Packard Forum Index » Post-War (1946-54)

Thanks Mike!

I was under the impression that the brake light pressure switch doesn't like DOT 5 silicone brake fluid. Is that true?

The original one probably won’t like it but a modern one shouldn’t care.

Quote:

I'd rather not replace the switch, since it's original and it works fine, unless a modern replacement is "sho nuff" going to tolerate the DOT 5 brake fluid.

Has anyone had experience with this?

You should be able to run (the idiotically named) DOT 5.1 brake fluid, which is virtually always DOT 3/4 compatible. But not as good as DOT 5.

End of the day who cares, if you want to keep the car original just change your DOT 4 fluid every 3 years. As long as the brake system works properly and you're not driving down mountains you won't notice much difference aside from the shorter maintenance schedule.

It has been the experience of many on the forum both here and at PAC that silicone fluid seems to hasten the failure of the hydraulic brake switches. Unknown why this happens or exactly what fails inside but while switches used with the older fluid seems to last for years many report them lasting only a year or two with silicone. New ones bought at a local parts store do not seem to be immune.

Usual symptom seems to be brake lights become intermittent or not coming on unless brakes applied quite hard and then progressing to not coming on at all. Many replaced the switches only to have a relatively quick failure and then ultimately decide to leave the switch in as a dummy to close the port but go to a mechanical switch operated by the pedal arm for the actual light operation..