Master cylinder help and testing.

[PandaSelecta]

Bit of help please

When the campervan went in for the mot back in October, the tester said the rear brakes didnt do anything, the front brakes i think were okay, but the pedal crept down when held under pressure.

Seeing as how the rear brakes were new, I expected that the previous owner just had'nt bled them.

I have now fitted new calipers, pads and discs to the front, but when I came to bleed the brakes, I have these problems....

1: the pedal goes down and doesnt come back up.
2: when pumping the pedal by hand, no fluid comes out of the bleed nipple and the fluid in the reservoir stays the same (you do get a glugging sound).

I guess the fluid is getting past the seals inside the cylinder, but need to know if there is any other possibilities as new master cylinder are not available, nor are the seals.

Also is there any way of testing the cylinder when its off the camper?

[composimmonite]

Try www.pastparts.co.uk/ as they can normally help.

Paul H

[PandaSelecta]

Thanks Paul, i have emailed them

[Clamity]

I had some old wheel cylinders sleeved in stainless by those guys after an MOT failure. They were very good and had a fast turnaround time too.

[ianboyd]

try vacuum bleeding if you haven't already, it may just be a huge airlock!

are the hoses recent?, they can break down internally and block!

[nigelbickle]

The master cylinder prob needs new seals -but it may be airlocked. Take off the m/cylinder cap, open a rear bleed nipple -fit a long length of clear washer tubing (so you can see it coming!) & suck. If the rear hoses are OK, you'll quickly get a stream of fluid through; and enough time to lock off the bleed nipple.
If that happens -you've prob got a pedal -albeit mushy. Try the others similarily- you should get a hard pedal. If it still sinks -it needs an overhaul or replacing,
If you cant get fluid through- you've either left the cap on or the hose has collapsed internally. If the rear cylinders have been changed- & there's no braking effort yet some sort of pedal -I'll bet they're borked.

[bortaf]

I get this all the time when bleeding a system by the old master and manual pump it method, the master cylinder bores wear in a short area where the seals allwatys sit and operate, pump the pedal all the way down and teh wear ridge clips the tips off the seals and the master goes.
I only ever use pressure bleeders on old systems and pump teh master very slowly if needed to clear an airlock but it rarely comse to that.
Resealing will be a temp fix IF the master bores are worn in any way so check for a ridge in the cylinder.

[ChasR]

Another shout on the hoses collapsing. I have seen this occur more than once. That can be easily be checked if you take the hose off at the metal pipe end.

However, on an original set of brakes manual pumping can spell disaster as I have seen on a number of occasions for the reasons Bortaf has mentioned.

When you say no fluid comes out of the nipple is it only the one nipple or all of them?

[monkeytennis]

+1 on the 'don't pump it to the floor'. This can even flip the seal inside out on the plunger.