The Stovebolt Site Forums The Shop Area Driveline Ready to Try a Steering Damper

I have a serious steering wobble, sometimes, in the 30-35 zone. I haven't been able to find anything out of spec so thought I would try a steering damper. Figure it would be an interesting experiment if nothing else.

Would appreciate any info/photos of what works for you. This is a 1940 Chev with a 1951 axle. TIA

Dennis

Like taking an aspirin for the headache caused by a brain tumor- - - -treating the symptom, not the cause!
Jerry

Well, I do agree with that, but I'm getting nowhere. Read on here some have tried it and are satisfied with the results. Thought I'd give it a go.
Dennis

Right. These trucks don't need steering dampers so try harder to figure out where your vibration is coming from.

If everything were within factory specifications, you wouldn't have a serious, intermittent steering wobble.

First, I'd swap the tires front to back and back to front. See what happens. Are they new tires? Are they new rims? When were they last balanced?

What items did you check and how did you check them?

Have you taken any frame measurements? Height from ground on both sides at different places? Diagonal front to back, etc?Are your cab mounts worn out/missing?

How did you test the steering gear?


Steering shaft, steering gear, Pitman arm, tie rod ends, drag link, king pins, front and rear springs, shackles, shocks, frame, tires, rims, axle, wheel bearings, caster angle (shims required), toe angle, probably stuff I'm forgetting.

Has the truck always had a wobble? If not when did it start and what was done to the truck immediately prior to the wobble?

To help debug the issue I would try using a GoPro camera and watch the suspension and linkages from different angles doing various test runs
The video may show something non intuitive happening.

I had a bad wobble once on a mid 70s pickup
It was a combination of a cheap tire and bad shock absorber.
Replacing either one stopped the wobble but I replaced both in the end

I was curious if it was just one of the two causing the issue but it required both the junk tire and bad shock to work together to get the wobble going
It could be pretty bad between 35-50mph if you sped up the wobble would go away

-s

First of all, I'd try installing a year-correct axle. The 1951 axle has a wider track width, and it messes up the entire geometry of the steering and suspension system of the narrower track original equipment item. The problem is probably not able to be corrected "as is".
Jerry

Our 2005 Ford 3/4 ton long wheelbase shop truck has three damper on it. It had terrible death wobble from the get go. Ford couldn't fix it so we added a aftermarket kit that made it drivable.

The damper may fix your issues, but it will be stiffer to drive if you get a decent damper. Cheap dampers are a waist of time.

We just purchased five new school buses at work with a lighter front axle, two out of the five wobbled. I found by tightening wheel bearings and giving them a little more toe-in helped. We also balanced the front tires, then knocked the front bead loose and dumped in a bag of balance beads. The balance beads helped a bunch. The light axle has smaller bearings and less distance between the bearings with the same size tires as the bigger set ups.

How much caster angle do you have, is it easy to turn setting still? Does the chassis lift up as you turn? Does it return to center on its own after mking a turn?

Is the steering box set dead ahead ( not the steering wheel ). The steering box has a tight spot dead center to help hold the steering linkage and keep you from sawing on the wheel all day just to go straight. This needs to be corrected if it's not. My '37 has a later axle and needed an adjustable draglink to get the box centered. I tried alll kinds of adjustments but never could get it right till I made the adjustable link.

How are the leaf spring bushings, loose bushing will cause all kinds of issues, the whole axle assembly can move around. As a test, pump in the thickest grease you can find at each bushing and go for a drive. We used to pump white wheel bearing grease into steering joints right before Highway Patrol bus inspections, it would tightened up the steering to like new! We kept the grease guns inside where it was warm, when cold you couldn't pump it.

When it starts the wobble, does it take a jolt in the road or is it speed only related? Speed only is likely a tire / wheel issue. Hitting a bump or step in the road is true death wobble and is related to alignment or loose components. Our '05 would hit a joint in the concrete and go into a wobble, at 65 mph you better be hanging on and getting it slowed down, about the time you come to a stop, the wobble would stop. Ours was a combinaton of tall tires, long wheel base, and long steering components, it was brand new and poorly designed.

OK, I'm holding off on the damper. I'm going to replace the front tires first. See what that does. I know they are not the greatest as far as roundness goes. Enough to make a difference. Dunno. Plenty of tread left. But I bought them in 2016 so need to be replaced anyway. I'll let you know what I find from that. Fingers crossed.

Dennis

I've had two recent experiences with old tires.

In one case the tires looked brand new. The tires had been place on the vehicle, hardly ever used for 5 years (less than 1000 miles), and then the car sat in a climate controlled garage for 15 years.

Even though the tires had no checking or cracking or even dry rot, the rubber had lost so much of its elasticity, that they handled really weird. They didn't grip the road properly and the front end would seem to slide on the pavement.

In another case, a single tire in a set of 10 year old tires with "like new" tread split apart while driving at 30 mph. The tread separated and beat the inner fender of the vehicle to death.

Can anyone provide a track width difference between the original axle and the one that's being used currently? There are a lot of steering geometry differences that can affect wheel wobble such as "Ackerman"- - - -AKA "toe out in turns". An imaginary line drawn from the king pin to the center of the rear axle should intersect the steering arms on both sides where the tie rods attach. If that is incorrect, a lot of strange things can happen to steering angles.
Jerry

1937 has a 56 3/8" tread width, 1952 has a 56 3/4" tread width, wheel and tire size will be more of a change then an axle will.

Jerry - According to the 1940 Chevy Truck Shop manual, the 1940 1/2 ton's front "tread width" (measured across center of tire treads) is listed as 56-3/8". The front "tread width" measurement for the 1951 1/2 ton is listed in the 1951 Chevy Truck Data as 56-3/4". Difference of only 3/8" overall.

Not sure how much of a difference it may make, but the rear axle "tread width" for the 1940 is listed as 59" while the 1951 is listed as 61". Wheel offsets are the same for both year original wheels, although the '51's are 4-1/2" wide VS the '40's being 4" wide.

Below are screenshots/pics of the tread width for the 1940 and alignment data for both trucks for comparison in case it may help.

Edit: Joe beat me to the post button with the tread width data.

That's probably not enough to matter, although changing wheel offset can create some nightmares for an alignment technician! The excuse "but it looks good!" doesn't make the cut in the real world of wheel alignment!
Jerry

My continuing saga... OK, so I put on new tires. That did help quite a bit, but still have a little shake 30-32. I wanted to test more caster so went from 4 degrees to 6. That made it more like what it was with the old tires giving the shakes 30-35. I've changed about everything so stock specs are just a suggestion.
To recap, here is what I have:
215 65R15s, 6 1/2" rims, 1951 front axle, mono-leaf spring, front sway bar, 47-55 style front shocks.

Would the age of the rear tires cause this? It does feel like it is coming from the front vs rear.

Dennis

Have you disassembled and inspected the tie rod ends and the drag link ends and then reassemble and adjust them to specs?
Have you disassembled and inspected the front leaf spring pins and bushings?
Are your kingpins in new condition?
Are your wheel bearing adjusted to specs?
I would check all of those items first.
If the wobble doesn't go away, then I would inspect the steering box to see if it is set to specs. I'd save that for last since it is more complicated to work on and labor intensive than the other items.
I work on trucks just like how I shoot pool. "Shoot the easy ones first."

If you suspect the old tires, swap the tires front to back and back to front. That will tell you immediately if they are the cause.

You said new tires made an improvement so you're on the right track. fix whatever else is worn out.

I've got new tie rod ends. I'll recheck the drag link ends.
Leaf spring pins and bushings. Ugh. I replaced them years ago but guess I won't really know without inspection.
I replaced the kingpins years ago and there is no play when I try to move the wheel with hands in 6:00 and 12:00
Wheel bearings are new (tapered rollers with disc brake conversion).

Otto, can't swap front/back tires because running 215s on front and 245s on rear.

I'll go back to the 4 degree wedges since they gave better results.

4 degree castor angle is pretty steep. Factory spec is 1 3/4 Perhaps a 2 degree shim is more appropriate..

Dennis - Did you only replace the front tires? Old rear tires could have an effect if they are the same age/condition as the old front tires. A tire imbalance or out of round issue in the rear could (perhaps) telegraph the vibration through the entire truck. Makes it hard to pin point where the vibration originates from. Just from a safety stand point, I would recommend the rear tires get replaced if they are the same age as the old front ones.

2ManyTrucks mentioned in his reply above about possible shock issues. How old are your shocks? Have you done a bounce test (by hand) on each corner? Checked that all the shock insulators are all present and snug?

Just a few thoughts to consider in further hopes you can resolve your vibration issue.

Usually a vibration/shake that occurs only between certain speeds, is caused by out of balance tires. Try rebalancing rear tires.

Yeah Dan, I only replaced the fronts. You're right, I should do the rears anyway. I'll get that going right away.

Just did new shocks. That's in another thread. I did that as part of this problem. I had converted to tube shocks years ago but the solution I came up with placed the shock in near vertical position. Reading from this site said it would be better to angle forward. I am now mimicking 47-55 shock mounts. It does ride better but had no effect on the vibration.

Are the new tie rod ends the original adjustable style. They are adjusted by tightening the end cap until the spring inside it is bottomed out then back the cap off just until the cotter pin will go in a hole.
How did you adjust the roller wheel bearings? The procedure is different than the original ball bearings. Many roller bearings require a final preload of 5-7 ft pounds of torque. The original ball bearings do not call for a final preload. They require a tiny bit of slack.

In the '51 GMC Maintenance Manual, front wheel ball bearing adjustment on 1/2 ton trucks (he has a '51 axle) calls for tightening the spindle nut to 33 ft/lbs, then backing off no more than 1/6th of a turn and inserting the cotter pin. This will result in some amount of pre-load on the stock ball bearings, not slack. 1/2 ton GMCs and Chevys of this era use the same bearings, hubs, spindles and nuts.

I have roller bearings Bill. I didn't use a torque wrench so don't know the preload. They are snug, not loose. Carl, is your procedure to just torque to 5-7 and get the cotter pin alignment in that range?

I removed the leaf spring rear bolt on one side today. The bolt is a loose fit. Can't say how much, but I can wiggle it. I'll order a pair up Monday. I see Filling Station and Old Chevy Trucks both have them. Can the bushings be replaced without a press?

Dennis - Is the "loose fit" between the bolt and the spring rear bushing inner diameter? Here's an on-topic older thread that provides some great info from fellow Bolters on how to replace the spring eye bushing. Let us know how things progress.

Right on Dan! I'm going to try Pre68 Dave's method. He was nice enough to install a '42 steering box for me a few years ago. Yes, loose between the bolt and bushing.

Dennis,
The way to properly torque roller hearings is to tighten to 19 foot pounds while turning the tire by hand, then loosen the nut, then tighten it again to 5-7 foot pounds while turning the tire by hand. And yes, that 5-7 range is to allow for insertion of the cotter pin in the nearest hole. 5-9 foot pounds would be close enough in my experience.
Quick question. Do you feel the vibration in the steering wheel?

Thanks for the explanation Carl. I feel the vibration in the steering wheel, but it spooks the passenger too! If I had a GoPro, I would expect to see the wheels pretty active.

Today I used some shim stock to get an approximation of the slop between the bolt and the spring rear bushing inner diameter. Somewhere in the .013 and .015.

I doubt that .013 and .015 "slop" in your spring bushings/pin is causing your vibration. The type of vibration which comes in at a specific speed is most likely due to a faulty rotating part. Other loose non-rotating components may well amplify the vibration caused by the defective or improperly adjusted rotating parts.

I've got new ones on the way so I'll take care of that anyway. Got rear tires delivered today but will wait to test whether the bushing/pins make any difference. Retorqued the bearings today. I may not find out what the problem is but working my way to know what it isn't.

As a rule of thumb, if you feel the vibration in the steering wheel it's steering related, if you feel the vibration in the seat it's driveline. You say the passenger can feel it as well, it very well be that you have more than one issue going on.

I like the way you're going with your approach of trying one thing at a time then test drive to see if that item fixes it, rather than throwing everything at it at once and keep your fingers crossed.