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MG MGA - Clutch Slave Piston Replacement

In response to the thread about clutch slave cylinders with aluminium pistons failing suddenly, I decided to do something about the clutch slave on my car, knowing it to be an after-market unit with an aluminium piston, before it too failed. I had replaced the clutch slave at least 16,000 miles ago and was a bit concerned that it had an aluminium piston, as I had read, probably on Barney's site, that they were prone to premature failure due to increased wear due to aluminium rubbing on aluminium. I applied plenty of silicon grease to the piston in an attempt to reduce wear, and it does seem to have helped, as I have had no problem with it, but not wanting to push it any further, I decided to take action.
Clutch slave cylinders with steel pistons are not easy to find and pricey, which is strange, as I thought aluminium was more expensive than steel! Then I chanced on an eBay listing for a clutch cylinder repair kit including what looked like a steel piston, for

Lindsay Sampford

I removed the clutch slave from the car and dismantled it and the aluminium piston was not as bad as I was expecting it to be, see picture. Maybe the silicon grease had helped.

Lindsay Sampford

The cylinder itself was pretty good too.

Lindsay Sampford

Hi Lindsay
I assume that is a steel piston? Have you taken the slave cylinder apart yet? It would be interesting to see the wear if any on the Aluminium piston. I have just changed mine for a Delphi(Lockheed) unit and started to re-bleed, but the weather got the better of me today and the car is back in the garage.
Brian
Brian Paddon

And the outside looked like new!

Lindsay Sampford

And here is the new steel piston just before it went in...with a smear of silicon grease for good measure. It is all working now, let's see if lasts!

Lindsay Sampford

Brian, you jumped the gun!
Lindsay Sampford

Yes Lindsay. I have just replaced the County cylinder as mine leaked within 60 miles.
Brian
Brian Paddon

Brian, if the cylinder bore is OK where the seal traverses on your old County one, don't throw it away, you could fit it with a steel piston and it will be a good one.
Just did a test drive with my re-con slave, and the clutch is lovely now. It always struck me as a bit slow to release before. I guess that was the aluminium piston binding in the bore.
Lindsay Sampford

Hi Lindsay
Good job done. How did you bleed your clutch?
Brian
Brian Paddon

I pushed the clutch release arm towards the cylinder to push the piston in and expel the air up through the master cylinder, then allowed the arm to restore naturally to pull fluid down towards the cylinder. I repeated this three or four times until I could open the bleed valve and have fluid dribble out. To finish, I opened the bleed valve and pushed the release arm into the cylinder to expel the air from the cylinder out through the bleed valve, and while holding the arm in, tightened the bleed valve before releasing the lever. I repeated this operation, probably four times, until no more air came out. Job done and no assistant needed!
Lindsay Sampford

This thread was discussed on 23/03/2017

MG MGA index

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