i have a new wobble in my 89 sas pickup. i put longer springs in the front and did a 3/4 elliptical in the rear. i drove it down the road and at about 25-30 mph it would start to shake, not the kind of shake like the wheel is out of balence. any ideas?

 

Sounds like it could be Death Wobble......maybe. I would have somebody drive next to you so they could actually see what is causing the shaking.

Could be loose ball joints, steering linkage, improper caster setup, pinion angle, tires out of balance, bend drive shaft.......could be quite a few things.

 

You forgot to mention U-Joints.

 

my guess would be driveline issues

 

what jason said !

 

i think it may be the caster now that you said that. i didnt realize that would be a problem but when i put the new spring on it moved the axle forward. so i took the shim out and the axle was turned.

 

What you want to do is disconnect (remove) the front drive shaft all together. Setup your caster correctly, ensure that all end-links and steering components are tight, then drive it. If its good, you're one step closer to figuring it out. Next, put the drive shaft back on, and test it again.

One step at a time will get your closer to figuring it out.

when I did my SAS, Death Wobble was a very large concern for me. I tripple checked my Caster and actually designed it for 2*. Currently I'm sitting at about 3* after a several hour alignment at Midas. At 2*, I could still do 80mph with no death wobble, but we were trying to eliminate a slight pull to the left.....

anyhow, Death Wobble is a real issue that can knock you off the road.

 

How many threads do you need there boss?

 

I don't want to hijack your thread, but "correct caster angle = death wobble"
catch my attention.

Recently my 4runner start getting death wobble at around 45 to 60miles. Just like yours. I found out my front shock lower both left and right brackets are bent! I used non-OEM Rancho shocks in order to adjust the BJ spacer lift length and these shock has narrower mounting area than OEM shocks.

I used washer to keep the shock to be mounted center, but these washers are gone!!! I do maintenance myself and very few times I go for service such as wheel alignment & balancing, etc.

Anyway. How can I fix the bent lower brackets to correct the caster angle?
I tried use long steel pipe to make original space in between, but too hard and maybe weaken the mounting points?
Do I have to removed it and welded on new lower brackets?

Please share with me if you have any good idea.

Thanks

 

Death Wobble as we are describing it is a Solid axle only problem. It is impossible to get on IFS, as the front tires are connected through the frame, and not by an axle housing. So, the caster solution does not work at all on an IFS truck. Caster being out makes an IFS truck harder to steer, but does not usually induce a wobble or heavy vibration.

 

Thanks, I didn't know the fact. i guess my wobble is not from the shock bracket to be bent. from other cause.....umm

 

ummmm.....who is this directed at?

 

On top of that, if I remember correctly, if you have caster out on an IFS rig, your problems are more likely frame damage. Camber and Toe-in is adjustable on an IFS rig, but not Caster (If I recall correctly).

Here is a pretty good article on Toe-in, Caster and Camber:

http://www.ozebiz.com.au/racetech/theory/align.html

 

Sorry, the OP. He has another thread in which a bunch of info has already been given to him about his vibration issue, including death wobble and getting his caster checked.

Actually, you can adjust the caster, using the camber bolts. If you adjust one, and not the other, for example, front, but not rear, you adjust both camber and caster at the same time.

But, its not that big of a deal, as long as you don't get crosscaster.

 

how many degrees in Caster can you get out of adjusting the Camber bolts? Aren't these the con-centric bolts that go through the frame mounts?

 

A fair bit.

You only move one bolt to adjust caster, not both.

So, if I leave the rear alone, and ONLY adust the front bolt, lets say, outward. So, I move the front of the LCA outwards with relation to the truck. With the rear stationary, this moves Balljoint mount outward, but also backward. Since the knuckle is fixed at the top by the upper balljoint, the caster moves positive. If I adjust the front LCA camber bolt inward, I move the lower balljoint mount inward and forward, thus moving the caster negative.

 

This would also affect you Toe-in, correct?

 

thanks steveo that website helped. but for a solid axle how would i fix the caster? shims? and i didnt really understand about which way is positive caster, is it with the diff. pointing more towards the tcase or pointing more down to the ground.

 

So, to adjust the caster on a solid axle, the easy method to fixing the caster, you would apply shims to the bottom of the leaf pack. The harder method is to cut the knuckles, rotate them to the desired caster setup (with the pinion pointing towards the transfer case) and then re-weld them back up.

These shims (depending on how you put them in, fat end towards the rear of the vehicle would be best for positive caster) would adjust the pinion nut (where the drive shaft attaches to the front diff) more towards the ground. This will adjust your caster to a more positive caster - which improves steering return-to-center when coming out of a corner, improves the vehicle handling when driving straight down the road, but also makes the steering a little heavier. This is why I adjusted my caster from 4* positive (stock for a D44) to 2* positive. I wanted the steering to be a little lighter due to larger tires. I ended up at 3* positive, which has been working out great for me.

If you are looking at the side of the vehicle, when the top knuckle is leaning further back (towards the rear of the vehicle) than the bottom knuckle, you have positive caster.

I would Google for steering caster. There is a wealth of information, especially from racers out there that can really help you get a good understanding of steering solutions.

 

Absolutely. When I do my alignments, I set my rear camber bolts fully outboard, which gives me a large range of negative caster to work from, since spec is like 1.5deg negative. I then adjust my front camber bolts to get my camber dialed in, keeping careful watch to make sure my caster is roughly the same side to side.

I then adjust toe.