Bumpsteer w/Bagged Suburban

[LooseCannon]

Here's the situation... I recently bagged my burb (see signature) and am experiencing what I think is bump steer. Basically, the front tires wonder the road and the steering wheel moves when hitting washboard or hard bumps like a man hole cover, etc... Both movements are minimal and more of a nuisance than anything.



@ ride height, which is about 4 1/2" drop


According to this article my suspension is not correct.

1. The red line should intersect the upper and lower ball joints and outer tie rod - IT DOESN'T.

1. The blue line should intersect the upper and lower pivot points and inner tie rod - IT DOESN'T.

1. The yellow lines should intersect to create instant center - IT DOESN'T.

Questions, based on the info do you think the handling problems are due to bumpsteer? Is there anything else that could cause the problems?

The rig has less than 30k miles and I replaced the ball joints and outer tie rods when swapping the spindles (because I ripped the boots) so the front end is tight. I also had it aligned but it pulls to the right. I can give the alignment numbers if it would help.

Thanks!!

[texastrendz]

i had a similar problem with bumpsteer. what i did is set the suspension at ride hieght. measure from ground to the frame in the front. i used blocks of wood to hold the vehicle from the crossmember to the ground. you also need to know the measurement from the lower control arm to the ground. once you know both these dimensions remove one of the front wheels. with the truck blocked up at ride hieght, set the suspension with a floor jack at ride hieght. now cycle the suspension up three inches from ride hieght. watch to see if the rotor is toeing in or out. then cycle the suspension down three inches and see if the rotor toes in or out. if it does you have bump steer. all vehicles have a minimal amount of bump steer. i made a make shift metal frame and put a run out gauge on the front of the rotor and rear. mine is not perfect but it is damn close. you have to change the tie rod angle to correct bump steer. i change my front end to heim style joints to correct this issue.

[LooseCannon]

Where did you purchase the heim joints and did they require modifications to the spindle? I think my next step is to build a bump steer gauge to more accurately illustrate the trouble.

Thanks.

[texastrendz]

yes you have to drill the spindle thru for a bolt. you will no longer have a taper. a bumpsteer gauge will be needed to do it properly. the pic i have is when i first installed the spacer, i have since trimmed it down to the proper length. what i did is stack several washers on the bolt and adjust as needed. when shimming the tie rod you have to also correct the toe as needed. it is a very time consuming affair to do this but the only way to correct the problem. this setup is identical as porterbuilt street rods when using his dropmember. take your time and measure a lot. you will be proud at the end that you yourself resolved the issue. at least i was. you can get rod ends at any local speed shop. the more you spend, the better the piece. the one i have in the picture was super cheap(used for mock up). i am going to order the one used by porterbuilt in his dropmember for the final piece.

[DKN]

I do not remember there being a bump steer problem for the 99 and later truck. The hiem joint pic is on the 88-98 chassis. You should get the Burb aligned at your new ride hieght. The Anti-dive geometry will have caused a large increase in caster, the new ride hieght will have changed the camber slightly, and I'm not exactly sure, but I think the toe will be out. Toe out will make the truck wonder more easily. GM had many versions of the 2 wheel drive wheel hub & bearing assembly, it caused the truck to shimmy. If you have a bearing & hub problem I would replace it with a 4 wheel drive hub, get a large nut and bolt, and tighten the bolt thru the center of the 4 wheel drive hub where the factory half shaft would be installed. There where no problems with the 4 wheel drive hub assemblies.

Danny Nix
CPP

[texastrendz]

the truck has already been aligned, noted in the first post. my truck is a old body style. ? don't know what that has to do with it. but i told you how to correct it. the rack output does look off but not as bad as the lines show in the pics because they are a little off.

[Innovation By Design]

easy fix, these are the ones I use on almost every truck I've ever built, all you need to do on yours is drill out the spindle for whatever size bolt your are going to use get and make or buy a hyme end setup and mount it on the bottom of the spindle instead of the top you could use a 1/2" spacer and should be fine since its not going that low just make sure you run misalignment bushings with the hymes. I usually use 3/4" shaft with 9/16" through hole

[DKN]

In the pictures it appears as though the little plastic parts are still in the upper arm alinment slots. The factory installs these on the assembly line and they need to be removed in order to adjust the alginment. If they plastic part is still in the alignment probably was not done.

Danny Nix
CPP

[LooseCannon]

Originally Posted by DKN

In the pictures it appears as though the little plastic parts are still in the upper arm alinment slots. The factory installs these on the assembly line and they need to be removed in order to adjust the alginment. If they plastic part is still in the alignment probably was not done.

Danny Nix
CPP

The rear camber adjusters were removed by the alignment shop to maximize positive camber adjustment. The front ones are still in and adjusted to the middle. Not sure if this is correct or not...

[DKN]

Originally Posted by LooseCannon

The rear camber adjusters were removed by the alignment shop to maximize positive camber adjustment. The front ones are still in and adjusted to the middle. Not sure if this is correct or not...

If the truck has a steady pull the caster is not right. Caster changes as the suspension moves. It's possible the caster could make the truck have a small amount of bump steer.

Toe out will make the front end dart around as it goes over small bumps, or changes in road crown. Toe in make the front slower to respond to steering inputs and bumps.

I have worked with suspensions that had so much bumbsteer that the tires will skid as the suspension moves, but the truck still drives straight thru bumps. The truck would leave skid marks from the bump, but felt just fine to drive. (This was a 2000 up 2wd 2500HD with a Fabtech 3" lift spindle. The spindle was designed for a 2500 and retrofit onto the 2500HD)

Danny Nix
CPP