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MG MGB Technical - clutch leaking air somewhere

i am restoring a 73b the clutch master, slave cyls. and hose are new. when trying to blreed same are not getting anywhere. tried bleeding with vacuum hand pump and keep getting air, there is no fluid leak.
l.f. frank

Try "pushing" fluid up from the slave bleed nipple. An Eezibleed is good but use very low air pressure. Or a jar with a sealing lid with a bicycle inner tube valve set in the lid and a rubber /plastic tube siliconed in thru the lid.

Michael
Michael Beswick

Or even easier connect the right-hand caliper to the clutch slave, interconnect (same size nipples) open both, and use the brake pedal gently. Make sure there is room for additional fluid at the top of the clutch master, and keep an eye on the level in the brake although just 2 or 3 pumps shoud be enough.
Paul Hunt

if i open the bleed from the right front brake and the slave cyl. do i loosen the master clutch cyl. cap or leave it tight. the air must go someplace. thanks les
l.f. frank

Another tried and true method is to unbolt the slave cylinder, use a "c" clamp to force the piston all the way in to the base of the bore and bleed. This eleminates the space inside the slave that tends to trap some air. RAY
rjm RAY

The caps are either vented to atmosphere or have a flexible diaphragm to cater for expansion and contraction, if they didn't the brakes would start to apply themselves as the fluid heats up and expands in normal use.

I've not found it necessary to use clamps to push the piston fully into the cylinder, steady hand pressure should be enough. This treatment can be useful to push air that has gathered in the loop at the top of the pipe back into the master reservoir, but it shouldn't be necessary for bleeding because if you look inside the cylinder you will see that the bleed hole is drilled along the join of the cylinder and back walls, cutting away an arc about 3/8" wide (see below, circled), rather than just being a small hole like the fluid entrance has, and the cylinder is also tipped up slightlky in that dirtection unless the car has a nose-doen attitude.

You also have to be careful after pushing it in, if you simply let it go the spring in the cylinder will tend to push the piston back out again, which can pull air in again past the seal, the seal only being effective in one direction - BT, DT. With the piston pushed in you (or someone else) should operate the clutch pedal to push the piston back out i.e. while you are still attempting to restrain it by hand.

Paul Hunt

Funnily enough I've had this problem too, and found that once you get fluid through the system just let it stand for a day or so and it self bleeds. I think that the air is slowly displaced by the fluid.
I've had this happen with my B and many moons ago with a 58 Austin Lancer.

Herb
H J Adler

Vacuum bleeding pumps will suck air right past the seals, since the pressure is contrary to the way the seal is designed. You can suck air forever, even if all the air is out of the system.

FRM
FR Millmore

This thread was discussed between 03/11/2009 and 06/11/2009

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