Mystery part/sensor??

[rudedog67]

Hello, been hanging out for awhile now, great site tons of info. I have a question about a mysterious part located on a 1987 silverado 350 tbi 700R LWB, it is below the radiator shroud, mounted on a metal crossmember type bracket.  Has a spade connection on it,  not connected and truck still runs good. Pics are too big too post.

Thanks in advance.

[zieg85]

My guess is the proportioning valve for the brakes.

[Captkaos]

Can you not resize the pics with MS Paint. Here is how to do it:
http://forum.73-87chevytrucks.com/smforum/index.php?topic=6428.0

[rudedog67]

Pic

[rudedog67]

That's it! thanks Capt.

[Captkaos]

Looks like your proportioning valve as zieg85 stated.  Is your brake light on in your cluster?

[Fordeatinz71]

unhooking the wire shuts off the brake light.  i know because my prop valve is bad and i unhooked the wire because i got tired of looking at a brake light and haven't had the spare cash for a new one

[VileZambonie]

That's for your differential pressure valve. It illuminates the brake warning lamp when there is a pressure loss in the hydraulic brake circuit. That valve block is called a combination valve and contains a proportioning valve which limits the pressure to the rear brakes to about 600psi and a metering valve which delays the application of the front brakes so the rear shoes have time to overcome the return spring pressure so they apply at the same time.

If the pressure differential switch is stuck on and when connected turns your brake light on you can try manually resetting it or else you would have to replace it. Otherwise just leave it unplugged.

[rudedog67]

Thanks to all. Just bought the truck and finding out all the electrical connections that are not plugged in to get it road ready. I'll check to see if that cluster light is on this evening Capt.