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MG MGB Technical - Bleeding Clutch Revisted, Help?

After experiencing difficult shifting, I replaced the hydraulic master cylinder, slave cylinder, and hose. Having a tuff time bleeding the system. Tried the pressurized reverse bleeding trick of pumping brake fluid from oiling can through the slave cylinder. Result: geyser of brake fluid from master onto fender. Please describe in detail your approach to bleeding the clutch. By the way, the clutch master cylinder is an after market non-stock appearing unit with a non-stock cap. Hints and suggestions welcome.
Steve M

Steve--- This won't help as I am having same problem, in fact I pumped the clutch pedal so much that I blew out the slave cylinder. Have that on order along with an aftermarket master from Moss. Is that what you have and does the original cluth pipe fit.
Now we can both wait for an answer to your ??? which may have something to do with how to bench bleed the master cylinder. BOB
Bob Radenbaugh

The only way I could successfully bleed the clutch system was to place a piece of plastic wrap under the screw on cap of the master clutch cylinder to make it air tight and then kick the clutch pedal about 50 times. Seems harsh, but it was the only thing that worked. Had to replace the return spring soon after that though.
Bob Johnson

This worked for me;

Fill resevoir, open bleed nipple at slave.
Let gravity drain for 15 minutes.
Remove nipple from slave.
Use finger at slave and do the open/pump/block/release method.
Do this several times until you get good flow at the slave.
Replace bleed nipple and do the open/pump/tighten/release method.
Do this several times until you get the system free of air.
Tighten up the bleed and check function of clutch.
Do this all the while never letting the fluid level fall more than 1/2".

Hope it works for you. -Brian.
Brian Johnson

Steve/Bob-
I think that the biggest reason it is so hard to bleed the clutch system is that the bleeder valve is not higher than the incoming fluid line. Gravity bleeding will work to clear the clutch line of air, but there will be a bubble left in the slave cylinder. What I have found that works is to simply unbolt the slave and hold it in such a way that the bleeder valve is at the highest point, relative to the incoming line. Holding it this way, the airbubble in the cylinder will naturally float up and out by gravity, e.g., the slave will fill with fluid from the bottom thus pushing the air out the top. since gravity is doing all the work, this is a one-man job. simply hold the slave with the bleeder at the highest point, crack open the valve, watch air bubbles escape, close valve once fluid comes out, and then reattach to the bellhousing.
HTH!
Ben Pender
Ben Pender

The easiest way tto get all of the air out of the clutch system is to blead in the normal way until no mor air comes out. Close the bleader valve and then manually push thpiston all the way into the slave cylinder. This pushes any remaining air back into the line from the master cylinder. Reblead the system in the normal manner to get the air in the line out. This may have to be repeated once or twice (seldom have I had to repeat the procedure) and the system will be free of air. This works on all the MGBs we have had and on our Mazda truck equally well.
Good luck - Dave
David DuBois

Ben and David,

I'll try a combination of your methods tonight.

Brain,

I tried something similar to your suggestion and went through too much brake fluid at resevoir.

Thanks everyone.

PS any thoughts of non-stock appearing master cylinder?
steve m

I also had problems after replacing the slave cylinder. I agree with the comment about pushing the pin back into slave cylinder with the master cap off. This did it for me.

John Harriott

This thread was discussed between 10/03/2003 and 11/03/2003

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