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MG MGB Technical - MGB Brake switch problem

I have a ongoing problem that is slowly becoming very expensive. I have now fitted five switches and all pack up soon after fitting. I know how to fit them correctly and even had the last one fitted by a mg specialist just in case it was something I am doing wrong but it still happened. The problem is this, on fitting the switch the brake lights work but very soon they stop. Fine adjustment is made but still they packup even after a few moments. Eventually the switch seizes. I am aware that if the switch is advanced too far the brake lever that presses the sprung ball will press too hard and damage will result but what ever I do this damage still happens. Is the part that presses sticking so that even when you think you have got it right you havent resulting in damage or what? your thoughts or experiences please would be appreciated as this is driving me mad and slowly broke as the next one I fit will be the sixth in ten months! Many thanks in anticipation.
Graham Palmer

Graham - Sound like you are another victum of the wimpy switch syndrom. Replacement switches today are such light duty units that I have had them fail after only two weeks. The answer is to install a relay and arc suppression circuit between the brake light switch and the brake lights. Since doing that, I have not had any more failures. Although they use a hydraulic switch rather than the mechanical switch used in the later MGBs, yo can read more about the problem in the current thread on brake light switches on the MGA BBS. For information on making a relay/arc suppression circuit and installing it, see my article at: http://www.omgtr.ca/technical/brakelightrelay/brakelightrelay.htm
Good luck - Dave
David DuBois

Graham,
The problem with my brake switch was apparent when I disassembled it. There's a shaft with a copper disk on the end of it, inside the switch housing. The disk got cockeyed with the terminals it contacted, and hung up at a canted angle. I trimmed the terminals back with a miniature cutoff tool, and reassembled the switch. A cautionary note: the switch was not intended to be repaired, so you may destroy it, if you're not careful.

The switch is very simple. I doubt all (or probably any) of your failures are electrical, so you are probably experiencing the mechanical failure I describe.
Fred Doyen

Fred - If you were able to open the switch and repair it, it was obviously one of the old Lucas switches. Those could be opened up and repaired and due to their size, a mechanical failure as you describe would not be unusual. Additionally, an electrical failure due to burned points could be repaired by disassembly and cleaning of hte points (I have done just that). Graham however, has put replacement switches in and in the past several years, the replacement switches cannot be disassembled, additionally they are extremely light duty and prone to burned contacts as I described in my posting. If Graham is fortunate enough to have one of the older Lucas switches installed, he should try disassembling it and checking for a mechanical malfunction as you describe. If, however is is one of the newer replacement switches, his only choice is to replace it againg, in which case, the relay/arc suppression circuit should be added to insure that the replacement will last. Cheers - Dave
David DuBois

Other car manufacturers used a similar type of switch and I think it's time to do some research and find out what else fits. The threaded part on the pedal box cover can be drilled and helicoiled to adapt it to another switch.

I have a 66 so I don't use that type of switch and I was fortunate enough to get a bunch of NOS switches a few years back.
Mike MaGee

I don't know your particular switch but a lot of these kind of switches are very intolerant to overtravel either on application or bouncing off the spring return system for the pedal.
CDD Dewey

Hi all and many thanks for all your kind offers of help and advice but my problem now seems to be cured. I am new to MG ownership and have little experience and presumed that the car I have only owned for the last 12 months was fitted out with nothing but what it was first built with. I had not realised that the 3rd high level brake light fitted along the top edge of my rear windscreen was infact an addition made by by the last owner who fitted it without a relay and because of this the system was over loading and burning out brake switches like they were going out of fashion. Since the removal of said 3rd light and the fitting of yet another switch I have brake lights that seem to want to keep working, oh bliss! One other comment I can make is that there is available a hydraulic switch that I was intending to have fitted by Andy Rickets of Wroughton (an MG specialist) but since it looks like the problem is now solved I can spend that money on something else that needs doing.
Many thanks once again to you all and happy MG motoring.
Graham Palmer

Hi all.

You could fit a hydraulic switch (as fitted to early B's, I believe, definitely fitted to Morris Minors), but there have been problems with aftermarket versions of those, too.

Don
Don

Hydraulic or mechanical, the aftermarket versions of all of them are junk. Graham, you may well find that the switch will still burn out well before a decent lifetime even without the high mount 3rd brake light. I would have opted for the relay over removal of the 3rd brake light, in fact that is what I did and installed a 3rd brake light on our MGB. If you go to the expense of modifying the brake system to install a hydraulic switch, order the switch from Ron Francis Wiring at: http://www.ronfrancis.com/showpage.php?page=main.htm These switches are expensive, but I have been told that they are bullet proof (as well as silicone fluid proof). Good luck - Dave
David DuBois

David,

I checked the Ron Francis site about switches and notices that he also sells an "under dashboard switch" which looks like it could be used where the original mechanical switch is used in the later B's? I can't remember if the MG unit is always "on" or not?

http://www.parts123.com/parts123/yb.dll?parta~dyndetail~0000278a~AAAJJ~9.95~~~~1NO0GVT2R65241416659b~

As Mike said, one could simply drill out the hole on the old brake box and insert the new switch.

Zach
Zach

FWIW the mechanically operated brake light switches are normally closed - they are pressed in when the brake pedal is released which opens the circuit. When the brake pedal is operated the switch is released and the contacts close to light the lamps.
Paul Hunt 2

Zach - Thanks for calling my attention to the mechanical switch, I had missed that when looking at the web site. It is good to know that there may be something that is a bit more robust that the standard replacement switches that are presently available (the one I installed lasted all of two weeks). Cheers - Dave
David DuBois

FWIW: After repalceing the switch in my TR6 for the third time, I went to the local auto parts store and looked over about a dozen or so switches for various makes of autos until I found one that I could make work for me. I think I paid under $10 for it and all I had to do to make it fit was file a flat spot on the mounting threads to match the "D" shaped hole in the TR. That was 14 years ago and it's still going strong. I'm sure you could find something to match the MGB as well.
Dan Masters

This thread was discussed between 31/10/2005 and 09/11/2005

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