MGB Brake Caliper Rebuild
March 27, 2011 - Streamwood, IL
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A few MGs and half a dozen club members assembled at Cowboy's garage to rebuild a couple of MGB brake calipers. The thin metal dust seal retaining ring is tricky to install without damage, so one objective was to test a new dust seal assembly tool. It is essentially a quick adjust C-clamp with a machined clamping plate that will center the caliper piston and press the dust seal and retaining ring into place. At first glance the tool looks like it might be a good design idea, but in practice it falls somewhat short in execution. Turns out it is hard to keep it straight to align the dust seal square away with the caliper, and a couple of seal retaining rings were smashed with the fiddling. In the end we went back to the tried and proven technique of using a flat board and squeezing the assembly in the bench vice. In this case the machined pusher plate from the new tool was used in place of the board with a large wrench socket to back it up, and the assembly went together easily. Sometimes the special purpose tools are a waste of time and money.
Cowboy likes to hone the bore of the caliper cylinder a bit as an expedient way of removing any dirt and easy cleaning. In fact the hydraulic seal surface is on the side of the sliding piston, not in the bore, but the hone does a really nice job of cleaning the bore in short order.
At first attempt of assembly a retaining ring was smashed. Then it was discovered that the old retaining ring was upside down, so it didn't hold the dust seal (which was long since lost), and the inverted ring was still in the caliper preventing installation of the new ring. These calipers came off of Cowboy's race car, which has been raced for more than a few seasons. This is the first time the calipers were disassembled by the current owner, so we can blame the first problem on the DPO (Dreaded Previous Owner).
After removal of the errant ring, on second attempt of assembly another ring was destroyed when the special tool became misaligned and pressed one side of the ring in first then smashed the other side. For third attempt the machined pusher plate was separated from the special tool and used to squeeze the assembly together in the parallel jaws of the bench vice, which went quite well. Then it was noticed that the rubber dust seal has a "V" groove inside, and that it had been switched with the pressure seal ring. Then the assembly had to come apart for rearrangement of the seals and assembled for the fourth time. Practice makes perfect, as the other three pistons with seals went together in short order with no problem.
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