mbean

We have an 86 951 track car with Big Red fronts, brake cooling hoses, Porsche rotors and hats, Castrol fluid and Pagid pads. New brake lines all around. Rears are original with Pagids. This summer I was unhappy with the pedal feel, which had too much travel before things got stopping right. We had a new master cylinder installed but the pedal still goes too far down, in spite of numerous bleedings by a pro mechanic. I've looked around and it seems like the issue might be that we need a bigger master cylinder because of the Big Reds needing more volume. When the present system starts to get firm, the car stops great, but I don't like the long travel before we get some serious stopping action. My instructor at our last DE at NHMS suggested a bigger master cylinder. Anyone know what part number we want?
Thanks,
Buzz

jerome951

Hey Buzz,
I'd suggest cross-posting this to the 951 forum. I think some folks over there have upgraded their MCs and can advise.

333pg333

It's a bit of a known phenom for some people who have to chase this for sometime. I used to have pretty similar mods to yours. Changed the m/c and did multiple bleeds. There was a bit of an internet rumour about swapping out to a BMW m/c that would fit but I could never get anyone from the manufacturer of those to approve the change (which isn't surprising). I found the best thing for me was a proper slotted rotor (+hat) from Coleman Racing and using PFC pads. While this shouldn't necessarily affect pressure it did improve the overall feel of the system. The initial bite with the PFCs was more aggressive than the Pagid Blacks and the slotted rotors seemed to help with cooling and or keeping the rotor and pad 'cleaner'. Have now switched to a different system but I found those 2 changes helped me back then.

Jimbo951

Are you sure it's the brakes?

On my 86 951 the rear wheel bearing kept shifting inside the rear trailing arm so the rotors weren't running "true" and this cause pad pushback. These cars are 30 years old the trailing arm is alum and wears out.

Just something to check before you start chasing the braking system.

dand86951

I would add a plus 1 to this. I kept having long brake pedal and would have to pump a couple of times on almost every corner. Replaced the rear bearings and the brakes are fine. My system does not have the Big red calipers but does have ST40 calipers which are the same size as the 88 Turbo S. So even though I should not have had a long pedal I did until I changed out the rear bearings.