Excessive Body Roll & Self-steer Over Bumps After Front End Overhaul

[squeeler642]

Hi folks. Just did a whole front end job 3 months back on my 2003 Z71 Tahoe w/375k miles. Did all new upper/lower control arms, knuckles, sway bar links, inner/outer tie rods, pitman and idler arms, and brake lines. All ball joints and bushings came pre-installed in their respective places and I did either Moog or Mevotech performance on everything, whatever I felt was the best quality. Got it aligned at my local shop and the thing drives like a DREAM compared to my old worn out suspension... for the most part.

Ever since the overhaul, the thing just doesn't feel right over large bumps at speed. It kinda self-steers, where a large bump making the suspension travel significantly (transition to/from bridges, humps in the road, etc.) cause the wheel to pull left/right depending on the case. Most of the time when I go through those road features dead on (straight) with it feels like the left side of the truck is really smooth and the right side is just bouncing excessively, almost like it doesn't have shocks on it at all, or like there's 500 lbs of cargo loaded on the left side of the truck. None of this behavior was present before the overhaul...

I should say, I obviously had it aligned after that whole job, ended up being 2 sperate alignments by the same shop after the issue initially presented. At first I figured the alignment would straighten it out. They said it was good even though the caster spec was out by about half a degree (one side -1.6°, the other -2.1°) and they kept telling me you won't be able to feel that and that it's not a tire wearing adjustment. Toe and camber are dead on and I fine tuned the torsion keys to get matching L/R ride height, about 36.5" without my ass in the truck.

(Side note: how do you even measure caster on these trucks? Since there's no strut tower to adjust at the top, wouldn't you have to essentially take the wheel off and measure the angle of the knuckle relative to the upper/lower control arm mounting points? Caster adjustment is done by making opposite adjustments go the front/rear upper control arm camber bolts if I understand correctly.)

Open to any dialogue. Some pics of the new suspension attached.

 

[Donal]

" I fine tuned the torsion keys to get matching L/R ride height, about 36.5" without my ass in the truck." Try the procedure from the repair manual. You can search for the procedure here and find it.

 

[89Suburban]

Hi folks. Just did a whole front end job 3 months back on my 2003 Z71 Tahoe w/375k miles. Did all new upper/lower control arms, knuckles, sway bar links, inner/outer tie rods, pitman and idler arms, and brake lines. All ball joints and bushings came pre-installed in their respective places and I did either Moog or Mevotech performance on everything, whatever I felt was the best quality. Got it aligned at my local shop and the thing drives like a DREAM compared to my old worn out suspension... for the most part.

Ever since the overhaul, the thing just doesn't feel right over large bumps at speed. It kinda self-steers, where a large bump making the suspension travel significantly (transition to/from bridges, humps in the road, etc.) cause the wheel to pull left/right depending on the case. Most of the time when I go through those road features dead on (straight) with it feels like the left side of the truck is really smooth and the right side is just bouncing excessively, almost like it doesn't have shocks on it at all, or like there's 500 lbs of cargo loaded on the left side of the truck. None of this behavior was present before the overhaul...

I should say, I obviously had it aligned after that whole job, ended up being 2 sperate alignments by the same shop after the issue initially presented. At first I figured the alignment would straighten it out. They said it was good even though the caster spec was out by about half a degree (one side -1.6°, the other -2.1°) and they kept telling me you won't be able to feel that and that it's not a tire wearing adjustment. Toe and camber are dead on and I fine tuned the torsion keys to get matching L/R ride height, about 36.5" without my ass in the truck.

(Side note: how do you even measure caster on these trucks? Since there's no strut tower to adjust at the top, wouldn't you have to essentially take the wheel off and measure the angle of the knuckle relative to the upper/lower control arm mounting points? Caster adjustment is done by making opposite adjustments go the front/rear upper control arm camber bolts if I understand correctly.)

Open to any dialogue. Some pics of the new suspension attached.

View attachment 435322View attachment 435323

Hello sir, welcome to the site. I think you would find this thread interesting and would like to have some of your thoughts added.

DIY Alignment 07 Tahoe 4WD

Moving all my R&D into this thread for my reference so its not skewed all over the GMT900 thread and anyone else that wants to follow along including the peanut gallery. I have been having issues getting the local shops to do an alignment on my truck because it is "modified" from stock which is...

www.tahoeyukonforum.com

 

[tom3]

Is this at the stock ride height? Lifted?

 

[89Suburban]

I see headers.

 

[B-train]

@squeeler642

I think you have an alignment issue. Tell the shop you want the specs in the middle of the range.......not just in the "Green is good" zone. I had a GM dealership do the last one on my 2017 and ended up wearing the front tires. Went to a private shop known for good work, told them WHAT I wanted, and it's been great ever since.

Caster helps steering feel and re-center. The more negative (like yours) it can feel twitchy and harder to control. Positive can feel more labored and less responsive, but wants to stay straight. Usually, a little positive is good. And staggering the LH vs RH will help with road crown on 2 lane roads.

Think of it like riding a chopper motorcycle with a long rake......positive caster. Then a unicycle.....neutral or negative caster........which one is more likely to be twitchy?

 

[squeeler642]

I see headers.

Hahaha. You caught me. Swapped a 6.0L crate motor (with a baby cam) last year. Thing PULLS on the highway and has a pretty rowdy idle w/the AC compressor off. Pretty fun for a daily.

Is this at the stock ride height? Lifted?

Bone stock suspension, pretty much factory ride height... not more than an inch higher than factory as the truck still has a rake. I think the factory torsion bar/key spec puts the top of the top of the fender well at ~36" from the ground, centered and straight over the hub. I know that isn't the best method for measurement, but it should be good enough to get me close. The front end measures 36" even on both sides with a half tank of gas. It has never been wrecked, and has never lived in the rust belt. The frame should be straight.

@squeeler642

I think you have an alignment issue. Tell the shop you want the specs in the middle of the range.......not just in the "Green is good" zone. I had a GM dealership do the last one on my 2017 and ended up wearing the front tires. Went to a private shop known for good work, told them WHAT I wanted, and it's been great ever since.

Caster helps steering feel and re-center. The more negative (like yours) it can feel twitchy and harder to control. Positive can feel more labored and less responsive, but wants to stay straight. Usually, a little positive is good. And staggering the LH vs RH will help with road crown on 2 lane roads.

Think of it like riding a chopper motorcycle with a long rake......positive caster. Then a unicycle.....neutral or negative caster........which one is more likely to be twitchy?

The chopper analogy rocks. This is EXACTLY what it feels like when I am driving it. It feels like the left/right wheels are fighting each other over bumps in the road... and I know toe can change as the suspension articulates. It just feels like the left and right sides are not in agreement about how to respond.

If I had to guess, I think one side is positive and the other is a little negative. Also I forgot to mention the truck pulls to the right if you let the wheel go. Even after the alignment.

So this begs the question... how do you do caster in the alignment? Does the shop have to remove the wheels and measure the knuckle angle relative to the ground? Or how does that work?

 

[89Suburban]

Hahaha. You caught me. Swapped a 6.0L crate motor (with a baby cam) last year. Thing PULLS on the highway and has a pretty rowdy idle w/the AC compressor off. Pretty fun for a daily.


Bone stock suspension, pretty much factory ride height... not more than an inch higher than factory as the truck still has a rake. I think the factory torsion bar/key spec puts the top of the top of the fender well at ~36" from the ground, centered and straight over the hub. I know that isn't the best method for measurement, but it should be good enough to get me close. The front end measures 36" even on both sides with a half tank of gas. It has never been wrecked, and has never lived in the rust belt. The frame should be straight.


The chopper analogy rocks. This is EXACTLY what it feels like when I am driving it. It feels like the left/right wheels are fighting each other over bumps in the road... and I know toe can change as the suspension articulates. It just feels like the left and right sides are not in agreement about how to respond.

If I had to guess, I think one side is positive and the other is a little negative. Also I forgot to mention the truck pulls to the right if you let the wheel go. Even after the alignment.

So this begs the question... how do you do caster in the alignment? Does the shop have to remove the wheels and measure the knuckle angle relative to the ground? Or how does that work?

It's all in the positioning of those upper control arm keys.

 

[OR VietVet]

For negative caster comparison, think of a shopping cart wheel and how it looks when you push forward. The right should have at least .3 degree more positive caster than the left, to allow for road crown and they both should be in the positive range. Why did you not change the sway bar frame bushings? Did you tighten all components while was suspended in air or after putting weight on ground?

 

[mattbta]

Did you fully remove the center link/relay rod/drag link when you did all the front end work?

 

[89Suburban]

Look what I did here. See how the rear of the arm is 1 notch/peg further in than the front? That's what gives me some positive caster. Once you have that dialed in you adjust them equally in or out to set your camber.

What did you do to your NNBS GMT900 Tahoe/Yukon Today?

Strut under arm flip with the GR9 hardware.

www.tahoeyukonforum.com

 

[Fless]

Did you fully remove the center link/relay rod/drag link when you did all the front end work?

Great question, and a common issue when re-assembling the center link is to mis-orient it.

Also, do the front jounce (bump) stops contact the lower control arms at ride height? If not, they should.

 

[Doubeleive]

probably your first answer was most likely, if the keys are not where they normally should be set it will not ride right period.
that is the primary problem with the gmt800's and handling issues.
once the keys are set stock then you can add some stiffer sway bars and tighten it up a bit

 

[squeeler642]

For negative caster comparison, think of a shopping cart wheel and how it looks when you push forward. The right should have at least .3 degree more positive caster than the left, to allow for road crown and they both should be in the positive range. Why did you not change the sway bar frame bushings? Did you tighten all components while was suspended in air or after putting weight on ground?

Good to note on the caster being slightly asymmetrical. Makes sense on road crown, etc.

Great question, and a common issue when re-assembling the center link is to mis-orient it.

Also, do the front jounce (bump) stops contact the lower control arms at ride height? If not, they should.

To address all the re-assembly related questions:
- I did a loose assembly of each side, put the torsion keys back in it, and then on each side used a jack to achieve the approximate hub position as it would be when loaded with the weight of the truck using the running board as a reference... likely got it to within ~1", measured it before disassembly with the wheels on. Then I tightened the UCA/LCA bolts. I only have one jack, so I left the sway bar links until the truck was back on the ground, which you want to do anyways.
- With the truck back at approx. factory ride height as I described using my approximate fender well measurement, the bump stops hover about 1/8" above the LCA contact point.
- I didn't ever have the drag link entirely removed from the truck. I did all the suspension stuff first, then went back in and replaced idler/pitman arms the next day. The drag link is in the same orientation it was originally.

 

[Fless]

If you're going to leave the keys cranked up, maybe you can find some longer jounce stops so they properly contact the lower control arms.

How about a couple of pics of the center link, from a few different views?

 

[nonickatall]

Side note: how do you even measure caster on these trucks?

You set the wheel upright and measure the angle to the ground, i.e. how the wheel stands in relation to the road. Then you turn the wheel 20 degrees outwards and measure the changed angle. The angle between the straight and 20° position is the caster.

But about your problem,. Have you adjusted the middle tie rod? I don't know if this works with our cars, but I know from BMW's, that if you replace or remove the middle tie rod, you have to adjust it by adjusting the height of the auxiliary steering lever.

The tie rod must be exactly parallel to the ground, because the angle between the tie rods and the wheel must be the same on both sides.

If these are unequal, the wheels steer differently when compressed and that can lead to your phenomenon...