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Proportioning valve?

clandr1

clandr1

1/2 ton status
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Read through a few threads on this topic and didn't see an answer:

If my proportioning valve is blocked or clogged, causing my truck to swerve to the right when I hit my brakes, will taking it off, spraying it with brake cleaner, and blowing compressed air through it solve the problem?

Or is it a situation where once it goes bad it must be replaced?


Thanks in advance.

Edit 7/19/11: After replacing the proportioning valve, front calipers, rear wheel cylinders and installing a new spring kit on the rear drums, I replaced the brake pads (which were new a year ago, less than 10k on them) that came with the original set of remanned calipers I bought when I first did a brake job in July '10.

This solved my pulling issue. Turns out the remanned calipers had two different types/lots of brake pads in the boxes which made one side stop quicker than the other. Talk about a pain in the ass to diagnose! Always start with the simplest solution first.
 
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Prop valve only biases the fluid front and rear not side 2 side.sounds like your caliper is sticking.whatever side its goin 2 when you hit the brakes check and back off that side by pushing the piston back in like you were doin new brake pads.if it wont back off you need to replace that caliper.
 
I've already replaced the calipers (they were both acquired at NAPA as remans) so they both should be working just fine.

It's not a major pull to one side, just more annoying than anything -- could it have anything to do with the steering components being worn out? Tie rod or drag link bushings bad?
 
Could be worn out parts, you might have gotten a bad caliper, you could have a bad seal leaking grease on the rotor, or your flexible brake hose could be coming apart inside.
Plus if you did not grease the slides on the calipers, one of them could be hanging up.

Or even something else.:D

However, good news, about the one thing it could not be is the proportioning valve.
 
comon overlooked item on our old trucks is 20-30 year old brake hoses. thay do go bad inside. and blug up and block flow .

and a prop valve does actualy control flow on the front brakes. its only a tee fitting so no press regulation. but its possible but not likly its pluged on 1 side of the internal tee portion.

and have you check the full function of the rear brakes ?

bad wheel cylinder / oil seal leaking on shoes makes bad pull at times. and if 1 drum is adjusted more than another. and dont think that those ( self adjusters ) realy do self adjust. you need to adjust them for best performance.

also a small air bubble in 1 side can make a brake work diffrent than the other side. just for kicks try a 4 wheel blead out of the fluid.
 
Since I bought the truck in May, I've replaced all soft brake lines, front calipers, pads, rotors, and just last week I had the rear brakes adjusted at a brake shop (did nothing to change/worsen/better the pull I was having).

I have also personally bled the system (pretty much flushed the fluid) twice now.

So, I'm thinking it's GOTTA be in the suspension. Any thoughts?
 
I have had the same problem for a few years...always pulls slightly to the right when braking.
I too have replaced and adjusted everything on the brakes... front calipers, rotors, pads, and lines as well as rear wheel cylinders, drums, shoes, and lines...and the master cylinder. I have not replaced the booster or combination valve...
I still have the same issue even though all those things have been replaced, some more than once.

I even had another set of axles with fairly new parts and tried those too...still the same slight pull to the right. What are the odds that the same exact parts on the right are bad 2 or 3 times?
I have also thought about the combination valve...the combination valve does have separate valving for each front caliper...there is a check valve in there that keeps slight pressure to keep the pads against the rotors.

I have wondered if there is a problem with one of the check valves, could it be possible to not give even pressure to each caliper when pressure is applied?

Just a thought...since I am having the same problem and I have heard others say this exact same thing. Most people seem to give up and just blame it on the lousy suspension and live with it...
 
Tell you what.
One of the biggest parts of fixing a problem is defining it. If you don't know whats broke, its darn hard to fix.

I don't know what your situation is out there in TX, but around here, before we rose up and threw the whole system out, every inspection station had a four wheel brake tester. You drove on at a slow speed, and slammed on the brakes.
The machine would tell you how much braking each wheel did.

Unless you were a numbnuts driving my Jeep, who kept missing the pads. Despite my begging him to let me do it, he was determined.
Last try, his foot slipped off the brake, and he took out the headlight tester and the back wall of the parts house.
Didn't bother my Jeep, it was built for stuff like that. Sure Pi**ed off the parts house guys though.

Anyway, if you can find one of those machines, see if they will let you test and see if one wheel is braking faster than the other.

If not, then take it out to some hard packed dirt or sandy rock.
Make sure you are going straight, and try coming to a stop, hitting the brakes harder and harder each time until you get the tires to slide.
See of one slides more than the other every time.
 
Fordum said:
Tell you what.
One of the biggest parts of fixing a problem is defining it. If you don't know whats broke, its darn hard to fix.

I don't know what your situation is out there in TX, but around here, before we rose up and threw the whole system out, every inspection station had a four wheel brake tester. You drove on at a slow speed, and slammed on the brakes.
The machine would tell you how much braking each wheel did.

Unless you were a numbnuts driving my Jeep, who kept missing the pads. Despite my begging him to let me do it, he was determined.
Last try, his foot slipped off the brake, and he took out the headlight tester and the back wall of the parts house.
Didn't bother my Jeep, it was built for stuff like that. Sure Pi**ed off the parts house guys though.

Anyway, if you can find one of those machines, see if they will let you test and see if one wheel is braking faster than the other.

If not, then take it out to some hard packed dirt or sandy rock.
Make sure you are going straight, and try coming to a stop, hitting the brakes harder and harder each time until you get the tires to slide.
See of one slides more than the other every time.
Click to expand...

I didn't just start replacing parts on a whim...I was replacing everything because I was restoring a 27 year old vehicle with 200,000 miles on.

The vehicle was a project...kind of made sense to replace the brake system after building a motor with more power than the stock dog that was in it, rebuilding the tranny, replacing the suspension, restoring the interior...maybe you would just keep the 27 year old brake system, but i felt i made good sense to do that after all that other work...maybe it's just me..

And yes, I know that the problem is too much pressure applies on the right caliper, or not enough on the left caliper...never said i didn't know what the symptom was...

When checking the braking on the road or on jack stands, it's obvious that it has more pressure on the right caliper when it is spinning and braking. You can even tell it when spinning it by hand.

My point is, it does the same thing with the old parts, new parts, and another set of axles that were put on when I switched to ones with lower gearing.

The only parts the same in all scenarios was the combination valve, booster, and hard brake lines...i doubt it's the booster...maybe I have an obstruction in the hard brake line or outlet of the combination valve?
 
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there is no check valve in the "t" that distributes the brake fluid to the front brakes.there is a check valve in the prop valve that holds 10 pounds of pressure to the rear brakes that keeps the brake cylanders from collapsing.if there is no air in the system and you are sure it is bled correctly,then the same amount of pressure should be applied on both sides of the truck.if there is that much off a difference just spinning by hand,you could put a adjustable prop valve in the front to make each side put out the same amount of pressure.i dont know if anyone has ever done this before but maybe someone will speak up.as to being a suspention problem,check all connections and bolts to make sure everything is tight.something loose could move the suspention in a way that can pull the springs outa place and make the axle cycle a lil to push it to one side.also worn out shocks can make the front end dive more in hard braking also and make it move more in the suspention.
 
Well, maybe I missed it, but I never saw the post where you said one front brake was grabbing.
The only symptom I saw was a pull to one side and you were suspecting the suspension.

So, I was trying to eliminate one or the other.
It seems that you have already determined that it is the brakes.

It does not matter what shape the suspension is in, if one front brake is stopping faster than the other, it is going to pull that way every time.

So, now that its narrowed down, lets look at what it might be.
The problem has to occur where or after the left-right split.

The booster and master cylinder won't cause it.
Now that you have replaced most of the stuff that would cause it, all of which is understandable, I have rebuilt old stuff too. You always replace everything while you are in there. Otherwise you will find yourself going back.
What in the left-right split have you not replaced?
That is the first place to look.

You may have a bad flare on one of the lines or fittings. You can see it when you take it loose, but you have to look. Almost nobody does. I don't usually. If it does not leak, I assume its good.

Odds are its going to be a part that was not replaced.
No guanetee though. The only reason I am giving the new parts a pass is because the problem did not change when you changed them.

Never ever totally trust new parts. Its OK to look elsewhere, but if you have a problem that could be caused by a part you have replaced, and all else is exonerated, then check the new part again.
Like I say, in this case, you would have to be unlucky enough to buy a part that has has exact same problem as the one you replaced. Unlikely, but not impossible.
 
Well, the suspension is brand new (installed about a month and a half ago) -- new shocks, springs, and steering stabilizer. All bolts/nuts have been retorqued.

A while ago, it was a hard pull to the right. I determined it may have been because I had new rotors installed about 300 miles after my brake pads, and did some hard braking to seat the pads to the new rotors.

The pull to the right went away, but now it is a slight pull to the left.

So, I'm not positive it's in the braking system. If a bushing was bad on the tie rod would that cause my front end to wander? I do have some play in the steering wheel, but not a ton. I'm thinking either worn bushings in the tie rods, or possibly the steering box gears are worn.
 
chulisohombre said:
there is no check valve in the "t" that distributes the brake fluid to the front brakes.there is a check valve in the prop valve that holds 10 pounds of pressure to the rear brakes that keeps the brake cylanders from collapsing.if there is no air in the system and you are sure it is bled correctly,then the same amount of pressure should be applied on both sides of the truck.if there is that much off a difference just spinning by hand,you could put a adjustable prop valve in the front to make each side put out the same amount of pressure.i dont know if anyone has ever done this before but maybe someone will speak up.as to being a suspention problem,check all connections and bolts to make sure everything is tight.something loose could move the suspention in a way that can pull the springs outa place and make the axle cycle a lil to push it to one side.also worn out shocks can make the front end dive more in hard braking also and make it move more in the suspention.
Click to expand...

I wrote that wrong; there is not actually a check valve ( haven't had much sleep for a week because I just got back from a business meeting in Korea)...I should have stated it differently...the metering valve does keep a little pressure to the front calipers so that the pads stay close to the rotors.

Mine seems to keep to much pressure on the right, or not enough pressure on the left. With the wheels turning and applying the brakes, the right one always stops faster. Again, too much pressure on right, or too little on left.
It has done this with two used sets on calipers and one new set of calipers...

Suspension is all new...tie rod ends, drag link ends, ball joints, etc. As someone else stated, I've taken the suspension out of the equation by checking the wheel rotation and caliper pressure on the pads with it on jack stands. Also, if i intentionally brake hard enough to lock up the wheels, the right locks first...shouldn't be suspension.

Sorry for high jacking the thread...was just wanting to share my same experience with brake issues.

Maybe I have an obstruction in the hard line, or combination valve outlet?
I cannot see the master cylinder or booster playing a part in this type of problem.
 
one more thought on my combination valve...possibly it's not engaging the rear brakes like it should either...
although more pressure is applied in the front, it's supposed to slightly engage the rear brakes right before the front brakes engage...maybe it's not operating properly for the rear brakes...
 
im pretty sure blazers pull to the right slightly when braking from factory. In a car and driver k5 blazer review video from the 80's it said that it pulls right while braking a bit and it was a brand new K5. Also,I redid all my brakes and they still pull right a lil bit when braking hard. If this is the case then it wont matter what you do short of installing a whole new brake system your going to get a little pulling right.
 
gotblazers said:
im pretty sure blazers pull to the right slightly when braking from factory. In a car and driver k5 blazer review video from the 80's it said that it pulls right while braking a bit and it was a brand new K5. Also,I redid all my brakes and they still pull right a lil bit when braking hard. If this is the case then it wont matter what you do short of installing a whole new brake system your going to get a little pulling right.
Click to expand...

maybe that is correct...i hear so many people give up trying to fix the pull and say it's because of the suspension and/or steering setup: push/pull drag link.
 
Ok, try this on for size:

I just installed new u joints on the rear driveshaft and took it out for a drive. The pull to the left got significantly worse the hotter the brakes got (I was getting on them pretty good).

Also, when I brake hard I hear a cracking/popping noise coming from the front as I get close to stopped.

Any ideas on either?
 
clandr1 said:
Ok, try this on for size:

I just installed new u joints on the rear driveshaft and took it out for a drive. The pull to the left got significantly worse the hotter the brakes got (I was getting on them pretty good).

Also, when I brake hard I hear a cracking/popping noise coming from the front as I get close to stopped.

Any ideas on either?
Click to expand...

Bump for replies... :bow:
 
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