The Stovebolt Site Forums The Shop Area Driveline Steering pull when braking

Following a rear end swap that required related brake work….I did a complete adjustment at all four wheels and a parking brake adjustment.

I now have a slight pull to the left when applying the brakes. Very subtle, probably not even worth fretting about. But it bugs me.

I know there are several things which can cause this. But before I just go willy nilly checking all kinds of things…..is there a logical place to start and sequence of diagnosis?

I would go back and adjust the brakes again. After a real world road test things settle in more than on jack stands. I would verify setting and adjust parking brake if needed. I would also bleed my brakes. That should solve the problem

Are the rear u-bolts tight?

Yessir

Brake adjustment is a waste of time when chasing a pull. None of the brakes will apply any stopping force until all the shoes are firmly against the drums. The only problem out of adjustment can cause is a low pedal. Look for sticky wheel cylinders (even new ones) and/or restricted brake flex lines at the front which will allow a pressure buildup before all the brakes are applied. Right pull- - - -change the LEFT front flex line, etc.
Jerry

What is the condition of all of the components which affect steering?
Tie rod ends, drag link ends, steering box, kingpins, wheel bearing adjustment, shocks.
What is your toe in set at?
Are all of the drums new, or at least all of them having similar inside diameter? A dissimilar diameter drum will not have the braking action as the rest of the wheels.
Did you adjust the position of the pivot pin which the tops of the shoes ride on? Adjusting the pivot pin will address the above mentioned "dissimilar drum" issue. A lot of people skip this step. It is important.

Only thing that has changed here is the rear axle and brakes. All front end components were replaced with “better” used stuff last year. And the pull was not there until this past weekend when I completed my axle swap.

I did adjust the fronts, but skipped the pivot bolt part. I did do the pivot bolt procedure on the rear.

It’s such a slight pull that I was thinking something might self clearance and cure itself. But I probably should have a look at a few things. Jerry’s comments on the hydraulic components makes sense. Rear cylinders are brand new but new doesn’t necessarily mean good nowadays.

Betting your life on "used" brake or steering parts is like drawing to an inside straight in 5 card poker. Brand new "best quality" stuff is just barely "good enough". You're also putting everyone who has to share the road with you at risk.
Jerry

Betting against a stand-pat in 7-card draw is equally risky. Buy new parts.

One rear brake applying before the other because of a weak spring will cause a drag and pull on that wheel under light braking. It is slight. I have identified which brake is the culprit by braking on a gravel hill and seeing which wheel leaves a skid mark in the gravel. If it's loose gravel it doesn't take much drag to show up in the tire track.

Strongly suspect the issue is in the rear, since that is what changed when this symptom appears.

Good tip on the gravel road. I used new hardware on the rear, but perhaps something isn’t moving freely. Drums and pads were in excellent shape. Must have been nearly new when this axle got pulled for a 5 lug swap.

Shouldn’t the direction of “pull” lend a clue as to which side is the problem? On a drive axle, in the rear…would a left pull most often be associated with a left wheel? (Truck pivots left around the wheel that stops first). Again, this is subtle.

Yes but that usually means the pull side is working/stopping. It's the other side that's still turning. That's why checking the right side components for a left pull is often the answer (collapsed rubber hose, etc)

One rubber line feeds both rears.

All the hard line along the rear axle is brand new. I suppose there could be some debris or perhaps some air in one side or the other after the tee. Both rear wheels seemed to bleed just fine and pedal is rock hard.

Just have to make some time and dig deeper. Perhaps get both wheels in the air and have someone depress the pedal. See if I can feel any difference. I did check to see that both wheels stopped before I ever got it off the jack stands. But maybe one hangs up hard at partial pedal or doesn’t release fully.

You may have the parking brake cables to tight holding the shoes off the anchor. Back the cable off or disconnect it. Adjust the brakes & hook the cable back up with a little slack.

George

I can try that easy enough. For what it’s worth, I did the parking brake adjustment exactly as the shop manual describes. Pedal depressed 1.5 inches or whatever. Brakes adjusted for proper drag at each wheel. Pull cable tight and adjust clevis accordingly.

Did you have the shoes arced to fit the drums? Uneven contact can cause a pull.

www.youtube.com/watch?v=H-ZF200ZSVs

In my experience that's true.

No, I sure didn’t. I’m not even sure I could find someone around here with that capability. Even the drum lathe itself is becoming a lost art.

Specializing in antique, vintage, classic, obsolete, unique and hard-to-find brake parts,bonding, riveting, rebuilding, drum and rotor machining, custom made brake hoses

Brake Materials & Parts Inc
800 Sherman Boulevard,
Fort Wayne, IN 46808
260-426-3331
http://www.brakematerialsandparts.webs.com/

Arcing the shoes to match the drums will be accomplished with wear on the shoes. The pull would eventually go away if you can put up with it till then. Adjust the brakes after while.

The problem with allowing the brakes "Wear" in, is it can cause hot spots which harden the drum in spots. Kind of like hot spots on a flywheel causing clutch chatter.

Why would it cause hot spots in the drum? They're always moving. I suppose that could happen, but I doubt it.

You mention that the pull is subtle. This might go away after driving for a while and the arc of the shoes wear to match the arc of the drums. I have experienced this very thing more than once with new brakes on these old trucks, Huck and Bendix. Once they wear in, you will want to adjust the brakes again by the book.

They happen. That's why they make drum grinders. Look like a washing machine motor with a long shaft and a 3" grinding wheel at the end. You chuck it in the brake lathe where the drum cutter mandrel would be. Treat it like you're turning a drum, after you actually cut the drum.

It's easy to arc brake linings to the radius of the drum. Glue a strip of coarse sandpaper (40 grit) to the inside of the drum with water soluble glue like Elmer's, and scuff the shoes vigorously against it until the radius matches the drum. Then use boiling water to remove the sandpaper. Instant radius matching for full lining contact!
Jerry

I’ve heard you mention that sandpaper thing before. I wonder if spray type contact cement would work. With a solvent cleanup.

I think you don't want to risk contaminating the brake shoes with solvents.

Wouldn’t be contaminating the shoes. Cleanup would be on the glue between the sandpaper and the drum. Only the drum gets the glue, whichever type a guy would use

Grinding the lining to fit the drum will not do any good unless the anchor pins are adjustable so the shoes can be centered.
Years ago newly lined shoes were cam ground at the factory & have a bevel on the ends. They were thicker at the center so the edges don't dig in to the drum.
The shoes are flexible enough that you get full contact with added pedal pressure. The lining soon wore enough to have full contact.
I always put a bevel on the end of each lining to keep the edge from digging into the drum & cause grabbing & pulling.

George

George brings up a good point. I was doing the anchor pin centering procedure on the sawhorses before I installed the new rear.

Despite doing it several times, I never was quite satisfied with one side (can’t remember which side). Couldn’t quite get an even feel to the drag over a full rotation.

Finally called it good enough and figured they would find their happy spot and self clearance under the truck. I ~think- I may have even loosened the anchor nut and tried stomping the pedal. If not, I sure intended to.

Would it be worth trying that again?

Lots of these little gremlins self-correct with a few miles of driving. How many flat rate mechanics' brake jobs got all these nitpicking details addressed back when these old rigs were daily drivers? A few hundred miles of running in normal traffic situations will cure a lot of imaginary problems, IMHO!
Jerry

When they wrote the manuals, I bet GM assumed that the mechanics doing the work on these trucks were Automotive Machinists Local xxxx. I was local 289 but we still had the service manager looking over our shoulder. This was much better than a flat rate shop where I also worked. If you could beat flat rate, you were some kind of good wrench. Those flat rate times were/are based on brand new cars and pickups that had never seen salt or mud. If you were paid on flat rate you were paid by the job and had to eat your comebacks. It's a hard way to make a living.

I don't remember ever seeing flat rate numbers for heavy trucks, where I worked mostly. I worked for a logging company in the Pacific Northwest near Canada and the boss didn't care how long it took so long as you never had to go rescue the truck out in the woods. We had a steam cleaner and it got used a lot. Over the road trucks were usually cleaner but sometimes you had to deal with the road kill stuck between the tandems.Yuck! Anyhow I don't remember ever moving an anchor pin or even arcing a shoe but I replaced lots of S-cam bushings. One trip down the mountain made sure shoes were arced. If the drums got thin and oversized there were shims you could put under the shoes to increase their diameter. We usually ran drums till they heat checked or cracked clear through. There was a pile of new drums on one side of the shop and a pile of scrap ones out back. Just remember to put antifreeze in the brake-water tank for the January haul. Somebody forgot one time and the lines froze up. So I was reminded on every job. This was before the days of Jake brakes except on the new trucks but even afterwards they used water coming out of the woods.

We weren't subject to DOT inspections except if trucks delivered to the mill so maybe we were a little sloppy. Years later as a driver I used to complain to the shop if they let a tanker out with grabbing brakes. Empty aluminum tankers are hard to stop in one lane on snowy roads if some of the trailer brakes grab. They're like an aluminum beer can on four axles and eight wheels.

One key to anchor pin adjustment is finding the sweet spot of loose enough to move by banging on the big nut on on the side with a SFH, but not too loose so that the pin is cocked, resulting in changing its position once you torque down the nut. You can feel/hear the sweet spot when you tap it with a hammer. It shouldn't be a hard knocking sound (too tight). It should be a softer sound feeling like hitting a strong spring, but you shouldn't see the pin move much if at all.
I strongly recommend that you remove the anchor pins and clean them, the nuts, and the mating surface on the backing plate thoroughly so that you have smooth movement when you tap it.