Brake booster

[AikenDrum105]

Hi Mick - sorry to hear your brakes are still giving you grief !

Perhaps pump it up so the back brakes are locked on,  and then crack open the input line to the proportioning valve and see if venting that lets the back brakes off - if it does, the problem is upstream (booster / master )  if it doesn't - then crack open the output line of the prop. valve - if that lets the brakes off - problem is definitely the prop valve - if not,  try either end of the flexible line between the body and the diff, they can swell inside and act like a one-way valve  (although from memory you already replaced them ?    Those prop valves do collect crud / guck over time.  They're not rocket science inside,  on opening there'll usually be the remains of the seals,  a bunch of goop and the moving piston rusted / stuck in the bore.   if you can get it apart,  a brake place should be able to renew it for you - or you can polish the bore with a drill and some 800 or so wet/dry,  same with the piston,  get some new seals and away you go.   A brake place would be able to knock you up a little bypass line cheaply enough,  so you could take it right out of circuit and see if that sorts the issue before you strip it down.    The Prop valve has zero effect on the front brake circuit however ...

Re the front brakes - if you can apply pressure to the pedal,  open the bleed nipples and get a good stream of fluid as Col said,  but with the nipples shut and pressure applied,  the pads don't move against the discs - the front calipers almost have to be seized (they were recently rebuilt too weren't they? )   if the pistons aren't already fully retracted in the calipers (flush with the caliper face)  see if you can push them back in using a large screwdriver between the outer edge (usually rusty)  of the disc and the metal backing of the pad. It shouldn't take so much force that you risk marking the disc with the screwdriver to do this. 

I hope that helps a little  !

[mickl]

I pumped the brake pedal 8 or 9 times then released the line between the proportioning valve and the master and it released fluid and the back brakes. I retightened it and then pumped the brake pedal again followed by releasing the brake line between the prop valve and the flex line back towards the axle and it also bled well and released the back brakes. Does that now mean I have problems in the valve and also maybe the master? I have not replaced the back flex line but it carries the fluid Ok.
Is there some way I can check the master without pulling it off....I have been assuming the brake people who overhauled it have done it correctly.
I removed the brake pads of one wheel at the front and replaced them with some soft pine timber of a similar thickness and then pressed the brake pedal and held it on....just the slightest of contact between the pistons and the timber inserts.
All calipers both front and back have just been overhauled at a brake specialist...as well as the master cyl,  with two new boosters from UK with all being installed by me.
Thanks again for continuing assistance.
Mickl

[AikenDrum105]

Hi mate - sorry for the delay in reply,  Moving house / renovating  has precluded internet for a while   Hopefully you've already fixed the brakes on the car   but if not, maybe:

Rear brake problem seems like the master cylinder to me,    You mentioned the bleed screw rather than nipple - the screw on the side of the master cylinder has a machined nose at the tip - this actually screws in during assembly of the master and restricts the travel of pistonspiston - the bleed nipple should be right up the top - it *might * be possible the side screw has jammed one of the pistons in the wrong position (or is limiting it's travel the wrong way)   

The fronts sound like seized calipers - you can bleed fluid through them under pressure, but the pistons only move a little under pressure...    It could still relate back to the master jammed / assembled incorrectly.... allowing enough pressure to bleed fluid, but nowhere near enough to extend the pistons.... 

I'd probably start by taking the master out and disassembling on a bench - did we already link / send you the assembly diagrams for the various bonaldi, benditalia, ate flavours ?

Once the master / rear brake circuit is sorted - if the fronts aren't fixed in the process still an issue - you might have to get stuck into those calipers.

Cheers,

[mickl]

This has been a long path, with a couple of "time outs" but I have working brakes at last. The solution to it seems to have been in the piston from the pedal which goes into the master...the adjustment had not been changed since I took the master off many months ago as I thought it would not need to be altered. However, when i wound it out further things started to work correctly and although I haven`t taken the car out (as it is unreg), brakes seem OK now when tested in the driveway. Thanks everyone who put in their comments and assistance over the period.
Mickl

[AikenDrum105]

Fantastic !   well chuffed to hear you have them sorted !


Cheers,