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Braking problem

B

bboyle

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I'm trying to solve a brake problem that brake shops I've taken the K5 to have not been able to resolve.

The vehicle is my "tow" vehicle. It's an old 1986 K5 (full size) Blazer 4x4.

Symptoms: When braking the truck veers to the right. The harder the stop, the more work you employ (correcting to the left) to stop straight. At a stop if you watch the steering wheel and let up on the brake pedal, there is movement in the steering wheel. It rotates slightly. This sympton has existed for thousands of miles now.

New rear drum brakes were installed, and just recently new calipers on the front were replaced. Nevertheless, the condition during braking perists. These new parts did nothing. New brake lines were also added to the front calipers to be certain pressure was equal. The behavior that I sense is happening is that one caliper is grabbing while the other is slow to react...if that makes any sense. I also suspect the rear not assisting the front to keep things in line, but I'm not sure.:confused:

I just returned from a highly respected hot rod shop that does a lot of work on old cars and trucks like we all own. The owner is a real car guy and the place is loaded with trophies. He took the truck for a spin and told me he believed the problem was related to the proportioning valve. The brakes on the truck are calipers up front and drums in the rear. (stock set up) He suggested I contact Year One or other aftermarket vendor to see if they have the correct proportioning valve for the truck. He didn't believe he'd find one locally.

I guess the big question is: Could a bad proportioning valve cause this peculiar braking? It does not appear to be related to the rear only the front brakes.

Something has to be done to fix this. When towing, it is really hairy (and scary) when you try to stop the truck with trailer loaded with a 3800 pound Trans Am.

In all my years as a gear head, I've never encountered a braking problem like this one. This is the first shop that mentioned the proportioning valve as the possible culprit. It's the only component, aside from the OEM steel brake lines, that have not been replaced during the truck's life. This problem is very frustrating. The last brake shop (earlier this week) kept the truck for 3.5 days before they finally diagnosed it as OK. OK????? They did nothing...probably didn't even test drive it...just wanted the truck and its problem to go away. :( Thanks for your help.

Bill Boyle
 
It took some time for me to diagnose my issue, but I found it. It wasnt in the brake system itself, its within the steering components. If yours is anything like my symptom, (sounds very similiar), the problem is similiar to bump steer.

Your mechanic may not acutally be *wrong* per se, the symptoms your describing are from excessive front spring compression upon braking.

By setting the porportining valve more biased to the rear, it would decrease the downward force on the front. The end result would be less front weight travel upon braking.

Try this test: go find a safe area to go up to 30mph. then let go of the steering wheel, and brake hard. If the truck brakes straight, repeat with you holding the steering wheel firmly (no correction) and try again.

If the first test showed straight braking, and the second didnt, its related to bump steer (compression of spring causes change in steering geometry, which is then passed up through the steering arm and pitman arm. into the steering wheel. THe power steering system compensates for your imput of staying "still" and therefore, you feel the truck pull.

I think I've posted this before, do a mild search, might be from a year or two ago.
 
just so ya know the porp valve only tees the front free flow. the back is regulated with the actual working guts.
 
btw, if you want the easy fix, get a good weight distributing setup and anti sway. (like the equalizer). It fixed my towing woes, by making the whole setup as stable as possible, thereby reducing weight transfer, and thereby reducing the wheel twist.

Try towing with a flexy k5, the shackle flip I have is no friend for towing.
 
the last shop you took it to is probraly right because thats the only thing that you have not replaced that will cause that.i have seen the valves go bad.it only happens onafew of them

surburban bus
 
Mine used to do that also I put on crossover and it went away. It is yet another side effect of the ****ty ass factory push pull steering.:mad:

Ira
 
Last evening my son, who drove the truck to work, complained about the severe braking behavior. He's been driving a car with straight line braking and ABS. He was appalled on the truck's braking. After dinner we went out and aligned the driver's tire with the fender making it parallel with the fender plane. He snapped a photo of that relationship. He did the same with the passenger side. What we saw was a toe out condition on the passenger side. This is the side the truck veers to when braking and drifts to while cruising.

The adjustment looks like it must be made to the passenger side to pull that side in. How difficult a job is it? Again, all this is original OEM equipment under there. Must the horizontal bar that connect both sides be made nearly equal in length? My service manual is lousy and simply states that the vehicle should be taken to an alignment shop. OK fine--

I'm taking the truck this morning to an alignment shop along with the photos to show them what I'm talking about. Hopefully, this will be corrected. The last shop (abovementioned) that suggested the new proportioning valve did not put the truck on an alignment machine he simply looked at the tires from the front of the vehicle. Funny, my wife, who puts up with all this car and truck stuff, commented last night that the passenger side front wheel didn't look equal to the opposite side. That's what prompted the photographs...she was right. More to come with this latter today.

Bill
 
BTW, I did the little test Pookster suggested. At low speed the car nose dived and the truck still pulled to the right. The steering wheel with no hands on it, turned counter clockwise while braking. At higher speed it did the same. It requires driving adjustment to keep it "kinda of straight."

When I reported this to my wife, she commented "we should of gotten rid of the truck a long time ago." [We bought it new. It's 20 years old.]
 
Sounds like your on the right track... A toe out condition could definitely do that...

I would highly doubt its a proportioning valve issue.. They only control front to rear, not left to right.. unless there was some sort of blockage, but I doubt it... I would have been much more likely to think it was your brake hoses than a p-valve for those symptoms...
 
Okay, here's the latest. I spent all day at the alignment shop. :eek1: The adjustment to the toe was finally made but only after being freed up with a torch. With everything aligned the vehicle stills veers to the right--forget the braking action. The truck wanders to the right on its own accord.

Every mechanic in the shop took the truck for a drive including the shop owner. Everyone is scratching their heads. According to them, everything is tight. When the brakes are applied the truck pulls to the right like before--no change. The owner has now made this his challenge and will double check the alignment, specifically the caster and camber tomorrow. The shop general manager thought there was a crimped line somewhere, a hydraulic problem, yet upon inspection nothing was found to support that theory. All the lines look good. The owner also called several fellow techs around town and bounced the problem off them. Some had good ideas which will be tried tomorrow. Most of these guys were older guys with knowledge of the K5...not just brake, alignment and front end men.

Well, I am exhausted after a long day. Will have a nice dinner and try to relax tonight. Tomorrow, I head back there to see what's happening and plan on taking my lunch this time.

I really hope they can solve this. If not, I'll try to sell the truck to one of you guys with off-roading in your veins. With a first rate aftermarket suspension there should be plenty of life left in the truck. [I'll then hunt for another vehicle to be my tow vehicle.] :(
 
Ive heard of debris in the brakeline causing what your talking about. Could be there is someting in the lines, or maybe the caliper is hanging up??
 
You probably already checked the front wheel bearings for proper adjustment,and ensured all 4 tires are the same size and construction I assume...we had one car at my friends tire shop drive us batty with similar symptoms--we finally discovered one rear tire was a different brand and had different ply ratings..it acted normal as soon as that tire was replaced!

Some other vehicles did the same thing that had squished metal brake lines --someone or something flattened them in one spot,and must have made the brake fluid take the path of least resistance,then go to the side with the crimp in the line..I suppose crud inside the lines could do it too..If there is some way to test the pressure at each wheel,that might help pin it down..
 
sandawgk5 said:
Mine used to do that also I put on crossover and it went away. It is yet another side effect of the ****ty ass factory push pull steering.
Click to expand...
That short drag link is mighty annoying, isn't it? Bump steer is another effect of that lame steering geometry. It's a mighty good reason to go crossover, and you were wise to do so (which you already know).
 
I have the same problem. I belive some of it is caster being pushed forewards on the left front making it pull rt. I had the pull gone for the most part untill today. I install fresh steel shims in the front axle. (a little history the ltft front ubolts were loose and smooshed the center of the perch and elongated the hole a smidge.) when loosening the ubolts it shifted forewards and after reinstalling everything with the new shims it pulls again. I am going to try and correct it in the next few weeks.If you have old bushings and worn springs maybe even a little droop in the axle these could contribute to caster. it is not adjustable and I am not sure if they make a adjustable Ball joint for the old 10b.

Keep us informed. I am totally interested in your results.
 
The saga continues....

The alignment shop put the truck back on the machine to check the caster. It was ok. However, the adjustment to the drag link and idlers were not done correctly. Adustment was made to the left idler only. This was faulty. The drag link must be equal on both sides. The first tech didn't do this. The senior man, found the error and corrected it. A test drive followed. The truck has lost the wander to the right and tracks straight. However, the pull during braking continued. Next...

Another set of calipers were ordered and the other new ones were sent back for "remanufacturing." The new calipers were installed the system bled and off for another test drive. SOMETHING NEW happened!

Braking to the right is now intermittent! On a flat road with no significant road crown, the truck stopped straight. Next time it pulled to the right. Maybe it would brake to the right 3 times in a row and the fourth it would be straight as could be. The shop owner is going crazy. He can't figure out what going on with this.

I've added my own two cents to the thinking and believe it still is a hydraulic problem. Fluid pressure is not the same to each caliper IMHO. Sometimes is is, sometimes not. BTW, the rear brakes checked out and we readjusted. Nothing unusual there at all.

We made several more calls in the afternoon to other brake specialists and the focus is again returning to the proportioning valve. We were told the proportioning valve on the 1986 Blazer is an X type. [news to me] From what I can tell it's different and works to balance the right front and left rear; the left front and right rear. Frustrated...I said get one and lets try it.
There's nothing else to replace.

I've been in the alignment shop for 2 days. Today I almost answered the phone when things were busy. I gotta get this fixed.

I return to the shop again tomorrow--good thing I'm not working--to wind things up for the better, I hope. :confused:

Bill
 
ryoken said:
Sounds like your on the right track... A toe out condition could definitely do that...

I would highly doubt its a proportioning valve issue.. They only control front to rear, not left to right.. unless there was some sort of blockage, but I doubt it... I would have been much more likely to think it was your brake hoses than a p-valve for those symptoms...
Click to expand...

I think he's closer to fixing it, but not on the right track, if that makes sense. If he ligned up the p/s wheel then it would look like toe-out on the drivers' side. I can only imagine that once you go down the road with a toe out, as with a toe in, that they find a medium where they are both toe out. Some racecars go with a toe-out condition for faster turns i'm told.

But I also don't think he can truely fix his problem without fixing this part. Assuming that he has true rotors (new has nothing to do with this!! are they TRUE), mid-to-high grade pads (consistency, not glazed), good-to-high grade calipers (I've seen calipers sieze up and stop functioning in less than a year in the rust belt). WELL GREASED caliper slides, correct size hard lines, nothing smaller than stock. No dent's/kinks/etc. in the hard lines.

I vote proportioning valve. "Eliminate everything that's impossible, and whatever is left, however improbable, must be the truth."
Good luck, if your in the rust belt you'll need it. :crazy:

Personally, I'm having similar problems but with ridged-for-my-displeasure rotors, glazed & cracked pads, I amy leaning towards that. :D
 
My K5 has been all over the country in all climates. It started it's life with me (new) in Fairbanks, Alaska. It spent 4 years in California, 3 years in Louisiana, 8 years in Virginia and now 3 in South Florida. Aside from normal wear and tear to the interior with 220k miles of family usage, and my wife bending the rear bumper backing into one of our former yard trees when we resided in Virginia, there's little body rust. Interesting, the first set of Laredo Uniroyal tires, lasted 90k miles. The truck pulled trailers with cars on board all over the US over all kinds of terrain. It struggled in the West with the mountains. Not enough power. At 161K miles I replaced the 305, which was still running good, with a new 350 crate engine. Still not enough towing power. It was installed at the dealership and was fully warranted. This engine still runs great and does the job on flat roads. The truck has been a great vehicle for us. I'm going all out to fix the braking problem.
 
When I first got my truck the PO said he had similar problems. I drove and found it would wander and pull all over the road. I took it to a local shop with a good rep. and they said it was the front right u-joint. I had them replace it and it drove straight, But still pulled when braking. It turned out to be the rubber brake lines. One had worn more than the other so it had some "give" when the brakes were applied. The truck would pull to the good side, more, the more I drove it. The line would "give" as it got warm and used.
 
Let me summarize this mess. Initial Sympton: The truck pulled to the right during braking.

Two sets of calipers have been tried. New hoses installed. The tires have been rotated and flipped. The system has been bled three times. A new proportioning valve is now in place. The alignment was off and it tracks beautifully now. The rear brakes have been checked and double-checked. Play in the steering box was adjusted. The discs have been miked at 1.226" Left and 1.257" right. Current status: The truck still pulls to the right while braking. No real change. I drove it and did not experience the intermittent behavior from yesterday. Strange!

The shop owner is totally perplexed and wanted the truck one more day. He called his retired master mechanic who agreed to look over the truck tomorrow.

This is entirely absurd. Like Groudhog Day! :crazy: I'm at my wits end. :confused:
 
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