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 allumium pistons and at least a regular check, if not replacing, seems a good idea."





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."