Where is the proportioner valves on this vehicle? on 1994 Buick LeSabre

I am having diagonal right front and left rear brake failure. I was told that it could be a proportioner valve
failure problem.

Asked by for the 1994 Buick LeSabre
Define brake failure on right front and left rear. No brakes on those two? Brakes locking up? It's not the porp. valve!
Yes,no brakes on left rear and right front. Did have a bad caliper on right front. Replaced and still no brakes. Left front and right rear fine. I don't know.
Poor/low brake pedal?
Yes, brake pedal low and sound like air flowing through when pedal compressed. Had good brake pressure and then lost again. Could it be booster?
No! Booster can NOT cause LOW pedal. Seek a mechanic's hands on help. It is time for that!
ok. Was leaning towards that. I've did all I can do on my own. Thanks.
Smart move! Hope you get it back on the road. Cant play around much with the brakes!
Your right about that. Thanks for your help. I'll stick to things I can do.
1 more answer , 1 more comment
That valve can fail but its very rare. It is typically located below master cylinder mounted on chassy frame.
Thank you. I did find where the valves are located on my vehicle.