Sudden Brake Failure

[Neil-yaj396]

My drive out in the sun today was spoiled somewhat when I went to brake and the pedal hit the floor before anything happened. I had to brake the rest of the way home by pumping the pedal, which would achieve adequate braking. The brakes had been pulling the car to the left slightly prior to the failure, which was not noticeably occurring before today.

No leaks or loss of fluid, no recent replacements or adjustments to the system. The front OS caliper has been a bit sticky on and off recently, and was on my to do list to strip and clean.

Possibly my imagination, but the servo pipe seemed soft when I gave it a squeeze, then seemed firm when I did the same 2 minutes later.

Any ideas where to start?

[WestonE]

That sounds truly scary Neil. A Servo fault alone would not do this. You could have a failing one way valve and or leaking Vacuum pipe to the Servo. This would mean more force on the pedal to stop the car. But this sounds like Master Cylinder seal failure for which the sensible solution is a new master cylinder. Are you sure there is not brake fluid leaking around the front caliper seals when you take them off the pads?. MCs Fail often on Betas where brake fluid is not regularly changed over their lives. The water in the fluid rusts the inside of the MC then when they are bleed the seals travel over the rust getting trashed. Beta MC is very similar to Early Integrale MCs BTW.
Do check slowly and carefully over every Brake fluid joint for the wet hand of doom. Good luck and well done for bringing it home un bent!   

[SanRemo78]

If there's no obvious puddles at any corner or joint I'd expect the sudden loss to be master cylinder related too. If there are no signs of leaks underneath the master cylinder itself then I'd remove it and check for fluid leaking from the pushrod into the servo itself which might explain the lack of puddles. If there is then remove the servo and clean that out too. Luckily that's one circlip and four nuts behind the passenger footwell and easy to get at.
Guy

[peteracs]

Hi

Does sound like M/C, but not sure why it should pull to one side, though may be two issues of course.

As mentioned new M/C is not too expensive and fairly easy swap assuming you can open the bleed nipples.

Peter

[stableblock]

or possibly corrosion on one side brake lines leading to fluid loss under pressue.  That would also result in the car pulling to one side. 

[SanRemo78]

What is the fluid level like? If it's not dropped in the reservoir check the brake flexis for bulging under pressure too.

[betabuoy]

I think you've got some great diagnosis in this thread Neil and it reads as if you have two braking problems.  First, get those front callipers stripped, pistons cleaned and new seals - at least the RHS anyway! Next, either recondition or replace the master cylinder... if there's no fluid loss and the pedal reaches the floor, this must surely be a damaged seal.

[Neil-yaj396]

Thanks for all the great replies. Should have mentioned that the reservoir was full to the brim, it was obviously the first thing I checked.

Back from Oxford now so can progress things.

Any known suppliers for and MC if I need it? Can't see any in stock with the usual suppliers?

[Nigel]

Neil,
I googled 2 part numbers: 82293524 and 82369266 and Spareto appears to have stock
of both. I can't see the difference, the piston diameter is the same, but best check other
details.

Nigel

[peteracs]

Hi

This Delphi is what I bought for the HPE (and may have done for the Spider)

https://cars245.com/en/item/delphi-LM29584-brake-master-cylinder

Peter