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MG Midget and Sprite Technical - Clutch - master or slave?

Ok noticed there was fluid on the driver's mat and running down the clutch pedal. Sure enough the seals in the master cylinder were past their best and were renewed.
Replaced the slave cylinder as a precaution as well and fitted a Lawrence/Guy remote bleeder where the nipple is at or slightly higher than the level of the master cylinder.
However I can't bleed the bleeder! The pedal is limp and doesn't have enough pressure to pump the brake fluid through the bleeding tube - it gets about halfway and that's it. I've checked for leaks and there aren't any. Begining to think the new seals in the master haven't worked; the bore seemed ok (no scoring) and it was thoroughly cleaned before putting them in.
Have I missd something 'bleeding' obvious?
Jeremy Tickle

Last time I had this, the groove in the master piston wasn't totally clean, and the skirt of the cup was out of shape - sort of convex when seen from the side, when it should have been straight or concave, and letting fluid by.
Nick and Cherry Scoop

If you are minded to buy a new master cylinder then check the MGA archive.
Lots of complaints about TRW Masters either leaking out of the wrapper or suffering residual pressure. The AP Caparo ones are favoured or you can have your own sleeved by the likes of Past Parts who have done some slaves for me.
Alan Anstead

Thanks for the responses chaps. I'll take the master apart again to check it. Alan thanks for the heads up about the new ones, I'll have a look at the MGA forum.
Jeremy Tickle

Did you bench bleed the master 1st
Prop and the Blackhole Midget

No I didn't Prop, how do you do that?
Jeremy Tickle

I think the essential part of all this is ensuring the new cylinder seal comes back far enough to open the transfer port

Make sure the push rod comes back enough for the seal to let fluid down out of the reservoir

And maybe make sure the transfer port is clear so fluid can descend into the master

The port is often just a very narrow hole between the reservoir and master

Maybe a new master would solve the problem, they arent very expensive
Bill sdgpM

I'm thinking that way myself Bill but the current one is NOS which I bought from a retired chap in the late 80s, is original looking and I'm loath to replace it if it can be repaired. But I would rather have a clutch which works!!
Jeremy Tickle

Well it looks as if you will have to open it out again, make sure the transfer port is a: open and b: doesnt have any 'fraise' sticking out into the swept volume the seals pass along

Any slightly raised metal will wreck the new seals

I found that the transfer ports in a 'new' twin master cylinder I had didnt have a clear port, it needed a tickle with a very fine needle to get fluid going again
Bill sdgpM

I think this is fairly common when the system has been fully emptied and there is just too much air in the pipe and slave for the hydraulic system even to build enough pressure to bleed. Sometimes you can get things started by rapid repeated pedal strokes, not letting the pedal rise more than about half way each time.

Another thing that helps is to reduce the overall volume of the system by pushing the slave piston as far up the bore as possible and locking it there by some sort of improvised clamp. Do this with the bleed valve open so that you dispel the air from the slave rather than pushing it back up the pipe. Then proceed with bleeding in the normal way.
Guy W

Cheers Bill, looks like its removal and disassembly may be on the cards (I may buy a replacement just in case).

Guy - the 'repeated pedal strokes' has worked in the past - more from frustration than design:) Haven't
done the 'clamping the piston' this time as I hoped having the bleeder higher up would remove that need. I'll try this first before biting the bullet and pulling it all apart again. Oh for a cable operated clutch!
Jeremy Tickle

How to bench bleed a master... it just gets fluid into the pump, so it can push it out

You want to keep the lines above the top of the resivor
Prop and the Blackhole Midget

Thanks Prop had not seen that before, never too old to learn something new!
Jeremy Tickle


I hadnt seen that before untill I got the midget.


Prop and the Blackhole Midget

This thread was discussed between 26/10/2015 and 29/10/2015

MG Midget and Sprite Technical index

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