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MG MGA - clutch won't disengage

I'm preparing my 1500 coupe for a return to the road after a long but satisfying complete restoration. Everything going well except that I can't get the clutch to disengage. Here's what I know...

The car "ran when parked" with the engine and transmission currently installed, although those have both been rebuilt.
The slave cylinder pops out when trying to operate the clutch.
The release bearing (new) and release arm are installed correctly, verified with borescope.
The carbon face of the release bearing is intact.
The release bearing does not contact the pressure plate at full extension of the slave cylinder push rod, even with the piston pushed out of its bore. The push rod is the original, and is the correct length.
The new pressure plate is correct per the Moss catalog.

The problem would seem to be something with the pressure plate. Sure hate to pull the motor at this point. Any other thoughts?

Thanks!
George
George G.

The clutch disc may be stuck to the flywheel. sometime they will break free if you push the car backwards with the gear selector in a forward gear and the clutch pedal pressed to the floor. No need to start the car, just some help to push the car. Their is other ways to do this as well, but usually you do not have to disassemble the car.

... CR
CR Tyrell

I had the same problem in 1988 when I restored my car. I didn't find out I had a problem until the clutch slave piston popped out on the road three miles from home on the drive to get it through a safety test.. That pressure plate measured in spec, but something wasn't right because the bearing also wore a set of V grooves in the release arms of the pressure plate. When I finally removed the engine again and took the clutch back to Motobuild, it was exchanged and all the problems went away.

I have a few questions

Is the release fork bent? Should be straight not curved (seen this a few times on midgets)
Can you move the fork through enough of an arc to bring the bearing into contact with the pressure plate
If you can do this, do you still l have enough of an arc of travel left for the fork in the aperture (about 1/2 inch )to operate the clutch (leave the boot off for this)

If so, try making the slave to fork rod longer so the release bearing is almost touching the pad on the pressure plate (weld a bolt to the end of it or add a 5/16 nut) - effectively you are compensating for the problem that exists.

This may allow you to check that the clutch is working and drive the car before solving the underlying issue in the autumn.

I have a collection of slave rods that I have removed from various repairs over the years, and sometimes dig one out when there is too much play in a system. It is amazing how many lengths I have found and how many have been lengthened for this issue - but it works!
Dominic Clancy

Has to be the pressure plate, sorry, that engine is out again ....
Chris at Octarine Services

I had a similar problem and agree there seem many different length rods around. BUT when talking to a friend who spent his live working in motor workshops going back to when this set up was common he told me about an mechanics trick to lengthen the rod. The rod goes into a conical shape in the slave piston so they used hammer a suitably sized nut onto the end of the rod which made the rod a bit longer bit more importantly wider which meant it pushed the piston further in. As a follow up story when some time later I had reason to remove my rod I found it had a nut hammered on the end.

Paul
Paul Dean

George said -

"The release bearing does not contact the pressure plate at full extension of the slave cylinder push rod, even with the piston pushed out of its bore. "

So lengthening the push rod ain't going to help!
Chris at Octarine Services

Dominic, the release fork is not bent, and no, it cannot be moved sufficient to bring the bearing to contact the pressure plate. It is the same release fork that was in the car when I was driving it before restoration.

I'm going to try to get an eyeball estimate of the pressure plate front to back length using the borescope, I can compare this to ones I have in the garage, looking for an inch+ difference here I think.

Thanks all for your comments, I'll report what I find.

George
George G.

Looks big numbers, as if you forgot to insert the clutch (driven plate)!

Steve
Steve Gyles

No plate would move the release pad nackwards - I wonder if the clutch disc is back to front - that would cause the release pad to move forward aeay from the gearbox.
Chris at Octarine Services

Good call Chris.
Steve Gyles

an inch is huge. It's engine out to investigate I fear
Dominic Clancy

The clutch is installed, I have a photo I took during assembly. And it is installed with proper face toward engine, I was sensitive to that requirement. Engine comes out today.
George G.

Paul,

I also found a nut hammered on the end of the clutch push-rod and my car spent its life in the USA so it is not just a British bodge. The problem they were trying to overcome was that the bush in the clutch lever was missing - surely it would have been simpler to replace the bush!

Malcolm
Malcolm Asquith

George, is the pressure plate the standard MGA one or have you uprated to a diaphragm type?

If so you will need the MGB early fork, 22B56.

Colin
Colin Parkinson

Colin, it is the standard MGA type per the Moss catalog.
George G.

Clutch now works. The release arm was installed backwards, the borescope inspection was a bit misleading I guess. Time to have a discussion with my gearbox rebuilder!

George
George G.

Send him a bill for the corrective work!
Chris at Octarine Services

How did the release bearing fit to a back to front fork?
Dominic Clancy

Lol Dominic, I wondered the same so had to go and get an MGA fork and bearing to try it out!

Yep - fits both ways!!





Chris at Octarine Services

Must have put the bearing on the input shaft before fitting the arm - that should have already raised the alarm that something was wrong - has the rebuilder done MGA gearboxes before ?
Dominic Clancy

The crank in the arm would actually have made it easier to fit than the right way round!
Chris at Octarine Services

I always take a quick photo with my mobile phone of any parts that I am about to remove from the engine, gearbox etc.
It is surprising how helpful that is when you are trying to reassemble them a few days (or weeks) later.
I remember using a picture to remind me which way the clutch release arm fitted on my 5-speed box when I installed it back into the car.
Colyn
Colyn Firth

I had thought of suggesting this but thought I would be laughed off the list at as it was so daft. Presumably if had made contact the wrong way round it may just pushed the bearing out?

Paul
Paul Dean

Yes - the bearing is only held in with wire clips that locate in the dimples so wouldn't have been strong enough to operate the clutch.
Chris at Octarine Services

Lucky it didn't travel far enough to get the fork tangled up with the p/plate--must have been close
I'd been thinking that it might have been assembled without the clips and the t/out had become misaligned with the fork, we've seen that before and that does make a noise--
William Revit

Dominic, the guy has rebuilt MANY MGA gearboxes. I'm sure he'll be quite embarrassed over this. In fact, he also knows the guy who found and corrected the problem!


George G.

Lol - he isn't as pernickety as I am about rebuilding - I always trim the excess paper gasket from around the front plate ....
Chris at Octarine Services

One last question...how far should the clutch pedal depress before the clutch disengages and you can effect a smooth gear change?

Thanks!

George
George G.

Set length of the clutch master cylinder pushrod for minimal free play I(1/4" free motion at teh pedal pad), and the clutch should disengage at about 2/3 stroke of the pedal.
Barney Gaylord

This thread was discussed between 18/06/2020 and 06/07/2020

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