idlook2
OBS Enthusiast
I have a feeling that the proportioning valve is only for non-abs equipped trucks. Most of the trucks in that vintage had the Kelsey-Hayees RWAL brakes and have a combination valve. I think the proportioning valve is used to "balance" the brake pressure front to rear but that's not needed with the ABS unit. I did see something like the part you're describing here:
89-94 Chevy Truck Brake Proportioning Valve - C/K 1500-3500 (carolinaclassictrucks.com)
Hope that helps. It's really expensive new so maybe a wrecking yard is your best bet. Also, maybe an 1987 truck will have it or other non-abs truck.
That new valve looks exactly like the one I purchased from Southwest Performance Parts. I would guess that all of these aftermarket valves are identical and just being re-branded and sold by various distributors.
The machining quality of the valve in person is not great and it leaked almost immediately out of the electrical connector. I would recommend staying away from these aftermarket valves.