New new, or old new?

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New new, or old new?

Postby ACourtney » Mon Aug 17, 2015 9:48 am

One of the problems with buying Austin/MG Metro, or Rover Metro/100, spares is that very few "new parts" are actually new. Certainly, the parts that wear quickly, such as brake discs, pads, drums, shoes, etc are still being made in small batches and can be found new.
Some parts are made in infrequent batches and become scarce for a while, becoming more expensive, and then suddenly they are available again at a more reasonable price (this has happened recently with rear slave cylinders).

Then there are the parts that only rarely need replacing and consequently sit on the shelves of the stockists for years, decades even. These are the parts that are often described as old new stock. This may not be a problem if the part has been stored properly in a nice dry, warm warehouse, but a lot of the parts being sold on ebay these days are spares that have changed hands several times and may not have always been looked after. For example, I recently had to buy an MG metro clutch lever arm for a hydraulically operated verto-type clutch. It arrived in its original packaging and had clearly never been used, but was covered with surface rust. The main thing was that the ball on the end was fine and the hardened surface was rust free, so I simply cleaned the surface rust off with a wire brush wheel and then chemically blacked the arm to keep the rust at bay in the future.

The main reason for this posting (some may say rant!) is that I have recently become aware of problems with some Rover Metro master cylinders bought from one of the main Rover spares specialists just over a year ago. Both David Johnson and Tony Moss had issues with the master cylinders, on their Mk4 Cortez coupes, leaking fluid into the servo and both replaced them with “new” master cylinders bought from the same supplier. At this year’s open day Gareth Woolridge, who had recently bought David’s Cortez, recounted how he had had to replace the master cylinder as it was leaking into the servo unit. Then a week ago Tony brought his car to me complaining of a loss of braking efficiency and a whistling brake servo. Further investigation showed that the servo was indeed whistling, but was also full of brake fluid. Tony sourced a replacement servo from a scrapyard and also another “new” master cylinder and I helped him fit them this weekend.

Inside Tony's servo2.jpg
Inside of Tony's servo
Inside Tony's servo2.jpg (72.45 KiB) Viewed 1475 times

However, I must admit that I do have some reservations about the new master cylinder that Tony had bought as it had come from the same source as the previous one and had clearly been sat on the shelf for many years. My preference would have been to rebuild the old master cylinder using a new set of rubber seals from a service kit. As the master cylinder had only been on the car for just over a year and only around 6000 miles it should not be scored on its bore, so my suspicions point towards failed seals. Brake service kits tend to be shared across many different cars as the innards of master cylinders tend to be identical, whereas the master cylinders themselves have different external dimensions for the different installations.
One clue as to what had happened to Tony’s master cylinder could be seen in the old brake fluid reservoir. There were traces of black gunge inside the reservoir close to where it connected to the master cylinder. This black gunge turned out to be tiny granules of rubber, further confirming my view. My suspicion was that the first replacement master cylinder had sat on a shelf for some time and the rubbers had hardened. As Tony left the failed master cylinder with me I shall strip it down when I get the chance and see what condition the seals are now in. If the latest replacement also fails, like its predecessor, then it may well be returned to his car after refurbishing with the service kit.

The “scrapyard” servo that Tony had sourced seemed to be okay, but it also had traces of brake fluid inside. A good operating servo should be dry inside and the diaphragm should still be grey with traces of the original talc on the rubber. The talc acts as a lubricant on the rubber diaphragm to make sure it doesn’t abrade against the servo body or the actuator piston. So we took the servo apart, dried up all traces of brake fluid, powdered the diaphragm with talc and then reassembled it. The service kit for the Rover Metro servo isn’t currently available from the major stockists, but the seals are the same as used in the later Mini servo – kit GSM120.

Mini servo kit.jpg
GSM120 Mini servo kit
Mini servo kit.jpg (12.45 KiB) Viewed 1475 times

The only difference is the length of the actuator rod, which incorporates the valve that controls the servo vacuum. The Metro actuator rod is a fixed length, whereas the Mini actuator rod incorporates a screw thread for adjusting the pedal position. It may be possible be to set the adjustable rod to the same length of that of the Metro, if not then the seals for the valve would need to swapped over to replace those on the old Metro actuator rod. I shall investigate this too when I have the time.
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Re: New new, or old new?

Postby manifold » Mon Aug 17, 2015 7:09 pm

....Talc is often used to stop the rubber perishing too.

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