The MGA With An Attitude
Aluminum Piston in CLUTCH SLAVE CYLINDER - FT-032

At 09:06 PM 9/15/2006 +0000, Werner Huybrechts in Belgium wrote:
>>"Around three years ago I replaced the clutch slave cylinder. I noticed the piston was aluminum instead of steel. Last month I suddenly felt a loss of pressure on the clutch pedal and the clutch didn't disengage. This happened just around the corner so returned slowly home. Brake fluid reservoir was very low, and slave cylinder leaked a lot.
>>The aluminum piston had so much worn on one side that it could tilt, and the rubber piston seal let all the oil escape. This as you can imagine is a potentially dangerous situation since the reservoir holds also the fluid for the brakes, and moreover this situation seems to happen very sudden with very little warning.
>>In my opinion a warning is in place against these slave cylinders with aluminum pistons and at least a regular check, if not replacing, seems a good idea."

Clutch slave cylinder with worn bore and badly worn aluminum piston

Badly worn aluminum pistonBadly worn aluminum piston

Werner also wrote:
>>"The dust cap still was in good condition and tight around the push rod. - I just went trough my invoices for the MGA, bought this part 3 years ago so milage wont be very important rough guess 30.000km? I bought this at a dealer in Belgium (Roes), but Anglo Parts tried to sell me the same a few weeks ago, I will try to find out where he bought them. So it seems more dealers sell these aluminum piston slave cylinders."

This is more than a little creepy. From my engineering experience it appears that the steel piston sees the softer aluminum cylinder wall as a bearing material and slips along easily with very little wear. The aluminum piston running against the aluminum cylinder wall will have higher friction, and the soft aluminum may gall up and sieze or otherwise suffer greatly accellerated wear.

I have spoken to a number of pro shops and parts vendors. Everyone I spoke to said the clutch slave pistons are always (or always were) steel, and no one has even seen a wear problem like this before. Having seen this one, I can only advise people to avoid the aluminum pistons when possible, and inspect your car to see if the clutch slave cylinder is still in serviceable condition.

Addendum Sepember 27, 2006:
Memo from Ronny at Anglo Parts:   "We will check our stock and see what product we can offer to keep our customers satisfied and our cars running."
        Until I have more information, this means the customer should ask first or check the parts before installation.

Addendum Sepember 28, 2006:
Memo from Kelvin Dodd, Moss Motors US:   "The cylinder we carry under the OE spec number #180-720 is sourced from Delphi Lockheed and carries the AP casting identification. It has a steel piston. - The cylinder we carry under the Classic Gold House Brand #180-715 is manufactured for us to our specification. It currently carries a 20168-3 with the numeral 8 below as a casting number. It also has a steel piston."

Addendum July 9, 2014:
On 7/6/2014, Rob Zucca wrote:
"I bought a new clutch slave from Moss and installed it. Hydraulic fluid filled the gaiter and ran out. I pulled it and disassembled on the bench. Guess what, .... an aluminum piston. I rebuilt the old one and reinstalled; works fine. The part number on the clutch slave is 180-715, Classic Gold line. The date of my invoice is 3/7/14".

Score one step backward for Moss Motors. I don't know yet if they even know that the current parts have aluminum pistons, but I'm checking. They did not respond to Rob's email notice (apparently lost the message).

On Jul 14, 2014 Kelvin Dodd of Moss Motors wrote:
"The aluminum piston in the slave cylinder was a surprise to me and to purchasing. We carry the AP/Lockheed version of the slave cylinder and also had our own version manufactured to original specs. That was expensive and we were being undercut by slave cylinders coming out of the UK that were flooding the market. Moss bowed to the pressure and switched supply to the cheaper product without adequate inspection. The cylinders have not had any failure issues, but there is a concern that the supplied piston will not be as durable as the steel ones originally specified. Based on that, we have asked out supplier to quote on installing the steel piston".

It is understandable that Moss will seek a less expensive supplier, which can be good for the customers. Nonetheless, it is not acceptable to sell bad parts on the basis that they do not have adequate Quality Assurance inspection before sales. Until there may be some additional follow-up word on this issue, we may expect (or at least suspect) that the Moss supplied clutch slave cylinders will continue to have an aluminum piston. As such, every customer will now be required to disassemble every clutch slave cylinder for internal inspection before installation. It is apparently Moss Motors way of doing business.

On 17 March 2017, Brian Paddon in the UK wrote:
"Noticed fluid dropping onto the drive, pouring out the slave cylinder. I have stripped the replacement cylinder, which was new during rebuild and noticed that the bore and piston is scored. The piston is aluminium, but the original Lockheed had a steel piston. I have also noticed that the return spring is shorter and different design to the Lockheed".
Short Sping in Slave Cylinder Scored piston in Slave Cylinder Faulty Slave Cylinder with aluminu piston
"I have just replaced the County cylinder as mine leaked within 60 miles".

On 23 March 2017, Lindsay Sampford in Cambridgeshire, UK wrote:
"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. I applied plenty of silicone 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. -- 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 silicone grease had helped. The cylinder itself was pretty good too. And the outside looked like new!
Scored piston in Slave Cylinder Housing for Slave Cylinder Clean bore in Slave Cylinder
Clutch slave cylinders with steel pistons are not easy to find and pricey. Then I chanced on an eBay listing for a clutch cylinder repair kit including what looked like a steel piston, for 9.20 (; a lot cheaper that a new steel-pistoned cylinder. I contacted the vender who confirmed that it looked and felt like steel. The kit arrived this morning. And here is the new steel piston just before it went in...with a smear of silicone grease for good measure. It is all working now, let's see if lasts!
Rebuild kit for Slave Cylinder with steel piston New steel piston for Slave Cylinder

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