Player0

I assume the brake master cylinder on my car is 30 years old. That along with the brake booster. Everything from the SS brake lines outwards has been replaced. I flush the system yearly and there's no leak or sign of anything wrong. But since I'm braking hard at the track, is this an item that should be replaced?

Van

If the system is working well, don't replace it.

It won't fail catastrophically... it will leak first and/or start to give you a spongy pedal feel. So if it's not doing either of those, then don't fret about it!

Player0

Okay, great thanks! I'm working to replace all of the things that might fail catastrophically and I'm glad to know there is one less thing

I also mention it because my brake fluid reservoir leaks a bit after each run. I put a new cap on it because the old one didn't have a seal. But I still get hot ATE superblue leaking out of the top. Not enough to be dangerous, but I'd like it to stop. It even happens when the fluid has leaked out enough to be half way between Max and Min.

Anyway, figured I'd throw a new res on it and see if that helped, then considered changing all brake parts.

harveyf

That doesn't sound like normal behavior. You can get a new steel MC for a little over $100. Might be a good investment. They will fail you on tech inspection if you are leaking any fluids. Obviously you won't be leaking when you go through tech with a cold car but do you really want to be the guy that is dripping brake fluid on the track?

Player0

Well, as I mentioned, a new res is going on, since the new cap itself didn't work.

I wasn't sure if it was just a '944 thing' but I asked around and no one else seemed to have the symptom.

car_slave

It's a 944 thing. Most people wrap a paper towel or a rag around the cap and secure it with a zip tie.

harveyf

Uh, not trying to be argumentative but losing fluid out of a properly filled MC reservoir is not typical behavior of a 944 or any other brake system.

It would be the behavior of a MC with a very slight seal leakage that is putting backpressure in to the reservoir (where there shouldn't be any).

JET951

30 year old brake master cylinder on a 951 ! , wait until you realise how hot the master cylinder & booster gets even after a few laps around a track ( heat soak from turbo )

When these master cylinders fail on the track ( club stuff ) the pedal goes straight to the floor , ask me how I know

Same goes for the 30 year old brake booster , but at least when it goes ( torn/ perished diaphragm ) the pedal will not go to the floor , it just feels bad with a vacuum leak from the rear of the booster

Player0

Oh, so you've seen that behavior before? And replacing the master corrected it?

Player0

It's simple enough to replace the master if I'm replacing the res anyway. If there's any question that its a bit leaky I might as well do it and keep the spare and rebuild it. I'm always happy to have a spare anything at the track since I don't have a trailer

I don't think I'll mess with the booster though. The OEM one looks like its $600-$700 new (ack) though there are off brand units for like $250. I don't know if that would be a good idea or not.

67King

I know you have more experience with these cars that probably half the RL posting community combined, but having experienced a MC failure, it happened relatively quickly on me. No signs of anything, then in one session, I started getting degraded performance. I made a mental note "this is what pad fad must feel like," and started adjusting my braking to account for it. And then it went to the floor in Turn 1 at Road Atlanta about 2 laps later. Was able to pump it up, and keep the car on the track, but while it didn't just go "boom," it didn't give me a whole lot of notice.

FWIW, what I believe caused it was that the reservoir had buildup in it. Black, gunk like stuff that you actually see on street cars more often than you should. I think that clean fluid served to break that loose, and it made its way into my brake system. I couldn't figure it out, as the performance seemingly returned to normal. If anyone in the Atlanta area knows him, Chris Smith spent some time looking at it, and diagnosed it on the spot. No charge, and I'm always grateful for that treatment.

67King

Have you found a rebuild kit? I was not able to.

Van

Hey, I can learn too! I've seen master cylinders leak where fluid dribbles down the brake booster (or gets inside the booster). I've also had them get pretty spongy. Maybe the OP should change it!

Player0

On a side note, who needs brakes anyway.

car_slave

Harvey, from what I've seen, having a little fluid leak out of the cap after running on the track seems to be common on these cars - at least on most of the track cars I see with the hood up; including both 944s I've run. I think it gets out through the electrical connector.
Here's a link which shows the kind of thing I'm referring to. http://www.phantasmusa.com/skunk2bcover.html