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Rear axle "alignment" and rear tire wear

12K views 94 replies 10 participants last post by  pmou 
#1 ·
OK so, got something weird going on with the rear end.. gonna try to explain as best as possible (and please be patient with my ignorance, I have not owned a solid axle vehicle before):

currently, i have the JOR kit installed with new shackles and hangers. I verified today that they are all in the correct orientation.. I will take pics (see next post) for sanity but for this moment let's assume I am not a total space cadet. Also did leaf spring bushings at that time and new shocks. Left the stock leaf springs (hence bushings). This van was in a front PS accident that required a new front body panel and new PS door. Nothing past that that i could see in the immediate area when i bought it. There's definitely something minor in the front rad support & bumper is slightly tweaked (the actual bumper, not mounts, crumple zones, etc). Subframe looked untouched as well as all suspension parts so i thought good.

The van had some real old tires on it, fine with me i was going to put bigger ones anyway. I noticed right away that the rear DS rear tire had heavy camber wear on the outside knobs. figured the van had just never been aligned at all. Installed lift & 30.5x10.5 tires on new rims. When i went to install the shocks, i noticed that the mounts seemed to be off to the PS. Enough so that the DS one would have rubbed the mount if I didn't space it out to the PS at the top mount about 3/4".. which I did just to have the thing be driveable. Thought maybe it had just been sitting and a quick drive around the block everything settles in and we are good. Well, it's still off. The tires are also noticeably sitting in different spots relative to the wheel wells, off to the PS. I did about 900 mi of driving on it over the weekend, was planning to get an alignment after that. Even just in that short amount of time the outside knobs on that driver side tire are wayy worn, like noticeably so and have lost some minor details that no other tire or part of a tire is showing.

Called firestone as that's where I'd usually get an alignment. They said there's no adjustments to be made there, and they will need to do a full inspection before the alignment to figure out what is bent or otherwise off.

Called a shop I usually use for diff and transmission work, they said this wouldn't be anything internal to the axle which is about where they stop. He suggested bent leafs.

Anyone else want to throw something out there? It'll be going to firestone on monday as that's the soonest i could get it over there, but I'd like to have a little better understanding as to what is going on before I hand it off to them.
 
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#2 ·
Also just want to mention that the "camber wear" was _definitely_ there before the lift, tires, wheels. Off center, I am unsure but it would seem to make sense in my head that it was as well.
 

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#3 ·
My only guess is that you swapped one side's leaf spring end to end.

The springs are not centered on the axle, they have a long and a short side. I don't remember which should be where, but you can still go look.
 
#4 ·
dcsleeper said:
My only guess is that you swapped one side's leaf spring end to end.

The springs are not centered on the axle, they have a long and a short side. I don't remember which should be where, but you can still go look.
This is possible, however it would not have been me as I didn't remove the leafs from the axle (nor loosen them, or anything of that nature). They are sitting relatively centered fore-aft in the wheel wells with the shackles so I am hesitant to think that is it. Is there any obvious identifying features other than length that would indicate orientation?
 
#6 ·
how about jacking up the rear on the body so the drivetrain is free and giving everything a good hands on shake and see if anything's loose. worn wheel bearings?
 
#7 ·
MiniAlt said:
how about jacking up the rear on the body so the drivetrain is free and giving everything a good hands on shake and see if anything's loose. worn wheel bearings?
So, i just did that as you suggested (i believe) -- both wheels can move laterally (axle in/ out of housing) slightly when in the air. I did one wheel at a time, and they both would turn both directions with some resistance, no grinding or noise. I figured the resistance is the mechanical disadvantage on the driveshaft / neutral gear?

When attempting to push / wiggle fore/aft (relative to the vehicle ie fore = towards driver seat) i got nothing, no movement. felt rock solid.

Vertical, i got a slight clunk on both wheels. A little hard to be certain it wasn't the lateral movement/ clunk i described in the first step there. I did my best to put all my weight into the top of the wheel during this, and then lifted the bottom of the wheel using my knee (so as to avoid pulling the wheel in/out) and i got a small clunk / movement.

Could this be bad wheel bearings? and if so, wouldn't that mean the wheels would be more likely to "sag" ie inside edge wear?
 
#8 ·
took the wheels off to look around and play with the axle. didn't really see anything glaring. I thought the leaf spring "center pins" might be bent, but I checked my housemates astro and his also appear to be not centered in the hole in the clamshell.

tool a couple pics of the lateral slop I described. I'm assuming this is not an issue? it's gotta be less than 1-2mm

PXL_20201104_231716247.jpg


PXL_20201104_231720072.jpg
 
#10 ·
That DS leaf does look weird.... If you have new hangers and shackles, it seems like the leafs and clamshells are the most likely thing that is wrong imo

Unless the whole axle assembly is bent or something, but that seems unlikely as all get out.
 
#11 ·
yeah.. that's what it's coming down to in my head. I'm comparing wheels to wheel well, and it doesn't change by rotation so that rules out hub/wheel/inner axle. shackles and hanger are brand new (and didn't get dinged). could be off, but the tire wear was present before the new parts. that leaves leaf springs (or possibly sleeves/bushings.. but those are new as well.. and should just center under the weight I'd think), where the leaf springs attach to the axle, or the axle housing. the shock mounts being off tells me that it's likely that the axle is ok, and whatever is positioning the axle relative to the body is the problem? which would put us at the mount that is welded onto the axle/clamshell/leaf springs...
 
#12 ·
however, would that explain the tire wear? is there some way that the leafs could be bent that would explain the weird pressure on the outside of the tire?

edit: I suppose this could be explained by "dog leg" ie the rear is not square to the front so when I'm driving straight I'm actually driving like 2deg to one side or another, and this is what is causing that weird wear.. not actual camber
 
#13 ·
ok also found this interesting:

https://www.knowyourparts.com/technical ... tire-wear/

they mention the thrust and setback angles.. which is more or less what I was describing. if the back isn't square to the front, it essentially is driving force against the front wheels and will cause excessive wear on the back tires, almost like toe in or out. My guess is that's what is going on. anyhow, I think this will all be more clear once firestone shoots a bunch of lasers at my car to measure stuff, I think that may be the best way to figure out what the hell is off.

edit: another good one - http://prod.lv2014.gener8cms.net/index. ... k-tracking
 
#14 ·
Note sure if this should be considered relevant.. since my rear issues were lift related.
My problem however did not cause unusual tire wear either.

I found my axle/springs were moving within the clamshell.
(it finally explained why I kept seeing different driveshaft-yoke engagement measurements)
They weren't always moved evenly or the same distance either.

I finally resolved "my" rear-end shifting by not only clamping the clamshells tighter (which distorts them if using lift blocks)... but I also added a wide-centering pin (not sure what to call it) to prevent the rear from being able to move withing the clamshell. I used literally a "socket" that fit the opening. It worked perfectly for me... no more movement.



Recently (while doing pinion shims with axle loose) I did some numerous and careful measurements (to various different frame points) to ensure the rear was tracking square. I found it still off a little and (in my case) attributed it to axle positioning under tall lift blocks. In my case.. I applied a little "DIY rear axle alignment".. pulling on the rear before positioning lift block and tightening it all up. Seems to have worked for me as well...



Understand that most of my issues were due to lift modifications and the vehicle no longer being stock.
Here's my post about the pinion shims...
https://www.astrosafari.com/viewtopic.p ... s#p1563390
 
#15 ·
Mmusicman said:
I found my axle/springs were moving within the clamshell.
Seems somewhat common, u-bolts and plates are a nice upgrade IMO.
 
#16 ·
Before getting carried away,take it to a good quality 4 wheel alignment shop.When an alignment is done,you can usually accomplish an acceptable "thrust" measurement,because the machine accounts for this while adjusting the front end,and if still out,most will try to shift the rear,as music has done.This is why we see very little "dog tracking" like the old 2 wheel alignment days.Also,if your suspension is "wacky" in a vertical plane,there will be no unusual tire wear from alignment,just the body would be "wacky".These small rear diffs are known for bending the axle tubes,up,down and front to rear,if smaller,an good alignment can make tire wear acceptable.Also,I have,over the years,seen what people assume is camber wear is actually from high speed long sweeping turns.Guilty of that myself.
 
#17 ·
Wow thanks for the detailed input mmusicman and mechbob. After seeing what you did there music, I'm thinking it may make sense (as bob said) to take this to a 4wd shop that won't just immediately blame the non stock parts (idk if firestone would do this, but it would make sense to me). I'm impressed by your resourcefulness music, but given how badly this is wearing the tires (and rubbing) i think i'd prefer to just hand it off to the pros and get it all looking good. I'm going to check today and see if there's a 4wd place in town that could take a look at it.
 
#18 ·
OK, i talked to Spruce 4x4 in boulder. they said i can stop in and take a look at it on the lift once they have measurements. Their opinion was if the back is off, it means that the center pins on the leaf(s) are bent, the axle is bent, or the body is bent (hopefully not that). They said if it's the body they would send me to a body shop to put it on a frame rack. It'll be there on wednesday.. see what we find out then.
 
#20 ·
yeah, the fact that it has been in an accident has me concerned.. and the fact that the tire wear happened in a really short amount of time. I think in this case I'll take the peace of mind for $100. also seems like a cool shop so I can see what they think and likely have them give it a look over.
 
#21 ·
haha so funny coincidence @Mmusicman in my deep search to figure out what the heck is going on i found another thread where you offered similar suggestions (and showed your alignment process).. maybe that is what just needs to happen.

The pros have said the alignment is spot on. And the mechanic was wracking his brain as to why the tire would have worn like that. I have 30.5x10.5 tires on stock rims at about 35psi (actually this was the shop that mounted them, so perhaps i should double check). Here's the alignment report, they said ignore the after as he had already messed with the alignment markers on the wheels (they were part way removed). He put it on the rack, measured, made sure all was tight, tried to figure out why that tire would wear like that, and then took it off the rack. They made no adjustments as everything was within acceptable range.

PXL_20201112_184012373.jpg


i am thoroughly confused, especially as the old tire wore in the same way. I guess the obvious answer is "nothing is wrong" however i got these current tires for real cheap, with the idea that i would do some trimming, etc and then figure out actual tires in a few months. I'm not overly concerned with how these wear, but before the next batch i really don't want to have this happening as this will seriously shorten the life of my tires.
 
#22 ·
pmou said:
The pros have said the alignment is spot on.
No, he said it was within acceptable range.
pmou said:
i am thoroughly confused,
How can you be confused? It needs an alignment. (somewhere else)
pmou said:
I guess the obvious answer is "nothing is wrong"
Nope. Not wearing the same way on two different set of tires.
signed
Sum Ting Wong
 
#23 ·
Haha thanks for stepping in as the voice of my subconscious --

I understand what you are saying -- it needs an alignment somewhere, however if all 4 wheels relative to each other is fine, then shouldn't it not even matter what else is out of line? Maybe the body would be travelling down the highway askew, but as far as the wheels are concerned that's irrelevant as long as these numbers make sense?

If this wear was happening while in some other part of the suspension travel, i could see this being true.. however that seems nearly impossible given the ratio of highway vs other miles on this trip (i'm implying that highway driving represents what they see on the alignment rack).

so i guess, if the wheels are all happy when in "rack position" then the only hypothesis I could offer is this:

Something in the suspension is not square.. let's say leafs as an easy discussion point (and i think probably the most likely culprit?). They are aligned correctly now, however once they start to travel within the suspension, they travel in a non-square direction. On the highway this could possibly happen from repeated high speed long turns (plenty of those on i70) and lead to strange contact patches on the tires leading to wear.

However, this still doesn't seem like a great explanation to me as that seems unlikely to cause a lot of suspension compression in the rear.. wouldn't that mostly be the front tires for high speed cornering? That, or the tire folds or otherwise some part of the suspension moves laterally when turning.. however if I am to trust the shop this wouldn't be happening.

edit: and yes, you are correct it's not spot on. But from these numbers it doesn't seem "wear tires weird within 1000mi" off.
 
#24 ·
Could this represent an issue with braking or power distribution? IE dragging park brake, somehow braking or drive power bias to this side in the rear axle, etc? Only other thought is that it rubs something somehow at some point... but seems unlikely given that the old tires were much smaller and had the same problem pre-lift.
 
#25 ·
pmou said:
Something in the suspension is not square.. let's say leafs as an easy discussion point (and i think probably the most likely culprit?). They are aligned correctly now, however once they start to travel within the suspension, they travel in a non-square direction..
You may have missed my point in my previous post.
I suggested that you "might" have suspension movement.... LIKE I DID.
I was actually able to put a tie-down strap on the rear, crank it, and see it move.

I literally found my springs MOVING within my clam-shells. Sometimes when I stopped hard.. they would shift rearward. When I accelerated it would move forward. Sometimes it was right... sometimes it was not.

I don't know if this is true in your case.
I also don't know if this type movement could cause tire issues.

Typically, the Astro rear has NO alignment that a shop is supposed to be able to adjust.
There simply are NO adjusters.

You photo (based on caked on dirt) doesn't necessarily indicate movement.
But shouldn't pins be centered and identical?
I would think as long as both sides are the same (and there's no movement).. then this wouldn't likely be much of an issue.



This may NOT be your issue whatsoever.. just something to possibly look at.

I also know for FACT that rear axles can and do bend over time.
Put a level on the rear wheels and see if they have zero camber.
Tops usually lean in slightly (from differential sag).
I've found this to typically cause inside wear on tires, not cupping.
But rear axles might bend in other directions too.
4x4 guys and racers often strengthen where the tubes meet the differential.

Note for reference: the rear wide-tracking wheelbase (spacing between rear tires) is DIFFERENT than the fronts.
Each rear tire should point to same spot on front tires (if square)

Wanna see something crazy?

Note: My following example is due to improper mismatch of lift blocks used with clamshells (I didn't do it).
In this case, the clamshells bend, and cause nuts and u-bolds to not be able to tighten down sufficiently.
This in turn allows the clamshell to slide forward and back on the spring (until the center pin stops it)
No way to assure BOTH sides moved same amount either.
That would depend on how much lateral force each side sees.

I would think this shouldn't be the case with the stock setup.. but who knows.
The tall lift-blocks in my case created different stresses.

Observe in this video while I'm pulling forward... my rear axles are shifted WAY forward (almost touching fender)
Toward end, when I let off the gas, the entire rear quickly snaps rearward.
This video is what caused me to discover the problem.

I never noticed any tire wear issues however.. but I wasn't watching that closely.
I also suspect both sides (in my case) were probably more than likely moving the same distance.
But possibly not always...

Again, this was an issue that affected me.. not necessarily your issue, but maybe worth considering.
I have also since resolved this problem (go back and see my original post pg.1) ...



Something certainly is off. I guess the pros that work the alignment machine couldn't figure it out.
But these types are not always smart enough to think outside the box either.
 
#26 ·
Ahhhh thanks for the clarification mmusicman. sounds like i gotta get this guy in the air at some point soon and yank stuff around. The high lift jack is turning out to pay for itself sooner than i anticipated...

I also have a 24" engineers ruler thats accurate to some number of thousands so I should be able to see if there's an obvious bend in the axle somewhere
 
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