cant diagnose brake problem

[liam012]

ok - since doing the rear disc conversion we have done two test runs
the first with long pedal travel feeble brakes and the the pedal going away from you under braking.
master cylinder replaced and go on second run- very deep pedal no brakes no feel then bang you lock up the wheels. no feel at all basically and to much pedal travel.
Ant has suggested a PRV below the master cylinder? what is this and what should i do when i find it and should it be there now i have discs all round?
any ideas on what is going wrong.

all discs and pads are new and calipers overhauled new braided brake hoses.

any suggestions most gratefuly accepted!

[zaust]

Just a thought.. when you jacked your car up have caught a breake line and squashed it ?.
When you changed the cylinder did you check if the servo had fluid leaked in it ?.

[liam012]

lines appear to be ok....
and no fluid leaked in as far as i could tell.

[zaust]

It dose sound like the servo from wht you have written.

[kam-325i]

Might not help...but cant hurt....

back in 19long gone....i had a Lancia Delta (HF wannabe !!), i had to do some work on the rear sub frame due to rust, so the back end was stripped....after putting it back together, i had a similliar problem with the rear breaks....after hours of bleeding the lines and banging head on wall, it turned out to be a bit of crap had gotten into the rear flexi hose, after getting it out, problem solved....

[Gortour]

It dose sound like the servo from wht you have written.

With engine off, pump the brake pedal half a dozen times, stand hard on pedal and start the engine. If the pedal drops when the engine starts, the servo should be OK. If pedal doesn't drop, servo is mullered. Hope this helps.

[liam012]

mmm servo seems good and they are bleeding normally which i presume they wouldn't do if the lines are blocked....
is it possible that this master cylinder is also not good as it was second hand and that its causing the problem?

[Fushion_Julz]

PRV is, I presume, the pressure regulator...No 5 in here:
http://www.realoem.com/bmw/showparts.do ... g=34&fg=15

Could be that, I suppose, but it sounds much more like the master cylinder has a duff seal and is leaking air...

You can get a service kit with new seals, etc, assuming the cylinder bore isn't corroded...

[316eyes]

Try bleeding the master cylinder as it can sometimes get an air lock.

Cured a similar, but not as bad, problem on my 316i.

[Gortour]

Well worth gettting a bleed kit to do the job easily. Gunson do one called Easi Bleed. Basically, you have a bottle filled with brake fluid, the bottle has 2 pipes, one pipe has a lid on it which screws onto your master cylinder, the other has a tyre valve on it. You pressurise the system with tyre pressure (reduced to about 15psi) and force the fluid into the brakes. Go round doing all the bleed valves on the brakes, let the air out till neat fluid comes out, job done. Only thing you need to do is make sure the level of brake fluid in the bleed bottle doesn't go down too far or you pump air in instead.