GM Brake Pressure Differential Switches?

[sah62]

I'm working on the parts needed to rebuild GM pressure differential switches like the one in the attached picture. I could use some help in figuring out the original applications, though. Can anyone explain the applications for these parts? Were they used on both disk/drum and drum brake cars? I've read that they were used from 1967 - 1974, is that correct?

[JohnZ]

As far as I know, they were used on all applications (drum/drum, drum/disc, and disc/disc) starting in 1967. The switch function was later integrated into the "combination valve" (which included the warning switch, metering/hold-off, and proportioning) in '75 or '76 (photo below).

[sah62]

Thanks, John.  My Chevy parts book also lists some 1975 applications, so I guess they were used from 1967 - 1975. I've seen a few of these valves with two different types of electrical contact terminals. One has a visible black plastic insulator, and the other is steel with an "internal" white plastic insulator. Do you have any thoughts on the rationale behind the different terminals? I'm wondering because they used different o-ring seals. I can provide both, but I don't understand why the two types were used.

[JohnZ]

Do you have any thoughts on the rationale behind the different terminals?

Nope - have no idea why they changed.

[Jon Mello]

Besides what John has already stated, maybe these are helpful to you as well.