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MG MGB Technical - No brakes lights until hard foot pressure

I've noticed I don't get brake lights on a light foot pressure, they only seem to come on under heavy pressure.
Is there some kind of adjustment?
Rob, novice ;o)
Rob Silkstone

Assuming that you have the hydraulic switch, then there is no adjustment. You might have an air bubble in the switch, or it could just be getting old. Try changing the switch - you can do that without having to bleed the brakes if you're careful.
Miles Banister

Having been through this loop, bleed the brakes before rushing to change the switch! This is a simple/cheap job. The air in the hydraulic line compresses when you press the pedal, so there is less force on the brakes but also on the pressure switch for the brake lights.
Steve Postins

Also take note if you happen to be useing Silcone BF it causes the switches to do this as well. Don't ask me why it just does. I have gone to making a bracket and mounting it above your feet using a standard chevy switch. Bob Thompson/International Auto Service
Bob Thompson

Most probably the brake light switch. It's cheap and easy to change, they don't last forever, might as well change it anyway.

One tip, before you do, remove the master cylinder cap, place a piece of clean soft polythene over the orifice, then screw the cap back on, over the polythene.

This will keep the fluid loss to a minimum. Have the new switch to hand, remove the old one, as the brake fluid is weeping out at a reduced rate, screw the new one in and tighten. This will avoid the need to bleed the brakes. Remove polythene and check level.

Mike.
Michael Watkins

Rob,

if it's the hydraulic switch, change it immediately!

For my MGB this was the first sign of the switch giving up. It then gave up in a big way: one minute brakes, next application no brakes... Fortunately nothing was coming, there was no camera, it happened in England and I stopped at a parts shop that was open. I was lucky.


Mike
Mike

Rob. What year is the car? I know the brake light switch on my 68 is mechanical, not hydraulic. The pressure of the brake pedal return spring holds the brake pedal against the switch, which is of the "normally on" type, not the normally off type. Thus, when the brake pedal moves away from the switch, it allows the spring to force the plunger outwards and turn the brake lights on. On the 68, the mechanical switch is mounted on the front of the brake cover and can be adjusted for "depth of engagement". You want to adjust so that the brake lights are off, but as the brake pedal begins to move, the plunger is released and the lights come on. On my 79, a similar mechanical switch is located to the rear of the brake pedals, near the top and behind the pedal cover. While I have never had to adjust this car's switch, it appears to be exactly the same as 68's switch. I think people got off on the wrong track here and are speaking of the brake light warning light switch which is hydraulic and only comes on when there is a failure in one portion of the dual hydraulic system. It has nothing to do with the brake lights which are operated by the mechanical switch near the pedal cover. Les
Les Bengtson

UK still had the hydraulic switch in 73, probably until the end of CB production.
Paul Hunt

This thread was discussed between 15/08/2002 and 19/08/2002

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