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MG MGB Technical - Clutch-ing at Straws

Hi Team!

Hope all is well. Am having a little problem with my clutch/ gear change. Basically the BGT doesnt want to go into gear. The little tank in the engine bay by the pedal box for the fluid is empty - presume I have a leak. I want to refill it so I can try to find the leak to fix the problem. What do I fill it with? I have been told to use brake fluid. Is this right, what type and where does one get some from?


JP Mutton

James, The clutch master cylinder calls for DOT 3 or DOT 4 available at any auto parts store. Your leak is probably at the slave cylinder mounted under the car. Ray


James, sometimes a leak in master cylinder (under the bonnet next to the brake master cyclinder) will show up with fluid leaking into the car. I have experienced this with fluid migrating down the clutch pedal onto the rubber mat. If you remover the cover from the clutch and brake master cyclinder (4 screws I think) you can see the rubber boot at the end of the master cyclinder. You can expect to see leaks here if the master cyclinder is the problem.

Seal kits are available for both master and slave cylinder. With the master cylinder there are a lot of good reasons to replace with a new one instead of trying to service an old one. The archives can help you with this. Also check the condition of the pipe to the slave cyclinder which can also degrade and cause a loss of pressure.


Also buy your self a small funnel. Super market for about a dollar. It is dreadfuly easy to spill brake fluid and of course it rips the paint off where ever it choses to flow.
If you have never topped up the reservoir before, then the master and slave cylinder might be OK. This should have been done as part of the service schedule, it may not have happened. Anyway you will need to refill the system in order to see if either the master or slave needs to be replaced

You will also have to bleed the slave cyliner down on the clutch. It's not hard to do (unlike the rear brakes) since gravity is assisting you. You need to get the air out of the line and the slave.
You can also buy cheap "brake bleeding" kits, which are just a small plastic bottle with a plastic tube that attaches to the cylinder niple and runs to the bottom of the bottle. About $5. You could make your own if you wanted to. You just need some plastic tubing the fits over the bleed nipple. Any clear plastic tubing will do, since it is a 'once of' use. It helps if you can see any bubbles of air, hence clear.
Fill the reservoir, Crawl under the car and you will see a nipple on the side of the cylinder. Unscrew this a few turns and let the air out. Tighten it up a little so fluid is just barely seeping out. You might want to attach your plastic tubing at this point. Give the clutch pedal a few pumps to force out any residual air. Then do up the nipple. Don't over tighten this and wreck the thread. It is a very small screw and it is tempting to over tighten.

Just thought, It may well be the hose at the bottom that is shot. In fact, the most likely candidate really. Rubber hose 40 years old etc. Have a look at this first and replace if dodgy. Also have a look at your brake hoses, which may well be the same age as your clutch hose.

This thread was discussed between 13/09/2007 and 15/09/2007

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