The Stovebolt Site Forums The Parking Lot Big Bolts 42 1.5 ton bump steer

Hey Guy's, what is the best thing to do on these trucks to help with bump steer. All the suspension parts, tie rods, King pins and steering box seem to be tight and in good shape very little play. Adjusted the toe to 1/8 in. Truck drives really good until you hit some rough road, dips and bumps. Can be a hand full, darts back and forth.

Hy Gulfsuper, have you checked or had the caster checked?

Drag link has to be horizontal.

Ed

Drag link not perfectly level but close. Have not checked camber but they look pretty even.

Where are you measuring to get your 1/8" toe-in reading?

Have you actually jacked the front end of the ground and put a pinch bar under the tire and checked for worn parts by moving the tire up and down?

Has a helper lightly turned the steering wheel back and forth while you were under the truck looking for movement?

It doesn't take a lot of wear to give you issues...wheel bearings, king pins, drag link & tie rod ends, spring shackles and spring pins can all be part of the problem.

Don't rule out old bias tires either...

Mike B

Thanks Mark, checked all the steering components for play. King pins, tie rod ends, drag link and steering box. There is a little play in steering box other than that everything is pretty tight. Checked the toe by clamping levels across the tires and measuring front and back. To center the tires I marked center on the axle and took measurements from the front and back of the wheel. Had to take one tie rod lose and change adjustment. When passenger wheel was straight the drivers wheel was toed out over an inch. Thinking of installing a stabilizer.

When I rebuilt the front end on my 38 Master, I first checked for wear on all the parts. Even the bushings didn’t seem worn. When I removed the axle I discovered that I could swing the springs from side to side. The bushings were worn in such a way that the vertical play was minimal in the bushings . The car wandered quite badly before the rebuild.

Need to check the spring mounts to frame for slop. The drivers side on mine was loose contributing to my truck wandering all over the road.

Thanks, will check the spring mounts for ware. Checked the toe again after driving it about 30 miles, found it to be about a 1\2 inch out. Readjusted it back to an 1\8 in made a nice improvement, less of the bump steer.

I was told these big truck tires didn't need balancing. Wrong, I would hit a bump and get a little shimmy. Had the fronts balanced ,no shimmy drives great for a 46 2 ton.

I agree, planning on having them balanced. Just now starting to stretch her legs on longer drives. Has a pretty good shimmy when I get her up to speed. Made nice improvement on handling with another toe in adjustment, going to go ahead and put a stabilizer shock on. I think it can only help overall drivability.

When I was in shop class in High School we had a toe-in fixture that sat on the floor and touched the inside sidewall of the tires about 4" off the floor. If your measuring much higher than that off the floor you won't have the same readings. Maybe Jerry can confirm the correct measurement off the floor?

Mike B

My toe measuring device had a pair of pointers that could be adjusted to approximately spindle height, after scribing a line at the center of the tread. I always kept a chunk of white sidewalk chalk handy to mark the center of the tire tread all the way around before scribing the line. We would set the distance at the rear of the tire first, and then very carefully move the fixture to the front to check for the difference in toe. It was very important to roll the vehicle forward a couple of feet and chock the front and rear of the tires before making a toe measurement. Even rolling back a little could unload whatever tension there was on the tie rods.

At the race track, we kept a pair of flat aluminum plates about 10" tall and a couple of feet long to prop up against the tire sidewalls, with slots for a tape measure front and rear. After a little wheel-rubbing out on the track, it was not uncommon to have to make a quick toe adjustment between races.
Jerry

I used a couple pieces of wood with double faced tape to stick to the tires. Seemed to work real well.

Thanks, all great advice. On mine the wheels stick out way past the sidewalls. I have been using 2 4 ft levels clampted to the bottom of the wheel that lays flat against the sidewalls. I measure a the top of the levels which are about 6 to 8 inches above the ground.

Gulf

using eye ball camber checker........both sides look off.

This was 1/2 ton picture of the bent axle cause excessive camber after 50 years of hard use.

A certain amount of bump-steer is inherent in the design and affects modern heavy trucks with straight axles too. The longer the drag link the less the bump steer. Changing the wheel offset to the outboard side will radically worsen bump steer as will wider tires on wider rims with the same offset. I was taught never to wrap my hand around the steering wheel with my thumb to the inside. Especially on rough ground the steering wheel can spin and a spoke can dislocate your thumb when one front wheel drops into a hole or such.

Front end alignment is part art and part science. In one of the better truck shops I worked in, the Bee Line rep came around with a half-day lesson on alignment. Two things have stuck with me: Engine torque will twist the frame and load one wheel more than the other and change the camber mostly on the passenger side. Not an issue with a 216 but certainly will if one stuffs a big block in an AD truck. Watch a long-wheelbase semi pulling a steep grade. You'll see the front bumper is way off level. When the driver shifts gears the cab and whole front end of the truck will untwist several inches when he throws out the clutch.

Second, crowned roads will need to be compensated for or the bias-ply, passenger-side tire will wear on the inside. Also caster should not be equal side to side to avoid pulling to the downhill side of the road crown. That leads to tired drivers and complaints to the shop. On a dead-level road it should pull slightly to the left. On trucks with dedicated drivers they'll tell you what they want if you ask. They know what routes they run. Also sagging springs will affect caster and handling, as will tire size and pressure. The latter two affect "trail" and make steering lighter of heavier with no change in caster angle. The list goes on. Any change from stock configurations will negatively affect handling, except on Jerry's circle-track cars.

Read Jerry's method of toe adjustment carefully. It makes a big difference. Few alignment shops will load the tie-rods when setting toe-in, even when the spec sheets requires it and I ask. Like on my 84 Mercedes. Make sure the springs in the adjustable tie-rod ends are under enough tension, likewise the drag link. If the springs are soft, toe-in will change on turns, especially at higher road speed.

On trucks that run on the interstate there is a different set of variables to take into account. And radial tires are aligned differently from bias ply tires.

I would interpret driver complaints of "shimmy" on a truck with 20" wheels to be worn parts, not balance. Balance will produce a "thump" with each wheel rotation. At 60 MPH it'll be about 550 RPM or about 9 cycles per second for an 8.25 X 20 tire. Maybe that could be called a shimmy, it's subjective. I'd ask the driver.

Gulfsuper I heard one mention of caster you said looked pretty evan...you know caster on straight axle trucks is adjusted with a tapered shim on the axle where it attaches to both springs. It has to do with how well your wheel (steering) returns to center after a turn. With these trucks the more + camber the more powerful the return to center . Also if the axle is twisted its harder to adjust and be equal. In your case would look at spring pivot bolts and you hit close to home on that tow out. I check tow in with 2 yard sticks inside the tires front and rear. If you walk down the driveway and look back at it you can see the toe and camber.

Chris's 46/515 I have noticed when you come in off the road and jack the truck up if you see the front wheels turn now you know they need balance help. Especially if you turn them up and they go back down !! Another thing when you grease king pins turn them both ways to distribute the grease !

Thanks for the info. Have made improvement playing with the toe setting. Front end looks pretty good from a distance. Definitely has positive camber, looks even side to side.

Bought a steering dampner/shock. Will get that set up and installed and see if that won't help with the bump steer,

Not expecting it to drive like a modern truck. But will be driving the truck around max speed, 45, on narrow windy roads and want it to be stable and predictable.