951 Big Reds soft pedal

[Mbean]

Hi,
We have an 86 951 track car with Big Red fronts, and standard rear brakes. It had new rotors (genuine Porsche), brake lines and Pagid pads last year. After the second DE, when I was familiar with the new car, the brake pedal felt soft. It had a lot of travel before things slowed down. It was bled numerous times (by an experienced mechanic), had new fluid, etc, but still didn't feel right. When the pedal got about half way down the brakes worked great, but I don't like the excessive pedal travel. The master cylinder was then replaced but things stayed the same. From my research, it seems like the master cylinder needs to be changed to accommodate the bigger Pistons, but I can't seem to find a part number. The other possible cause was a wheel bearing, but these are all fine. Any suggestions for what master cylinder would be appreciated!

[Bill Verburg]

Originally Posted by Mbean

Hi,
We have an 86 951 track car with Big Red fronts, and standard rear brakes. It had new rotors (genuine Porsche), brake lines and Pagid pads last year. After the second DE, when I was familiar with the new car, the brake pedal felt soft. It had a lot of travel before things slowed down. It was bled numerous times (by an experienced mechanic), had new fluid, etc, but still didn't feel right. When the pedal got about half way down the brakes worked great, but I don't like the excessive pedal travel. The master cylinder was then replaced but things stayed the same. From my research, it seems like the master cylinder needs to be changed to accommodate the bigger Pistons, but I can't seem to find a part number. The other possible cause was a wheel bearing, but these are all fine. Any suggestions for what master cylinder would be appreciated!

It does sound like a small m/c issue, as I recall those cars used a stepped m/c, w/ different bores for front and rear.


Check out the m/c for a 951T/S or 968t, I'm not at all familiar w/ 951/968 but I think one or both of those had the big red fronts.

You might also want to look into what they used on the back of the T/S. Most 951 and 928 w/ the Brembos used the small caliper 28/30. Not at all sure what they used w/ the big red fronts(which are black) from the factory.

[cstreit]

What Bill said. Upgrade your m/c. That's a lot of volume for an early cars master...

[Cory M]

When was the last time the calipers were rebuilt? I had a similar issue with my big reds and tried several things. I rebuilt the calipers with new seals, pistons, and anti-knockback springs and that fixed it.