I thought I would put this info on here in the hope that someone will find it helpful. When I redid my wife's truck last year I installed disk brakes in the front and kept drums in the rear. When this is done you need to install metering and proportioning valves. The metering valve allows pressure to build in the rear drum circuit before pressure flows to the front discs helping with nose dive. The proportioning valve limits the total amount of pressure to the rear drums to prevent rear wheel lockup. A easy way to accomplish both functions is to install a GM PV2 proportioning (combination) valve and this is what I installed. Then the problems started. The first valve had a oil leak from inside one of the mounting bolt holes, no problem they shipped a new valve. New valve was installed and on the first trip after coming to a stop the front brakes were locked, they eventually released and I was able to drive home. I was told I had not bled the brakes properly, after numerous bleeding procedures the truck would still occasionally lock the fronts which required crawling under the front to loosen the brake line to relieve the pressure then it might work dozens of times. I finally decided it was a problem in the combination vale and had my wife pick up a different brand while in Phoenix. I took the old one apart and found the oring had failed in the metering valve causing the problem. Installed the new valve and everything was great for the next 1000 miles. One day my wife told me on her way home from a show the truck didn't seem to want to move at first then was fine, and it stayed fine for another 400 miles. Recently while I was driving I had the feeling the truck was initially hard to move from a stop. I decided to do a check for a dragging brake and though the drivers front was tighter than the passenger everything seemed fine until I had my wife brake while I rotated the front wheels. The wheels would rotate easily and she would apply the brake, they would stop as they should. She then released the brake and the fronts would stay locked for 1/2 to 4 seconds before they would release. I was sure there was a problem with the metering valve and called the manufacturer of the first valve that had been installed (they had a tech department). Explained the problem and asked if they had ever heard of it, why yes they had seems some valves when made were out of alignment and would leak, they are sending a reseal kit no charge. I ordered a new valve from this same brand as I knew the one currently installed was different with different threads and the seal kit probably wouldn't work. Of course I originally had the correct brand but after the replacement worked so well I threw it away! So valve number FOUR is now in and working fine, a seal kit is on the way just in case things go south again. I took valve number three apart and found it had failed the same as valve number two. I have spoken to a few people at shows who have told me they also had multiple combination valve problems.

As for me I believe that since this is the only GM part on the wife's truck it is pissed and refuses to work with it.





GM proportioning (combination) valve.





Seal dislocated from the metering valve. This is what happened to valve two also. Very disconcerting when the light turns green and the truck won't move.

 

Were the valves AC Delco (GM), or made in China ?

 

If it isn't an adjustable PV, I'd go to the boneyard and look for a clean OEM piece. It seems like at least half of the new brake parts are junk out of the box. Even brand name stuff like Wilwood.

 

Ditto.
I grabbed one from the local pull-a-part. I think it was from an early 70's A body GM car (Olds Cutlass). Seems to work pretty good.


Bobby

 

They are not marked for country of origin but I would guess China. First and last are Classic Performance Products. The one from Phoenix was from So.Cal.


I am going to watch for a original. Have had a couple people that told me they had problems ended up finding a original.