Unibody Twisted

[Xjman1]

A friend just installed a 3" lift and when he took it to get aligned they informed him his rear axle was crooked. The right side was at .04 and the left side was at .44. I measured from the front LCA bucket to the front leaf spring bucket and it seemed off by approx. .25". How can this be fixed? Can it be fixed cheaply?

He has been experiencing tire wear and this is more than likely the cause. Also did not notice any body damage under it so it does not look like it was in an accident.

Thanks and look forward to some insight from the pros.

 

[Eagle]

What do the .04 and .44 measurements refer to? You don't even tell us if that's inches, degrees, or radians.

If that's camber, if the axle were straight the camber should be the same on both sides. If it's not, that means the axle is bent, not that the unibody is twisted.

If those numbers don't refer to camber, tell us what they are.

 

[Xjman1]

What do the .04 and .44 measurements refer to? You don't even tell us if that's inches, degrees, or radians.

If that's camber, if the axle were straight the camber should be the same on both sides. If it's not, that means the axle is bent, not that the unibody is twisted.

If those numbers don't refer to camber, tell us what they are.

Rear axle thrust,

Toe left = -.40* and the right is .69*
Camber left = .4* and the right is -.6*


Hope this helps.

 

[Eagle]

Rear axle thrust,

Toe left = -.40* and the right is .69*
Camber left = .4* and the right is -.6*


Hope this helps.

I'm not an alignment guy, so maybe someone who is can explain ... what the f*** is "rear axle thrust"?

The rear axle in an XJ is called a "solid" axle for a good reason -- everything is pressed and welded together into a one-piece assembly that runs the full width of the vehicle. If the axle is straight, the two rear wheels MUST be parallel to each other. The axle can be installed at an angle to the chassis, but if that's the case a negative number on one side should be matched by a positive number of equal magnitude on the other side.

The numbers you're showing tell me that the axle is bent.

 

[Xjman1]

what the f*** is "rear axle thrust"?

The rear axle in an XJ is called a "solid" axle for a good reason -- everything is pressed and welded together into a one-piece assembly that runs the full width of the vehicle. If the axle is straight, the two rear wheels MUST be parallel to each other. The axle can be installed at an angle to the chassis, but if that's the case a negative number on one side should be matched by a positive number of equal magnitude on the other side.

The numbers you're showing tell me that the axle is bent.

Funny, you just about said what I said, so I guess I am still sane :clap: I did not notice any twisting of the tubes or anything but need to take it off and square it up to see if it is bent. Thanks for the confirmation of my first guess.

 

[pfogle]

Rear Axle thrust, is the direction that the rear axle will want to drive the vehicle.

Example, if the rear axle is off center slightly, so that the left wheel is slightly behind the right wheel, the thrust will want to move the vehicle to the left... and you'll have to slightly turn right to counteract it.

At extreme differences, this can cause what looks like crabwalking..

 

[bryanv]

thrust angle is the toe on the rear wheels. they will push your car in one direction or the other depending on how sever it is. there is no adjustment for this on xjs. you could have a number of problems measure from your leaf spring mount to the shock mount of each side of the xj they should be the same if they arent your leaf spring brackets could be twist or your leaf springs may be bad. if the lenght is the same from your leaf spring mount to the shock mount then it could be as little as a bent wheel or your housing flanges could be bent. do some investiating. ask the alignment shop if they have equipment to do a true-trac(applys to hunter alignment and wheel balancing equipment) with your wheels.

 

[8Mud]

Not with the XJ, but some other trucks. I learned to do the final tightening and torque, with the vehicle on the ground. Have had urethane bushings, shackles and other parts, load up in strange ways, when tightening everything in the air. Some driveing around and some good bounces, will usually work out the kinks.
A fairly level concrete pad and a plum bob, a piece of chalk, some crawling around and a few X´s on the ground, can tell a great deal about a vehicle that has suffered a major collision.
May sound silly, but have noticed many springs are unequal from center to end, can´t really remeber if XJ´s are this way or not. Would it be possible to have one spring in backwords?

 

[Xjman1]

Not with the XJ, but some other trucks. I learned to do the final tightening and torque, with the vehicle on the ground. Have had urethane bushings, shackles and other parts, load up in strange ways, when tightening everything in the air. Some driveing around and some good bounces, will usually work out the kinks.
A fairly level concrete pad and a plum bob, a piece of chalk, some crawling around and a few X´s on the ground, can tell a great deal about a vehicle that has suffered a major collision.
May sound silly, but have noticed many springs are unequal from center to end, can´t really remeber if XJ´s are this way or not. Would it be possible to have one spring in backwords?

We measured the springs as I thought one may have been in backwards as well. All measurements were ok. The only measurement that was off was from the front LCA Buckets to the rear leafs front mountbucket by about 1/4".

 

[8Mud]

When messing with ladder frames, I usually measure in an X, from the front spring bracket (might work out the same at the control arm bracket), to the opposite side rear spring bracket (might have to use a plum bob to clear the undercarriage). Tell you pretty quick how far out of wack the frame is, usual allowable tolerance in most vehicles, is around an eight of an inch. Same check should work for the unibody also. Most of my frame and alignment checks are of the crash and burn variety and not with laser alignment machines.
If the frame checks out, the same technique to the spring pad bolts, should tell you if it´s the diff or the frame. Measuring in a straight line can be deceiving on occasion. Amazing the difference in true wheelbase, in XJ´s on occasion. Wouldn´t count on mounting brackets (LCA), to be perfectly spaced. Multiple measurements from various hard points, might be a better indicator.
Hope the spring, alignment pin holes, are drilled correctly.
Had an old Dodge that was 2 inches out of parallel, I drove it for years. It would track straight, but the rears followed the fronts 2 inches to the right.
Wouldn´t get real excited about perfect meausrements on an alignment machine. Have had some hard used 4X work trucks that were pretty bent, that could be driven at 80 MPH with one fingure on the steering wheel, with acceptable tire wear.
Measuring from the inside rear rim, front side and rear side, left to right, could be an indicator of a bent axle tube (or rim). Most bent axle tubes I´ve seen are bent up, kind of a smile. If they are bent front to rear, usually a rim or shock mount was involved and leaves some sign.
Did you have shims with the kit? Was a shim installed backwords?
Interesting problem :huh:

 

[Xjman1]

When messing with ladder frames, I usually measure in an X, from the front spring bracket (might work out the same at the control arm bracket), to the opposite side rear spring bracket (might have to use a plum bob to clear the undercarriage). Tell you pretty quick how far out of wack the frame is, usual allowable tolerance in most vehicles, is around an eight of an inch. Same check should work for the unibody also. Most of my frame and alignment checks are of the crash and burn variety and not with laser alignment machines.
If the frame checks out, the same technique to the spring pad bolts, should tell you if it´s the diff or the frame. Measuring in a straight line can be deceiving on occasion. Amazing the difference in true wheelbase, in XJ´s on occasion. Wouldn´t count on mounting brackets (LCA), to be perfectly spaced. Multiple measurements from various hard points, might be a better indicator.
Hope the spring, alignment pin holes, are drilled correctly.
Had an old Dodge that was 2 inches out of parallel, I drove it for years. It would track straight, but the rears followed the fronts 2 inches to the right.
Wouldn´t get real excited about perfect meausrements on an alignment machine. Have had some hard used 4X work trucks that were pretty bent, that could be driven at 80 MPH with one fingure on the steering wheel, with acceptable tire wear.
Measuring from the inside rear rim, front side and rear side, left to right, could be an indicator of a bent axle tube (or rim). Most bent axle tubes I´ve seen are bent up, kind of a smile. If they are bent front to rear, usually a rim or shock mount was involved and leaves some sign.
Did you have shims with the kit? Was a shim installed backwords?
Interesting problem :huh:

Nope, no shims installed, yet. Have not gotten in to multiple measurements yet as time has not allowed, but thanks for some new points of reference for us. Axle "looks" straight but that will be my first check. It does not ride wierd according to him, but he says his tire wear is BAD on the right side and we just need to make sure it is not something that will make him "That XJ" on the trail.