Brake Problem

[tomhunt85]

For a number of weeks I've been stumped by a braking problem that is pretty persistent and won't go away. At first the symptoms were of air in the system as the pedal had too much travel but then did stop well at the bottom of the pedal travel.

So far to solve this I've:
Replaced a rear caliper that was past it.
New seals on the Brembos
New discs as one was warped
197 master cylinder
ABS pump

It's been checked over and over for leaks and nothing's been found. The pedal is a little higher but does have too much initial pedal travel for my liking. Anyone had a similar experience or can shed any light on this?

 

[chaski]

How old are your brake hoses/are they OE?

 

[tomhunt85]

They're new custom ones to be the right length for the Brembos. Can't see any issues with them.

 

[f0xy]

What does the pedal feel like with the car off/servo disconnected?

I've had servo's go bad before where the diaphragm inside is at fault and causes all sorts of different feelings through the pedal.

 

[tomhunt85]

Annoyingly it seemed fine last time I tried it, admittedly haven't tried it since it's had the ABS pump changed though. From advice from a mechanic was that they didn't think it was the servo. You feel that's a realistic possibility?

 

[f0xy]

I never had a problem on my Clio ones, even with the heat from the exhaust manifold closer to it on a Mk1 than a Mk2 (ran a 172 servo on the Mk1).

Its possible, but id just give it a try, even with the car off just pump it a few times and hold, see if it stays solid or slowly goes down/feels spongy. If its the latter there is air in there somewhere still, possibly inside the ABS pump if its not been bled through fully..

 

[bashracing]

try it on the brake rollers at your local test station this could possibly show up a dodgy calliper

 

[tomhunt85]

It's definitely bled properly. Has been the same with two different ABS pumps and 4 litres of Superblue through it. The problem only seems to start once the car's started.

If I press the pedal twice when stopping the bite point of the brakes rises for the second press, so long as it's done soon after.

Don't think it's a caliper problem as we've replaced one and refurbished the front two. Also isolated individual calipers on the ramp and when started the pedal bite point drops.

 

[f0xy]

If its only happening with the car running I'd say it could be the servo - as with it off you're not pulling any vacuum through it. Obviously driving it without the servo connected is pretty sketchy as you've got no assistance or real braking power, but it could be worth a try if you've got a quiet back road local and keep it at very low speed. If you do try that make sure you block off the pipe when removed from the servo..

 

[tomhunt85]

For how much I've spent already, and that I'm running out of things to change to solve it, I might as well look to change it. Isn't the biggest or most expensive job. Thanks for the advice.