I think.
    "Where can we get hold of a Vincent Black Shadow?" "Whats that?" "A fantastic bike," I said. "The new model is something like two thousand cubic inches, developing two hundred brake-horsepower at four thousand revolutions per minute on a magnesium frame with two styrofoam seats and a total curb weight of exactly two hundred pounds."

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    While not a 4 piston, The caliper and rotor on mitsubishi lancer / galant etc is a 294mm x 24mm vented DBA417, the caliper is the same caliper and padshape that gets used under the evo gravel rally 15in wheels. Good size, vented and heaps of pad compounds available. In the old Legnum we ran Winmax W6.5 with shims and CRC anti squeal paste, 200awkw and 1600kg. stopped from dead cold to over 700˚C

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    Ok so Ive had a bit of a head scratch and this is how i think im going to do it.

    FRONT

    Protex DR545 / DBA DBA4545



    Application: Mazda MX5 NB SE
    Disc Diam: 270mm
    Hat height: 46mm
    Thickness: 22 Max / 20 Min
    Centrebore: 55
    Caliper: FC/FD RX7 4 spot Alloy.

    Disc compared to Gemini disc – 1mm less hat height, centre bore substantially smaller, drilled for 4 x 100. FC disc is 276 Diam, 22 Max / 20 Min so only 3mm different in radius vs MX5 disc so there shouldn’t be any issues with regards to pad over hanging disc. Spent a fair bit of the arvo searching online and have found brake upgrade kits for AE86 that use this caliper with a 260mm Civic disc, so Im confident that pad contact patch should be ok.

    Plan to do the following – redrill MX5 disc to 4 x 88, machine centre bore to 68mm. Bolt behind Gemini hub as per standard arrangement. Plan to correct hat height difference [its one mm, I know its fuck all but this is brakes we are talking about – I want to get it right] via the caliper dog bone/adaptor.

    Leaning towards this disc as the thickness is correct for the RX7 Caliper, diameter is almost the same as OEM RX7, and hat height is almost-perfect for Gemini. This should theoretically give me the least amount of headaches in terms of interference and non-compatibility. Disc availability is also quite good given that the MX5 is quite popular, modern and driven hard – so stuff like 4000 series slotted DBAs are available off the shelf etc.

    Thoughts? All sound ok? Should I still have the disc plugged anyway given that its 4 x 100 and the new PCD will be roughly centred between original PCD? Need to take some measurements of the Gemini hub and work out if I have wheel clearance.

    REAR

    DBA020 / Protex DR020
    VN Commodore backing plates inc integral drum for handbrake, bolts on to Gemini diff – just requires an extension to be welded on for handbrake cable



    The part im getting stuck on is the alloy caliper. Been trawling the DBA/Protex listings and based off what has been suggested so far, I have looked up the following:

    Brembo 2 piston CT9A EVO – 22mm thick
    Brembo 2 Piston CT9A EVO RS – 20mm Thick
    300ZX, R32/33 GTST – 18mm thick
    Early R32 GTR Rear – 18mm thick
    Later R32 GTR Rear – 22mm thick

    So now im confused [yeah yeah I know not hard].

    -Are the calipers on the normal Evo and Evo RS the same thing? Ie does the same caliper work on both disc thicknesses?

    -Z32/R32/R33/R34 rear calipers are meant for an 18mm disc, DBA020 is 20mm thick. Would this slip over that disc without mods? Want to avoid fucking around and making spacers to split calipers in half and make them wider – reliability/less things to go wrong standpoint.

    -Is +/-2mm fuck all in the scheme of things and wont cause a problem with brakes dragging or pads falling out [ie am i over thinking shit?]



    Cheers

    N-

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    FRONT - your reasoning sounds OK to me. I wouldn't bother about the original holes myself, there's still plenty of material in the rotor.

    REAR - Why don't you just use a single piston caliper? Lots more options, and the rear does a lot less work than the front. I would not stress about +/- 2mm.
    Last edited by Sprinkles; 13-07-17 at 09:32 AM.

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    Quote Originally Posted by Sprinkles View Post
    FRONT - your reasoning sounds OK to me. I wouldn't bother about the original holes myself, there's still plenty of material in the rotor.

    REAR - Why don't you just use a single piston caliper? Lots more options, and the rear does a lot less work than the front. I would not stress about +/- 2mm.
    Couple of reasons really; i know that the caliper suited to the 020/vented rear disc is still available and technically it should bolt straight up to the diff without any problem. Having said that though they are a big, decently heavy lump of weight and known to chew pads at angles. It is the fall back position, however id still like to look at going better in principle even if in the real world the difference isnt that noticable. Piston size between the normal VN caliper and R32 is the same, which is kind of important given that i intend to go booster-less.

    N-

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    Look to see if any of those pad shapes come in different thckness?

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    Quote Originally Posted by F3ARED View Post
    Couple of reasons really; i know that the caliper suited to the 020/vented rear disc is still available and technically it should bolt straight up to the diff without any problem. Having said that though they are a big, decently heavy lump of weight and known to chew pads at angles.

    N-
    Where did you get this info
    They are a light alloy slider... nothing heavy about them but the bracket
    Piston size is bigger than stock commy too.... and as far as easy to get... really ??

    The prob with using a different caliper will be mounting it... get yourself some backing plates and a disc first... worry about caliper later once you see what I mean
    Location Perth Western Australia

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    Quote Originally Posted by dattoman1000 View Post
    Where did you get this info
    They are a light alloy slider... nothing heavy about them but the bracket
    Piston size is bigger than stock commy too.... and as far as easy to get... really ??

    The prob with using a different caliper will be mounting it... get yourself some backing plates and a disc first... worry about caliper later once you see what I mean
    We are talking about the PBR that matches the 020 disc yes? I was under the impression it was cast iron but anyway. As far as im aware and from what I could find online [Torana forums from memory, and yes i know caveat emptor], caliper was available new as recently as 2012 and fits onto the VN-VS live axle backing plate without any mods. Given the 020 goes onto the same backing plate, and shares almost identical dimensions to the 016, I dont have any reason to doubt that it wont - unless there is something im missing that you know that I dont?

    Regardless. Id still rather use an alloy two pot if i can. Going to all the effort of fucking around with brackets, may as well use something that is better [on paper at least]

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    Absolutely use a 2 pot
    PBR sold out to Bosch... didn't get the caliper factories
    Calipers are hard to come by now
    All commy calipers are alloy body , cast bracket
    Torana forums are great for info...I know... the one you read it on I co-run
    Location Perth Western Australia

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