LocostBuilders - powered by XMB

brake master cyclinder - repair or replace?

aka Keith - 19/3/12 at 10:35 AM

It is beginning to look like the master brake cylinder in my car is on the way out (brakes bind on after a 10 miles or so) and my thinking is that one of the seals in the MC has swollen and not allowing the compensation ports to work properly..
..
so how easy a job is it to service a MC with a kit or should I simply replace the MC?

Cheers
Craig

pekwah1 - 19/3/12 at 11:33 AM

are you sure it's the MC?
I would have thought brakes binding would point more to the calipers?

If it is though, a MC refurb isn't too tricky assuming it's in reasonable condition.
The difficult part is getting it primed correctly to reinstall...

aka Keith - 19/3/12 at 11:54 AM

pekwah1

I am assuming it is the MC.

I have bled the brakes and when cold there is no binding at all
When warm (ie a few hard stops) the rears and fronts (in pairs) bind so unless all 4 calipers are on the way out then my logical thought process is is that the MC seals have swollen and the compensating valves are not clear, therefore after a few hard stops the fluid heats up and the valve does not allow the pressure to be released ergo binding.

Got home on Sat after a shakedown and both fronts were binding
Got home yesterday after bleeding the brakes and both rears were binding

whipped out a spanner and released the pipe to the rears at the MC end and bingo the car was movable

Yours
Craig

owelly - 19/3/12 at 12:23 PM

Are you sure the m/c is adjusted cotrectly? It sounds more like the piston isn't fully returning when the pedal is released.
Back to the original question......
If a new m/c is a few quid, just buy new. If you do decide to rebuild, check the bore/bores are perfect. Any scratching or pitting and you're wasting your time.

aka Keith - 19/3/12 at 12:41 PM

quote:
Originally posted by owelly
Are you sure the m/c is adjusted cotrectly? It sounds more like the piston isn't fully returning when the pedal is released.
Back to the original question......
If a new m/c is a few quid, just buy new. If you do decide to rebuild, check the bore/bores are perfect. Any scratching or pitting and you're wasting your time.

Owelly, I thought about that, but then I have been driving the car for the last 4 years with the same set up and it has only just started to happen.

I have not mucked about with the pedal and box - so why would it start happening now?

Cheers
Craig

britishtrident - 19/3/12 at 12:43 PM

It is likely the pushrod isn't allowing the master cylinder piston to come fully back, the mushroomed end of the pushrod should always come full back against the stop washer at the end of the cylinder when the brake is off.

aka Keith - 19/3/12 at 12:55 PM

quote:
Originally posted by britishtrident
It is likely the pushrod isn't allowing the master cylinder piston to come fully back, the mushroomed end of the pushrod should always come full back against the stop washer at the end of the cylinder when the brake is off.

Britishtrident, thanks for the note, but my prior question I think still stands, if the issues is pedal and piston, why has it only just started to happen after 4 years on the road?

Cheers
Craig

big_wasa - 19/3/12 at 01:13 PM

I've had the same problem with a wildwood mc.
They look like Sealed unit so I've replaced it and it has sorted the problem.

aka Keith - 23/3/12 at 12:19 PM

A quick update.

Took the brake pedal assembly off adn removed the pushrod likage from the pedal.

there is now a drip of brakefulid coming out of the mast cylinders.past the bore hydraulic seal and snap ring so I assume that the mc is fubarred - correct?