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Strange brake master cly problems ?
Jon Ison - 7/7/10 at 06:23 PM

Anyone ever had this ?

Brake pedal without any warning gone absolutely rock solid ?

Thanks to Chris Mason had a go at looking into it but got no where other than I had moving brake pedal again but no brakes, zero.

I have cylinder in bench right now, put fluid in top absolutely nothing flows from the outlets, I know its fubard but never ever gained a solid pedal, lost one yes but stuck solid ?

btw, it decided to do this at the end of a 120mph (GPS reading) straight earlier today at cadewll which leads nicely onto wanted......

Pair rear arches and sheet for a back panel, I count myself very lucky, bit of a stiffy in the neck and minimal damage to car considering...........

A) it could have been on the road
B) it was a genuine 120mph incident only throwing it into a spin with the handbrake then making sure it went in backwards saved the day to minimal damage.

Anyone ever had this or heard of such a failure before ? ?


britishtrident - 7/7/10 at 06:38 PM

Sounds like the push rod isn't allowing the master cylinder piston to come fully back, this is a very common problem with home builds.


Jon Ison - 7/7/10 at 06:40 PM

That was my though but doesn't explain the malfunction on the bench ? The piston is full retracted.


tomgregory2000 - 7/7/10 at 06:44 PM

Bent push rod?


britishtrident - 7/7/10 at 06:48 PM

quote:
Originally posted by Jon Ison
That was my though but doesn't explain the malfunction on the bench ? The piston is full retracted.


Pushrod is usually at an angle in the at rest position.
It just needs to block the piston by a tiny amount the size and shape of the mushroom end of the pushrod is critical.


mangogrooveworkshop - 7/7/10 at 07:08 PM

just had a mc do a very similar thing. It kept on locking up and the wheel cylinders would eventually clamp the fronts until they stopped only letting go once I cracked a brake union nut letting out the pressure. The mc had been pushed a few times dry as we were repositioning the pedals. It also had a leak into the footwell...
replaced it 38 quid

[Edited on 7-7-10 by mangogrooveworkshop]


Jon Ison - 7/7/10 at 07:09 PM

but..........

The cylinder is on the bench, reservoirs out, pistons fully retracted, fill with fluid just sits there nothing is flowing ?

What am I missing ? Obviously some sort of blockage but what ?

Ive always bled brakes this way on 1st install, remove all bleed nipples fill with fluid, let it bleed itself ?


Jon Ison - 7/7/10 at 07:10 PM

quote:
Originally posted by mangogrooveworkshop
just had a mc do a very similar thing. It kept on locking up and the wheel cylinders would eventually clamp the fronts until they stopped only letting go once I cracked a brake union nut letting out the pressure. The mc had been pushed a few times dry as we were repositioning the pedals. It also had a leak into the footwell...
replaced it 38 quid

[Edited on 7-7-10 by mangogrooveworkshop]


This was the opposite, the brake pedal was stuck at the top, solid as a rock not brakes locked on, locked off ?