Time for adjustable proportioning valve?

[Dragstart]

Just got a new-to-me 1991 Supercab. It has a pulsing in the brakes, which I assumed was bad rotors. Took a look, and it just recently had a brake job done. Lines, rotors, calipers..........everything. Rotors are smooth surfaced, but still suspected they were warped from improper break-in.
I also had a drum in the rear that had a piece missing on the outer rim, so replaced that. Adjusted and bled, got good fluid when I bled it.
Afterwards, checked to see how the rears were working, and the answer was not too good. The left rear gets just warm to the touch and the right rear barely has any heat in it at all. You could fry an egg on the front rotors after the same test drive.
That sort of solved the why? of the new rotors getting warped. Previous owner just drove the truck not knowing about the bias problem and overheated the new rotors.
So, here's the question. Is this bias problem common, and is it time to install a manual proportioning valve? If any a of you have done it, what is a good valve to use and what problems and cautions are there with the install? TIA

 

[Dragstart]

Just got a new-to-me 1991 Supercab. It has a pulsing in the brakes, which I assumed was bad rotors. Took a look, and it just recently had a brake job done. Lines, rotors, calipers..........everything. Rotors are smooth surfaced, but still suspected they were warped from improper break-in.
I also had a drum in the rear that had a piece missing on the outer rim, so replaced that. Adjusted and bled, got good fluid when I bled it.
Afterwards, checked to see how the rears were working, and the answer was not too good. The left rear gets just warm to the touch and the right rear barely has any heat in it at all. You could fry an egg on the front rotors after the same test drive.
That sort of solved the why? of the new rotors getting warped. Previous owner just drove the truck not knowing about the bias problem and overheated the new rotors.
So, here's the question. Is this bias problem common, and is it time to install a manual proportioning valve? If any a of you have done it, what is a good valve to use and what problems and cautions are there with the install? TIA

BTW, new rotors are coming. NAPA is dumping their old line of rotors, part #PFR24885865. $25. There are some left in the system, they're scattered around, but you can have them ordered if you have a parts counter person willing to do it. That's the two WD rotor, but the picture on the website is wrong, it shows a 4WD.

 

[Uncle Gump]

Did you give the rear brakes a proper adjustment?

 

[Dragstart]

YES.

 

[Uncle Gump]

So.... no. Its not a common problem.

You got a good stream of fluid to the rear? These older trucks with RABS have been known to have the RABS valve go bad. It will limit fluid flow to the rear brakes at times when they fail. Or even fail and hold fluid pressure to the rears. Does it even still have the RABS system in tact and functional? Also the rear flex hose has been known to collapse and again limit fluid flow to the rear and hold pressure.

I'm curious where you want to put this proportioning valve? Are you saying you want to put it in the front line to limit fluid to the front brakes? That doesn't sound like a good idea to me.

I've heard of people putting one on the rear line in an attempt to not have the rear brakes lock up. But you have an entirely different symptom.

Rear brake adjustment is crucial for disc/drum brake configurations to work properly.

How does to pedal feel?

 

[bobbywalter]

is there a rabs valve?

i would go around that and revisit it.

from there its a master thing possible...the qtu systems bias usually stays pretty good with properly adjusted rear brakes.

i run a proportioning valve, but only because i swapped in rear disk brakes

 

[bobbywalter]

we posted at the same time apparently

 

[Uncle Gump]

Looks like we did...

 

[Dragstart]

The RABS system is intact. I pulled the fuse to see if it changed the symptoms of pulsing, it did not. I only bled one side of the rear to check for fluid flow, it was good. Adjusted both sides in rear to a slight drag. I will go through everything again. The pedal is good. What is the bias in the system as designed? Those are pretty hefty brakes on the rear and I understand trying to prevent rear lock-up. But front lock-up with no rear brakes coming into play is just as bad, of course.