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

V2Rocket

Easy pedal modulation but long travel is typical of a smaller cylinder.
Going larger makes a harder pedal and shorter travel.
But there is no factory 944 larger cylinder - they are all the same size.
So you will have to find a universal cylinder, or one off another car that will work.

I believe the 944 master cylinder bore for the front brakes is 15/16", so a 1" or 1-1/16" might be a nice swap for you.

Humboldtgrin

Mine feel fine and I have the same setup. You must have air in the brake lines still.

Van

I agree, it sounds like the master cylinder and the brake calipers are an ill-suited size for each other. Try a larger master cylinder or smaller calipers. There is a lot that can be done with pads and brake bias that should be able to equal, and exceed, the stopping performance you're currently getting.

Humboldtgrin

I take back what I said. I have the M030 front calipers and 951 87 rear calipers. Not the same. But if you have a lot of brake pedal you may want to look at the rear calipers for air in the line or a bad piston seal because that's what the MC pushes fluid to at the first bit of brake travel. And yes you may have a small MC but look for air first. Sometimes it takes a while to get it all out. And make sure the MC is bench bleaded before installing if you didn't. I say this because my set up is rock hard and the Pistons are bigger in the rear caliper on my 87 951 vs the 86 951's and the M030 calipers also take a bit of fluid to perform.

ramius665

So there seems to be an issue with 86 951s, especially those pressed into track duty suffering from long pedal travel but still having good stopping power ones the pads bite. A good friend of mine took the plunge and swapped the Girling brake booster for the later ATE one on his 86 951 and reported a marked improvement in travel and initial bite. I've got an 86 951 which is used for street and autocross and can report the same issue. System has been thoroughly bled, pads are new and recently rebuilt calipers. Another good friend has 996 GT3 6 piston calipers on his 944 S2 and the pedal travel is much shorter than my 951. The pedal travel on my 951 is "different" than our 944S and 968, both of which have the ATE booster. Might be worth doing some research on the used market to see if you can get one for a decent price and try the swap, it might be exactly what you're looking for.

944crazy

Another thing that could be adding to long peddle feel is firewall flex. I have found that the firewall on my car flexes quite a bit when I firmly depress the brake peddle. The master cylinder itself seems to move a good 5mm or more which translates to around 1 to 2cm of extra pedal travel under heavy pressure. This is a stark contrast to my brothers R33 GTR which has hardly any firewall flex, and I can push on the peddle as hard as I can and it won't budge.

For now, I have made up a rudimentary brace that attaches to the strut tower and prevents the master cylinder from moving as much. If you google 'brake master cylinder brace' you will find that it is a popular modification for a whole range of cars. Strangely though I couldn't find anyone that makes them for the 944.

Player0

I run the S4 brakes on my 86 and did have noticeable travel increase. But I actually prefer having that extra bit of play to help keep the brakes from locking up. It never felt out of place or dangerous though. The S4 brakes are supposed to have the same piston diameter as the 993 brakes, so I'm curious as to why the travel should be so much more with your set up.

Humboldtgrin

There are two types made for our cars. The whole plate that mounts onto the firewall and a brace just like you have made. Do a search for 944 braces and I'm sure you will find them. The plate is one eBay. I forgot who carried the brace thou.
Edit:Looking for the other one. Found it! A fellow rennlister makes them but there for the clutch MC.https://rennlist.com/forums/944-turb...forcement.htmlhttp://pages.ebay.com/link/?nav=item...obalID=EBAY-US

Dimi 944

Look into changing the brake booster with one from '87 and later 951/944 S2 or 968. Porsche upgraded the brake booster on all '87 and on models to minimize the dead travel that '86 and earlier cars had.