sawood12

I installed my 928GTS Big Black calipers last year and they are simply superb. However I did notice an increase in brake pedal travel and although i've got used to it now i'm in the process of replacing all my key brake components as I feel after 20yrs of service they deserve to be replaced. I was wondering about installing a 928GTS master cylinder to redress the brake pedal travel issue and wondered if anyone has already done this and if it can be bolted straight onto the 951 servo, or will I need a 928 servo as well?

Cheers.
Scott

Epic2112

First you should double check and see if the Turbo S (and 89 turbo) uses a different master cylinder than the regular turbos. The Turbo S had the big blacks from the factory, and if it uses the same master cylinder as the base model turbos then you can save yourself the trouble of finding a 928GTS MC and whatever parts may be needed to make it work.

sawood12

Kevin, The 250 turbos had the 'medium' blacks fitted, i.e. calipers carried over from the 928S4. The 928GTS Big Blacks are identical to the 993TT Big Reds apart from colour and the position of the u-shaped brake pipe. I've already checked and the 928GTS Big Black master cylinder part number is different from the 220 and 250 951's.

However you've just stirred a vague memory of something i'm sure i've read. I 'think' the piston sizes on the medium blacks are the same as the piston sizes on the Big Blacks so the 250 951 master cylinder might work fine - the big black calipers were just physically larger with bigger rotors and larger pads (30% more area IIRC). I'll have to check. Thanks for jogging my memory though.

Jeremy Himsel

You are correct. Piston size is identical between the two. The big blacks have a taller pad (about 10mm's). I also have big blacks and have quite a bit more travel then stock that I like and want to shorten it up. I changed the proportioning valve to the 5/33 but it locks up quite easily in the front with medium pedal pressure. What year car do you have?

Oddjob

No change in MC for the late model 944s. Depending on caliper size, you will get more pedal travel.

Im not aware of anyone that has installed a MC with different piston ratios, to reduce pedal travel with the larger calipers (larger pistons), but it can probably be done. Not sure if you will run into bolt-up problems or not with any of the stock porsche MCs from other cars.

Need to find the MC piston diameters for the various ones available and see if any have a larger front piston but keep the same rear piston size.

PorscheDoc

87 and on MC's are all the same for the turbos.

sawood12

I've got an '87 car. I'm surprised there is more pedal travel if the piston sizes are the same between the big and medium black's. There must be more to it than the MC then. Oh well like I say i've got used to the longer travel but it is more difficult to heel and toe as the accelaration is higher up which means I need to raise my heel a bit higher, it just feels a bit more awkward so I'd have liked to correct the longer travel.

Cheers anyway.

Epic2112

Yeah, I don't understand why pedal travel would change if the piston diameters are the same.

sawood12

Is there anyone out there with a post '87 250 turbo that has carried out the big black upgrade? If so did you notice an increase in brake pedal travel? Maybe i've now got the same brake pedal travel as a 250 turbo with medium blacks.

333pg333

So do we therefore assume that if we can fit a larger m/c it will provide more pressure and push more fluid and create less travel? I remember my '89 with the Mid Blacks having times of long brake travel. I have now upgraded to BR's and while I had my car back for a few days, the travel didn't feel any more increased. I also had my old m/c replaced by a new one. I am actually looking at increasing my brake capacity again so is increased brake travel going to hound me as I up the ante?