Combination valve

[idlook2]

I’m looking for a replacement combination valve for my 1990 k1500 as mine was leaking out of the front metering valve.

I thought this would be something easy to find, but I am having a heck of a time finding one that matches the original. My original valve has a metering valve on the front and a proportioning valve on the rear. I actually bought one from a parts truck as it looked the same from the front and got home only to find it did not have the proportioning valve part in the rear (just solid aluminum). I’ve since looked at several other trucks in salvage yards and none of them have the proportioning valve in the rear. What gives? What year/options do I need to be looking for to have the proportioning valve?

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[Schurkey]

That stinks. Not something I'd have expected.

Try a GM dealership. They've probably been discontinued...but you can hope.

Theoretically, they're not repairable. Since you've got one you can't use anyway, pull the metering valve out, see if you can match-up the seals--hopefully they're common O-rings. If you can find replacements, and pulling the valve isn't too difficult, you could maybe fix the leak on the original valve.

 

[Supercharged111]

That's weird, the one I ganked from the junkyard looks like your original. I plucked mine from an 88-89 eons ago. Was it an early/late thing?

 

[idlook2]

I was finally able to find one at a salvage yard in Kansas City. I must have called at least 10 yards to find a combo valve that included both the metering and proportioning valve. There does not seem to be an obvious connection between which trucks have the proportioning valve included in the combination valve and which trucks do not.

And regarding the dealership, the combination valve was discontinued long ago. There is a knockoff valve that you can buy (some eBay and Amazon sellers even claim it is AC Delco), but it is horrible quality. I already tried buying one and it leaked out of the electrical switch on top. After contacting the seller, they confirmed it was just “AC Delco inspired.”

 

[Schurkey]

Yeah, I've heard of aftermarket brake hydraulic valves being piss-poor quality, even when purchased from "big name" brake suppliers at significant cost.

Seems like the ones that don't obviously leak fluid OUT, insidiously leak air IN. I think I'd rather have an obvious fluid leak than to have a perpetually-worsening low brake pedal from air intrusion.

 

[someotherguy]

It would seem any GMT400 pickup from 1988-1994 would have that same valve. Note I said pickup. The SUV's 1992-1994 had 4WAL and while IIRC they used an external valve like that along with the enormous early 4WAL unit, I wouldn't expect it to be functionally the same.

Could be wrong; it's happened before.

What exact year and model of truck did the incorrect valves come from in the boneyard?

Richard

 

[67GMC]

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.

 

[arrg]

I have the "no proportioning valve" model in my 1988, and it has RWAL, so that's not it either. I suspect it has to do with LD vs HD brakes difference in the 88-91 reg cab models, but I haven't confirmed that.

 

[idlook2]

It would seem any GMT400 pickup from 1988-1994 would have that same valve. Note I said pickup. The SUV's 1992-1994 had 4WAL and while IIRC they used an external valve like that along with the enormous early 4WAL unit, I wouldn't expect it to be functionally the same.

Could be wrong; it's happened before.

What exact year and model of truck did the incorrect valves come from in the boneyard?

Richard

I bought one out of a 1992 K1500 (picture below).

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It had the rear wheel abs system just like my 1990. Didn’t notice until I got home that the it did not have the proportioning valve. I’ve got pictures of several other valves from salvage yards from various trucks (88-94) that also did not have the proportioning valve but did have rear wheel abs systems. It’s a small sample size, but to me it seems like combination valves with proportioning valves are more rare than without.

Here is another one out of a 1993 that does not have the proportioning valve but the bracket definitely has provisions for the abs system:

https://www.ebay.com/itm/gmc-Chevro...-/143761500789?_trksid=p2349624.m46890.l49292

 

[someotherguy]

Weird. If this subject had come up, oh, 10 years ago.. I'd have a really large selection of examples to check to try to form a pattern of which model had what.

Richard