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MG MGB Technical - caliper rebuild

Hi Everybody. I am trying to rebuild my MGB calipers. I am having huge amount of trouble getting the metal dust seals into place. Any hints or tips. Also the pistons have cut outs. I understand the cutout goes towards the hub. Any help greatfully recieved. Thanks
s page

The rubber seals and metal seal are best installed with the caliper halves separated. Much easier to get them in straight that way. If you have not separated the halves, you need to get the metal seal centralized as well as possible and use a plate, slightly larger than the seal, and a C clamp to draw it into place. If you do not have a C clamp suitable, it is possible to use a set of ViseGrip (Mole Grip_ pliers to work the seal down, a little at a time, going around the rim. Be careful not to damage it where it meets the rubber seal. The outer/upper surface is not quite as important.

Les Bengtson

Manuals, and Moss catalogue, says to avoid splitting caliper.

Use a fine file and gently taper the edge that presses in. Sometimes there is a bit of a burr left from the stamping process that makes it difficult to set in (very tight fit). Avoid splitting the calipers.
Rob Carleen

I have posted on this before, with genuine AP kits they fit quite easily. I have found with pattern parts from some "mg specialists" that you have to save and re-use the old ones as the new ones just will not go on. Splitting the calipers is best avoided.
Stan Best

The cutout faces the hub.

Fit the inner seal, and lubricate with a sear of brake rubber grease (red) or fluid.

Push the piston in half way.
fit the dust seal inside the metal ring, lightly grease and slip over the sticking out piston. (about 1/2 way, make sure they are square)
Find some flat 1/4 steel plate that will bridge the piston and seal, and use a G clamp to flatten the plate against the calliper, squashing the metal retainer into the groove.

If you over do it, like me, the dust seals are a bit over enthusiastic about returning the piston, and you don't get any brakes without pumping the pedal, cured by blowing the pistons almost out and pushing back in fully a few times.
Martin Layton

Neal and Stan. The factory workshop manual states, "Unless it is absolutely unavoidable the caliper should not be separated into two halves." Then, it goes on to give instructions on how to do it and reassemble them. Unfortunately, they do not define what "absolutely unavoidable" means, nor do they define when it is wise to separate the calipers. Thus, we are left with instructions designed for use by a factory trained mechanic whom, we assume, was taught under what circumstances it would be advisable to split the caliper halves. These instructions provide little insight to the hobbyist of today.

John Twist, in his excellent, "University Motors Ltd Technical Book" (available from University Motors Ltd) mentions that he always splits the calipers during a rebuild as that is the only way that he can ensure that they are fully cleaned. I have split several pairs of calipers, throughly cleaned them, coated them with a specialty coating, then reassembled them with excellent results. The only area to watch out for is that some of the rebuild kits do not include the square cross section O ring which provides the seal between the two halves. Thus, a good idea to make sure you have all of the parts necessary before doing the work. Results are cleaner insides, a specialty finish that is resistant to water, chemical solvents and salt spray, easier installation of the seals, metal retainers and pistons, and a better understanding of how the system is built.

To my mind, one of the best reasons to split the calipers is the fact that all of them are now more than 25 years old. That rubber O ring between the two halves has probably not been replaced since the calipers were originally built. If you are going to replace the old seals (because they are degraded), the pistons (because they are degraded), the rubber flex hose (because it is degraded) and the copper washer that provides a tight seal between the flex hose and the caliper, are you going to leave in a 25+ year old O ring in hopes it will hold up?

But, everyone will have to make their own decision on this.

Les Bengtson

This thread was discussed between 03/11/2007 and 05/11/2007

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