Mopar Muscle Association UK

Hi all, got a bit of a problem with the Chevette. I replaced the seals in the brake master cylinder last week due brakes randomly turning to spongy poo. They were fine for the week but have gone naff again and are like it most of the time. They do work but there is mega travel on the pedal before they do anything. I have never had a car do this before, its like having permanent brake fade. Is this likely to be the master cylinder or am I barking up the wrong tree?

If you hold your foot on the brake pedal and push down progressively, if the pedal sinks I would think the M/C seals have had it. Just a thought.

Either that or you do have a leak or air is getting in the system.

Another good test is to clamp the hoses off in turn and see if that changes the pedal fall.

Perished flexi hose ballooning under pressure?,maybe a wheel cyl seal worn and leaking/sealing on and off.

Interesting thought on the pipe. I replaced both the rear wheel cylinders a few months ago and the seals in the master cylinder are all new so they should be fine too.

You have brake fluid passing the new seals in your old M/C

Replacing the seals in an old M/C rarely works, this is because as the old seals were actually remove some of the bore of the M/C this causes a small ridge in the M/C and as you bleed the brakes the piston travels a lot further down the bore, this has the effect of chopping off the nice crisp edges of the new seals rendering them next to useless and the will get worse the more you use them as the reduced effort means longer pedal travel which again attacks the seals. The only way to do it probably is to hone the M/C before fitting the new seal kit and to be honest with you it just is not worth the hassle or the risk. Get a new M/C and the problem will go away..

Guy wrote:Get a new M/C and the problem will go away..

Dammit! That's easier said than done for one of these, no one lists one .

The car has done very low mileage (just gone over 22,000) and the old seals weren't worn they had gone hard. I'm starting to wonder if it has a brake binding and causing brake fade after 20 mins of driving, as I have just popped down the road to get some bread and the brakes were spot on. I'll investigate for a sticky caliper tomorrow.

when was the brake fluid last changed? and i mean totally

smacks of water in brake fluid

the stuff is like a sponge.

brakes work
brake fluid gets hot

water boils off to make bubbles
brakes don't work

brake fluid cools off water disolves into fluid again

brakes work

water boils
makes bubbles
brakes don't work

brake fluid cools

only had this once and it made the master cylinder seals and plungers go perrished and act like sponges they used to swell up when the water in them boiled and either not work or lock the brakes

tis the cheapest option before you go an get you MC honed out and if necessary sleaved.


Opel kadet one fits i would think but the pipes may come out on the wrong side.... look for german Opel Manta sites

Dave

Would the Chevrolet Chevette one be the same?
http://cgi.ebay.com/ebaymotors/1976-82- ... 61223423QQ

Dave999 wrote:when was the brake fluid last changed? and i mean totally

last week. While I had the master cylinder off I vacked out the lines with my air bleeder, and when bled the through I did it the good old fashioned pumpy pedal way.

I think I may have sussed it though. about a month ago I had to remove the exhaust fannimould to change the starter motor and I snapped a stud causing a blow. Last night in the dark I was revving the engine while under the bonnet, and it was popping big blue flames out of the joint straight onto the compensator valve. I would imagine that after 20 Minuit's or so of driving that valve gets bloody hot, probably boiling the brake fluid and probably causing brake fade. I have made a crude heat shield from tin foil to see if that makes a difference until I get round to finishing my 4 branch manifold I am fabricating for it.

Yup, thats it. I wraped the manifold to front pipe joint in foil to keef the heat from the front/rear compensator valve, and the brakes are fine all the time. I took the foil off and after 15-20 mins of driving the brake pedal went spongy. So I pulled over and the valve was way to hot to touch and I burnt my hand on it . Best I hurry up and sort that.