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MG MGA - Caliper bore question

Hi folks. I got my spare calipers apart, and am about to rebuild it. I notice one bore has numerous small pits. The other bore as one fairly large pit. It is my understanding that such blemishes in the bores dont affect hydraulic sealing, since the hydraulic seal is dependant on the piston surface only. So how badly scored can the caliper bores be, before a problem exists with a caliper rebuild? My worst bore is unpitted about 90 per cent of the total area. thanks! Glenn
Glenn

If a new restangular section seal ring will seal in the groove, the conditin of the bore is irrelevant. You are right, the seal is against the OD of the pistion.
Barney Gaylord

Barney is right, but you should also check the condition of the recess where the square section seal fits. this would include the back and sides of this groove. It could leak around the back. How does one clean this area to be sure?
Art

Remember, the seal doesn't sit in the bore on ALL MGAs - Twincams with Dunlop brakes carry the seal on the piston, which means that you need the bores to be in excellent shape (I hard chrome them and regrind to size for the race car)

On a Lockheed braked car, as long as the seal groove is OK (and I don't think I've ever seen one that wasn't), you are set to go.

BTW, when you say you 'got your calipers apart' I assume that you split them. There are two schools of thought on this. Some say never split them as the seal in the bridge is working fine and disturbing it can only introduce the chance of problems when you have to replace it. Others say that splitting the caliper gives you better access to clean out the halves and there should be no trouble with the bridge seal.

I am in the first camp.
Bill Spohn

Hi Art. To clean the seal groove, I used a tiny rotary steel wire brush chucked into my dremel tool. This little wire brush is very effective at removing rust, and chunks of old rubber seal that vulcanize to the seal channel walls. Hi Bill. Yes I did split the caliper halves. I did this once before on MGB calipers, and had no problems with leakage. The square section O ring seal between the caliper halves HAS TO be replaced though, or there will be leaks for sure. Splitting the calipers does make inspecting, cleaning, and seal installation much easier. In this case, I HAD to split the calipers to remove the piston guide pins. My replacement MGB pistons could not be installed otherwise. Thanks for the comments and advice. Cheers! Glenn
Glenn

This thread was discussed between 25/02/2006 and 26/02/2006

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