333pg333

This is in response to my continuing quest for a more solid pedal and I'm not the only one out there. I have found that many people in fact complain of a 'mushy pedal' on our cars.
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:

"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."

This could be an easy fix and would be interested if anyone's tried the above?

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), pretty decent sized sticky rubber, and yes, plenty of power bleeding.

Olli Snellman

I have not ever ran into the same kind of problem you have. Is there any possibilty that this is more RHD problem? after all there is somekind of mechanism (different compared to LHD cars) from pedal to MC inside cockpit, after all MC is located to the same side as LHD cars have.

anders44

I will use a manual twin master setup, with balance bars, no power assist, and nice firm feel (hopefully)

333pg333

Olli, I have thought of that, but I've read plenty of people who have LHD cars and have complained of similar symptoms to me. That's not to say that everyone with soft pedal has the same cause though.
Anders, yes I'll have something like this on the trackbeast, but I'll just stick to Porsche for the car in my avatar so I'd like to still improve the feel. A comment comment is when people have changed from a 944/68 into a 911 variant and say how much firmer the 911 pedal feels. I want this feeling.

Olli Snellman

I just made some time ago a complete overhaul to a friends 964 C2 brakes. It has same baby Brembos as 951 but 2 piston rear calipers. I changed all gaskets and also installed new pistons. I have to say there was not any difference how pedal feels compared to stock 951 brakes. Brake pads i use were Porsche OEM.

sawood12

Well my setup is refreshed ATE Super Blue, brand new Big Blacks, New Goodrich SS hoses & EBC yellows (rubbish but better than reds) and my pedal doesn't feel rock hard. I'm going to ditch the EBC yellows and re-fit stock pads on the basis that they are probably the best pad for my needs - i.e. prodominantly street with the odd track-day. Will be interesting to see if I feel any difference in pedal feel.

Next time I refresh brake fluid i'm going to replace the M/C with stock. I think after 21yrs of service my current one deserves to be retired!

What about the ABS unit? Presumably there are a plethora of internal pistons, seals and other opportunities to introduce some sponginess into the brake pedal? Can you get these units overhauled or reconditioned?

anders44

my 986 boxster has a very nice firm pedal compared to 951. so I see what your point is.

333pg333

Well that's another angle that I neglected to mention Scott. I have had some experienced racers suggest that ABS can indeed be the cause of brake issues. My understanding was that they were implying that with a lot of repeated heavy brake usage, the ABS just can't keep up and this can lead to brake failure. Well that would almost certainly only be on the track and brake failure (pedal to the floor) is not necessarily what we're discussing here. Having said that, I did have maybe 3 occasions of this back when I first started to track the car. Guess what pads I was using. EBC Greens & Yellows. I changed to PFC pads and the difference was immense. Yet even though the bite and retardation was increased 100 fold, the pedal still isn't as solid as I'd like. Also I'd like to say that 99% of the time my brakes pull me up very well, it's more the modulation that I want to change.
I am quite sure that the ABS could be problematic. I don't want to remove mine from the street car. I like it for backup. The trackcar won't have this and will have something similar to what Anders described. I look forward to seeing your results with this setup Anders. When are you going to install it?

anders44

ebc has good marketing, and really really bad products

sometime this winter most likely, Im still working on my application to the DMV for my v8 swap. my car needs to have license plates, I paied a LOT for them, so wanna keep them. (silly cartax)

ABS is good to have, I kinda want it. anyone got any tips for dedicated RACE abs systems? might be possible to adapt a GT3 997 unit? it sucks flatspotting brand new huuuuge tires.

eniac

I noticed a big improvement when switching to ATE Super Blue. The pedal on my 88 is rock solid until I overheat the cheap pads that I have. With better pads my brakes feel great. I have driven many 951's with squishy pedals which I'm not sure what the variance would be. Mine is all stock except crossed drilled rotors which really don't matter. I prefer the feel of my 951 brakes over any stock 911 that I have driven.

I don't have ABS, this is one reason why. I don't like how ABS feels in dry weather under hard braking/cornering even on newer cars. That's one of the many things I loved about my old 88 325iX. It had a unigue switch that would temporarly switch of the ABS under certain forces such as when going hard downhill into a turn and you want the back end to trail out some before gettng back on the throttle.

eniac

As noted in my previous post, something like the mercury switch used in the 88-92 325iX would be great to have on a track car fitted with ABS. Just would need some way to adjust sensitivity. ABS most the time when you need it, no ABS when you don't want it.

PorscheDoc

I've seen in in a few cars with stock calipers, so it isn't a caliper size issue. I run calipers from a 91 965, EBC yellows, 5/33 valve, stock master cylinder, SS braided lines, I swap between ATE blue and Motul, and vented rotors. When I first installed the setup, I had a semi soft pedal as I had seen in a few other cars, and figured I would have to look at a master cylinder upgrade, but I rebled the system with the air bleeder, and my firm pedal came back (which is what I had when I ran the stock calipers). I have never had any issues running EBC pads, and I run the crap out of the car on the track. They don't bite as good as the pagid oranges/blacks, but they are also 1/3 of the cost. I'd rather put that extra money towards hoosiers Now that someone brings up the ABS, the issues I have seen have been in ABS cars.

Papamurphdog

There is one more important item to consider; wheel bearings! I check and adjsut mine before every event to be sure there is no lateral play. If so, I adjust. What can happen is the pistons can be pushed away from the rotor under cornering and then you blast down the straight expecting a good pedal and you get mush, until you give it a pump.

If the symptom is a consistantly soft pedal, bearings are likely not the issue. If the pedal is soft and comes back with a pump, check you bearings.

Just an FYI...

333pg333

That's funny Rick as I do pump them but I think that's just habit from having old vehicles in the past that responded to this. I'd feel confidant about the bearings but will check them out.
I'm not sure how a gravity switch could work Stephen as it's under that type of load that you want your brakes and that's when the mercury would be activating wouldn't it? Ha, maybe voice activated. 'no, no, no, smash.....yes'

Papamurphdog

That's the sign... when fixed I have no "pump" issues. Put the car up, grab the tire at 12 and 6 and try to move it toward and away from the car, if it moves at all its not to spec. If it moves a teeensy bit it's ok. Mine actually moved noticably. Tightened up things and no more soft pedal during recent RA D.E.

On mine, I suspect the inside races are worn and it's simply time to install new bearings on each. The rears are more of a PIA and they seem fine, so not sure there. Might do them too.

Lemeno what you find.

BTW, first happened at the Glen and it is quite unsetteling to have to pump the pedal going around that tracki...certainly was a Depends event for me!!!