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MG MGB Technical - Clutch slipping

Strted to notice that I have a slight clutch slip. It is noticable when I make a fast change into 3rd or 4th with quite high revs.


Is this the symptoms of an oil leak? My father commented that this was a real problem with his old BL Maxi and he 'thinks' this is the same engine and box? He said he used to keep 2 clutch plates and swap them out for cleaning every service (maybe that was just an excuse to hide out in the garage).

What is the best way to change the clutch? Engine & box out as one, or just drop the box? I only have a home set up so no ramp but I will have an engine crane soon. How long is this job and is there anything that I should look out for?

What else should I do while I am doing this job? Is it a good time to service the overdrive etc?

Cheers all


G Lewis

Oil on the clutch will usually cause a shudder when letting out the clutch, sounds like yours may be just worn out. You will need to pull the engine to replace the clutch, the trans can't be removed with the engine in. You may want to have the flywheel resurfaced if worn or grooved, replace the throw out bearing and pressure plate. If you buy a "clutch kit" it will come with all three pieces. You may want to replace the engine rear main seal and the trasmission first motion shaft seal while you are in their.
John H

Just looked over the past recipts and it had a clutch (though no details of which parts) 4000 miles ago. Should last longer than that, though it has had 2 owners since so I don't know how it was treated.

G Lewis

A new clutch should easily last 40,000 miles or much more. Check that the clutch hydraulics are working correctly, if the hydraulic system is keeping pressure on the slave cylinder when the pedal is all the way up this could be causing the problem. When the clutch was replaced was the pressure plate also replaced? If not it could be tired. If one of the previous owners could have worn it out depending on driving styles, it is possible to toast one quickly.
John H

I'm not sure what was replaced, I'll have a look at what was charged for parts later, that might give me an idea.

Never having worked with a hydraulic clutch before what should I be checking for?


G Lewis

One of the previous owners might have been what I call a "clutch rider." Some people develope horrible habits and one of these is that of continually leaving one's left foot on the clutch pedal, either consciously or otherwise. This, of course, has the effect of slightly depressing the clutch - or letting it slip a bit. Over time, this adds wear and takes a toll. John is right - a new clutch should easily last well over 40,000 miles.

Another possibility is that you live in hilly country. When stopped on a hill, many people "hold" their vehicle with the clutch. Of course, this means they have it in first gear with the clutch depressed just enough to keep the machine from rolling backwards. What they often don't realize is that this is really just slipping the clutch and contributing enormously to wear on the clutch plate.
If the area where the car is driven has lots of hills with stops required often - well I think you see the picture.

A much better proceedure to follow when stopped on a hill is to use the brakes to "hold" the car. Or you can even use the emergency brake to hold the car. Using the emergency brake has the advantage of allowing you to have the car in first gear with the clutch fully depressed. Then, when you want to go forward, you gradually let out on the clutch while gradually releasing the emergency brake.
Tom Fisher

Check your trans oil level. With OD, it could be that the pressure is too low and allowing the OD clutch to slip momentarilly. Ray

For the hydraulics check that there is some free play in the pedal when fully released. It should move very free for about 1/4" before you feel the linkage push against the piston in the master cylinder. Jack up the car and check for some free play at the clutch lever. with the clutch pedal released you should feel a little free play in the lever comming out of the trans connected to the rod from the slave cylinder. You should be able to move the lever forward/backward a small amount. If it's tight something in the slave or master is keeping pressure on the throw out bearing causing the cluth to slip, this will also quickly ruin the throw out bearing and the clutch.
John H

While I don't have an MGB (sorry), I think your problem may be a restricted hydraulic hose to the slave cylinder. Just replace it. They should cost less than $20.

Thanks for all the help so far.

While I have not had a chance to start investigating, I have noticed (bear with me here, its an odd description) When I depress the clutch pedal I can feel kind of friction/movement until the very last fraction (1/4 inch or so)push to the floor. I can engage a gear from about half the pedals travel though.

Does this narrow it down any more?


G Lewis

Whilst there will almost certainly be free play at the pedal there shouldn't be under normal conditions at the slave cylinder. This is because a spring in the slave cylinder pushes the piston, pushrod, release lever, release bearing and cover plate together to *eliminate* play in order to give a consistent release/biting point. However you should be able to push the slave push-rod and piston *deeper* into the cylinder and *create* free play. If you can't, then for some reason possibly incorrect mechanical parts the slave piston is bottoming in the cylinder and so not allowing the full pressure of the springs on the cover plate to be applied to the friction plate. When pushing the slave back watch out for fluid overflow from the master. After doing this give the pedal a couple of pumps to remove the free play before engaging a gear.

If you have that free play then it does sound like insufficient spring tension from the cover plate, or a worn friction plate and/or flywheel, which normally shows clutch slip in 4th gear before lower gears.
Paul Hunt 2

This thread was discussed between 29/08/2006 and 31/08/2006

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