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MG Midget and Sprite Technical - Hydraulic Brake Switch Upgrade (?)


The single-circuit brake systems in older midgets used a hydraulically-actuated brake light switch while a mechanical switch was screwed into the front side of the brake pedal box when the factory changed over to a dual brake circuit system.

This week, I am sending my dual line master brake cylinder [1972 Midget RWA] to be re-built this week by White Post Restorations in sunny (and hot...) Virginia.

Has anyone adapted a pressure switch (hydraulic switch) to the dual line setup?

I am getting tired of replacing a corroded mechanical switch every few years...Or Plan
Mike Pelone

I connected a relay to the brake light switch on my 1971. The original switch lasted 25 years. Replacements were only good for a year or so. I finally got a used switch (probably original), connected the relay and have gotten almost 10 years of trouble free service from the setup.
Glenn Mallory

Hydraulic switches tend to fail after a couple of years (or is it the silicone brake fluid?) so why do you want to change from something that lasts 25 years to something that probably lasts for about 5 years?
Bas Timmermans

Glenn has it.
Install a relay in the circuit with the "modern" junk switches and they will last a long time as only switching voltage goes through them. The originals were much, much better.
Lee Fox

Glen - How do you rate? Crappy replacement mechanical switch only lasted 2 weeks for me :-(

Mike - the others are absolutely correct, replacement switches are junk. At least there is a high quality/high price hydraulic switch available for those with earlier cars. All is not lost though, as the others reported, a relay in the circuit will make even the crappy replacement switches last a reasonable amount of time. For instructions on making and installing a relay/arc suppression circuit for you car, see the article, Brake Light Relay in the Other Tech Articles section of my web site at: Cheers - Dave
David DuBois

I don't doubt that replacement switchs are k-r-a-p, but I have never had one fail from a mechanical point of view...but in my part of the world, the last few have died from corrosion. 99 percent of the time the button is held back by the brake pedal when it is at "rest" when the car is parked for the winter, a spring time inspection - plus some time with a small wire brush is usually enough to keep the corrosion gremlins at bay...

Dave: I did find your page before [plus a few other sites that feature installation of relays..] - very useful information...

I just thought that since that a lot of other manufacturers of vehicles use hydraulic pressure switches - that a "technology transfer" might be in order...

I also plan to install front headlight relays later this Fall - perhaps a "relay party" might be in order...could be a win-win situation: I can see where I am going plus those behind me can see me stop!

Thanks for the comments - the master brake cylinder is off to Virginia for a re-sleeve..should be back by next week...might be time to move the brake relay project up since the pedal box cover will be off and switch will be accessible...

Mike P.
Retired On The Shoreline of Lake Erie
Mike Pelone

This thread was discussed between 14/07/2010 and 15/07/2010

MG Midget and Sprite Technical index

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