VT front brake conversion onto VP with ABS

[RB30DEVL]

We have recently fitted a front VT brake conversion onto our VP Commodore wagon with ABS braking.

The conversion includes:- wheel hubs (which the ABS sensor interruptor ring is pressed onto),DBA gold drilled & slotted rotors , VS Commodore booster unit (plastic type) and a VX Commodore master cylinder,this is a straight bolt on fit onto the VS booster unit.

The trouble we are having is when coming to either a complete halt or almost when the car stops, the pedal is pushed up and a loud vibration is heard & felt through the dash,firewall,etc.

I assume this is coming from the ABS solenoids which for some reason are pulsating more than normal,note when the car is standing,it doesn't do it,it only does it when the car is moving to a halt.

Would anyone know what is causing this?

I was thinking either not enough pressure (i.e. the system still has some air in it) or too much pressure (i.e. from the bigger master cylinder) was causing it.

[dbasteve]

Pull the ABS fuse and see what happens.

[dattoman1000]

Um
Just one thing I'd like to mention.....not thats its about the question your asking.
VX master doesn't go straight onto VS booster. You need to shorten the pushrod out the front of the booster by 10mm.
I point this out so people don't make the mistake of trying to fit it straight up and encounter problems.
Usually we also remove the VT fluid bottle and refit the VS unit as it sits better. To do this you have to drill and tap to accept the screw that holds the bottle on beside the existing bottle bolthole.

Try the fuse thingy too.

[RB30DEVL]

Um
Just one thing I'd like to mention.....not thats its about the question your asking.
VX master doesn't go straight onto VS booster. You need to shorten the pushrod out the front of the booster by 10mm.
I point this out so people don't make the mistake of trying to fit it straight up and encounter problems.
Usually we also remove the VT fluid bottle and refit the VS unit as it sits better. To do this you have to drill and tap to accept the screw that holds the bottle on beside the existing bottle bolthole.


Try the fuse thingy too.

We were told to shorten the rod into the booster unit,we removed the adjusting screw as there was 5 -10mm of clearance between the booster and M/C,it now mounts flush to the booster,we tried removing the rod but it didn't appear that it could come out.

Changing the reservoir sounds like a good idea as it does sit at an awkward angle.

Regarding removing the ABS fuse,I believe it will only prove what I know already,i.e. that the ABS unit is causing the vibration for some reason or another,I read somewhere that if one wheel is spinning faster than the others for any reason,it will cause that sort of vibration.

[RB30DEVL]

We pulled the fuse out which supplies the ABS system and as I mention on the previous post it did fix the symptom,not the cause of the ABS problem meaning we still have a problem with the ABS system,we fitted new rear discs,etc this weekend and went through and rebled the system,but we haven't tried it with the ABS system operating.

[Jim]

are you sure the pick-ups for the sensors are all identical? sounds like the ABS is trying to prevent an imaginary wheel lockup by operating. Is there different sensor disks? if there is a different number of teeth between them then it'd think one wheel is turning faster than the other.

[RB30DEVL]

I couldn't imagine the chopper discs on the front being any different to each other,but the rear has only 1 disc on the final drive housing which wasn't touched (the original front chopper discs were fitted onto the new hubs).

We may have to try the ABS unit out again (put the fuse back in) since the brake system has been rebled.

[carcrazy]

Does the bosch abs modulator require bleeding too? I cant for the life of me remember and im a brake mechanic lol!

[Jim]

I couldn't imagine the chopper discs on the front being any different to each other


so in other words, you didn't check? I'd start counting teeth before you go too far. I don't know a lot about ABS but it sounds logical to me from the symptoms you are describing. the violent pulsing at the pedal is usually the ABS unit trying to do it's job. if it thinks one wheel is going slower than the other because it's getting different readings it may well think one wheel is trying to lock up and counter that by operating the ABS.

[RB30DEVL]

We did refit the fuse initially and the ABS system worked a little better but not much,the brakes work far better (more like my VL with big brakes and no ABS),as far as bleeding goes,we bleed our ABS equipped VX Commodore with no problems.

I has either got to be something to do with the pickups (air gap,No of teeth,etc) or the program in the ABS control module itself.

I downloaded some info on ABS braking which says it should come into affect only after the wheels have locked up,but it does it regardless of how hard the pedal is pressed when coming to a stop.

The car may not even come to a complete stop and it is noticeable,like when we slow down to pull up our driveway,say for example, at speeds of 5 KPH.

[Jim]

I'd start counting teeth before you go too far. I don't know a lot about ABS but it sounds logical to me from the symptoms you are describing. the violent pulsing at the pedal is usually the ABS unit trying to do it's job. if it thinks one wheel is going slower than the other because it's getting different readings it may well think one wheel is trying to lock up and counter that by operating the ABS.

[Glenno]

IIRC ABS doesn't activate below 10kmh or so

[Jim]

no but it will continue to stay activated if it's engaged at over 10k or so until rest. (AFAIK)

[GTSBoy]

correct.

If the VT chopper wheels are significantly different to the VP ones, then the VP ABS computer will not be able to reconcile the signal difference between the front ones and the rear one. There will be an apparent speed difference between them. You would be best to follow Secoh's counting advice, and then maybe think about ways to get the VP wheels onto the VT hubs.

cheers

[Jimbo123]

Usually we also remove the VT fluid bottle and refit the VS unit as it sits better. To do this you have to drill and tap to accept the screw that holds the bottle on beside the existing bottle bolthole.Currently I still have the VT fluid reservior on ther with my master/booster mod, but I planned to change it when I finally get to put the 4pots on,... any more to add, or will it become obvious after I get the VS reservior and remove the VT one ? Any pics ?

Thanks,

Jim.....

[RB30-POWER]

On a seperate note, when fitting up the VX master to earlier commodores you would have to use line adapters right? Don't VX have different thread type on the lines?

Also are the VT and VX masters the same (1" Fast fill type)

Thanks for any clarification

Mick

[Jimbo123]

On a seperate note, when fitting up the VX master to earlier commodores you would have to use line adapters right? Don't VX have different thread type on the lines?Yes, you should use the adaptors if running lines not intended for use with the master.

The threads are the same, the flare isn't - I could stand corrected <___ looks around for dattoman___> but I believe there's a chance the line would collapse inwards if overtightened. My site has moved, still shuffling it around,... I have somewhat of a walkthrough,.. pics,.. etc,.. in the MODS section of http://users.bigpond.net.au/jimbo123/VN/

The flare is a single type or ball type on the ?? (not sure if VR or VS upwards), but definitely on the VT+ anyhow.

On the earlier models its a double flare.

Also are the VT and VX masters the same (1" Fast fill type)Yup.

Jim.....

[RB30-POWER]

Cheers mate,

If i shortened the VS push rod won't it remove the nipple part (narrower on end/smaller diamter on pushrod) and this part sits in the master cylinder to stop it sliding around so to speak.

I know the early commodores have the smaller diameter at the end of the push rod that slides into the hole in the master cylinder.

Or do i have to get the pushrod machined on a lathe back down to a suitable diamter to slide into the master cylinder properly??

If that makes sense.


Secondly how much more assistance is the double diaphrapm booster going to offer over a single such as the VS unit. Much? or is the VT master the primary component that will add braking performance.


Im currently running Nissan 4 Spots and the pedal is a bit too low, extended travel over standard and braking performance is not as good as it is in the skylines. (Using Double Diaphram and 1" master at the moment)

Will the larger VT master cylinder fix this or is the shit brake performance caused by the commdore pedal ratio?

Should i modify the pedal box to skyline specs?

Any thoughts.


Regards
Mick

[RB30-POWER]

Re-reading what has been said, I don't shortern the rod at the front of the booster but on the other side (pedal side)???

Is that right, just cut and re-drill a hole 10mm towards the booster itself, from original hole? Like you did on the VT booster on your site?

[Jimbo123]

Re-reading what has been said, I don't shortern the rod at the front of the booster but on the other side (pedal side)???

Is that right, just cut and re-drill a hole 10mm towards the booster itself, from original hole? Like you did on the VT booster on your site?I've never seen the inside of a booster,.. logically though what you say makes sense; when I was looking into all this stuff ages ago I was corresponding with dattoman for most of the details and felt more comfortable with using the total VT setup and make the bracket rather than hacking into a VS one.

Also, with much of your other questions, re: double diaphram, etc,.. unfortunately its way over my head. They did use the same booster with the larger brakes they put on some of the GroupAs didn't they ?

With respect to the pedal ratios,.. I remembered a very old thread, about the time I was researching all this, that's now been archived. A fellow that goes by the name of twinvl actually altered the ratio to better suit what he was after,.. I tracked it down here for you: http://pforums.company-hosting.com/forums/archive/index.php/t-67128863.html

Jim.....

[dattoman1000]

GTS Boy.......no chopper wheels on VT-.....its all controlled in the hub.

Jimbo......I know you'll cope with the resi swap if you do it. Easy job.
Your right on the flares......up to mid VP they are inverted.....after that they are drill point seat.

RB30
VT-X masters are the same.


Booster ratio from 1-2 diaphragms would be close to 3:1 on single 4.25:1 on double.(vt unit) or just under 4:1 on VN unit.