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MG MGB Technical - Rear-end clunk and difficulty shifting

I just got my '79 MGB running again this weekend -- dead starter and bad battery -- and I've been enjoying the spring weather since. However, I've noticed for the past few days that every once in a while -- especially when braking or going over larger bumps -- there will come a slight clunk from the rear end. At first I thought that perhaps I had just mis-seated the new battery, but I no longer think that's the case.

Yesterday, I noticed that it was getting difficult to put the B into gear. This morning, I could not get it into reverse at all. I eventually turned the car off, shifted into reverse (shifting while the car off was and remains very easy), and turned it back on. To my incredible surprise, I was able to simply take my foot off the clutch and the car started rolling! I didn't need to apply any gas at all -- it was like driving an automatic.

Shifting continued to be difficult all the way to work.

Coming home today, I backed out of my parking space and could not physically shift the car into first. I didn't want to break anything, but I pushed pretty damn hard and it would not go into first. Most of the way home, I had to turn the car off at red lights and shift into first. I also found that it would roll quite happily without any gas applied. Moreover, if I got going and pushed in the clutch and let off the gas in first, I immediately deccelerated as if the clutch was not put in.

Then, about halfway home, I heard the phantom rear end clunk, and shifting immediately got a LOT easier. I could put it into first without turning off the car. It continued to clunk occasionally the rest of the way, and shifting got variously easier or harder. By the time I got home, shifting posed no problems at all and it felt as slick and easy as it should. I could put the car into first and reverse without any problems.

What the heck is wrong with my MG?

Let me rephrase that: Please don't tell me my clutch needs to be replaced.

I'm pretty stupid when it comes to anything aft of the engine, so I haven't the foggiest idea about this. I searched the archives, but most rear end clunks sounded axle- or diff-related, not clutch-related. As usual, any help you guys can provide would be most appreciated. Thanks.
Chris St. Pierre

Chris,

If you could get the car on jackstands and have someone depress the clutch while you examined the clutch slave cylinder for movement. You should see the rod move about 3/4 inch. If it doesn't move you have an issue with it or the master cylinder.

As far as the clunk, check for loose items in the trunk, ie spare tire not bolted down, etc. Carefully examine the u joints on the driveshaft. There should be no play.

Doubt your clutch needs replacement. Most of the time its hydraulic related. hth

Paul Hanley

Took it for a brief drive tonight, and it only got worse. I'm going to garage it until the weekend, when I'll have time to take a look at the slave cylinder rod.

I've done a little more reading up on the matter, and your suggestion certainly seems in line with what I understand. If you're correct, and it sounds like you probably are, how would I proceed to determine which cylinder is bad? If I figure out which is bad, would you recommend ordering a repair kit ($5-$15, depending on which cylinder) or a new cylinder ($50-$110, ditto)?

Or, is it possible that maybe I'm just low on fluid in the circuit?

Sorry so many questions, but I'd like to get this figured out this weekend, so I can get back on the road in time for nice weather!

As for the clunk, you were right -- it was a red herring. My knockoff wrench was floating around in the trunk.

Thanks for all your help!
Chris St. Pierre

Chris
"Automatic clutch" when there is no fluid loss is almost always leaking master cylinder seals - the fluid leaks back past the piston and into the reservoir. The loss of disengagement when pressed also accounts for the difficulty shifting.
It's possible air has got into the system though and hust bleeding it may effect a cure. Rich.
Have a look on this recent thread,
http://www2.mgcars.org.uk/cgi-bin/gen5?runprog=mgbbs&mode=thread&access=&subject=71&source=T&thread=2005022411004010519
Rich

This thread was discussed between 10/03/2005 and 11/03/2005

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