My brake proportioning valve in my 84 is pretty gummed up and I'm having trouble finding a replacement. the only valves I can find say they fit most GM vehicles but look nothing like mine. Does anyone have a part number for one that will work, or do I have to just buy an adjustable one?

1984 Pontiac Fiero VALVE, Hydraulic Brake Combo/Monitoring {a.k.a. Combination Proportional}

GM 10026021 / GM 10036563 which of course were discontinued...

For Informational Purposes Only

That Combination Proportional Valve
https://www.fiero.nl/forum/Forum2/HTML/109173.html

PFF "Proportional Valve" Search
https://www.fierosearch.com...alve&Action=DoSearch

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Original Owner of a Silver '88 GT
Under 'Production Refurbishment' @ 136k Miles

quote Originally posted by GreggDauer: My brake proportioning valve in my 84 is pretty gummed up and I'm having trouble finding a replacement. the only valves I can find say they fit most GM vehicles but look nothing like mine. Does anyone have a part number for one that will work, or do I have to just buy an adjustable one?

I could ship you the one I just took out of my 85 we replaced it but I’m pretty sure it wasn’t the issue and still works. I’ll send you a PM

I wasn't able to find one for my 87 either. Do any of you know how to tell if it's working properly?

The brake proportioning valve doesn't break too often. If you ask around the there are probably dozens of used units available that could work.
The S10 proportional valve looks like a very close duplicate of the Fieros.
S-10 Brake Proportioning Valve

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" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

quote Originally posted by donuteater306:... Do any of you know how to tell if it's working properly?

Seems to me a few threshold brake stops should tell.

In a safe location, drive up to 35 mph and hit brakes to just beyond threshold. Have an observer note which wheel locks. The front brakes should lock and the rears should still be rolling.

Next, repeat except hit the brakes with full leg strength; all 4 wheels should lock.

If the brakes perform this way, the proportioning valve is working correctly.

Experts: Do this sound right? My concern is if the proportioning valve (by design) reduces rear brake pressure so nonlinierly that it would never allow the rear brakes to lock in the second test.