The dreaded right pull!

[LostWoods]

I understand that it's a solid axle, but you also have a little give in the control arm bushings.

After installing my Clayton lift I ended up with a caster split, 5.4 on the lift and 5.8 on the right. It pulled to the left as well. I was able to shorten the left upper control arm one turn to get to 5.8 degrees on both sides. Loosening the control arms helps. It drives straight as an arrow now.

Give doesn't matter - you aren't changing actual caster. If there was a difference it wasn't because you twisted one end of the axle and not the other. It's not the control arm length that does it, it's how the line drawn through the king pins or in our case, the ball joints compares to perfectly vertical. You can pull or push all you want, you can't change the angle of the line through the ball joints on one end and not the other. And compressing bushings is a bad thing, not a good thing. Loosening control arms? Hope you don't mean as in loosening the bolts that hold the control arms to the frame brackets or the axle brackets.
Caster is set by turning the axle, rotating the top of the axle tube either forward for less caster, or rearward for more caster. you can't possibly change one side and not the other. Physically not possible
Bushings being compressed won't matter because all you are doing is compressing bushings!
If you try to pull back on the top of one side of the axle, the other side follows and compresses the bushings but the caster split cannot be changed. There's hundreds of posts out there on that fact.
Most likely what you have done is pulled one side or end of the axle back or forward a bit and not factually changed caster because again, you cannot.
It is truly as basic as the dowel explanation - ALL you can do is move the entire axle back or forward on one end, you can't possible twist one side forward or backward and not do the same on the other end.
I've also seen many posts over the years where shops check caster - then a different shop checks caster - and the measurements are different although nothing was done to change caster, only toe, etc. - meaning you could measure it 3 times and get 3 different numbers.
You didn't change caster split is the bottom line because it's impossible. Go out and check.
(I've done alignments on vehicles since the 70s)

I too did more alignment work than I'd like to admit, and you can actually get caster out of a solid axle beacuse it's not a perfectly rigid system. As was said, those bushings have give, and that give means the arms are not a fixed length. It may only be an 1/8" but you can in fact force caster out of a solid axle with a large enough prybar to force a too-short or too long arm into position.

But that said, preloading like that is super bad for longevity and you're not getting any meaningful numbers out of it... maybe 1-2 tenths at best. Anything more than that and you're likely just seeing measurement variance.

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[ShadowsPapa]

So you are saying that by pushing harder, you are actually twisting one end of the axle and not the other. Bushing compression doesn't count because that's just a flattened bushing. You can take one end of a pipe and rotate it and not the other is what's being said. (even though all other sources say it can't be done)
The entire end of the axle is being shoved ahead.
Lay an axle assembly on the floor. Now take one end and rotate it - which is what caster is, and do so without moving the other end at all.

Great trick - being able to twist the axle tube on one side and not the other to tip the upper ball joint forward or backward and not effect the other end of a solid piece of steel.

 

[LostWoods]

So you are saying that by pushing harder, you are actually twisting one end of the axle and not the other. Bushing compression doesn't count because that's just a flattened bushing. You can take one end of a pipe and rotate it and not the other is what's being said. (even though all other sources say it can't be done)
The entire end of the axle is being shoved ahead.
Lay an axle assembly on the floor. Now take one end and rotate it - which is what caster is, and do so without moving the other end at all.

Great trick - being able to twist the axle tube on one side and not the other to tip the upper ball joint forward or backward and not effect the other end of a solid piece of steel.

I know it sounds batshit crazy and I'm being entirely pedantic but caster isn't measured relative to the axle, it's measured parallel to the centerline of the vehicle. When you do as I'm describing you aren't just rotating the axle along its' length, you're also shifting it in space which is changing both sides' caster, camber, and steer-ahead by adding stress on one arm. Stressing one joint stresses all joints but because the suspension isn't perfectly square, the way the angles change isn't a perfect 1:1.

It's a completely meaningless effort that fixes absolutely nothing but shutting up crotchety customers by making the numbers pretty. I just found that acknowledging that it's not a perfect system and that bushings have play that allows for that adjustment as a baseline was the best way to talk these customers off the ledge. Once you set that baseline and explain how it's preloading the suspension they tended to back off and realize how bad an idea it was.

 

[Pescado]

I fixed my pull and wondering! I posted about it here

Link to thread

 

[Maximus Gladius]

So OP, I’ve read a LOT of technical, and thank GOD for all the technical physics and mechanical types. But what I haven’t read yet is anybody asking, what are the psi readings on both front tires?

They are the same? This, I’m getting a sense, from these pages, may take a while to figure out so what I would do to just suggest some driving relief while you figure things out, I would correct the “pull to the left” by inflating the left tire a couple lbs and deflating the right tire a couple lbs and see what happens. (I’m no steering suspension expert but it’s worked for me in the past)

 

[Pescado]

That sounds like a band aid for the issue and not an actual fix. The more adjustability in your suspension allows you to dial in the correct alignment to compensate for whatever lift or wheels you have aded to your truck.

 

[ShadowsPapa]

I have to sort of smile and chuckle to myself as most of the online experts have never even worked in a shop doing alignments.
Very few in any forum have ever taken months of training or worked for years doing alignments and dealing with all possible combinations of things and yet............

 

[Maximus Gladius]

That sounds like a band aid for the issue and not an actual fix. The more adjustability in your suspension allows you to dial in the correct alignment to compensate for whatever lift or wheels you have aded to your truck.

Yes, it’s just a band aid temp fix.

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