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MG MGB Technical - Brake Pressure Failure Switch

Hello -

After a great ride celebrating this 75 degree evening I changed the air filters in my 72B. While removing the cans I just touched against the brake pressure failure switch and the electrical connector popped off. Looking closer it seems that corrosion got to the connector.

Now, my brake pressure is fine but the warning light won't work. It looks like I need to replace the pressure failure switch - but not the body. Good thing because I see in Moss that it is a $300+ part. Although Moss doesn't sell the switch separately, VB (and I assume others) do for about $22.

My question is: Since I can't seem to find directions on replacing just the switch, will it mean I'll end up opening the hydraulics and needing to bleed the system? (Hate to do that cause I just did it in the fall and all is well otherwise!)

Thanks!
Greg
Greg Smela

I forgot to add that since I guess this is just an idiot light I only want to replace it if it is a fairly simple task since in my mind it would only come on after it was needed!
Greg Smela

Greg,

As I recall, the nylon switch simply unscrews. The fluid won't leak out.
Steve Lipofsky

The switch is dry, or should be since there is a double ended piston inside the "T" which has "O" rings on it to seal out the brake fluid. Should one side of the double circuit brakes leak the piston moves in that direction and triggers the switch and thus the warning light.
If when you uncrew the switch, you see fluid in it's mounting, then you are going to need to take the body off and ovehaul it much the same way you would a slave cylinder by honing and then replacing the "O" rings on the piston. The seals failed on my 72 and drained the master cylinder while the car was in storage one winter. It seems like that body is just a great place for lots of crud inside the system to accumulate.
Thomas Rynne

Thanks! That's exactly what I was looking (and hoping) for since the Bentley manual doesn't make that clear - at least to me!

Greg
Greg Smela

"it would only come on after it was needed"

Whilst one would already be aware of catastrophic brake failure one side by the time the light lit, if there were a slow leakage on one side the light would come on *before* you were aware through loss of braking effectiveness. Some warning is better than none.
Paul Hunt

Good point Paul, thanks.
Greg Smela

This thread was discussed between 16/03/2002 and 18/03/2002

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