Brake master cylinder won't bleed

[jocklow]

I have been rebuilding my discs (TR3A) with new pistons and seals. But now that I need to bleed the system  I cannot get the master cylinder to pump fluid  ( with a brake bleeding non return valve on the caliper bleed screw. I've even tried disconnecting the outlet at the master cylinder and putting my finger over it. When I compress the piston it pushes air out of the outlet past my finger but it doesn't suck in fluid on the return stroke. I've dismantled the cylinder and the spring pushing the the piston and seal that closes the line to the reservoir is so strong I can't compress it by hand. I can see that this could work when it's all got fluid in it, but when both calipers and the pipes to then , and the master cylinder, have air, then I don't see how it'll ever get going.

Or do you have to somehow fill it all with oil first. If so, how?

Does this ring a bell with anyone ?

[Lebro]

It only "sucks in" fluid when the piston has traveled all the way back away from the cylinder. check that it can do that, & the pedal adjustment is not stopping it from doing so.

Bob.

[jocklow]

Not the problem. But I do see what you mean. That would require the little mini piston and seal at the inlet end of the cylinder to slip backwards freely, because when the whole system has air in it instead of fluid, there's not going to be much suck. What is the purpose of the nylon cage that sits on the end of the mini pistion and holds the seal on the end of the piston. I can't find a drawing of the cylinder , just sketches of the exterior.

[BlueTR3A-5EKT]

Here you go out of the Girling parts catalogue.  This is an original Girling CV cylinder in pdf format

Cheers

Peter W

PS  N.S. next to the item description means Not Serviced, so it was not a spare part that could be bought from Girling.

scan0034.pdf

Edited August 25, 2020 by BlueTR3A-5EKT