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MG MGB Technical - Stange clutch issue....

So the clutch on my car is behaving quite oddly. When the car is cold, depressing the clutch pedal does not fully open the clutch. But after the car warms up, it opperates just fine. Pumping the clutch pedal prior to starting the car does not have any effect, nor did bleeding the system. But after about 1/4 mile of driving the clutch operates normally, and will for at least a few hours after the engine cools down again... I have no idea what is going on here, any help?
Ben

Are the symptoms difficult gear engagement, as in lever seems hard to push, or slight crunch on moving into a gear?
Or does the car creep forwards when in gear with foot on clutch?

May just be thick cold oil in the gearbox, thins out when it warms up after a couple of miles. Mine suffers from this, ever since I changed the gearbox oil. I did think of filling it with ATF next time.
Martin Layton

Yes, the car creeps forward when I try to put it into gear... It also wont roll down an incline with the car in gear when I push in the clutch with the engine off.

If its the thick gearbox oil... Is this (hard to engage gear, car creeping forward) going to damage my transmission if I dont get it sorted out promptly? I should mentione that i havent changed to oil in the gearbox recently, and this just started happening... and it hotter here now than it has been in previous months when it did work fine. Also... From a stop, its far easier to get it into 2nd-4th... and if put it into 4th, and clear the gearbox REALLY FAST it slips into 1st fine. It will not go into reverse until its "warmed up"...

Thanks for the reply.
Ben Davids

It does sound like the clutch is dragging.
Why it should stop when it has warmed up I don't know.

Possibilities that I can think of:

Contaminated clutch plate, sticky when cool? (Doesn't seem very likely)
Clutch plate sticking on gearbox splines?
Input shaft bearing inside crank seized, and frees off when the engine is hot?

It is quite hard on the gearbox, so I would try and get it sorted.

Doesn't sound like hydraulics as pumping the clutch doesn't make any difference, or gearbox oil (as long as it hasn't run dry), so it looks like the engine has to come out, but I would wait for more suggestions before taking this step.
Martin Layton


A worn clutch can give dragging symptoms. My 65 MGB started having trouble intermittently and finally wouldn't release. I drove about 15 miles home without a clutch. Upon disassembly it was obvious the disk was worn close to the rivets and several fingers on the pressure plate were broken.

By the way pumping the clutch hydraulics won't increase release stroke due to the design of the master cylinder.

The slave cylinders are quite hard to bleed and it doesn't take much loss of stroke to cause clutch drag. A worn slave cylinder can also leak and allow air in. I'd double check this again before I pull the engine/trans.
Robert McCoy

There have been numberous threads regarding gearbox oil. The majority have gone to using 20/50. You might want to check the archives before attempting to use ATF. If I remember correctly that was a no-no.

Even though the system is blead you might still want to make certain the hose from the slave cylinder is not soft. Just like brake lines if the hoses are not in good condition the hydraulics will not operate properly.
Lee

Ill try a re-bleed,

Regarding the gearbox oil... Should I try changing it out? Is it likely to cause these symptoms? The bit that has me confused, as I stated, is the car runs perfectly after about a 3 minute drive. I should also mention... when I first get in, the catch point of the clutch is with the pedal ON the firewall... And it progressivly moves to its regular position as the engine / transmission warms up. I havent checked if the slave is moving its full length prior to the warm up... Ill check that out this evening. If it isnt, im asuming that its either a bum slave, or air / water in the system? And it isnt leaking any haydraulic fluid... I checked that.

And regarding the worn clutch... The current clutch had about 3,000 miles on it. The previous one I had used for over 75,000mi... Im not sure, but its possible that it may be the original clutch. My father cant recall replacing it whil he drove the car. (from 1979-1996) We replaced it while the engine was out of the car, and it still had plenty of wear left. I mention this only to point out that I dont abuse the clutch. I would be surprised if this one was worn...
Ben

And thanks again for the input fellas.
Ben

This thread was discussed between 23/08/2007 and 27/08/2007

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