Brake Switch Failure

[svs451]

Hi out there,  I seem to remember an article about brake light switch failure which may be caused by using  Silicone fluid.

 

I have now lost two swictches one on the trusty TR3 (on the way to lemans I must add) and the second on my wifes car a MG V8!!  Both were fitted and purchased (new) around the same time.

 

Does anyone have any comments or suffered the same problem.

 

Regards

 

Dave

[Don Elliott]

Dave - I have had several that went bad.  About 10 years ago, I bought two at the same time and kept one in my tool box as a spare.  I checked them both when I bought them.  I adjusted the air pressure from my air compressor and with a continuity checker on my multimeter, I checked that they both worked at about 20 to 35 psi air pressure.  When one went bad after 5 years of use, I figured, no problem, I have a spare.  So I re-checked the spare one before installing it - using the compressed air and it wouldn't make contact - even at 125 psi air pressure.

 

So I turned this new unused switch down on a lathe and found out how they are made.  Inside there is a copper disc that makes the contact when the brakes are applied and the brake fluid pressurises a rubber seal which moves the copper disc moves forward to close the contact and make the rear lights come on.

 

The copper disc had turned black !!!!  It was still in the original box !!!  (I think it was by Interstate - Nottingham).  In the 5 years in my tool box, it looks like oxidation had built up on the copper.  I don't know why they don't make the disc out of stainless steel.  When I explained this to the supplier, he gave me a new one.  This one has been fine for the last 5 years.

 

The silicone fluid I have been using for 15 years has never affected the rubber seal next to the copper disc.  I had heard the reported rumours about the defects being caused by the silicone fluid, but I don't see that this is the cause.

 

Now carry a small microswitch with a normally open switch on a bracket that I can secure between the dashboard and the brake arm for my brake pedal.  When I push on the pedal, the suspended arm moves forward and the microswitch contact closes to actuate the rear lights.  If the pressure switch goes bad again, I'll install the bracket and run the wire to the connection at the pressure switch.  Make sure you connect it to the wire going to the rear or you won't be able to start the TR if you also have your foot on the brake pedal.

 

Don Elliott, Original Owner, 1958 TR3A, Montreal, Canada

http://mysite.wanadoo-members.co.uk/trebor/don3a_big.JPG

[tony13579]

We had a problem at work with a waterproofing spray called darathene after about 6 months any thing made of bakalite disintergrated.

 

some of these mistakes were VERY costly!