Packard Forum Index » Pre-War (1899-1942)

My brake light switch failed due to a loose terminal. I found one that will fit locally. (Standard brand)

When I went to install it, I found the box had a slip of paper inside advising that "This part is not certified for use with silicone fluid".
I'm pretty sure my car has DOT 5 fluid in it. Has anyone had any issues with typical brake light switches and DOT 5 or other modern fluids? The replacement switch does not appear to be very old. That type switch will fit a very wide range of older vehicles and some fairly late model HD motorcycles.

Cannot speak to 37 specifically but many reports would indicate silicone fluid results in a shortened life when used with original postwar switches. The 3 terminal 55-6 switches seem to be particularly affected.

This has been my experience with DOT 5 fluid and brake light switches:
I converted a 1937 120C to DOT 5 fluid in the late 1970's, never had a problem with it. I sold that car in 2003;
I switched my 1933 Packard 1002 that had been converted to a hydraulic braking system, probably around 1940, to DOT 5 fluid in the mid-1990's, have yet to experience a problem with that brake light switch;
I converted my 1954 Convertible, bought in 2005, to DOT 5 fluid around 2008 and did experience a switch failure within a couple of years. The fluid leaked through the switch and shorted it out. I bought 2 switches at that time, have yet to need the second switch.
To me, the benefits of DOT 5 fluid far outweigh the potential detriments in shortened switch life. It is also helpful that these switches are easy to replace, inexpensive and readily available.

That's encouraging. The note doesn't say don't use it; it only says it is not "certified" for "silicone fluid". My car has probably had DOT 5 in it for a number of years, and the brakes work fine. The switch on the car appears to have failed due to mechanical injury. (loose terminal) It never leaked or shorted.

Converted to dot 5 over a year ago… same switch I had in it before…. Running fine.