Failed Prop Valve?

[jastewart25]

my 85 k10 has pulled to the right when braking (hard or just tapping brakes) ever since i bought it.

i have replaced hoses/calipers/pads etc... bled the brakes and so on

could this be due to a failed prop valve? i have read about resetting prop valves-is this a possibility? wouldn't know how to do this.

it has been suggested that i remove the prop valve all together and run all new lines. and then i would have just 50 percent braking in the front and 50 to the rear. any dangers in doing this?

i'm dying to be able to drive this truck on the highway!

if i got a new valve, can anyone recommend a place to buy them for my model. disc brakes in front/drum in back

here is a photo of my prop valve

[SkinnyG]

A proportioning valve shouldn't affect a brake pull.

Removing the proportioning valve may make your truck swap ends under heavy braking. You really want the fronts to lock up before the rears. Light braking can get away with more brake pressure to the back, but heavy braking needs the maximum pressure limited so it doesn't lock as it is unweighted (or it swaps ends).

If the brakes are working properly (check them first), check your alignment. A bent control arm (or something) that can cause a large caster spread left-to-right could cause a braking pull.

[old Rusty C10]

are you sure there isn't something worn in the front end or another issue

[jastewart25]

i will go get an alignment tomorrow. the thinking with the prop valve effecting brake pull is that it's not releasing to one side/or coming back?

i'm not mechanical but my mechanic is so sorry if my terminology isn't the best.

as for something worn, i have checked every single thing that i can think of.

just to give you an idea of brake pull, a light tap of the brakes yanks steering wheel right each time. it does not pull when off the brakes and drives straight.

i do have a 4" lift if you think that has something to do with it (from po)

[hatzie]

Air in the Right hand brake lines or caliper.
Something is loose or bent in the suspension.
Another alignment issue.
or some combination of the three...

The combination valve affects Front to Rear bias not Left to Right. If it were a problem you would likely just have increased pedal effort not bias favoring the left caliper.

There's a very good explanation that demystifies the Combination valve in the GM Service Training Group Textbook "GM_STG_15000_01_1_Base_Brake_Systems" in the 1973-1991 RTFM link below.
The description starts on PDF page 123 (Section 7 Balance Control Systems)

[jastewart25]

Originally Posted by hatzie

Air in the Right hand brake lines or caliper.
Something is loose or bent in the suspension.
Another alignment issue.
or some combination of the three...

New Calipers as of yesterday.
New Brake Hoses

I've asked if it could be suspension related but was assured it wasn't. Any advice on what to check for suspension related? No cracks or warn bushings or anything I can find so far

Thank you

[SkinnyG]

On my previous truck (a "rebuilt" write-off Nissan Hardbody), it would almost change lanes when you braked. Brakes checked out perfectly fine.

Finally took a good long look at the control arms and discovered one was actually bent. Replaced the arm and it was golden.

If the direction it pulls under braking changes depending on road crown (or tire "grooves" in the pavement), check toe. Or something worn/loose in suspension and steering parts.

[jastewart25]

Originally Posted by SkinnyG

Finally took a good long look at the control arms and discovered one was actually bent. Replaced the arm and it was golden.

where is the location of these control arms?

it always pulls to the right and it most definitely throws me into the other lane when i brake.

i have started just tapping brakes lightly many times for one stop. also, we tried the slam on the brakes hard to reset it trick and almost ended up in the ditch.

i'm almost at my wits end with this. hope it can be fixed.

thank you for advice

[hatzie]

Read the tire wear. It'll tell you a lot about the front end condition.
Bad shocks can do this but not as badly with the leaf spring K series front.
Bad or missing Steering stabilizer/damper... Lifts are rough on this part.
Any loose tie rod ends or ball joints.
lift kit more than 3" installed without the modified draglink, pitman arm, and steering knuckle arms.

If the pins are sticking on the new RH caliper it would do this too... I usually use a light coat of Sil-GLyde high temp silicone grease on new caliper pins.

[jastewart25]

Originally Posted by hatzie

Bad shocks can do this but not as badly with the leaf spring K series front.

here's a few of the only photos i have right now of the setup

[jastewart25]

Originally Posted by hatzie

Any loose tie rod ends or ball joints.

i'll have them check during the alignment

as for the bad steering stabilizer/dampener, where is this part located? i will check for it tomorrow.

a BIG THANK YOU for all of your help. truly, i am flying blind if not for you guys

[Koffer]

Did you check the hard lines to the front left wheel ?, I've had one that was crushed / kinked by j hook tow chain and that could cause a hard pull to the right .

[jastewart25]

Originally Posted by Koffer

Did you check the hard lines to the front left wheel ?, I've had one that was crushed / kinked by j hook tow chain and that could cause a hard pull to the right .

will double and triple check this weekend.

[jastewart25]

well, life got in the way of checking things on truck this weekend but i do have a question.

would you be more inclined to say it is a brake problem or steering wheel problem if the wheel actually turns right when i tap the brakes.

it doesn't happen every single time at slow speeds but it does at faster speeds.

i can tap the brakes 10 times or 2 and the steering wheel turns right each time.

[hatzie]

Originally Posted by jastewart25

i'll have them check during the alignment

as for the bad steering stabilizer/dampener, where is this part located? i will check for it tomorrow.

a BIG THANK YOU for all of your help. truly, i am flying blind if not for you guys

Stabilizer third picture down...http://67-72chevytrucks.com/vboard/s...8&postcount=35

[jastewart25]

thank you hatzie.

it looks like mine has one installed that came with the rancho shocks. shoot, i was hoping it was something simple.

i also checked the control arms and they look good.

i guess i will call up the local alignment place and let them have a look at it. not sure what else to do.

pictures of my setup (sorry it's dark out)

[v30crewcab]

you have a lifted 4x4. if it doesn't have steering correction for the lift, it will pull to one side when the frontend dives as you hit the brakes. its the nature of the stock push/pull steering on a lifted truck.

[Koffer]

The other things to check is the ball joints , spring eye bushings and loose Ubolts

[jastewart25]

Originally Posted by v30crewcab

you have a lifted 4x4. if it doesn't have steering correction for the lift, it will pull to one side when the frontend dives as you hit the brakes. its the nature of the stock push/pull steering on a lifted truck.

i was asking around if it could be due to the lift. i did find a steering stabilizer is that the same thing you are referring to? if so, is it possible for them to go bad? i guess i could always replace it and find out.

[Just call me Sean]

A steering stabilizer is just a shock for the steering. Most vehicles don't even have them.

[andrewmp6]

measure the lift blocks in the rear that will tell you how big of a lift it has on it.Once we know how big the lift is you can buy the parts to fix the steering.

[jjzepplin]

Originally Posted by v30crewcab

you have a lifted 4x4. if it doesn't have steering correction for the lift, it will pull to one side when the frontend dives as you hit the brakes. its the nature of the stock push/pull steering on a lifted truck.

This ^^^. This really happens. My truck had some wedge shims in the front spring pack a PO had installed them backwards. Made the dip even worse! Took it apart and turned them around. Much better. Only pulls very slightly on real hard stops. But I try not to do that. HAHA!

[jastewart25]

Originally Posted by andrewmp6

measure the lift blocks in the rear that will tell you how big of a lift it has on it.Once we know how big the lift is you can buy the parts to fix the steering.

no blocks. all leaf springs. had a guy who specializes in lifts at his shop check it out. can't find a single thing wrong with lift.

as far as steering, everything is tight and good. no play whatsoever.

no brake drag.

now i'm going back to maybe it is the prop valve??

[hatzie]

You can throw a proportioning valve at it but I doubt it will fix the problem. Make sure all your brake lines are clear and make sure a chunk of crud isn't hanging the piston in the weak caliper.

There are some big lift blocks in the rear.
The front springs will never have lift blocks (DOT illegal at the federal level) but in some cases they will have pinion angle wedges.
The steering geometry was modified by the lift. The steering needs to be setup properly to make up for the lift. She still will not ever operate the same as a truck without a lift kit. This is why you see two and sometimes four huge dampers in some lifted trucks.
Diving to one side is symptomatic of poorly adjusted toe or badly off camber and or caster angles. Camber and Caster are not adjustable on most GM solid axles... If they are off then something may be bent.
Lifted trucks are reputed to follow the ruts and road grooves a bit more aggressively than stock so that's not a good indicator of adjustment issues.

[donut]

Originally Posted by jastewart25

no blocks. all leaf springs. had a guy who specializes in lifts at his shop check it out. can't find a single thing wrong with lift.

as far as steering, everything is tight and good. no play whatsoever.

no brake drag.

now i'm going back to maybe it is the prop valve??

Your guy won't find a problem with the lift, Truck is still lifted isn't it?
Prop valve, throw it on the back burner. Many auto parts stores don't carry it because they don't go bad.

Alignment guy may or may not have found anything, if they found it they may be asked to fix it.

When you did the front brakes, was everything clean? or by chance did one pad get dropped in a bucket of oil?

You need to approach your truck with the mindset that your dealing with someone elses' problem.