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MG MGA - What is 'Normal' re: clutch slave cylinder?

Several questions after pulling my clutch slave cylinder for inspection after lack of success bleeding the clutch.


first...what should the clearance be between the slave cylinder body and the frame cross member? My slave cylinder was tight to the cross member to the point where I had to jack slightly under the bell housing to relieve enough pressure to remove it after loosening the mounting bolts...doesn't feel good... that it is removed, I can compress the cylinder push rod, and it will not 'return' under it's own power. Shouldn't the return spring inside have enough return force to extend the cylinder?

furthermore...what is the maximum allowable ID of the cylinder bore after honing? I have some pitting that needs to be smoothed with honing, and want to be certain that I have a useful part afterwards.

and finally...the rebuild kit that I purchased through Moss has only two of the three rubber components of the slave cylinder...the external boot, and the cylinder seal. What about the diaphragm at the end of the spring? doesn't this normally get replaced?


rpb bunch

As far as I know, there is no return spring or diaphram in a MGA clutch slave cylinder. There are only two rubber parts, the seal and the boot. The slave cylinder is returned by the pressure from the clutch. Can't comment on the clearance, but I can check it if needed. Are you sure you have a proper slave cylinder?
G T Foster

I think so...Moss shows this exploded view. Mine has a 3rd rubber part where Moss shows a white plastic disc. Also Moss does not show a small ~1/2" ID ring that captures the boot onto the plunger.



rpb bunch

Interesting. I have just done my clutch cylinder. there was no spring in my kit from Moss, nor was there a spring in the old cylinder. But h push rod backwards.
I see one unlisted in the Moss Catalogue. I would have thought that the spring would cause constant rubbing on the clutch release bearing, and that theoretically there should be a return spring working to pull the clutc
Art Pearse

The spring is very weak so you can compress it with two fingers. Its primary purpose is to hold the plastic expander piece against the rubber seal cup. It may also prevent unwanted retraction of the slave piston due to vibration while at rest. The few ounces of force on the spring is nil compared to about 200 pounds of force applied to the release arm while traveling both directions. The release bearing will not wear out due to force of that light spring.
Barney Gaylord

So I take it the cylinder does have a spring?
Where could I get one as the Moss rebuild did not include it. Thanks!
JW Colson

See Service Parts List here:

Plate E.2, Item 17, Part No. 7H7959.
Do an internet search for that part number. Good luck hunting, as I have never seen that spring sold by itself. Perhaps someone has a used cylinder with a good spring.
Barney Gaylord

Let me have a look in the graveyard box......
dominic clancy

I have had a good root around (I also had to find some Judson bits) and am sorry to say I have apparently already given away or thrown away the old slave and its innards.

A new slave is actually pretty cheap, I would suggest going that route if you cannot find a spring.
dominic clancy

This thread was discussed between 06/09/2010 and 10/07/2013

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