69 k2500 4wd disc brake conversion problem

[smoke308]

First time to post. Have a braking problem on my 69 GMC 2500 4wd. Converted front brakes to disc with a kit from RAM Man out of Ft. Worth. At this point, everything is new. Pwr brake booster kit from Tuckers specifically for disc/drum setup. New rear drums and shoes. New flex lines. The only things not brand new are the rear wheel cylinders (no leaks, look nearly new) and the return springs in the rear drum brakes (kit was backordered when everything else came in so went with the old ones). Did not replace hard lines, but blew them clear.
Before the conversion, the old girl didn't stop fast, but she didn't pull either.
Now, when I step on the brakes hard the truck pulls hard right. To me it feels like the back end is trying to come around. The right rear wheel locks up right away. It does not "feel" like the front brakes are pulling. To me it feels like something in the rear. I have adjusted the rears manually a half dozen times -- loose, what feels right, and a little tighter than I normally would on my other vehicles that need adjusting -- no change. Any ideas appreciated. Thanks

[franken]

If one of the rears is locking it's adjusted more tightly than the other or there's a bleeding issue (air in the line). If there's air in the rear, there's probably air in the front. Bleed from farthest away to closest to the MC.
There's usually a prop valve with a call it a hydraulic switch under the MC. That can switch and send pressure to one end (front/rear). The manual shows how to keep that from happening when bleeding with a stop.
I'd start by checking the prop valve, then a do over with adjusting the rears to drag, back off, then bleed.
Sorry, it is a pain to do it over...

[smoke308]

Franken,

Thanks for the reply. I have bled the thing silly, near to far, but will try again. I did not know that the proportioning valve could get out of whack while bleeding. No instructions in the kit, but Tuckers, so far, has been a lot of help. I bet they have directions.

[smoke308]

Well, after re-bleeding, and bleeding some more, and pulling the rear drums, wiping everything down just make sure there was no contamination, and readjusting — the rear brakes lock simultaneously — and then the back end tries to swap with the front. Confirmed with Tuckers that we have the correct proportioning valve GM PV2 for disc/drum set up. Could there be a "geometry" problem given that the master cylinder/prop valve set up was meant for a 2wd truck, but is now on a 4wd? Master cylinder and prop came from Performance Online. Talking with them they said they didn't make anything for 4wds, and then went over the possibilities we have already explored -- no help.
Would it make sense to install an adjustable proportioning valve?

[BigBird05]

I just read a post that 2 wd master cyl that the front line goes to the rear of the valve and the 4wd master cyl that the front line goes to the front of the valve. Or vise versa. You might check that info out and see if it is correct.

[Bigdav160]

This is the routing for the PV2



The purpose of the metering valve is to bring on the rear brakes first and let them build some pressure before bringing on the front.

The OE master cylinder with four wheel drums would have had residual check valves in the ports. The port going to disc brakes would not have this as the valves job is to leave a little bit of pressure in the circuit to keep the wheel cylinder seals inflated.

[67 chevelle]

You may have the lines reversed on the combo valve , that would make the rears lock first , dirt road test works great for brakes , and also lifting truck in air and aplying brakes , withanother person checking how the wheels spin , or not