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MG MGB Technical - Proper brake light switch installation?


Hello!

I need to replace the brake light switch on my 1967 B. I see that it is crucial not to thread it in all the way due to pressure figures. Should I just install the new one down to the same numer of threads as the old one was? If I'm quick enough, will I still need to bleed the brakes?

Thanks in advance!
Joseph
Joseph

Joseph How tight should the switch be? As I remember the switch has a tapered thread and the trick is to tighten until you feel good resistence so as to seal the conection. If you have no air in the system now, changeing the switch should not introduce any, but after you install the switch check the pedal pressure before you drive the car and if it needs bleeding take care of the problem before you drive the car RIC
R E L Lloyd

Joseph - As REL says, just tighten until you feel good resistance, then kep an eye on it for awhile to see if it is leaking. If it does leak, another 1/8 - 1/4 turn at a time until the leaking stops. Since the master cylinder is mounted higher than the brake light switch union, there is no chance of air entering the system regardles of how quick (or slow) you are. If you are slow, brake fluid will leak out of the union, but the only worry there is to keep it off of the painted surfaces. After numerous switch replacements in our TD and MGB, I have never had to bleed the system.

If you want the new switch to last longer than just a short period of time (I had one fail in only 2 weeks), install a relay and arc suppression circuit at the same time you install the switch. If you use the switch, even just a few times before installing the relay and arc suppression circuit, the contacts in the switch will arc and build up resistance and if the resistance is high enough, the relay will not be activated. For a drawing and information on installing a relay and arc suppression circuit, see my write up at:
http://www.omgtr.ca/technical/brakelightrelay/brakelightrelay.htm
Good luck - Dave
David DuBois

This thread was discussed between 09/04/2004 and 10/04/2004

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