Proportioning valve?

[CUCV2]

Does bump steer have anything to do with this? When you hit the brakes, the front end will dip some. This will change the geometry of the stock push/pull set-up. The cure would be a cross-over steering set-up which would mean throwing out the swaybar. I personally like swaybars in a daily driver and would prefer to keep it. Just my .02 cents here. Curious what others think of this theory.

 

[bp71k5]

Just to be clear, it's not possible for any of the calipers to be getting too much pressure. If one side is higher than the other, than the lower side is the one with an issue.

My brakes work very well and don't pull left or right, so I'm pretty sure it's not a factory defect. If you have bad steering ends, wheel bearings, or even crappy tires, all of that could cause a pull, especially if it switches from right to left.

I'd suspect whatever is making the clunking noise, is the problem. The combo valve could also be clogged, but that doesnt make any noise.

 

[sweetk30]

Just to be clear, it's not possible for any of the calipers to be getting too much pressure.

i take it you have never seen a bad / defective hose then this will hold pressure and burn up brakes and make a pull. and or restrict flow and not work right.

 

[bp71k5]

i take it you have never seen a bad / defective hose then this will hold pressure and burn up brakes and make a pull. and or restrict flow and not work right.

I wouldn't call that too much pressure. The brake system is supposed to generate that amount of pressure and the pressure gets released when you take your foot off of the pedal. He said the problem happens during braking and I assume that means the problem goes away when he takes his foot off.

If the brakes are dragging when the pedal isn't being touched, then yea a bad or clogged hose could do that.

 

[chulisohombre]

he said he had new hoses.but a kinked hardline will act the same way and restrict flow either direction also and cause a pull oe drag to one side.if the rear brakes arent adjusted properly and one is farther away from the drum it will pull also.have you tryed adjusting the rear brakes to make sure they are contacting the drum at the same time?

 

[clandr1]

he said he had new hoses.but a kinked hardline will act the same way and restrict flow either direction also and cause a pull oe drag to one side.if the rear brakes arent adjusted properly and one is farther away from the drum it will pull also.have you tryed adjusting the rear brakes to make sure they are contacting the drum at the same time?

Yeah, I just had the rear brakes adjusted last week (shoes & cylinders are in good shape, as are the drums) and it didn't change anything.

I took the caliper on the right side back to NAPA and replaced it, but it didn't help either.

I need to check the front steering components for slop. I wonder if the drag link or TRE's are bad, causing the front end to pull when all the weight is thrown forward on the truck. I also have some play in the steering wheel when driving straight down the road, so I need to address that at some point.

This truck has led a babied life and I highly doubt it's a crimped hardline. I'm leaning towards either debris in the lines causing blockage, or bad steering components.

 

[clandr1]

I'm bringing this thread back from the dead because I just flushed the brake lines again & re-bled, and now the severe pull to the right has come back.

In an effort to narrow down the problem, I replaced the driver side caliper, thinking it might be bad and not putting as much pressure on the rotor as the passenger side. This did not fix the problem.

The ONLY things that haven't been replaced in my system is the MC, the hard lines, and the proportioning valve.

Is it possible there is air in the proportioning valve, or maybe the infamous "reset button" is stuck, restricting the flow of fluid to the driver’s side caliper? I'm also wondering if the original fluid that was in there when I bought it caused a bunch of crud to build up in the valve.

Would anyone recommend removing it, soaking in brake cleaner/acetone and blowing with compressed air to remove any potential debris?

Diagram of valve:

 

[496truck]

If you're gonna go through the trouble of removing it, then just replace it.

You are positive you bled all the air out of the system?

 

[clandr1]

If you're gonna go through the trouble of removing it, then just replace it.

You are positive you bled all the air out of the system?

I don't know where I can even find another proportioning valve, and I'm leery of using an aftermarket reproduction.

Never been more sure. I've bled this thing countless times, from using an air pump systems to the old pedal bleed, and it continues to be an issue.

 

[496truck]

Can you get the right one from the dealer still?

 

[Amtek]

With your suspension lift, did you install a taller steering arm on the knuckle? (is the point where the draglink attaches to the steering arm above the leaf spring?)

If so, I can garauntee that is the cause. As the axle wraps under heavy braking, the axle tube bends back but the top of the knuckle twists forward, pushing against the draglink and causes the wheels to turn right slightly. The harder you brake, the more it will pull to the right.

The steering wheel doesnt actually pull in any direction. You hold the steering wheel straight and hit the brakes and the truck will dive to the right, correct? If the issue was with the brakes, you would have to fight with the steering wheel to keep it straight.

 

[clandr1]

I haven't checked with the dealer since last August, and if I remember right they didn't have any stock proportioning valves since they've been discontinued. I'll check again to be sure.

As for the modified pitman/steering knuckle, I do not have an adjustment on there because it was only a 2.5" lift, and from what I read here it is really only required on 4" lifts and above. There isn't much of an angle on the drag link, and given that the problem got much worse after a brake bleed leads me to believe it's not a suspension problem.

I'm going to start with pulling off the proportioning valve and cleaning it (when I first changed the brake fluid last year it was rust colored and I assume there's junk stuck in it) and if that doesn't fix it, I'll order a new one from Year One, unless anyone suggests against that brand/product.

http://www.yearone.com/serverfiles/fbshopmain2.asp?hid=C18AC56977

 

[496truck]

Well, they don't have a raised steering arm for a 2.5" lift but they do have a drop pitman arm that would level out your draglink. Actually, GM made a stock one and put it on the K20/K30 because they sat higher. So you can buy a new one or go to the junkyard and pull one cheap. Having the draglink at an angle will definitely add to the right pull feel when braking. Heck, even the level ones in stock form pull right under hard braking (as evidenced by the new car review vid posted recently). Whether it may be your issue or not, fix this first and go from there.