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MG Midget and Sprite Technical - Clutch won't release

Hi all,

Im nearing the end of my 1500 rebuild and am having a problem with the clutch. I have replaced the clutch plate, slave and master cylinders and hose and have bleed the system several times however the clutch will not release. I have left the clutch for 4 weeks with fluid in the system and bled again, all to no avail. I've even gone to the extent of towing the car in gear and pumping the clutch pedal as i was told that new clutches can often stick and need a forceful hand to release.

Does anyone have any ideas as to whats gone wrong? My principal concern is that the clutch plate has been fitted the wrong way round, in which case i might be slightly embarrassed....

Cheers!
Jamie Watt

Check that the hydraulic line where it goes through the battery tray isn't kinked. You've covered everything else!

Steve
Steve H K-ser

Cheers Steve, the pipe looks to be in good order and not kinked anywhere. Is it possible to put the clutch on the wrong way round? I would've thought that this would give the opposite problem of what i've got?

Jamie
Jamie Watt

Check also that the pivot pin for the clutch release lever hasn't dropped out. But it does sound like the driven plate could be in the wrong way around. :-(
Guy

If the driven plate was the wrong way round (oh please god, no) then would it not be the case that the clutch would never engage rather than be unable to disengage? Im REALLY hoping i don't have to take the engine out again!
Jamie Watt

Jamie

I had a problem with my 1500 clutch after a rebuild, not as bad as yours, in that the pedal went all the way to the floor before it disengaged. The answer was to wedge the clutch pedal down with a piece of wood and leave it overnight. The next day the clutch was perfect and has been ever since. It may not be the answer to your problem but it's an easy one to try

Bob
R.A Davis

Cheers Bob, i'll give it a try. I phoned the kind chaps at MGOC technical last night and they told me the clutch is notoriously difficult to bleed and as long as the nipple is above the input (tee hee) then its just a case of perseverance. Wish me luck!
Jamie Watt

You should be able to tell by the feel of the pedal. If it still needs bleeding it will feel "soft", as if it isn't really doing anything.
If it were the driven plate in the wrong way round you would feel the heavier action as the cover plate springs move, providing a heavier and slightly springy feel to the pedal.
Did you check that the pivot pin is still there? If it is missing the lever will still work but pivots against the cut out in the bellhousing and slops around so may not disengage properly.

Guy
Guy

Im still having a nightmare with this clutch! I've bled it now approximately 10 times and tried wedging it down overnight with a block of wood and it still won't release. I've taken the slave cylinder off and asked someone to press the pedal - the piston moves cleanly and there are no leaks, its a new slave so it shouldn't be that! The only thing i can see which may or may not be causing the problem is the release pin which is attached to the fork has about an inch of play before it hits the clutch, i.e. the piston has to push the pin about an inch before anything makes contact. Is this correct?
Jamie Watt

Is it possible that the disc is stuck to the flywheel? How long has it been since installation?
Sandy
ss sanders

Jamie, Sorry to hear about your stuck clutch.

My thoughts concur with those of our friend from Florida. If it's been some months since you fitted the clutch, it could have stuck itself against the flywheel. You'll have to either use method (a) keep the clutch pedal depressed for 24 hours and see if the driven plates frees itself, or (b) CAREFULLY AND SECURELY have the rear of the car supported on axle stands (with chocked front wheels) and, at low speed in gear, slam on the brakes with the clutch pedal fully depressed.

Irrespective of the above, it is possible to fit the slave cylinder incorrectly, not fully inserted in the bell housing recess. There is a 'cut away' in the slave cylinder body which accommodates the shaft of the (IIRC) securing bolt 7/16" bolt.

Regarding the horizontal release pin, and any possible play. When fitted 'properly' it's all a bit 'floppy' with movement, I wouldn't worry about the one inch play except to ask, how much of the pin is visible when it's pressed up against the clutch cover?

Regarding the vertical swivel pin that's held (by its top and bottom) in the bell housing. Don't worry too much about it - the clutch release fork still works without any swivel pin fitted (they often drop out onto the road from the lower hole in the bell housing unbeknown to the driver - but the clutch will still work!)

As has been mentioned before, a properly bled clutch pedal will feel quite firm - not at all soft or spongey. But it is possible that you are seeing slave cylinder piston movement (with the cylinder disconnected from the bell housing) even if you have air in the system.

Andy Hock

Thanks for replying, guys. The clutch has been in situ for about 5 months now without the engine turning so it could be that the clutch is stuck to the plate. A while ago we tried to tow the car slowly with the clutch depressed and the car in gear to see if that would shift anything but the tow rope snapped, we then chickened out and ended that test! The pin with the movement is number 76 in the attached pic. It moves in and out of the bell housing horizontally and when fully pressed into the bell housing (with the slave off) there is only approx 1/2 inch or less still protruding, is this right?


Jamie Watt

>>Jamie Watt writes>>there is only approx 1/2 inch or less still protruding, is this right?

>>AH replies>>From memory, that sounds correct. (Unless somebody else wants to correct me.).

Jamie, have you used a gunson Eezibleed to bleed the clutch? If not, you need to because of the weird 'uphill' pipe route and problematic slave cylinder design.

===================================================

Now, assuming that an Eezibleed has been used and the problem remains. . . . . . thinking out loud, and knowing what a bar steward the clutch bleeding process can be . . . . . . if I had Jamie's problem, I would want to 100% confirm that there is no air in my clutch hydraulics. With the clutch hose still connected and the slave cylinder removed from the bell housing, I would devise a way of preventing the piston from being ejected from the slave, maybe using a G-clamp across the body of the slave or some other bolt/clamp arrangement. I would then depress the clutch pedal and see what happens . . . . if the pedal is solid, then that confirms there is no air in the system. If the pedal goes to the floor, then I have found the answer to the problem . . .

Anybody got any other thoughts . . . ?

Andy Hock

Jamie,
With the clutch pedal released, the thing that normally pushes the piston in the slave cylinder back up the bore ready for its next stroke is the spring of the clutch cover. In other words, with foot off the pedal the pin, (76) should be being pushed back out against the slave piston. From your description, it doesn't sound as if this is happening. If it were, you wouldn't have that 1" of free play.

I would agree with Andy, check that he slave is properly fitted such that the pin (74) locates into the groove in the side of the cylinder - you can see it in the drawing you posted.

I disagree that it makes no difference if the pivot pin (65) is missing. This does make a difference. Yes the clutch may still work, but a lot of the leverage is lost without that fulcrum pin so check it is still in place. If it is missing an easy temporary fix is just to drop a new bolt in to replace it, which you can do with everything in situ. I ran mine for years like this, with an old flat-headed carriage bolt for the pivot.

Failing that, I still fear that the driven plate may be in the wrong way round. The central hub extends further on one side and if put in the wrong way around it would hold the driven plate away from the flywheel. It would then be in permanent contact with the pressure plate, pushing it back against its diaphragm spring. This moves the spring fingers towards the flywheel and would produce the 1" free play in the pushrod (76) that you mention.

Guy
Guy

Andy,
sorry we were cross-posting then! I think that is an excellent suggestion of yours for checking on air in the system.

One other point, when bleeding. These hydraulics suffer the same design problem as on the A-series cars. The bleed nipple in the slave is next to the inlet feed pipe. This means that when bleeding it is possible for clean fluid to be pumped into the slave and straight out again through the adjacent bleed nipple, leaving air-contaminated fluid in the body of the slave.

The trick to avoid this is to push the slave piston back up the bore as far as possible and secure it there in some fashion (maybe use a small G-clamp)before then bleeding in the usual way - preferably with an eezibleed. This will ensure that there is no "hiding place" for air bubbles in the slave cylinder.

Guy
Guy

Jamie,

I'm not familiar with the 1500 arrangement but it seems similar to many others so your comment about the slave cylinder having to push the pin an inch before anything makes contact is odd indicating that maybe something is wrong with the release arm or its pivot. Normally the slave cylinder might have to move a very small way before the clutch release bearing acted on the clutch cover release fingers to start relieving pressure on the pressure plate, the amount required for full release being dependant on the cover.

David Billington

Jamie

I had a similar problem with my 1500 a number of years ago. It turned out that the hole in the clutch pedal that the clevis pin (117) went through had elongated slightly.
Even though the hole had only opened up a few millimeters it made it impossible to disengage the clutch.
If you take the top plate off the pedal box you may be able to see if there is any excessive play.
The way I fixed it was to add some weld to the hole where the it had worn and re-drilled it to the correct size.
Seemed to work fine after that.
Cheers
Steve


S Sloan

Guys,

Thanks for all your responses. I'll have a bash at using a G-clamp to secure the slave and bleed with the Eezibleed system once more. The retaining bolt (74) is definitely in the right position although the play in the pin (76) is a worry. Having said that, although the clutch feels soft the pedal definitely springs back with good force and when you remove the slave the bore has always been pushed back to it's original starting position which indicates something must be pushing back on it.
Jamie Watt

Just remembered there is a return spring on the clutch pedal which would account for the pedal returning to its original position!
Jamie Watt

. . . . . thinking out loud to myself (again) . . . . but there's also a spring inside the slave cylinder whose action is to keep the slave's piston recess against the tip of the push rod.

This has got me thinking further. . . Jamie - in one of your earlier posts, when you say that you've got somebody to depress the clutch pedal with the slave cylinder hanging free, you say that you can see the slave piston moving?

Something is wrong with the image I have in my mind's eye . . . . in my 1976 1500 midget, if the slave cylinder is hanging free and somebody depresses the clutch pedal, then the slave piston will be ejected from the slave barrel. Why hasn't this happened in your case?
Andy Hock

Turns out i can't get the lines clear of air. Apparently it is litterally impossible to fit the clutch in the wrong way round. I think the problem is being exacerbated by the driven plate being stuck to the cover. I haven't attempted any of the (scary) remedies above but i'll keep you posted...
Jamie Watt

This thread was discussed between 27/01/2011 and 15/02/2011

MG Midget and Sprite Technical index

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