Rear Axle Alignment? Cupping

[Jason N]

Sooooo, I now have close to 9000 miles on my suspension since I did it. King coil overs with rock jock links upper and lower in the rear and rock jock adjustable pan hard bar. Way more flex than stock. I will tell you that. The one thing I noticed when it was first done and I got the truck back from the shop is there is a hell of a lot of bump steer. I'm guessing cause the rock jock bar ends are non-forgiving and don't have any cushion or give like stock. AnyWho, fast-forward about 5 to 6000 miles and I did my first tire rotation after putting new 37s on it at the same time as the lift. Shop cannot balance the wheels properly. Took it to another shop. They had a hell of a time trying to balance the wheels. Turns out the one that was on the rear left is way out of whack and can't really be balanced and is cupping. The shop I had to work done at is a reputable 4X4 shop that knows what they're doing so I trust them that the work/alignment was done properly. Tires on the front are perfect no issues with wear on those. Would it be because I have so much bumps steer now it's causing the cupping on the rear left tire? Or would it just be bad alignment on the rear axle? Or both?

It's so significant that it really feels like riding a bronco. Every little bump in anything you hit the back end is zigzag and back-and-forth. Constantly feels like someone is smacking me in the back.

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[Brian_B]

I’ve heard of internal differential issues causing this

 

[F-Spot]

My rear differential caused cupping when it needed to be rebuilt. However, yours might be cupping from all the bouncing. Try a track bar relocation bracket to see if it helps the bump steer. You may need to get a new tire for that one that won’t balance…or just use that as a spare and just do 4 wheel rotations for this set of tires.

 

[F-Spot]

Also, have an alignment to check your thrust angle.

 

[Jason N]

My rear differential caused cupping when it needed to be rebuilt. However, yours might be cupping from all the bouncing. Try a track bar relocation bracket to see if it helps the bump steer. You may need to get a new tire for that one that won’t balance…or just use that as a spare and just do 4 wheel rotations for this set of tires.

I do have a track bar relocation bracket with the rock jock pan hard bar. It sits almost flat horizontal. Truck only has 18,000 miles on it so hopefully not needing a rear diff rebuild. Yeah, I was thinking it was probably due to the side to side motion in the rear and I am going to take it in for an alignment, but just thought I'd check here to see what other people's experiences are.

 

[F-Spot]

I do have a track bar relocation bracket with the rock jock pan hard bar. It sits almost flat horizontal. Truck only has 18,000 miles on it so hopefully not needing a rear diff rebuild. Yeah, I was thinking it was probably due to the side to side motion in the rear and I am going to take it in for an alignment, but just thought I'd check here to see what other people's experiences are.

Do you know if the preload is the same for both driver's and passenger's rear coilovers? Mine was sitting higher on the passenger side rear after installing Fox coilovers. I ended up adding preload to the driver's rear to equal out the rear height. I believe that threw off my thrust angle a little and it had some slight vibration when driving. I then adjusted both sides to have equal preload and it drives smooth now. I have now learned that preload should be be equal for both sides. Fronts and rears can be different, but side to side should be the same.

 

[telenerd]

Whatcha got for tires and any pictures of your alignment chart? Did they also adjust wheel set back and center the axle? What’s your pinion angle at?

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