Brake setup still soft after massive upgrade

[Jason Broadhurst]

So I now run a

1" master (second hand from a grand vitara)
GTR 4 pot fronts with lucas pads
GTR 2 pot rear calipers with lucas pads
6 new braided brake lines ADR approved
$15 a bottle Dot 4 fluid

And after all this, my pedal still seems soft.

It is pretty hard when the motor is off and there is no vacuum assist, but squishy with no feel when it is on.

It doesn't fade at all, or get longer with heat what so ever but it has a horrible feel after countless bleeding.

Any ideas guys, I would like to have a bit of confidence in it before I take it racing in week or so.

[Dicko]

easy fix. leave the vacuum hose off. :)

[Zac]

Does it have a booster or not?

[Sicarius123]

What car is it in? The older and shittier the car, the more it'll benefit from a master cylinder stopper

[RB30-POWER]

shit master.

fairly sure the gtr ran bigger then 1"

my brakes didn't become awesome until i fitted vt commodore fast fill master cylinder.

other things can contribute as well, shit pedal ratios and the like.

[Jason Broadhurst]

E30 BMW. I have checked flex of the firewall and it moves maybe 1mm at the most when really giving it a stomp.

It runs a booster yeah, suzuki grand vitara jobbie double diaphram. I used it because of space limitations.

Do you think a master rebuild could fix the problem, or is it shit design of the master?

[Dicko]

I would be leaning towards a bigger master.

More volume being pushed should be less pedal travel to get the same result.

[RB30-POWER]

rebuilding, i reckon will not make a difference, if it were bypassing, i'm sure you would feel it.

apparently the gtr uses 1" and brembo model 1 1/16", so pedal ratio is only thing i can put it down to really.

not an easy fix, unless you like stuffing about, usually rewelding pedals and the like.

does the e30 run that abortion, 3 meter rod from one side of the firewall to the other? may never fix it, with all that flexing?

[out_in_front]

Get a harder leg - thats sems to be the only bit not replaced :D

[Jason Broadhurst]

RB30 - It does run that huge abortion bar along the back, but when there is no booster there is SFA chance of moving the pedal once the slight slack from all the linkages is taken up.

With the booster the pedal travells another 5cm until it gets hard!

I have no dramas rewelding the pedal to get more leverage, is that a fix though?

[Zac]

When I went sans-booster on my car I fitted a smaller master which made the pedal softer. I'm not sure if this logic carries over on cars with boosters.

It is also my understanding that the booster 'covers' for a large master cylinder, which manufacturers prefer for some reason. Without them the combination of a large cylinder and no booster would be too hard for most drivers.

[GTV]

With the booster the pedal travells another 5cm until it gets hard!



:wtf: that sounds wrong. booster shouldn't really give you any more travel, just less effort. is it leaking vaccuum maybe (guessing only)?

[Jason Broadhurst]

Well if I put my foot as hard as I can it goes rock hard at about 1cm, then i start the car and it travels another 5cm.

I thought most cars did that?

[Jason Broadhurst]

How does a fast fill master work?

[RB30-POWER]

i'm sure a google link will explain it better then i can.

but in simple terms, it basically draws alot of fluid in a short distance of piston stroke, i think they are only like a 1" cylinder but the fast fill design make it effectively a 1 1/6" master or bigger, just an example.

if that makes any sense at all.

atleast that is my understanding, it has higher initial fluid flow then drops to normal?

this is from a quick google patent search, says it's kind of like a stepped bore.


A fast-fill master cylinder with integral proportioning includes a housing with a stepped bore defining a large diameter and a small diameter. A piston is disposed with the large diameter and the small diameter to form a fast-fill chamber in the large diameter and a pressure chamber in the small diameter. A passage extends between the fast-fill chamber and an outlet port to bypass the pressure chamber.

[xwavgas]

I am pretty sure that those Fast Fill master cylinders had a different bleeding procedure, back in the day I had a Ford Meteor that ran a FF cylinder, pretty sure there was this deal where you only push the pedal to half way during the bleed and then had to have someone close off the bleed nipple whilst the pedal is held there, It has something to do with air being drawn back into the FF valve when you release the pedal.

Also had to do them in a diagonal pattern ie LHF, RHR, RHF, LHR

[Jason Broadhurst]

So I took it for a good hiding at the time trials and the brakes performed flawlessly. Didn't come close to fading, ~okay~ feel for the pedal softness and pulled me up nicely.

They are still quite a deep pedal, but very soft to touch and lock up without much effort.

Is it a wise idea to modify the pivot/pedal ratio or should I just put up with poor feel and a deep pedal?

[RB30-POWER]

if the master is too small you get an easy pedal that is long travel and easy to lock up.

if the master is too big you get limited/reduced travel and requires a fair bit more effort to get the same line pressures as the smaller masters offer.

if you think it performs good, maybe fiddle with improving the pivot point as the solution.

if you can't modify the pivot point, maybe look at a fast fill master in a similar size to what you have now, to solve the problem.

if you think the pedal is to easy to lock, i.e. to much assistance, go bigger master.

none of these solutions are all that easy to carry out because it's no longer standard spec.

[bigmuz]

Is there a slightly bigger master available that would bolt in?

[Jason Broadhurst]

http://www.dairally.net/e30/E30SR/files/images/conversion-pics/brakes/DSC00707.JPG

The 1 inch wasn't bolt on, the 4 small pilot holes are the patturn for the 1" suzuki master/booster which was fitted. This was done for space more than capacity.

http://www.dairally.net/e30/E30SR/files/images/conversion-pics/brakes/DSC00740.JPG

I could fit anything so long as it has a small booster and is stubby. The suzuki master is recessed in to the master also making it short.