Wheelbase adjustment issue

[tantotrailers]

I’m installing some upgrades and I was having some clearance issues when at the suspension limits so I did some measuring and my driver side wheelbase is off from 101.4” by about a half inch and the passenger is off by a full 1.5”! I have CavFab adjustable upper and lower short control arms and they are supposed to cover 0-6” of lift. I am on a 3.5” lift so within the range….but I just can’t see how these can have that much adjustment. From my research I need to have 1.5x the diameter of the threaded rod inside the end of the control arm, which brings me to about 1.3” threaded in, which is what the picture shows on the heim, that is pretty much where I had them set when I started…I did order some alignment shoe shims to push that forward at the lower body bracket, if the nuts turn…but that will only get me a little over a quarter inch forward.

 

[RCP Phx]

How are you getting your measurements?

 

[tantotrailers]

How are you getting your measurements?

String and marker on my garage floor with a tape measure. Going from the center of rear wheel to center of front wheel.

 

[tantotrailers]

Photos that didn’t post with my original post.

 

[Phil]

For clarity, is your wheelbase short or long? Or one of each?

 

[tantotrailers]

For clarity, is your wheelbase short or long? Or one of each?

Short on both sides, I’m at 100” on the passenger side and 101” on driver side.

 

[RCP Phx]

It would measure short with lift.......but you may also have a skewed rear axle so I would not count on your measurements.

 

[tantotrailers]

It would measure short with lift.......but you may also have a skewed rear axle so I would not count on your measurements.

My rear axle is square, measured it at multiple points to the body and passenger and driver side are perfectly square, same measurements all around. Adjustable control arms should allow the necessary adjustment to counter the lift.

 

[maxbraketorque]

Short on both sides, I’m at 100” on the passenger side and 101” on driver side.

That's a huge difference. If its real, your XJ is either going to pull really badly to one side or its going to drive sideways down the road.

I'm not sure why you can't discern the source of the WB difference. You checked that the rear axle is square to the body. How about the front axle? Do you have both axles level? The wheel mounting surface sits well beyond the knuckle rotation centerline, so the knuckles need to be turned perfectly forward for an accurate measurement. Also, has the lower arm mounting bracket at the unibody been replaced or modified?

But that aside, as RCP Phx said, the wheelbase is going to be less than stock if its a 3.5" lift with the arms are set to stock length.

 

[tantotrailers]

That's a huge difference. If its real, your XJ is either going to pull really badly to one side or its going to drive sideways down the road.

I'm not sure why you can't discern the source of the WB difference. You checked that the rear axle is square to the body. How about the front axle? Do you have both axles level? The wheel mounting surface sits well beyond the knuckle rotation centerline, so the knuckles need to be turned perfectly forward for an accurate measurement. Also, has the lower arm mounting bracket at the unibody been replaced or modified?

But that aside, as RCP Phx said, the wheelbase is going to be less than stock if its a 3.5" lift with the arms are set to stock length.

I'm stumped myself! I checked my rear axle, multiple places from body to axle on passenger and driver and everything measures the same in the rear. My adjustable CAs are at max length on the lowers and I'm still just over 100" on the passenger side. I'm waiting for some shoe shims to adjust the alignment shoes forward but I'm running out of options...longer magnum heims maybe...my control arm mounting brackets are stock and not modified or replaced, also look undamaged/untweaked

 

[Phil]

What is the center to center length on the arm as installed on each side?

 

[tantotrailers]

What is the center to center length on the arm as installed on each side?

Passenger LCA is 16.5"
Passenger UCA is 15.5"
Driver LCA is 16.25"
Friver UCA is 15.25"

 

[maxbraketorque]

You're missing something somewhere. Is this being done with the wheels on the ground and vehicle supported by suspension?

 

[Root Moose]

Are the rear springs compressed the same amount side to side? Is the shackle angle the same on both sides? You say the axle is square with the body but is that longitudinally or transversely?

Being close the vehicle can make it easy to miss something obvious - step back a few dozen feet and look at it (roll it outside of it's in a garage).

 

[tantotrailers]

You're missing something somewhere. Is this being done with the wheels on the ground and vehicle supported by suspension?

Yes wheels on the ground on its own weight.

 

[tantotrailers]

Are the rear springs compressed the same amount side to side? Is the shackle angle the same on both sides? You say the axle is square with the body but is that longitudinally or transversely?

Being close the vehicle can make it easy to miss something obvious - step back a few dozen feet and look at it (roll it outside of it's in a garage).

Rear springs are compressed the same side to side
Rear shackle angles are the same
Rear axle is square to the body both longitudinally and transversely

I will roll it outside soon it’s been in the garage but I’m starting to pull my hair out because I’m running out of excuses here…

I measured from the rear axle on both sides to the body, same distance, I measure the unibody rails between front leaf bolt and body lower control arm mount, same distance, and my passenger control arms are slid forward as far as they will go in the alignment shoe plus they are about an inch longer than driver. I did a simple measurement from the corner of the body to the front tire and my passenger side is 1/2” farther forward than my driver…..yet after all this the wheelbase is 101” on the driver side and now 100.5” on passenger.

 

[Phil]

You wrote before that you are measuring on the floor, with strings. What are your reference points on the tires, hubs, or axles?

 

[tantotrailers]

You wrote before that you are measuring on the floor, with strings. What are your reference points on the tires, hubs, or axles?

I’m using a plumb bob which is where the string comes in, going from center of the wheel center cap to the ground making a mark, same on the front with wheels straight forward and then measuring between marks. I’m on a level floor in my garage with a clean slab.

 

[Phil]

Have you checked with a non-movable point like the center of the lower ball joint, to eliminate any variation caused by the wheels being less than straight? It will not be the same 101.3” nominal factory wheelbase but it would be consistent.

 

[maxbraketorque]

Have you checked with a non-movable point like the center of the lower ball joint, to eliminate any variation caused by the wheels being less than straight? It will not be the same 101.3” nominal factory wheelbase but it would be consistent.

Yeah, I agree that the WB measurement should be made from fixed parts. For the front axle, I measure at the bolt that secures the lower arm mounts to the axle.