Death Wobble After Adding 4 Degree Shims (1 Viewer)

[SUMMIT CRUISERS]

My 78 had this problem with 33X 12.5 BFG's on 8" wheels. I got the truck up to about 57 on the odometer and the front end did the death wobble thing. I rotated my front tires to the rear and no wobble, just a little vibration from the rear. Not a big fan on BFG's for good balancing. All 8 BFG's I own are relatively new and have about a 5" long weight on the wheel (both aluminum and steel). Just my experience.

 

[PabloCruise]

loose U bolts

and you installed them correctly right?

Mace wins. I *thought* they were tight last night when I took it for a drive, but they sure weren't today. That right there is the danger of getting too tired to do good work...

install and torqe(sp) them with the rig at rest or off the jackstands and all the weight on the suspension.
this is also when everything that has to do with the suspension is torqed.
not when its all hanging in the air, but on the ground.
take the shims out and see what happens.moab is soon, don't delay

edit:
did you replace everything before taking it to the shop?

I did not know you were supposed to torque u-bolts on the ground! I did them up in the air today, and then set it down and re-torqued. Sure enough - they took more

I think I wrote poorly last night. I took it to the front end shop almost a year ago and they measured negative caster. I just kept driving it. Now w/ Moab coming up, I wanted to shim it so the drive over is a bit easier.

I'm assuming you tightened the top left shackle bolt when looking at it from the front.

Try this. Tighten the shackles more and re-drive. I bet they are your
source.

Yes I did, I just clicked the pic at that time to show that the shackles are now parallel vs bowed out - like the DS pic shows when I had the wrong bushings on the fram spring hanger.

Your passenger side shackle bolts look a bit loose. You can still see the shape of the lock washers which aren't flattened out.

Also, the right-side plate of the driver's side shackle has a weird angle to it, unless that's just the perspective from the photo.

Now, are 4 degree caster shims 'standard'? If you were -1* caster, and you put on 4 degree shims, that works out to +3* caster (in my simple mind anyway). I wonder if this could also cause the problem? I haven't done any axle shimming before, so I'm just taking a shot in the dark.

I was hoping that getting 3 degrees of caster would make the 40 travel down the road a bit easier, not 'dart around' so much when there are ruts in the road or when I dive on the brakes.

actually you should check with the spring shop about what they call negative and positive caster.Negative caster is the bottom trunion forward of the top trunion. If this is how they measured it and you added 4 degree shims then you would be at 5 degrees negative caster .(maybe a bit too much?) Do you have any play anywhere with the tires hanging in the air? Maybe get a buddy to turn the wheel left and right with the tires on the ground to see what is flexing /moving that maybe shouldn't be.

This shop defined negative caster as top trunion forward of bottom. I measured -.7 and -.8 degrees. The shop listed the factory spec as +0.8 degrees.

I believe this to be negative caster:

And this to be positive caster:

A lot of aftermarket springs are not as wide as stock springs. If your springs fall in that category, take a close look at your spring shackle pin. You are using stock shackle pins that are shouldered. You would need to use spring bushings with wider flanges to take up the extra space to get a snug fit. Yours look a little loose.

Good Luck

Yep, I switched the bushings to a narrower shoulder up top on the frame mount and that got the shackles hanging rather nicely - no more bowed out up top.

you should have installed all that stuff first then had the alignment checked .alittle extra neg castor doesnt hurt with bigger tires as they require a little more neg castor than stock tires take out the shims and try it again since thats how your trouble started . i have also found alignment shops and cruisers dont always get along. also if you have wore a bunch of rubber off your tires since they were balanced last that will also effect handling good luck

I got tired of daily driving it with negative caster. It darted around too easily and got squirrely over RR tracks or when I hit the brakes and the road had some ruts...

Top trunion behind bottom trunion is POSITIVE caster, not negative. So if you were -1 and added 4 degrees you should be +3, which is perfect.

So I also wonder if your new parts and adjustments didn't change something or bring some other problem to the forefront. Seems like I remember you already rebuilt your knuckles and wheel bearings, but not sure. If not you could check for bearing play and low trunion preload. Just a thought.

Yes...

 

[2badfjs]

sweet TJ!

have a blast in moab!!!!

 

[PabloCruise]

So after torquing my u-bolts to 80 ft-lbs while on jackstands and then re-torquing while on the ground, I have no more death wobble.

I also snugged up the shackle bolts, but they still flex.

I hammered the RR tracks that produced the death wobble originally and could not get any wobble today. I hit the tracks at 50 MPH and the 40 definitely takes it better than before I shimmed the front end.

So far I am glad I got the shims in. The 40 drives a lot nicer. The wheel feels a little heavier, but nothing unreasonable.

If I had to do it over again, I probably would NOT get the u-bolt plates from SOR. These deformed quite a bit when I was torquing. To the point where I could not get my socket out of the hole!!! We'll see how they do when I drag them over a rock or two.

 

[PabloCruise]

sweet TJ!

have a blast in moab!!!!

Yes sir!

Do you think you might add u-bolt plates to your product line?

 

[2badfjs]

Yes sir!

Do you think you might add u-bolt plates to your product line?

those are a piece of cake. i've made some for my 40.
if you have your old ones , send them to me and i'll plate them for you.

glad it was a easy fix on the wobble

my 60 had me worried
tires

 

[PabloCruise]

I got a PM asking more about the shims, so I thought I would post up here.

I got the shims from Roger Brown, who does the truck/4Runner tech in Toyota Trails. You can read more about his products here:

http://www.4crawler.com/4x4/ForSale/Shims.shtml#CustomWidthShim

I did order longer center pins, but the head size was too small for the Land Cruiser perches. The Downey cneter pins had a little bit smaller head than the stock Cruiser center pins. I think the Downey pins ended up being perfect after the shims make the perch sit at a 4 degree angle to the pin.

I just got back from Moab, so I drove the 40 ~900 miles. I think it drives much more nicely with some positive caster in the front end. It felt much more stable.

I feel like the positive caster puts more effort on the PS system - translating into more heat in the PS fluid. My PS Pump was barfing when I worked it hard, so I will be adding a cooler soon.

HTH,

 

[Adolf]

You can also get the shims from ProComp Suspension!

Done the same, I mean installing 4deg shims after installing Parabolics. Man, did they change the ride. Also installed them on rear for diff angle.