death wobble with 35's ????????????

[1971ford]

I couldn't help myself so i swapped the racetruck's aluminum rims/35's onto the highboy.
The highboy drove PERFECT with the smaller wheels. The 35's are just for a week or so. Just for fun.

But the second I put the 35's on I now have a death wobble of some sort. If i drive in a straight line going about 40mph or higher, after maybe 5 seconds the truck starts to wobble, feels like its coming from driver front. It progressively gets way worse. If I let it wobble it gets progressively worse, I can stop it by jerking the wheel either way then when it happens again and starts getting worse I jerk it again and its gone again.
All 35's are balanced, have good tread, and should be perfectly fine to run.


How come the highboy drives perfect and holds a perfectly straight line with hands off the wheel for as long as the road is straight, the i swap 35's on and do nothing else and now I have some bad wobble.

Only thing i can possibly think of is that the front left tire that SEEMS to be the source of the wobbling is the tire that has the least tread out of the 4. the other 3 have anywhere from 65-90% and this tire has about 25%. Could the 1/4" difference in tire heights on the front end cause this wabble? I'd think not but i dont have any solid axle experience besides this truck.

[BRUTUS_T_HOG]

bad shocks? sloppy steering parts?

[Racer Z]

The taller tires change the suspension and steering geometry. I don't have a clear answer though, so muddle through this with me.

The effective caster has been changed. The caster angle did not change, but the point of intersection in relation to the plane where the bottom of the tire touches the ground has changed. The steering knuckle has been moved up and now the effective caster is greater or lesser than it should be. You probably have negative caster and each tire is trying to point backwards.

The toe has not changed, but, wider tires or rims with greater offset stress everything beyond designed intent. These greater forces flex the tie rod ends, tie rods, wheel bearings and all other related parts. Slightly worn parts are now being pushed or pulled further than the smaller tires did. This can change the effective toe-in /toe-out.

The combination of both of the effective changes forces the wheels to toe out and then they spring back. Keep driving like this and something will break.

Right or wrong, that's my thoughts on the subject.

[1971ford]

shocks are brand new

Interesting... thanks for the input. Not that i am goign to be driving on these tires for much longer but I want to be able to put 35's on the truck whenever I please and drive down the freeway.
What parts do i need to start replacing?? I know there are LOTS of people running 35's on a stock highboy, mine should be no different.

[Racer Z]

I wouldn't just replace things mindlessly. Check the suspension/steering parts for normal wear and play. Check the alignment too. You should have:
Tie rod ends;
Ball joints (not king pins);
maybe a pitman arm and idler arm;
Wheel bearings;
Check the steering gear box while your at it, but I don't expect it to be part of the problem.
You probably have leaf springs, so that eliminates radius rod bushings and thrust bushings.

I don't know what kind of alignment settings your 4x4 has other than the toe. The toe you can set with a tape measure if you know how. 1/8 to 1/4 inch toe-in is standard for a truck. As the vehicle rolls forward, the normal forces try to toe-out the tires. This will bring the wheels to near zero toe during use. Any actual toe-out will allow the truck to wonder as you cruise on the highway. Excessive toe (in/out) will wear the tires and lower your MPG.

Checking the camber/caster requires a special gauge. Don't know if you have a camber/caster gauge, most don't. Even if your truck does not have any camber/caster adjustment, you always want to know if it's within the allowed range. For non-adjustable vehicles, like my F250 and Datsun 240z, if it's out of spec, you can replace parts or have the frame straightened.

There are plenty of alignment shops around. It could be as simple as readjusting the toe.

[71highboy]

wheels need balanced

[Racer Z]

Let us know if balancing fixes it.

I thought your OP stated the wheel were balanced properly. I went back to re-read and it seems different somehow. Did you edit it after the fact?

[averagef250]

Death wobble is a caster issue, pure and simple. With correct caster tires self center regardless of how worn out or messed up the other stuff is. Your camber can be off an inch from toasted trunnion bearings or a bent housing, tie rods can have 1/2" play in them, tread can be chunking off the tires from being so far out of whack, but if the caster is right the tires will tend to self center and resist wobble from worn parts.

Most 4x4's run 4 degrees caster angle. That means an imaginary line through the balljoints/trunnion bearings/kingpins leans to the rear of the truck 4 degrees. As it so happens Ford 4x4's have thier front axle spring perches perfectly perpendicular to the kingpin angle.

You can have wear in other components that will effect the dynamic caster. Bottom line is you have to measure everything, figure out what's off. The factory alignment specs should work fine if the wheel offset is apprpriate for the height of tire you are running.

The way to determine wheel offset that's ideal for your front suspension is to plot an imaginary camber line to the tires contact patch on the ground. The camber line should be in the center of the tire tread. Usually it's not perfect and works fine.

"Death wobble" is too much positive caster. Too negative and steering effort gets real high. Caster and camber are adjustable on solid axle 4x4's, but not easily, especially in the older stuff. Bad caster/camber usually is the product of worn out/bent parts in the front axle, even the housing itself or more common than not somebodies uneducated attempt at a front suspension lift with longer shackles or a taller front crossmember.

[averagef250]

A machinist protractor bubble level is all that's needed to measure any chassis angle. I have an old sanp-on caster/camber gauge, but it's pretty useless without turning plates (which I don't have) and the bubble protractor is really accurate and gives you a first-hand understanding of what angle does what.

[1971ford]

Interesting, thanks for the info!
I'm going to have to check out some things for sure.

[BigBlueF250]

How did it look?? Got pics?

[1971ford]

Haven't had a chance to look at anything yet. Dustin you mentioned wheel offset... is this just a factor for when you are measuring to compare to stock specs or can this affect the ride. For some reason I understand caster on i-beams but I can't understand it on solid axles, hence the stupid questions.
I dont think the wheel offset is ideal for a 4x4, the tires stick out to the fender. THe passenger side tire sticks out much more than the drivers side as well but the offset is the same on each rim, i measured to double check. Reason behind the difference in width I believe is because my d44 seems to have mismatched parts. The drivers side i believe has a slip on drum where you dont need to take the hub apart and the passenger side you have to take the hub apart. If i remember correctly.

If i am understanding these posts correctly, swapping 31's to 35's should have NO change in drive-ability correct? My truck has to have something worn out or out of alignment? And If i fix it with the 35's on then it should be perfectly fine with whatever tire size i wish to run.

[averagef250]

THe passenger side tire sticks out much more than the drivers side

How much? If you can see a difference, there's a big problem somewhere.

an old 3/4 ton truck will ride better with good 35" radials compared to 31's. The larger tires smooth out the ride. Other than that you should not notice much difference besides sitting 2" higher.

[1971ford]

THe passenger side tire sticks out much more than the drivers side

How much? If you can see a difference, there's a big problem somewhere.

an old 3/4 ton truck will ride better with good 35" radials compared to 31's. The larger tires smooth out the ride. Other than that you should not notice much difference besides sitting 2" higher.

Noticeably. Drivers side is tucked in the fender and passenger side just outside fender lip. Never noticed it with the smaller tire on there. I'm sure it's because of the funky different drums on each side. I really need to spend a weekend just on the front axle.

Only pictures I have as of tonight. They're better than nothing for now. you can clearly see the passenger tire sticking out in this shot. Granted wheels are slightly turned to the right.


Here its hard to tell but the second shot doesn't do too bad of a job showing the tire is tucked in.

[BigBlueF250]

Looks real good!! When are you going to paint the hood red? I'm really diggin this whole project.