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MG MGB Technical - Broken pressure differential switch

I loosened the nylon brake pressure differential switch prior to bleeding the brakes, just to make sure it would be do-able when I actually bled the brakes. Then screwed it back in, confident that I'd be able to do that step later. Unfortunately, it broke, overtightened. It doesn't leak, though, because half of the nylon plug is still down in there. I'd like to take it out and replace it, either with a new switch or a steel plug. Not sure how to go about getting the piece out. Does anyone know the thread size, were I to try putting in a plug? Thanks.
C. P. Fox

It shouldn't leak even with the switch out as there is a metal shuttle inside the master cylinder with O-rings on it.

In practice I could never get mine not to leak. I replaced mine with a short bolt and a copper washer. I can't remember the thread size but it is one of the common MG ones.

I did find there are two different types of shuttles and switches. I don't know which goes with what car. One of the switches isn't a switch at all but just a metal pin.

There are pictures here:

Basically you can leave the switch out, it doesn't affect anything except for not having a warning light come on if half the brake circuit fails.

Simon Jansen

CP. You can pick out the broken plastic from the hole. Hard to do with the master cylinder in place, but it can be done using a dental pick and an inspection mirror.

The thread size of the hole is 3/8"-24 tpi and the bolt needs to be about 3/8" long. One of the copper washers used with the brake system can be inserted between the bolt head and the master cylinder as an added form of insurance should that portion of the master cylinder ever develop a leak. This seems to have worked for Simon. I used some non-hardening Form A Gasket and have not had any problems myself.

All of this is assuming that you have the later model master cylinder with the attached brake booster. Since you do not note the model year, we are making assumptions based on our reading of your posting.

Les Bengtson

I had the same problem on my 77B. An E-ZEE out got the remnance out with no problem.

This thread was discussed between 28/07/2009 and 30/08/2009

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