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MG Midget and Sprite Technical - Clutching at straws

Well not quite, but baffled. The setup is 948 block, 1098 gearbox, thick backplate, 1275 clutch (flywheel drilled for that), 1275 slave, 3/4" master. This has worked OK for a few years. While the engine was out the other week I put in a new friction plate, but nothing else. I have a roller release bearing which has also worked superbly for about 2 years.

All back together now, but the clutch bites too soon - about half an inch from the floor. Car is OK to drive but this is a bit annoying. The slave free play is spot on, as is the master free play. I have bled the system repeatedly and it makes no difference. Jacked the car up high on the right in case of trapped air, but nothing came out.

What I don't understand is that only one thing has been changed, the friction plate. Being new it is thicker than the old one, so I'd have thought the effect if any would be in the other direction. I took the engine out without the gearbox so didn't disconnect the hydraulics. It should all be back exactly where it was, but it isn't.

Les
L B Rose

I replaced the clutch friction plate in my first midget, way back in 1981 and had the same result.

After a short while, the biting point got higher.
Dave O'Neill 2

The thicker the clutch disc the closer to the floor it will engage. As the disc wears / gets thinner, the later the pressure plate will make contact. It will get better with wear.
Stan Kowznofski

Not strictly true, Stan, for a hydraulic clutch. Yes the thicker plate will move the release bearing forwards and therefore the slave piston 'at ease' position will be further down the bore. ( diaphragm clutch) But this just moves the operating movement of the slave piston down; the distance travelled remains the same. With cable or rod operated systems this does move the pedal down as well but with a hydraulic system it just means more fluid held in the slave.

Les, what do you mean by the slave free play being spot on? There shouldn't be free play there, other than the slightest bit of slack to show that the clutch plate is being fully clamped.I

Have you got the pedal pull off springs in the footwell fitted?
GuyW

Guy, yes I mean the slightest bit of slack. Any more and the bearing would be in contact all the time. And yes I have the pull-off springs.

Les
L B Rose

Les, most modern cars use a release bearing that does run in constant light contact with the clutch. My DIY concentric slave one does. But I am not suggesting yours should be set up that way.

The only other suggestion is that a new driven plate may need time to bed in so that 'off' and 'on' for the clutch is a bit more definite. And the other is I always find that the hydraulics on both brakes and clutch do improve after a bit of a shake down over a 100 miles or so followed by a final re-bleed.
GuyW

A workaround would be to shorten the slave pushrod (or a spare one if you think it might bed in). Pretty sure I had one gearbox that used a threaded rod with a locknut on so as to be adjustable.

Or do I mean lengthen...
AdrianR

Thanks folks. I'd need to lengthen the pushrod to get more travel I think. I'll wait a bit and see if it improves, the car is perfectly driveable.

Les
L B Rose

This thread was discussed between 14/12/2018 and 17/12/2018

MG Midget and Sprite Technical index

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