Rear axle "alignment" and rear tire wear

[pmou]

Well, went out to the driveway with a plumb bob, chalk, and measuring tape this morning. I would say the results are inconclusive.. I have a mostly level driveway (not perfect poured concrete). Its made of a few different concrete slabs that aren't necessarily all on the same plane, so I have to assume some margin of error (its 2deg off level approx at at least one spot) so I figured about 1-2% error in measurements, accounting for the driveway and the fact that this was done by a grown man playing with chalk in the driveway.

Within that margin, I actually measured nothing off. Some things differed side to side within that margin, but nothing glaring. measured all subframe points relative to each other, leaf attachment f/r, and leaf mount point on axle. figured that mount point on the axle to the subframe points would be the obvious one, and some longer distances so errors would be more obvious. I found a place that says they will take a look / have a frame rack that they can put the vehicle on, will have it over there wednesday.

I think measuring in this way is a bit of a fools errand.. maybe if you had a poured concrete surface and the level of damage was going to be very high you could come up with something.

[Mmusicman]

here's the center pins

After 4 pages.. you may just want to go back to page one.
Why are these center pins not centered?
Mine are (at least they are now)
(I don't think ANY of this has anything to do with a crooked frame.. were you in an accident?)
Again, are they moving?
Seriously, this shouldn't be rocket science to measure the rear in relation to some fixed points.

[pmou]

they aren't moving. mechanic that did the alignment agreed they are not moving from his assessment. I looked at 2 other astro/safaris that are at my house, neither had the pins centered. also measured from the leaf attachment point on the axle to all 3 subframe bolts on the opposite side (via my driveway method) and they were within 2% of each other. i think the longest span was approaching 200cm, so within 2cm of each other on that measurement. same for leaf attachment point on axle to front spring hanger bolt head on opposite side. also measured distances of the clamshells on the leafs (think that's back a page) and got not appreciable difference (I think they were < .5cm difference unweighted). I'm done with tape measures at this point, going to leave it to the computers.

edit: also, as both those photos were taken from the outside of the van, they are both shift in the same direction although the photos show they are opposite

last edit: yes, the van had a front passenger collision before I purchased it that resulted in front fender panel and passenger door being replaced, that's all I know

[pmou]

either my methods aren't accurate enough or there's not an issue with the frame. unfortunately I think due to the variables with the first assumption, it can't be eliminated. the fact remains it's still wearing that tire. I'd like the peace of mind knowing that it's square following that accident (I think was about 4 years ago now). if that comes back fine only thing left is the leafs. I'd rather not remove the leafs before having someone measure things, as I'd like the van as close to the condition that is causing the issue as possible when the professionals look at it.

[dcsleeper]

To get a quick assessment of this situation:
go buy some kind of laser.
From a novel pointer to a level spinning laser, anything.
Sight down the edge of the rear tires on both sides.
see if/where the beam hits the front tires.
percentages are masking your results. a 2 cm difference is rather large, even though you distilled it to 2%. don't do that. deal in absolutes.

[dcsleeper]

To get a quick assessment of this situation:
go buy some kind of laser.
From a novel pointer to a level spinning laser, anything.
Sight down the edge of the rear tires on both sides.
see if/where the beam hits the front tires.
percentages are masking your results. a 2 cm difference is rather large, even though you distilled it to 2%. don't do that. deal in absolutes.

[Mmusicman]

Either the rear-end is crooked (or bent).. or it's not.
There is NO alignment.
It should be measurable if it's bad enough to wear tires.
If it's positioned crooked... straighten it.
If it's bent... replace it.

[WoodButcher]

Your thinking too hard, it makes no difference what the other astro in the yard look like.

Either the rear-end is crooked (or bent).. or it's not.
There is NO alignment.
It should be measurable if it's bad enough to wear tires.
If it's positioned crooked... straighten it.
If it's bent... replace it.

[pmou]

To get a quick assessment of this situation:
go buy some kind of laser.
From a novel pointer to a level spinning laser, anything.
Sight down the edge of the rear tires on both sides.
see if/where the beam hits the front tires.
percentages are masking your results. a 2 cm difference is rather large, even though you distilled it to 2%. don't do that. deal in absolutes.

I would love to deal in absolutes, however i think parking my not-level sitting van, on a not-level driveway, measuring frame points by plumb-bobbing them onto said driveway, marking with chalk (by eye), repeating four times, measuring opposite pairs with a 25$ tape measure, and comparing just introduces too many things that move you away from absolute. I don't think you can say that measuring method has a tolerance tighter than +/- 0.5cm (< 1/4") on each of those points, that's why i tried to go for some long spans. it's not about how accurately i can use a tape measure, it's about how accurate the measurement i get represents the frame of the vehicle, which is about 4 steps away at the time i measure. The measurements disagreed in ways that didn't show any obvious trends (every measurement to one side of axle shorter than the other, ie), so then what?

It seems like what you are describing is basically one step closer to an alignment / frame rack, but i still don't see how I can come up with accurate measuring points if my reference is a pneumatic tire.

i think if i do anything today i'm going to pull the leaf springs off the van and compare them.

[pmou]

took the leafs off because why not. Can't say I've hung out with my leaf springs before.. how similar are they supposed to be (i guess, also factor in 17 years)? My thought would be pretty damn close?

first, couple pics along the way..

DS, before removal

PS rubber bit and center pin

The rubber on both actually looked in decent shape, I'm willing to believe it was being clamped and holding stuff in place. no obvious friction marks or anything like that to suggest sliding around.

Once i got them off, i came up with this little jig to "compare them". Front of leafs towards camera, DS on the left.

DS is left, PS is right

clamped them both tightly in the wood blocks to hopefully "level" them to each other. Also put a bolt in there to have the same-ish eye starting point. already, noticeable that they appear not quite the same. 2 pieces of 3/4" plywood on the ground to stop the center bolts from being rested on.

Here's the eyes next to each other, can't tell if the curves are obviously different. wood for less distracting background.

DS far, PS near

Took a few points down each to see how close they were to each other. up until the center pin, they seemed pretty close actually. Note now in this direction the DS is on the right, PS on the left. DS has the tire wear.

1st measure, right near eyes/clamp

little further along

close to center, notice plywood it's resting on

now it get's a little more interesting?

rock the straightedge level for a different perspective on the difference. same position along as last pic.

futher along

squared to DS leaf again, same position

right before the rear eyes of the springs

same spot, squared

Any thoughts?

[pmou]

I'm somewhat tempted to swap them when i re-install and see if that changes anything.. if now the rear end is sticking out on the DS then likely most of the off squareness is in the leafs.

[pmou]

swapped leaf springs, seems to have made no difference in axle position relative to the body. my guess now is as good as yours. gonna take a few days to do something other than stress over my car, it will be at a collision center/frame rack on Wednesday, we'll see what we walk away from that with. the springs seemed to more or less center right back into there spot on the axle, there doesn't actually seem to be much room for them to move with the rubber insert intact.

the clamshells tightened down ok, but I'd say I "torqued to yield" on the u-bolt side. It felt like something was just stretching, at a certain point torque didn't really seem to increase for a bit. I can see why people just go to ubolts and plates

[dcsleeper]

I'm skilled at fretting a guitar which is way more complicated than this.

Your springs are junk. Time for replacement.

[pmou]

I'm skilled at fretting a guitar which is way more complicated than this.

Your springs are junk. Time for replacement.

so you think that even though swapping them seems to have changed nothing, that replacing both of them would magically fix everything? I don't follow the logic.

[dcsleeper]

I didn't say it would fix anything.
But they still need replacement.
If the answer was in your head you would have found it already.

[pmou]

well if you have a reason that the springs should be replaced, I'll hear it out. that they are junk doesn't really point to anything at all.

got an alignment report from the collision place, they said it was spot on and there was nothing to be done (except replacing idler arms, and a motor mount). Didn't put it on a frame rack as they saw nothing out of place. is alignment subjective? I don't even know anymore.

sorry, they did say the front toe should be adjusted but only once the idler arms are replaced.

[WoodButcher]

I didn't see that anyone asked, I know I didn't, was that worn rear tire on in that position when you got the van?

Perhaps it was on the front and wore from a bad toe?

[pmou]

Hey woodbutcher, appreciate anything you can offer at this point! there's a lot to follow, so no worries--

Some of the photos in this thread should be identified, but --

The wear I am describing and time frame I described for this wear is on a set of tires I put on, and that tire was always in that location.

The previous tires, which were on there before I got the van also had a similar wear on the rear tire in this location (driver's side). Whether this could have come from another location the tire was used in, I can't say. the fact that both tires had this happen in that rear DS spot made me think that was the cause (as well as the axle being off towards the passenger side at least a bit).

Perhaps the front toe could contribute to some weird overall tracking that is causing the wear in the rear? I'm not sure

[MI_Ghost]

Lets start at that 121K mileage. Any original rubber bushings & pads have had a good life. It is time to order up replacements. The spring pads clearly show that they are collapsing and allowing the axle to move. Note center pin shoved into the lip. I would not be surprised if the spring eye bushings are starting to show signs of tearing also.

The clamshell clamps are simple stamped steel parts. It takes very little effort to stretch and deform them. Upgrading to a proper u-bolt & plate to insure proper clamping force on the springs is recommended.

Also check the front subframe bushings. If the have degraded they will allow the subframe to shift.
I did not notice if you used the pucks on the front lift or just cranked up the torsion bars.

Torqueing to yield on suspension components is a very bad idea. You will never get proper clamping/holding force. If the fastener feels like it is stretching. Throw it out and get new.

[pmou]

Hey Ghost -- thanks for your input! I have replaced the subframe bushings when i did the front lift, they were definitely not looking so good at that time. I also replaced the leaf spring eye bushings as a part of the lift as well, used poly inserts.. you are correct again they were looking pretty bad at that point. The rubber spring isolators I thought didn't look terrible, but i will probably replace them at some point here -- some of this is a bit moot as I've done some work in the meantime.

I ended up ordering 22-1195 springs from sdtrucksprings to replace my possibly worn springs. dcsleeper gave the nudge, and they had a black friday sale so i ordered a pair, they arrived a couple weeks ago. Just got them installed this weekend when an upcoming long drive (8hrs, to SLC) lit a fire under my butt. I thought it was a bit odd that they are very different dimensions than the stock springs, mainly the arch height -- I think it's about 2" shorter on the SD springs. Oh well, I actually didn't measure before/after ride height as my driveway is not level at all, i feel like it may have not changed much as it just sits higher in the travel on these.

Anyway, that went pretty smoothly. Had to ditch the rubber inserts, but kept the clamshells. Also had to cut the bottom of the center pins off, they were too long to fit in the cradles. It did not seem to changed the angle that the DS shock is at relative to the axle. At the wheel wells, I think it may have evened things out slightly, but a little hard to say. Guess the tire rub will tell.

install

Also, used @mmusicman's socket trick to get the center pin in place -- thanks for sharing that, huge help. I was able to get it close, then when i tightened it halfway i hit the socket with a hammer to shift the leaf ever so slightly before the full tightening. 15mm deep impact was the magic size for me.

Pins are centered now, I'll probably double check after the big drive (mostly just big highways) to see if they moved.

I think I also would like to go to u-bolts / plates now -- mainly to get some insulators in there. I feel like i can notice the ride sounding a bit harsher and noisier in the back with that metal on metal. See how this goes first.

I also noticed that the front DS tire is having what appears toe / camber outer edge wear. Looks like that idler arm was rough and letting that wheel flop around a bit - maybe related to wear on the back as well? Have that replaced now so we will see. May swap tires PS / DS before the drive as well to see if the wear is still present.