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MG Midget and Sprite Technical - MG Midget 1500 - brake regulating valve

Hi Guys,

I have a very low mileage midget (2,500 miles from new). MG Midget 1500 - Feb 1981

A recent service and MoT determined that there was a brake problem. Specifically, the brake pedal had to be pumped in order to stop the car.

The garage doing the work found that there was shredded rubber in the brake pipes and so the hydraulic system was blown out with compressed air. The source of the rubber debris was the brake pressure regulating valve. I have been able to source a seal kit but this only comprises four small rubber washers and larger copper washer.

The mechanic who undertook the work insists that there should be another rubber washer which sits at the bottom of the chamfered chamber of the valve. I have not been able to source this rubber washer.

I attach below a photographs of the regulating valve.

Can anyone confirm that this type of valve (which is made of brass and only featured on the very late Midgets) did have a rubber valve at the bottom of the chamber, and if so, any ideas how I might source one ?


Kieron West

Hiya,

I rebuilt mime a few years ago. As far as i remember the kit was exactly as you describe.


The large copper washer is for the big plug obviously and the small o-rings fit on the piston.



There is no rubber washer in the centre as there should never be any brake fluid in the centre chamber!


When the system is operting correctly the pressure is the same in both sides of the valve and the shuttle valve stays central, holding the switch closed. IF there was a rubber washer in the centre it would impair the operation of the shuttle valve. If you fluid dripping from the plastic switch hole the seals have failed.


If the pressure fails in one circuit, ie a leak. the valve moves across to the side with no pressure and the switch closes, illuminating the warning brake lamp.



Quite why BL felt you needed a light to tell you half the brakes had failed beats me. The pedal losing travel and the big brown mark on the seat should be warning enough!




Another oddity is the way the warning lamp is wired. As you know it doubles as a handbrake "on" warning lamp.


For some reason best known to the BL boffins the lamp also should illuminate on cranking via the white/red starter solenoid wire. There ius a diode fitted in this circuit to prevent the brake check circuit back feeding into the starter.


If this diode fails open circuit, you get the strange situation whereby the starter cranks when you apply the handbrake!



The late MGB's where just the same, and the first time I came across it, it fooled me for a while until I sussed out what was going on.



Hope that helps.



Regards Steve
SR Smith 1

Gday Keiron
The other option is to bypass the silly thing by using a T piece for the front circuit and a straight joiner for the rear. only of course if this is allowable under your MOT rules. This removes the possibility that a failure in this switch will, ironically, cause brake failure LOL Which is what has happened.
HTH Rod
R W Bowers

Why not just rebuild it correctly as you have the kit?


It's not difficult after all. It's lasted nearly 30 years and will be good for another 30 if repaired.
SR Smith 1

This thread was discussed between 11/12/2014 and 12/12/2014

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