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MG Midget and Sprite Technical - Midget clutch wont disengage

I have a 1968 1275 midget which was in storage for a number of years. When first driven, for some time, the clutch operated normally but after some couple of hundred kilometers it started to cause problems. When cold it normally disengages the clutch but after just a kilometer or so it does no fully disengage. I have replaced the master cylinder seals and noted that it had been resleeved in the master cylinder bore with stainless steel. I believe that it has been successfully bled. After this I considered that the clutch plate might be sticking to either the flywheel of clutch plate and deliberately slipped the cluth quite hard. Strangely it then operated normally for a week and then the old problem returned. I would have thought that I had found the problem but subsequent deliberate slipping has not cleared the problem. I have read a previous thread on this site that was for the same problem but there was not result published..presuming it was corrected. Can you help me
G Dunn

As you are aware the clutch works by the cover plate being compressed and this frees the driven plate and stops the transmission.
What can go wrong.

The driven plate/friction plate can stick on the splined gearbox shaft and cause disengagement problems

The clutch cover fails to compress far enough. This is caused by the hydraulics not moving the actuator shaft far enough. This can easily be checked by looking beneath the car and seeing how far the shaft moves when the clutch is pressed.

So the very first thing to check is the hydraulics as above.
Bob Turbo Midget England

As Bob says, but just to add - the clutch actuating rod doesn't have to move very far to disengage the clutch, so don't expect to see lots of movement. Somewhere around 1/2" or even a little less is sufficient.

Are you sure that you have full movement at the pedal? Is the pedal returning upwards freely? They can stick. If not, then even with a properly bled system you won't get a "full cylinderfull" of fluid pumped from the master cylinder.

Is the M/C pushrod adjustable on your car? Some are, some not.

I wonder a little about the m/c sleeving? I presume it is an ok modification but doesn't sleeving reduce the bore size and thus reduce the amount of fluid pumped - and therefore the travel at the slave pushrod? M/C and slave do need to be matched by design to get the right amount of movement. Maybe sleeving makes so little difference that it is of no consequence.
Guy Oneandahalf Sprites

if you don't know Shawn in Perth with the awesome Midget, then you should! He'll be your closest with hands-on advice...
David Smith

Resleeving here leaves the bore original size, I presume the Aussies are the same.

Something about the symptoms rings a bell, but I can't quite remember the details.

Mmmm ... maybe I can. I think it may have been the case of the pressure plate release ring being slightly out of true. It slowly batted the clutch arm back, so using up quite a bit of travel to get into proper contact and not enough of it left to disengage the clutch. (A bit like divorce on the Stelvio Pass, when I didn't believe the wife who radioed such symptoms to me and unreasonably claimed she couldn't get the car into gear. We were already one clutchless Midget down, doing a U-turn on Stelvio without a clutch to rescue grumpy wife is a challenge.)

Not for this one, the symptoms are different, but over heare in the '80's we had a spate of locally produced 1275 clutch plates which were too thick in the linings. Not by much. Harmless you might think, but it turned out the diaphragm started off that much further inwards, and so the release ring ended up making contact with the plate by the time the pedal was on the floor.

The effect was observed by removing the flyweel from the engine, assembling the clutch onto it and operating it with a press. Counter-intuitively, the only was to engage gear in this condition was to release the pedal a bit. there was a sweet spot in the travel where the release ring separated from the plate before the plate was engaged by the pressure plate.

Unfortunately the first time we discovered it was after a heroic clutch change for a friend in the middle of a national championship autotest: many hands to the pump and a rope over a handy tree branch. Got it done in record time without missing a runs, only to find the new clutch wouldn't disengage :-(
Paul Walbran

Thanks chaps, I havent had time to do very much investigation but this morning it worked fine. Bloody confounding. I am also thinking the clutch return spring may ...oh doesnt matter Ive been thinking a lot about this for some time. I just don't want to pull the engine. Any other thoughts welcome.
The resleeve returns master cylinder bore to original.
G Dunn

Sorry about my "red herring" about sleeving. It didn't seem likely to me so that a recognised refurbishment would be the problem so it was more of a question really.

I think that Paul has the answer with the release bearing getting jostled away from the clutch cover springs. But a rapid double press of the clutch pedal would still disengage the clutch if this is the case.
Guy Oneandahalf Sprites

It improved it, but took several, sometimes. Any improvement would be a clue to that as a cause. If none, likely something else.
Paul Walbran

This thread was discussed between 30/11/2010 and 01/12/2010

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