Brake pedal goes to floor after hard braking...

[derekgale]

1983 Pininfarina Spidereuropa

I took "The Pinin" out for a drive today - here in the south of the UK. I have my annual safety test (MOT test) coming up, so I did a brake test during my drive. Recently the front brakes have been pulling to one side on light braking, but OK with more pressure on the brake pedal. I did a few "emergency stops" and they seemed OK, but when I came to brake again the pedal went to the floor - and there was a nasty smell (not me!). No change with pumping the pedal up and down - still no pressure. I drove slowly, so I could stop and check what was happening. No fluid leaks visible anywhere, so I assume it was the brakes getting very hot and the brake fluid boiling. On leaving the car to cool for a while the pedal pressure came back and the brakes were OK.

This has not happened to me before. Is it normal with these cars for the fluid to boil, or is there something else happening?

Having working brakes is kind of important to me...

Derek

[kilrwail]

It would take a LOT of hard braking to boil the fluid - like you'd experience on a track. I'd be suspicious of sticking calipers, which might also explain the previous pulling. It was a warning sign.

[majicwrench]

I have seen brake fluid boiling problems with customers driving down some of the big hills in my area....I have done it once myself years ago. It is very possible, esp if you have old brake fluid. When moisture gets in the fluid the boiling point goes way down.
Make sure calipers not sticking, flush brake fluid.

[djchan]

If you have a sticking caliper, or after extended hard braking, all the metal in that caliper area will heat up so much that the brake hose will soften up, and blow up like a balloon when the pedal is depressed, hence steel braided lines.

[derekgale]

Thanks for the responses. It's on my list to do a complete brake service, and will take into consideration the idea of fitting braided hoses.

Test yesterday was fine, and it seemed to be braking in a straighter line - perhaps the heat de-stuck a sticky caliper?

Safety test due on Saturday. I'll report back...

[derekgale]

Ok, here's where we are today (23rd Oct 2010) ...

Car is now MoT tested (UK safety test) and is back in my garage. It's been an interesting excercise to get it sorted, not helped by me being away in Ontario on vacation for 2 weeks.

Car now has 2 new front calipers, new front brake pads, and (mostly*) new brake fluid. It was fun getting the new calipers. My car is a late 1983 model and the front brake caliper** sent originally was for a later car. It would seem my car was made during the time Pininfarina was switching caliper types - or they grabbed whatever was in the parts bin. The 2 "New old stock" (NOS) refurbished calipers of the right type bought subsequently from a specialist were both faulty, and leaked. The banjo bolt theads on both calipers were stripped. Turns out all their NOS stock is like this! A second pair of rebuilt calipers, not NOS, from the same supplier fitted perfectly - and didn't leak.

It's all part of the game of owning a classic car I suppose.

* rear caliper bleed nipples are stuck.

** thought the garage told me it only needed 1 caliper, but it actually need a pair.

Cheers,

Derek.

[TulsaSpider]

Glad you are making progress! The rears on mine were completely non functioning, so after that was remedied it made a nice difference!

[Hvnfn]

Quick question on the hard line to soft line on the brakes... Because the hard line screw and the metal used on the soft lines are dissimilar, what is your opinions upon using loctite blue or some thread sealant in order to prevent oxidization leading to future frozen brake screws? OK to do, or serious no no?

I apologize if this was covered in some other thread, I didnt see it when I searched...