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brake master cylinders

sawood12

sawood12

New member
Anyone know much about brake master cylinders? All the talk and speculation following Paul Smiths unfortunate accidnt in Lil has prompted me to look into replacing all my major brake components that after providing the car with 20yrs of sterling service deserve to be retired. Since i've changed my front calipers to Big Blacks I was thinking about fitting the brake master cylinder off a 928 GTS that had the Big Blacks and restoring my brake travel as it did lengthen when I fitted the Big Blacks. Anyone know if the 928GTS master cylinder will fit onto the servo?

I am planning on replacing the master cylinder as described, replacing the brake fluid to Castrol SRF and the brake bias valve. Not sure what to do about the ABS unit though. Can you get reconditioned units?
 
Surely the ABS unit is designed in such a way that if it fails you lose ABS function but not brakes?
 
Yes but i'm worried about seals failing and leaking fluid. Unlikely I know but just trying to consider every link in the chain.
 
I'd be interested too in whether the 928 m/c fits Scott. I have fitted some BR's and replaced my old m/c to a new one based on the age of the original however I don't want longer travel. I'd like to have less travel if possible. I will ask my mechanics who are experts on front engined Porsches, they'll know.
 
Calling those with 250 turbos who have gone down the big black upgrade route - Fen and Pat? Did you also notice an increase in brake pedal travel when you carried out the upgrade? I've consulted Rennlist and i've established that the 250T meduim blacks have the same piston diameters than the Big Blacks and they had the same master cylinder as the 220 turbo cars. So if you noticed a longer pedal travel then it is obviously not the master cylinder alone that is controlling pedal travel.
 
I didn't notice any longer a pedal, but bear in mind it was 3 years between me driving the car standard and driving it with the Big Blacks and I had driven a lot of miles in a few different cars in between. What I can say is that it felt fine and if I had to choose I'd say was the same as previously.

Paul Hilux drove mine and his own (I think?) on the same day so maybe he can comment?
 
The piston sizes are the same, from memory they are 36mm and 44mm, the only difference is a bigger caliper allowing deeper pads and a larger discs - increasing the swept area/ contact patch by a substantial amount. Never heard of any master cylinder upgrades in my time.
 
Yep, agree with Nick. When I changed mine I also changed the m/s. I didn't notice any more travel but the old one may have been leaking a little, it never felt totally secure on the track. I sometimes felt like Fred Flintstone with the brakes. I will know in a few weeks what the BR's are like under pressure.
 
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