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MG MGB Technical - Clutch

Taking out engine and gearbox soon due to problem with clutch. Question is what could be the cause of higher engine revs (by approx. 200 rpm) when in neutral and tickover. When clutch pedal depressed to the floor revs go back to normal (800 rpm). So this points to clutch/transmission issue but what could it be?

Have also discovered that there are bolts missing from where the crossmember and rear of gearbox are supposed to bolt together.

Any suggestions anyone?
/Moss
Moss

It's quite common for people to report the revs dropping when the clutch is pushed down, other people (like myself) don't. It could be friction between the carbon release bearing and the cover plate, but why don't they all do that? Both my cars have roller bearing release bearings at the moment, so that could explain why my don't do it, but I can't recall ever having had it on other cars or when the roadster had a carbon bearing. It could also be caused by the crank moving back and fore and so down to the thrust washers, or if the little ends don't float on the gudgeon pin it could even be the big ends angling on the crank. With the engine running have someone look closely at the crank pulley while you operate and release the clutch pedal, and see if it is moving back and fore. Even if it is, unless there is any other reason to dig into the engine I'd leave it alone, just replace the clutch. Personally I wouldn't splash out on a roller bearing either, I shall be replacing mine with a carbon next time. As long as you don't ride the clutch or otherwise abuse it the release bearing should outlive the friction plate.

There is no need to remove the gearbox to replace the clutch, it's additional work (not least unbolting and refitting the rear crossmember), and depending on what hoist/lift you have the additional weight may cause problems. As it was the hoist I used on a rubber bumper car had to be pushed in from the side before it would reach the middle of the engine, and getting the angles of engine plus gearbox right for removal and refitting can be a pain (the rear of the car has to be raised or the middle over a pit) unless you have a tilter. I used a rope round the back and front of the engine, which equalised the tension in each part (twang them to test it). While replacing the clutch and doing other work I left the engine on the ropes on the hoist, just resting lightly on a saw-bench, so when I came to refit it the engine was correctly aligned for the gearbox input shaft to slide right in.

What bolts? The rubber mounts are what joins the gearbox to the crossmember, plus variously a pin in a bush, and/or maybe one of two restraint bars, depending on year and market, see http://www.mgb-stuff.org.uk/xmember.htm
PaulH Solihull

Thanks for response Paul.
In addition to the named 'problem' there is also a constant noise (whinning and almost a rattle but not quite).

Re bolts: these are the two bolts that hold the bracket with the rubber mounting bracket in place through the crossmember - they are missing, and on one side the bolt through the bracket to the rubber mounting to the gearbox is half out at an angle! (Model rubber bumper roadster 1977)

...And two bolts are missing at the bellhouse to the engine backplate

I'd like to take engine and gearbox out to have a look (there is oil leaking out somewhere at the back of the gearbox - probably a seal)

The bolt problem looks as though the PO or his mechanic has changed the clutch without taking the engine out, could'nt work out how to connect the bolts from crossmemebr to bracket and also lost the bolts for gearbox to engine!

Have to get hold of a engine lift....

.../Moss
Moss

It's almost impossible to remove the gearbox to replace the clutch by leaving the engine in place. I suspect the problems you describe are because the gearbox *has* been removed at some time, at the same time as or after the engine was removed. Those mountings are tricky to deal with unless you drill the additional holes in the crossmember as described.

The gearbox rear oil seal is actually easier to replace on-car as you have something (the body) to both hold the gearbox steady and stop the rear flange turning while you undo the nut.
PaulH Solihull

This thread was discussed between 22/08/2011 and 23/08/2011

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