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MG Midget and Sprite Technical - Brake Pressure Switch


This is a comparison of the brake pressure differential switch on my 1972 midget 1275cc. Not leaking but my investigation was prompted by producing only minimal brake fluid from the rear wheel cylinders after replacing my brake master cylinder. Anyway, here is the problem. New switch is bright white and checks out O.K. when using my meter versus the old switch which does not create a circuit when brass plunger is pushed into the switch body. Definitely an internal problem.

Original was an easy removal from the brass housing – but when I screw the NEW switch into the brass body, the extra long plastic neck seems to bottom out after less than a half turn of the switch. It seems to me that the extended neck COULD be removed using a hot razor blade to create a similar length to the original.

Plan “B” would be to find a short bolt with proper threads to seal the switch position off after removing the internal shuttle piece. I don’t know how effective a light on the dashboard is if it only comes on 3 seconds before hitting the car ahead of you or when that pesky bridge abutment jumps out at you when you round the next corner!

Switch is Moss part #181-955 ($27.95)
Rebuild kit #181-995 ($12.95)

This may be just another example of the high quality we all know & love from China…And don’t get me going on the intrinsic value of those 4 O-rings and the single flat copper washer in the repair kit. Good Grief! Almost $40 when a stubby bolt solves the whole problem.

Thoughts? See photos below...



Mike Pelone

And here is another picture of the switch sizes...



Mike Pelone

Rebecca Harvey (R HARVEY) had the same problem, extensively discussed about two months ago. Don't remember what she found out. Clearly a wrong part from big M, might call them and see if they got their info straight yet. The OE switch does not make contact between the two terminals, it makes contact between them and ground through the brass plunger. The other switch is for something different, Triumph perhaps, which use a different system. Do not remove the shuttle, as that will cause the good circuit to bypass into the dead side, making the tandem cylinder useless. Since you have the old switch, just put it back and leave the wire off.

FRM
FR Millmore

FR Millmore:

Since discretion is the better part of valor - I will take your suggestion and just replace the original switch since it is NOT leaking. The upside to this whole affair is that now I better understand the mechanical aspects of the safety design of the brass pressure switch after cracking open all of the inlet / outlet lines, etc.

For others that might have a similar problem - here is a link I found that provides some decent background plus the identification of the wiring pins behind the dashboard switch...

http://www.british-cars.net/mg-midget-sprite-technical-bbs/brake-failure-test-switch-explained-2009092401171913539.htm

My indicator light has never come on - but that is because the "purple" feed wire from the center console was cut off by the Previous Owner, plus the door switches & interior convenience light have been disconnected. At the moment, I want to solve the master cylinder problem before I start a re-wiring project lying on my back! Thanks for the comment...

Mike P.
Buffalo, NY
Mike Pelone

This thread was discussed on 27/08/2010

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.