unstable steering, alignment specifications?

[jeffwest]

replaced tie rod ends and drag link, toe in probably really bad, no alignment yet other than counting the turns out and then turning the same count when installing tie rod ends.

going to replace spring bushings tomorrow and then have a friend come over to adjust toe-in.

What are the specifications? A quick search does not find them.

I drove it today around the block (6 miles) to see if steering play was impacted, it was reduced significantly.

However, when I accelerated to 55, I got into a steering oscillation. The steering gear was not shaking, this is not death wobble. Instead, when I was correcting to stay in my lane, side to side oscillation amplified. I had to under-correct to stop the oscillation. This was scary. Before the tie rod/drag link, I drove about 75 miles similarly and no such symptoms occurred.

Can bad toe-in cause this? Or just less play in the steering gear?

The front/rear weight is different, I replaced the slant 6 with a 5.3 LS with a gas tank behind the differential and an under-bed battery mount. I do not think the balance is THAT much different. I did add electric power steering, the level of assist is variable and if nothing else helps, I will reduce the assist.

Thoughts?

[Wildergarten]

What is the frequency of the oscillation? Is it speed dependent?

[PwrWgnDrvr]

Best I recall from 1978 when I set it once, the toe in spec is 1/8". (on a 70 W200)

[jeffwest]

speed of oscillation: about 1.5 times faster than I could turn the wheel back and forth. About once (full cycle side to side) every 2 seconds I would guess...

I was behind it, overcorrecting, and getting further behind...

So I purposefully got a lot further behind and limited how far I was turning the wheel in each direction. Thankfully it damped.

[jeffwest]

thanks for the setting!

Is there no place on the forum where this information is located?

I am assuming that if I have larger tires now I should adjust the dimension to maintain the angle this value provides with the original wheels/tires?

I just realized that I failed to mention the wheel/tire change from stock in my original post.

[Wildergarten]

speed of oscillation: about 1.5 times faster than I could turn the wheel back and forth. About once (full cycle side to side) every 2 seconds I would guess...

Got it. Try changing the tire pressure to see if the behavior changes. PwrWgnDrvi is correct about the toe spec at 1/8". A good way to set it is to jack up the wheel, spin it, and scribe a line on the tire if you can't get a tape from wheel to wheel. I'm guessnig you have a "toe out" condition, but...

This kind of problem can arise from one thing as exacerbated by another. Are you sure the frame is straight (there is a procedure to check in the factory manual)? Your original post didn't describe king pins. Are they tight? Getting the spring bushings done at this late age is a good idea no matter what you do but it shouldn't affect the toe setting. How did you do the drag link? Some W trucks have plates on the end of the axle for changing camber. One can also shim the axle with wedges on the perch to increase caster, which would likely improve stability. That's all I can think of.

[PwrWgnDrvr]

Toe in spec is in the factory service manual.
I had that kind of wobble yrs ago. It was due to an internal structural failure in a tire that wasn't visible outside. Was a *#%^$ to figure it out.
You have non stock mods that could also cause unknown problems due to incompatibility with the original engineering. Good luck figuring it all out.

[Hobcobble]

I did add electric power steering, the level of assist is variable and if nothing else helps, I will reduce the assist.

Thoughts?

The factory power steering system [hydraulic ram assist] included axle shims.
You might want to check your aftermarket system to see if it specifies any
modifications to the axle angle vis-a-vis shims.

John

[BigJimG]

A "Toe-out" condition, in an otherwise acceptable alignment would mostly cause a lot of tire noise and perennial understeer. Excessive toe-in could cause similar tire noise, but the driving dynamics would tend towards oversteer. Neither of which you are describing. Your description is the exact description of my truck after I swapped out the rear axle.

The factory caster angle on these trucks is only about +0.5 degrees on a NON-power steering truck, with shims added to increase the caster on the power steering trucks. (about 2-3 degrees, i'm sure someone with more knowledge of those parts will chime in)

In my case, the rear axle swap, coupled with the tire swap (about 1" difference in diameter front to rear) gave me a net negative caster angle which resulted in some interesting handling characteristics at speed, very similar to what you experienced. After a trip to the local heavy truck shop, to pick up some 3 degree shims, AND new spring pins (longer head, or use captured shims), Now my truck is a lot smoother going down the road, with me going as fast as I want to down a bumpy back country road with deep ditches and no seat belts...

Make sure when you use the shims, to BE SURE the spring pin still properly engages with the axle, failure to do so is probably the number one cause of all of the "front shim issues" many people like to parrot around the internet.

To put it in perspective, newer solid axle vehicles like Jeeps and Trucks, are typically specced around 3-5 degrees of positive caster, depending on other desired handling characteristics.

For every one inch of delta between the front and rear ride heights (i.e. rear raised inch, or front dropped inch, split 50/50, etc) results in a 0.5 degree caster change in a 114" wheelbase truck.

And yes, I said, and meant, REAR axle swap, the axle tubes were a larger diameter, coupled with my slightly too tall spring perches raised my rear end somewhere around 1.5", coupled with the tire difference, meant close to a 1 degree change of caster. The shop talked me out of the 6 degree shims that I originally wanted, but if I ever do the EPS conversion like you did, that is probably what I would change to.

[PwrWgnDrvr]

For every one inch of delta between the front and rear ride heights (i.e. rear raised inch, or front dropped inch, split 50/50, etc) results in a .05 degree caster change in a 114" wheelbase truck.

Did u mean 0.5 degree rather than .05?
(that would be 1/2 degree, rather than 1/20th degree)

[jeffwest]

thanks for the toe-in/castor explanation. A good bit to think about... Anybody know where to get shims?

I am in the middle of changing spring bushings, they are horrible, almost non-existant on the rear eye of the front springs.

I found something really funny/concerning in the disassembly: There was a 1 degree castor shim on the right side and no castor shim at all on the driver's side.

Also, the front spring front shackles: The right hand side has significant (1/4 to 3/8) side to side slip. The whole assembly is sliding side to side in the bushing. The bushing is not allowing rock or radial play, it is tight in that respect. The driver's side has no slip/rocking/radial play whatsoever. I suspect that the steering linkage rebuild and spring bushing upgrade to urethane will not be very productive without the shackle rebuild. Anybody got thoughts on how the right side can be so bad while the driver's side is good?

Also, several posts I found say the metal bushing is no longer available. Anyone have dimensions of the part in order to locate a generic replacement?

[BigJimG]

For every one inch of delta between the front and rear ride heights (i.e. rear raised inch, or front dropped inch, split 50/50, etc) results in a .05 degree caster change in a 114" wheelbase truck.

Did u mean 0.5 degree rather than .05?
(that would be 1/2 degree, rather than 1/20th degree)

Yeah, you're right, I fixed it in my post. Must have been not enough coffee yet when I wrote that.

[Wildergarten]

I found something really funny/concerning in the disassembly: There was a 1 degree castor shim on the right side and no castor shim at all on the driver's side.

At this point, it might be profitable to lay the two sets of springs on each other to see if the arc is the same. This sounds like somebody was compensating for something by putting some "wind up" into the spring.

[jeffwest]

Turns out I overestimated the side-to-side play in the front spring front shackle shoulder bolt and bushing: A 0.032" spring steel sholder bolt shim from McMaster-Carr removed the play completely. I guess the shock the hands feel when metal hits metal fools the senses. A $0.80 fix.

I finished the urethane bushing install on the front.

I also added a 6 degree shim to each side to create more positive caster.

No wander at all. I found the worst backroad I could and it tracks exactly where I point it.

Very stable at 65 mph. It pulls a little to the right, that is probably why the one degree shim was on the right in a negative caster configuration. I may look for a 5 degree shim to see if that amount of cross caster is better or worse.

Still have to get the toe-in set.

Quite happy. Getting the kit from ESPO Springs and Things is absolutely the thing to do when putting one of these trucks back on the road.

[Conrad]

Turns out I overestimated the side-to-side play in the front spring front shackle shoulder bolt and bushing: A 0.032" spring steel sholder bolt shim from McMaster-Carr removed the play completely.

They list shortening and lengthening - not sure exactly what part you are referring to?

[jeffwest]

sorry.

Shoulder was too long. I put a shortening shim on it.