Anoher Death Wobble thread

[albee]

My 1967' is almost at the end of a two year body off rebuild. When I drive about 30 mph the wobble starts.

Some of the things that I have done are...
*Sag power steering
*Replace tie rods and ends
*4 degree caster shims because of new 4" skyjacker spring lift
*New U bolts
*Upgraded to a front axle from a 76' fj40
*Replace knuckle bearings (preloads tested and within specs)
*New Bilstein shocks
*Alignment 1/8" plus toe in.
*Upgraded to fine spline rear axles out of a 75' because one of the
old shafts was bent
*BFG AT 33"x12.5 tires rebalanced using dyno beads. 8oz per tire.
*Lowered air pressure in tires from 25lbs to 15lbs and down to 10lbs
*Added about 250lbs of weight to rear

The only other thing that I can think of trying, is to replace the tires. The P.O. said that he bought them at a garage sale, but never put them on. I dont think my wife will let me buy a new set right now, even though I have a set of stock rims all painted and ready.

If anyone has any ideas for me to consider, I would be greatful. I would really like to drive this thing at least once before they start putting salt on the roads here in MA. Thank you Albee



BTW I have searched and searched for for ideas to try.

 

[Poser]

Death wobble from 33"s? and a radial all terrain to boot....





What is your measured caster angle?


Are your ubolts tight?

What is the condition of the knuckle bearings on the front axle you installed?


" Alignment 1/8" plus toe in. "


Clarify this statement please... does this mean that you have a 1/4" or 1/2" toe-in condition?

 

[rabid]

I take it the tires were mounted on rims? If it is starting at a specific MPH, could it be bad balance in a tire?

Check the tightness of the ubolts, and the ujoints for play.

Make sure your shims are in the right direction. Actually, you do not need the shims in at all with 4" springs, just with larger shackles, right?

Check all the spring bushings as well.

Hope this helps.

 

[John Smith]

I think the tires may be your issue. Dynabeads will not balance all tires.

 

[Blue77FJ40]

Why did you lower your air pressure - I'm guessing it's still for street at present?

I'd focus on shims. Mount them:
fat to the front if sprung under.
fat to the rear if sprung over.

If you have it backwards, I'd say that's your problem.

 

[albee]

*U bolts are tight.
*The old knuckle bearings were in ok shape w/o much groving in he races, but they were replaced with new.
*Toe in on front axle is 3/16" / \ Meaning 6" forward of the center of the hub is 3/16" shorter then 6" behind the hub.
*No play in ujoints
*The fat part of the caster shims is towards the front
*Tires were balance with lead at tire the shop when I put them on my rims.
I only tried the dyno beads because it still had the wobble. Their was a lot of
lead both inside and out and it rubbed on my old tie rod end.
* I will remeasure the caster angle w/ the 4 degree shims in. No caster shims and the truck darted all over the road. 2 degree shims better. 4 degree shims and it tracks down the road pretty well.


I will try and take a tire or two to the shop and have them re-spun to see if the dyno beads do their job.

Thanks please keep the suggestions comming. Albee

 

[albee]

Why did you lower your air pressure - I'm guessing it's still for street at present?

I dont know why, but on alot of other threads poser says lower the tire pressure to 8-10psi. So I did before he could tell me to do it here.

I measured the caster angle wih the 4 degree shims. It is neg 2.5 degrees. Meaning the pinion flange is 2.5 degrees closer to the ground.

Thanks Albee

 

[matt the sign]

I have death wobble at the same speed of 30mph, I spoke to a tyre guy who said it wouldn't be the balancing at such a low speed - balancing affects the handling from 60mph and above ?!?!

 

[REZARF]

You have knocked out a lot of possible culprits.

I would suggest, finding a cruiser buddy and simply swap out the tires for a drive. Then you can totally eliminate the tires... this was my problem.

Have you driven the cruiser before the death wobble started?

Rezarf <><

 

[brider]

It's your driveshaft...

I've had tires with too LOW of pressure give me the same symptoms. When the pressure is that low, the sidewalls really flex and generate a lot of heat, I'd say it's NOT recommended for street driving. Put the tires back to a sane pressure, 25-30 psi.

I'll bet it's the driveshaft. I had the EXACT same thing develop on a truck that had too little spline engagement betwen the front and rear shafts (2-piece shaft, but your situation is similar). As a result of too little engagement and wear, the shaft developed a "whip" at about 25 mph. Yours may have too little engagement due to your lift. I had the shaft lengthened 1.5", and it went away. ALSO, new u-joints? Did you assemble the shaft/yoke with the yokes in phase? Check your manual for proper orientation, out-of-phase driveshaft will also wobble and vibrate.

 

[missipboy]

I'll bet it's the driveshaft. I had the EXACT same thing develop on a truck that had too little spline engagement betwen the front and rear shafts (2-piece shaft, but your situation is similar). As a result of too little engagement and wear, the shaft developed a "whip" at about 25 mph. Yours may have too little engagement due to your lift. I had the shaft lengthened 1.5", and it went away. ALSO, new u-joints? Did you assemble the shaft/yoke with the yokes in phase? Check your manual for proper orientation, out-of-phase driveshaft will also wobble and vibrate.

that sounds pretty reasonable to me.

what about your spring bushings?

 

[ranger]

Also check to see if your wheel bearings are loose..

 

[albee]

The rear drive shaft was cut and balanced while the front was made longer. This was done at the same time as the stroked SBC and TH350 and 4" skyjacker spring lift.

Spring bushings are new.

I only lowered the tire pressure to see if it would help, then put it back up to .20psi.

I have never driven this cruiser further then up and down the country road in front of my house just to check the condition of the steering. It was rolled off a trailor into my shop over 2 years ago.

Wheel bearings were inspected and repacked, then checked with a fish scale on the lug. I think they were tightened to 43ftlbs.

Great ideas. Thanks Albee

 

[theo]

I dont know why, but on alot of other threads poser says lower the tire pressure to 8-10psi. So I did before he could tell me to do it here.

So what you're saying is you fear Poser?!

I measured the caster angle wih the 4 degree shims. It is neg 2.5 degrees. Meaning the pinion flange is 2.5 degrees closer to the ground.

Just nitpicking here, but with front pinion pointing down you have positive castor, not negative. (Assuming nobody has cut and turned your knuckles. You might try measuring castor at the knuckles just to be sure.) Stock is +1 degree so +2.5 degrees should be fine.

Can't offer more. (Knuckle rebuild cured my DW.) Maybe the driveshaft thing. Maybe. I second (third?) trying different front tires. Or at least rotating yours and see if it changes.

 

[G-Cat]

Did you box your front frame rails before installing the Saginaw pump? I knew a 40 with the Saginaw's bracket welded directly to the frame...frame horns developed several hairline cracks which resulted in a death wobble at moderate speed. Had the frame horns boxed and the problem went away.

 

[Pin_Head]

*Toe in on front axle is 3/16" / \ Meaning 6" forward of the center of the hub is 3/16" shorter then 6" behind the hub.
*

Yikes.

That is too much toe in and that is not the proper definition of toe in. Proper toe in would be about 1/8 to 1/4 less on the leading surface of the tire compared to the back surface. Try setting the toe in and see what happens. If that doesn't cut it, start looking for slop in anything that locates the wheel. Jack up the front end under the spring perches and start jerking around the tires. Anything that moves when it shouldn't should be replaced.

 

[trainrech]

How rough is the country road? Ok, don't have anything to add here, but you might try something as simple as jacking up the front end and spinning the tires by hand to look for oddities in the way the tire and/or wheel rotate.

 

[Poser]

*The old knuckle bearings were in ok shape w/o much groving in he races, but they were replaced with new.

*Toe in on front axle is 3/16" / \ Meaning 6" forward of the center of the hub is 3/16" shorter then 6" behind the hub.

What preload did the new knuckle bearings have when you replaced them?


Did you check the preload after installing the new bearings?


Did you do this with the wiper seals on the rear side of the knuckle? If so, your indicated drag is not accurate as you are supposed to check preload on the knuckle bearings with the wiper seals removed.

The FSM states that preload is supposed to be around 4-7# of drag (or something very close to that, I do not have the FSM in front of me right now)...I set them up tighter than that when I go through them, (10-12#) since most that I have done are being used with significantly larger tires than the H78-15's that they came with.



Your toe-in seems a bit much. I would measure it with the wheel on the hub at the leading edge and trailing edge of the tire at the 3 and 9 o’clock position, and try and keep it in the 3/16” to a 1/4" area.


Radial or Bias-ply tires? How long have they been sitting? Have you ran it down the road long enough to get them warm to run the flat spots out?

I've had tires with too LOW of pressure give me the same symptoms. When the pressure is that low, the sidewalls really flex and generate a lot of heat, I'd say it's NOT recommended for street driving. Put the tires back to a sane pressure, 25-30 psi.

I'll bet it's the driveshaft. I had the EXACT same thing develop on a truck that had too little spline engagement betwen the front and rear shafts (2-piece shaft, but your situation is similar). As a result of too little engagement and wear, the shaft developed a "whip" at about 25 mph. Yours may have too little engagement due to your lift. I had the shaft lengthened 1.5", and it went away. ALSO, new u-joints? Did you assemble the shaft/yoke with the yokes in phase? Check your manual for proper orientation, out-of-phase driveshaft will also wobble and vibrate.

On the lowering tire pressure idea…

I have done this with my 38.5” and continue to do so with my 42” Swampers, both with and without bead lock wheels and it has worked for me just fine both off road and on road at highway speeds of over 60. I have also tried this on two other 40’s and a 4Runner that are using 38.5” Swampers on Toyota axles that have been built by me, and all other component having anything to do with this equation are new, and caster is at least 2 degrees positive. Do I, or have I suggested this as a cure? If you have read it that way, I am sorry. It was a suggestion as a trouble shooting tool, since increasing the amount of contact surface the tire has with the road, seems to lessen the effects of death wobble on the vehicles that I have tried it with.



I would like to know more about how a drive shaft could possible have an effect on steering as you have described. Please expand on how you derived this conclusion.


Thanks!


-Steve

 

[REZARF]

Did you assemble the shaft/yoke with the yokes in phase? Check your manual for proper orientation, out-of-phase driveshaft will also wobble and vibrate.

Death Wobble and vibration are two radically different things... if you have to get out of the gas, and jam on the brakes in fear of the front end coming loose... then you have death wobble, anything less is just a vibration.

Rezarf <><

 

[Colorado Boy-74-FJ40]

Brian in Oregon solved his death wobble by re balancing his tires. Pretty cheap start.