Turbo S Soft Brake Solutions

[xupkid2]

So I just picked up a race prepped 89 Turbo S. At the track this weekend I had major issues with the brakes. I replaced the rotors, put on new Pagid Oranges and blead the brakes. The issue I have is with a soft pedal. From what I have heard, the pedal is always soft. I have removed the dust shield and have 968 control arms with GT3 ducts to help with cooling but still have a soft pedal.

I was thinking of replacing the master cylinder with a larger one but don't see anyone who makes one. I also see Porsche has a 5/33" bias valve which may help. Does any one have any solutions to firming up the pedal?

Over the winter I will upgrade to a big red set up but I am feeling I may still have the soft pedal issue since I can't find a new master cylinder.

Thoughts?

[ryan951s]

I have an '89 Turbo as well, and the brake pedal is definitely not rock-hard. I've driven 3 '89s and all were the same as mine. I've also driven a few 964 - 911s and they have a much firmer brake pedal, so I posted this same question on the PCA technical forum and their response was as long as the pedal isn't going to the floor, it's OK.

I run pagid oranges on the track with zimmerman cross-drilled rotors and they bite well. I also up-graded to the 5/33 rear brake bias valve, and it made a big difference. It obviously nets you more rear-braking, but it also seems to help transfer a bit more weight on to the nose and lets the fronts work a bit harder too. The only caution I've heard with this mod is if you have disabled the ABS, it can cause the rear-end to lock-up during corner entry and spin the car off track. I've only had 2 DE days with this mod and have the ABS still working, and found it to be a useful change.

Good luck with the brakes, and let us know the difference with the Big Reds!

Ryan

[aj951]

+1^ on the pedal not being extremely stiff on the '89.


A.J.

[kdjones2000]

See my reply in the NA section....

[BRIT944TS]

Had the same problem with my ´89. went to Cross drilled Zimmermanns, Pagid Orange pads and "blue" fliud, that helped but what made a difference was new Stainless Brake hoses (the ones with Teflon liners). Pressure filled and bled the system and I am now happy with the Brakes. Would be interested on your thoughts of using Big Reds............just in case I need to upgrade in the future. Good Luck

[333pg333]

I've done a bit of research on this issue and some of you may have seen me on other forums asking similar questions. I was under the impression that it may have been due to the stock m/cylinder not supplying enough hydraulic pressure to the upgraded or upsized calipers with larger pistons. I have heard what is so far turning into a story of mythical proportions that there was a 7 series BMW from the 90s that had a m/c with the same fittings as ours but bigger pistons. This was the advice of Sam Lin on 951Forums http://951forums.com/forums/index.php?topic=204.0
I have pressed him for more info but he has remained dormant on that thread.
I had also thought that perhaps it was something more common to cars with RHD, but I now don't believe this to be true as others can testify. I contacted ATE who make the m/c for our cars but they didn't want to know me as modifying the stock setup could have legal ramifications if I crash due to their advice. Here's another idea from Tony G on Rennlist:

"If the issue is simply pedal travel, then you could simply pull the brake pedal and drill in 2nd hole in the pedal so the the clevis ratio is faster (which would be away from the pedal pivot point). Go small. 1/4" should make it quite a bit faster and should make the pedal harder since the leverage will be reduced."

I put the larger m/c concept to Markus Blaszak in Canada (long time Porsche mechanic) and this was his reply to my question below:

Markus,
If the piston size in the caliper is increased like going from standard
> 951
> brakes to Big Reds or 6 piston calipers then wouldn't the larger m/c move
> correspondingly more fluid commensurate with the larger calipers?
> I'll check the firewall, but in the past I've had my pedal go to the floor
> on the track. That was a long time ago before I made some changes though.

"Yes and no.

You are dealing with pressure and MINUTE piston movement... what you are
saying applies ONLY if your brake pads are 1/8" AWAY from your rotor!
Think about it, your pads are always touching the rotor. The piston is
always touching the pad backing plate... so how much movement is there to
lock up the brakes??? About 0.015" that is it!! How much fluid is that in
each system?? about 1cc of brake fluid! So, what you want is pressure,
not fluid volume.

Look up hydraulic principles on the internet or go to a good hydraulic
shop near you... To lift a huge load they use a large piston and the pump
feeding it has a small piston. The larger the feed piston the faster the
main ram moves but the less pressure it can exert! Since you need minimal
fluid (you are not moving a huge distance) your focus needs to be on
pressure.

If you have excessive pedal movement and a soft pedal, you have:

1) air in the system still
2) swelling lines, yes even if they are SS lines!
3) a leak! check calipers, line fittings, hose joints and master cylinder
4) internal leak in master cylinder... pressure is blowing past seals
internally so you do not get press. to calipers AND you get a long pedal
5) cracked firewall and master moves when brake pressed."

So I'm not sure of the answer. I have changed my pads to Pagid Blues at the behest of my mechanic who is very happy with them in his '86. I have upgraded my setup over time and unfortunately due to a lot of bad luck, haven't had much tracktime recently so hopefully I can do some more testing of the current setup pretty soon. Find below my setup.

My setup is direct to rotor venting/ducting, 928GTS discs, Big Reds, s/s braideds, SFR fluid, new M/C, rear bias 5/33 valve, PFC pads (now Pagid Blues), and yes, plenty of power bleeding.

[taki944]

Originally Posted by 333pg333

I've done a bit of research on this issue and some of you may have seen me on other forums asking similar questions. I was under the impression that it may have been due to the stock m/cylinder not supplying enough hydraulic pressure to the upgraded or upsized calipers with larger pistons. I have heard what is so far turning into a story of mythical proportions that there was a 7 series BMW from the 90s that had a m/c with the same fittings as ours but bigger pistons. This was the advice of Sam Lin on 951Forums http://951forums.com/forums/index.php?topic=204.0
I have pressed him for more info but he has remained dormant on that thread.
I had also thought that perhaps it was something more common to cars with RHD, but I now don't believe this to be true as others can testify. I contacted ATE who make the m/c for our cars but they didn't want to know me as modifying the stock setup could have legal ramifications if I crash due to their advice. Here's another idea from Tony G on Rennlist:

"If the issue is simply pedal travel, then you could simply pull the brake pedal and drill in 2nd hole in the pedal so the the clevis ratio is faster (which would be away from the pedal pivot point). Go small. 1/4" should make it quite a bit faster and should make the pedal harder since the leverage will be reduced."

I put the larger m/c concept to Markus Blaszak in Canada (long time Porsche mechanic) and this was his reply to my question below:

Markus,
If the piston size in the caliper is increased like going from standard
> 951
> brakes to Big Reds or 6 piston calipers then wouldn't the larger m/c move
> correspondingly more fluid commensurate with the larger calipers?
> I'll check the firewall, but in the past I've had my pedal go to the floor
> on the track. That was a long time ago before I made some changes though.

"Yes and no.

You are dealing with pressure and MINUTE piston movement... what you are
saying applies ONLY if your brake pads are 1/8" AWAY from your rotor!
Think about it, your pads are always touching the rotor. The piston is
always touching the pad backing plate... so how much movement is there to
lock up the brakes??? About 0.015" that is it!! How much fluid is that in
each system?? about 1cc of brake fluid! So, what you want is pressure,
not fluid volume.

Look up hydraulic principles on the internet or go to a good hydraulic
shop near you... To lift a huge load they use a large piston and the pump
feeding it has a small piston. The larger the feed piston the faster the
main ram moves but the less pressure it can exert! Since you need minimal
fluid (you are not moving a huge distance) your focus needs to be on
pressure.

If you have excessive pedal movement and a soft pedal, you have:

1) air in the system still
2) swelling lines, yes even if they are SS lines!
3) a leak! check calipers, line fittings, hose joints and master cylinder
4) internal leak in master cylinder... pressure is blowing past seals
internally so you do not get press. to calipers AND you get a long pedal
5) cracked firewall and master moves when brake pressed."

So I'm not sure of the answer. I have changed my pads to Pagid Blues at the behest of my mechanic who is very happy with them in his '86. I have upgraded my setup over time and unfortunately due to a lot of bad luck, haven't had much tracktime recently so hopefully I can do some more testing of the current setup pretty soon. Find below my setup.

My setup is direct to rotor venting/ducting, 928GTS discs, Big Reds, s/s braideds, SFR fluid, new M/C, rear bias 5/33 valve, PFC pads (now Pagid Blues), and yes, plenty of power bleeding.

The problem with the BMW 7 series ones are that there way to many different ones you would really need to know exactly which one to use. I'm new here with my 951 but if you guy's need any BMW info let me know I am a BMW master tech and would be happy to help Pete

[333pg333]

Pete, what info do you need? I've actually got my old stock 1989 951 m/c in the garage so if I can give you any details that would narrow your search let me know. I'd sort of like some closure on this. As you can see, going up in size with the m/c is not everyone's idea of a solution but if there was something available that allowed me to basically just bolt it on and try I would jump at the chance. The consensus is that by increasing m/c size you will shorten the travel but need an increase in pressure to exact the same force.

[333pg333]

Good pic of the stock one.

[taki944]

Originally Posted by 333pg333

Good pic of the stock one.

Thanks for the pic I will see what lines up but I dont remember and 7 series with 3 lines going to it Pete

[Jotronic]

Whatever happened to this informaiton? Where did it lead? ABS master cylinders are ridiculously expensive now so we need a reliable cheaper source.