Urgent help with brakes required!

[mingmong]

Help! I'm within a gnats whisker of finally getting my car (1977 C3) finished after 2 and a half years of work...BUT I've come across a slight problem. Taken it for some test drives and it runs beautifully for a few miles then seizes up, stalls and dies! Took the rear wheels off and found them both to be locked up. Thought it was the handbrake shoes (new) rubbing and getting hot and then expanding to lock the hubs but it's not. Looks more likely to be the calipers binding. Thing is it's a heat related problem 'cos if I wait a bit (15mins or so) the brakes then free up and I'm off again. Question to you all is could this be the case? Could it be air trapped in the lines expanding when it gets hot? The brakes themselves are good and firm, not spongy, so perhaps not? Is my master cylinder shot? (It's was replaced by PO about 5 yrs' ago) Any helpful replies would be nice...I'm SOOO close to having this beauty on the road and I'm only posting pics when it's all working!
Cheers Mark

[tonythetarga]

You probably need to replace the brake hoses. The OEM rubber lines tend to swell from the inside, causing a restriction of the fluid to return and that keeps your calipers and pads engaged. Get yourself some new lines, either rubber or braided steel and this might be the fix you need.
What is a C3?

[masraum]

If you haven't already, like Tony said, replace the rubber lines, rebuild the calipers too.

[DW SD]

I'm not sure I would have guessed brakes, when you write: "seizes up, stalls and dies!".

Are you sure it is not an engine problem?

Maybe you could clarify the symptoms more? If it is a brake issue, can you try manually releasing pressure from the bleeders to see if that resolves the problem? I think you could bring a hose and wrench to open up the bleeder and see what happens. Bring a friend so you can bleed them, if necessary.

I think this test would confirm the issue with the soft lines (or possibly with your master cylinder.)

Doug

[madmmac]

2 1/2 years of sitting I would guess the calipers have frozen up and are not releasing and heating up.

[Bill in OKC]

There is a similar problem on Brembo equipped motorcycles. If the master cylinder doesn't release fully, the piston still covers a bleed-back port inside the cylinder wall. After a few uses the fluid expands in the lines from heat and cannot escape back to the reservoir when the brake is released. A kind of feedback starts where the expanding fluid presses on the pads and this creates more heat expanding the fluid until the brake locks up solid. I don't know enough about Porsches (yet ) to say if something similar could be happening.

[mingmong]

Thanks for your replies.
Doug, It's definately the brakes 'cos I can't turn the wheels if I jack the car up. Nothing to do with the engine. That runs fine in neutral. I'll bleed them again today and see what happens.
Everyone else..Brake calipers stripped down, rebuilt, new seals, pads, springs. Fitted on about 1 month ago. Got stainless briaded lines fitted too filled with 'racing blue fluid' so don't think it's any of them. Checked for leaks and found none.
Bill..you might be right about the MC. I'll do some testing today.
I'm thinking it might be the vacuum line. Apparently there's a 'check valve' on it somewhere. Perhaps this is the wrong way round. Anyone know where it's located on a C3 (Carrera 3.0)
Keep 'em coming or you get no pictures!
Mark

[POKDUB]

Maybe with your recent rebuild this is not your particular issue, however here is my recent experiences.

I had exactly the same thing happen to me two weeks ago. After about 20 mins of driving the car would grind to a halt. Wait 15 mins and off again.

After the discs cooled, I drove for another 5 mins, felt the four discs, one was much hotter than the rest. Took off the calipers and pushed out the caliper pistons, light ring of rust on both was preventing the pistons from properly retracting, cleaned with a cloth, and put back on, now brakes are 100%

The most difficulty I had was with getting the pistons out. With caliper off and drained, I managed to get one out using a electric tyre pump pushed against the brake fluid inlet. Used piece of rubber glove with small hole in it to effect a simple air seal. Pressure built up and she popped out, gave me a bit of a fright.

The second piston would not budge so I had to refit the caliper and reconnect the hydraulics. Clamping the other side, with pads out, I was able get the stubborn one out far enough, then removed caliper again, cleaned the light rust ring on this as well.

My car had been lying idle for a time so I think with more activity on the pistons now this wont happen again in the near future.

[DW SD]

Since it is a brake issue, can you try manually releasing pressure from the bleeders to see if that resolves the problem? I think you could bring a hose and wrench to open up the bleeder and see what happens. Bring a friend so you can bleed them, if necessary.

I think this test would confirm the issue with the soft lines (or possibly with your master cylinder.)

Good luck!

Doug

[mingmong]

Problem solved! After bleeding all the brakes I discovered that sometimes the footpedal wouldn't return fully. This was enough to make the brakes stay on. Adjusted the push rod connecting from foot pedal to MC lever et voila...problem appears to have gone. Now I just need to wait for the sun to come out and I'll take some pics of my new car in all it's glory. (Assuming something else doesn't go wrong betwen now and then!) Cheers for your replies everyone.
Mark

[stevepaa]

I would suggest replacing the lines. They do swell with age and then when you apply the brakes, one may restict fluid and you pull abruptly to one side. Took me quite some time to figure that out.