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MG MGA - Having fun with a clutch

I have a friend's 1500 MGA in my workshop. Having overhauled the rear axle, installed a 5 speed box and a new engine plus Judson, I am getting real probe with the clutch.

The clutch is all standard 1500, and all new apart from the slave cylinder and the pushrod to the clutch fork.

All the hydraulics have been reused from the previous installation. The clutch slave is marked County brand. The pushrod is 75mm long (three inches)

The movement at the clutch lever is about 1/3 inch. Pushing the clutch pedal to the floor completely causes the clutch slave piston to pop pom of the bore. It is an aluminum piston, but does not appear to be worn.

The clutch will not disengage as the travel is too small at the fork. The fork is correct for an MGA (checked carefully before fitting, and is the one specified by HiGear for the kit), the bearing, cover and driven plate are all new. There is no air in the system, I pressure bled comprehensively and get no air bubbles.

The pivot at the pedal has minimal play, about a hairbreadth of movement in total, so the system is not under pressure when the pedal is at rest.

The longer pushrod at the slave has some wear, but I tried threading the end and using a nit on the end to make it even longer, and the piston still pops out but the clutch does not disengage.

In frustration before I have to take the engine out again all ideas will be gratefully received.

dominic clancy

There are different heights for the pivot where the fork rests.Add 1 cm alu piece under Yours and it will be OK.
Dirk/Antwerp
D. Van Ussel

Hi Dominic,

Strangely, I fitted a 5 speed conversion last Tuesday and has a similar problem, Following assembly and installation, I started the engine and pushed down the clutch. I couldn't engage any gears and surmised the clutch wasn't disengaging properly.

After messing around with the clutch slave trying to increase the throw I found the problem was the clutch plate, stuck to the flywheel.

The simple solution was to select 1st gear, depress the clutch and start the engine. The clutch popped off instantly and is now perfect.

It was a very worrying hour of thinking the whole engine was going to need removing again.

Paddy
P Reardon

Hi Paddy

The clutch was only fitted last week, so I can't imagine that it is stuck to the flywheel, that only happens if it has been standing for a long while.

I also don't feel I am getting any resistance on the pedal that would suggest the clutch diaphragm is operating
dominic clancy

Hi Dominic,

My clutch was only fitted for 3 hours and it stuck. I am assuming some form of contamination. Whatever it was it's gone now and behaving itself.

In my case the pedal had the expected resistance but the gearbox was still being driven. The sign was a very slight tendency for the car to pull forward when the baulk rings engaged as I pushed it into gear.

I will note; the Hi-Gear clutch action seems very light compared to the original set-up. I have no idea why, it is all the same geometry and mostly the same components.

I suggest you don't take the engine out until you've tried to free the plate. It may be all it was.
If you want the safer version, take out the plugs and put the car in gear. Then get someone to turn the cranking handle while you hold the clutch down.

While I was trying to diagnose the problem I did discover an MGB clutch input rod is able to be fitted in place of the MGA one. It's about 10mm longer. I tried it but was unhappy that it was pressing quite firmly on the release bearing with the clutch engaged (would cause high bearing wear).

Best of luck.

Paddy

P Reardon

That was my first check, had the DPO put in a shorter pushrod, but checking the B&G catalog, its shows the same part number for MGA and MGB. I had a spare A one in the cellar (which surprised me) and it is a good 25mm shorter than the one in the car.

Given that the rod in the car is already short enough to allow the piston to pop out of the slave, a shorter rod is not going to help at all.

I have ordered a new slave cylinder because it's clearly an inferior one with an aluminum piston. The old installation is also wrong, putting the flex hose into the bleed valve position, and missing the necessary banjo as a result. So I've ordered all the bits and will have another go tomorrow. It was such a pig to get all the stuff back in this car, I really don't want to have to pull it all out again, even though it will probably be a lot easier now that I have done all the fettling that was required.

dominic clancy

If the piston can pop out of the cylinder, even with a nut on the the pushrod then surely you can still try a longer (extended - bolt in the nut?) pushrod? Sounds like a good idea to sort the slave cylinder first.
N McGurk

Well something somewhere is definitely not right. I installed the new clutch slave with correct rod and clevis pin, and the piston popped straight out.

Installed the longer rod, and there is still massive free play in the fork. I'll have to call Peter Gamble tomorrow and make sure he did send me the mounting for an A fork and not a B one. I do have a B fork and bearing, so I can swap if that is all that is causing the problem.

So it looks like I will have to pull everything out again. It's a good job I can get an engine out in about an hour on a good day providing all the bolts play nice (which they should having only been in a week)
dominic clancy

Well here's what caused it

On pulling the engine again (didn't quite match my record because of a stubborn bell-housing nut that required the use of the air driven saw to convince it that it was not going to stay on the bolt) I found that one of the clutch bearing retaining springs had sheared where it goes into the clutch fork, and the release bearing was only fixed at one pivot. This allowed it to float free at that end, with the result that the clutch wasn't ever going to work without removing the engine again.

Fortunately I had another fork and springs in the cellar, and could replace the one installed without having to figure out how to remove the stub of the broken spring from the original fork.

The engine is almost reassembled, should be ready to run with about another hour's work tomorrow evening.

dominic clancy

This thread was discussed between 21/04/2012 and 25/04/2012

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This thread is from the archive. The Live MG MGA BBS is active now.