Rear axle "alignment" and rear tire wear

Re: Rear axle "alignment" and rear tire wear

Postby Mmusicman » November 13th 2020, 10:21pm

A slightly bent clamshell (at the bolts) does not mean the spring is mis-positioned or moving inside it.

But if the nuts won't tighten sufficiently causing the clam-shell to bend and not have enough clamping power.. then there might be an issue. But in the stock application, I'm still not sure it could even an issue regardless. This you should determine more closely.

But then why is the visible center-pin not centered in the clamshell?
Did it or does it move? Or has it just always been like that? Is this normal?

Look everything over.. don't make assumptions
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Re: Rear axle "alignment" and rear tire wear

Postby MechBob » November 13th 2020, 10:44pm

His alignment readout shows the rear end is sitting in there sideways,as per one of my earlier posts.
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Re: Rear axle "alignment" and rear tire wear

Postby pmou [OP] » November 13th 2020, 11:30pm

I'm having a hell of a time even getting a shop to acknowledge what I'm talking about. Called a couple more and explained that the clamshell is damaged, and i believe the thrust angle is off, would they be able to re-seat the leaf springs on the axle as a part of an alignment... They are all saying there's no adjustment, the axle is bent, we don't regularly service astro/safari, we'd probably send you to a body shop bc something is bent, we'll happily take an hour labor from you, etc.

One place did mention that there's a leaf spring specific place in denver, sounds like they would do more fab / custom springs / perches / etc. Good to know about as a last resort i suppose.

i think part of the temptation of the plates is having an actual center hole for the centering pin that is centered over the axle. Mmusicman I like your solution as well. anyhow, this is all just speculation til I take things apart.

Edit: I'm calling around asking this because even if i do lockdown what is happening here, and manage to get everything "figured out" and get the springs to not move on the axle, I am not feeling especially confident that I'd be able to get the thrust angle correct. If the issue is that the springs are not centered on the axle properly, then I'd like to have a shop that can come in and follow up with an alignment and set the thrust angle if that needs to happen.
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Re: Rear axle "alignment" and rear tire wear

Postby MechBob » November 14th 2020, 12:21am

As a general rule,nothing badly bent,you can loosen the bolts,center the spring pins inside the holes,top of the clams, with straps,like Mmusicman has said, and it will be within specs,and fix your problem,But,if you still have the rubbers,and they are not in good shape,may move again.As far as an alignment shop that does not want to talk to you about shifting the rear end, never go there.Even the lesser shops should talk to you about it,the place you went to already should have offered it.Get in touch with local off road group,and see whom they use.
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Re: Rear axle "alignment" and rear tire wear

Postby pmou [OP] » November 14th 2020, 1:19am

Haha yes, i think you are correct Bob. One place I called basically said "This is sort of outside what we usually do... usually we do Jeeps" which, looking around Boulder I would take to mean they polish tires, install offroad bumpers, and paint things red.
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Re: Rear axle "alignment" and rear tire wear

Postby MechBob » November 14th 2020, 1:40am

LOL!
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Re: Rear axle "alignment" and rear tire wear

Postby dcsleeperdcsleeper is online! » November 14th 2020, 1:54am

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Re: Rear axle "alignment" and rear tire wear

Postby pmou [OP] » November 14th 2020, 8:08pm

Alright well I got out there and measured some things with the wheels in the air. I can't find anything in the leaf/clamshell area that seems no good. Got it up in the air, both wheels off. Yanked everything around and couldn't get anything to move. Also put ratchet straps from the axles to the hangers and could not get the clamshell to shift on the spring (on either side).

PXL_20201114_180726129.jpg


Here's the measurements I took of the leaves. The top ones are inside of eye to center pin. lower ones are inside of eye to clamshell. middle there is how far it was hanging from the framerail on the body.

PXL_20201114_185141370.jpg


It was basically all spot on, mind you this was done with a tape measure. I also snagged a few photos of the tires while they were off to give a more square on view. At first i thought it was wearing differently fore/aft along those side knobs but I think that's just the way the knobs are shaped.

PXL_20201114_183014781.jpg
DS


PXL_20201114_183021113.jpg
DS


PXL_20201114_183051352.jpg
PS


PXL_20201114_183055749.jpg
PS


Looking more closely at the shock mounts, if the axle is askew and that's what's causing this -- based on which parts of the shock mounts are too close it should mean that the DS is to far rear, and the PS is too far forward.

I also conveniently have 2 other astros for observation at the moment. Both driver side clamshells seem to have that same bend and gap I pointed out earlier. Neither of them have the center pin in the middle of the hole in the top of the clamshell.

I double checked tire pressure, mind you this wasn't on level ground.. The fronts were both at 35. Rear PS was at 31, rear DS was at... 27. I'm going to run out to a gas station where i can park level and verify / add air as needed. Seems like something must be off due to the slope of the driveway, how would it coincidentally be that the one tire that's low is the one that previously had strange wear... ?

edit: also these are new rims so it couldn't be that there's just a leaky / not well seating rim that's ended up on that corner more than once.
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Re: Rear axle "alignment" and rear tire wear

Postby pmou [OP] » November 14th 2020, 9:11pm

Alright well that RR DS tire was definitely the lowest of any of them, on level ground it appeared to be about 28psi, the RR PS was about 30-31. front both were 35+. got them all at 37psi now. Guess i shouldn't have trusted the shop that they were all at 35? or I have a decent leak on that rr DS. Could that have caused this sort of wear? I would think low pressure wear would be even left/right edges? but perhaps with the AWD that would somehow cause some sort of strange rotational wear with one tire being low
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Re: Rear axle "alignment" and rear tire wear

Postby pmou [OP] » November 24th 2020, 10:35pm

Alright well, an update of sorts --

Went to RPM in Broomfield CO to see Levi. Good dude, great shop. was very honest, willing to discuss, and seems to know his stuff.

Here's the alignment report I got from them, including Levi's drawing of what seems to be going on.

PXL_20201124_183153016.jpg
malignment


He said he believes that the axle is good (based on comparing toe & camber relative to each other, irrespective of the center of the vehicle) and that there is something in the frame that is not square. He said this is based on the wildly different toe values, that line up with how the axle is clearly off. The setback as well is a bit discerning.. for some reason when i was talking with him i thought he said that it was the rear, but on this report it looks like a front setback measurement.. which.. i would think would mean something in the subframe is off? maybe i need to call to clarify...

Anyhow, i'm calling around to body shops.. turns out most don't have a frame rack big enough to put this van on.

In the meantime, what i'm wondering is would the frame/body being bent explain the axle being off to one side? that doesn't totally check out to me.. if the body was bent i would think the relative position of the front to rear wheels would be messed up.. but that wouldn't mean the relative position of the body to the rear wheels would be off? maybe i'm not thinking about this quite right..
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Re: Rear axle "alignment" and rear tire wear

Postby Sparkydog » November 24th 2020, 11:12pm

My brain interprets that sketch to mean that the rear end is jacked up in some manner and is causing the van to want to track to the right when its moving.
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Re: Rear axle "alignment" and rear tire wear

Postby dcsleeperdcsleeper is online! » November 24th 2020, 11:21pm

I call **** on the lack of frame racks. My podunk location has two that could a lil ole Astro.
I also can't believe you're having trouble getting this fixed. Might try the next town over?
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Re: Rear axle "alignment" and rear tire wear

Postby pmou [OP] » November 24th 2020, 11:41pm

OK so here's the notes as well --

PXL_20201124_214332863.jpg
notes


Re: lack of frame racks, I got one shop that said they only take insurance contracts for vehicles of this size.. he made it sound like the insurance companies somehow pay for the rack in exchange for their cooperation or something.. i don't know. Sounds like they don't have total control over what it get's used for. Another shop said they don't have a rack big enough. I've got a couple more leads at this point, and i'm already looking around in about a 20mi radius. Denver for sure will have something, trying to avoid driving that far if possible though.

I still am not feeling settled as to why the wheels would not be in the right spot relative to the body if the frame was not square.
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Re: Rear axle "alignment" and rear tire wear

Postby dcsleeperdcsleeper is online! » November 25th 2020, 12:00am

There is no frame. There is a body. At this point I'm thinking maybe the front subframe is shifted.

You should be able to see any out of square. measure with a tape measure.

This is not hard, believe in yourself. When you find out where it's off, you will be surprised at how simple it is.
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Re: Rear axle "alignment" and rear tire wear

Postby pmou [OP] » November 25th 2020, 12:05am

dcsleeper wrote:There is no frame. There is a body. At this point I'm thinking maybe the front subframe is shifted.

You should be able to see any out of square. measure with a tape measure.

This is not hard, believe in yourself. When you find out where it's off, you will be surprised at how simple it is.


Yeah i understand that.. sorry most places i've been speaking with just say frame (i've corrected them several times to see if it changes their opinion.. it does not).

I do have the factory manual that lists all the square points on the subframe/body to measure for squareness and approx measurements, etc. perhaps that can be a fun solo thanksgiving adventure or black friday. It's possible i guess that the subframe shifted, however this wear was present both before and after the body lift, which obviously involved removing and re-installing the subframe 1/2 at a time.

edit: as a part of my leaf spring measuring, i measured from a few points on the axle to the subframe and could find no difference, at least at the time.

2nd edit: looks like it just has suggestions for how to measure the subframe... which, wouldn't there be a ton of junk in the way of getting a real measurement? like directly from point to point on the subframe? Also, even if i figured out the issue (unless it's the subframe shifting) this would be out of my power most likely to fix, so i'm inclined to just have someone who can fix it measure it. I guess knowledge is power, knowing what the hell is going on is a leg up on anyone i've talked to so far.
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Re: Rear axle "alignment" and rear tire wear

Postby AstroWill » November 25th 2020, 12:35am

Depends on which points you are measuring. Use a plumb bob from each point and mark it on the ground, then measure it.

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Re: Rear axle "alignment" and rear tire wear

Postby pmou [OP] » November 25th 2020, 12:41am

AstroWill wrote:Depends on which points you are measuring. Use a plumb bob from each point and mark it on the ground, then measure it.


so simple yet genius... hadn't actually thought of that. with that in mind, i could just about map out the whole car on my driveway in chalk and then measure it all. rear axle spots, front lower ball joint, subframe points, points along the frame rails on the body, etc. i'm feeling more inspired to attempt this, thanks Will!
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Re: Rear axle "alignment" and rear tire wear

Postby MechBob » November 25th 2020, 6:54pm

You found a good honest shop.So,3 things tha could be(well,mostly) 1 Whole rear body section is bent,twisted,and/ or rear spring mounting points have been rewelded on wrong. All highly unlikely,but you need to measure points on the axle housing itself,to the body measuring points,from to back,and x pattern.I think you have already done some of this.2,front subframe not mounted properly in the body.Highly unlikely.3 Front subframe has been hit hard,and has "scissored".You can look that up on the net for pictures and explanation.I bet it is #3, but possibly #1.
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Re: Rear axle "alignment" and rear tire wear

Postby pmou [OP] » November 25th 2020, 7:15pm

Hah hey bob! when i got that alignment report back i was hoping you would turn up again...

Thanks for your sane assessment. I'm with you except for a one caveat.. re #3 -- if it is the subframe that is scissored (from what i gathered, this is similar to "diamond frame condition"), then there would need to be something additional going on in the backend as well to explain the tires being off relative to the body (whole axle off to the PS, tire rubbing more on DS) i believe? Certainly will measure both the subframe and rear axle position to the best of my ability while i'm rolling around on the ground.

One issue I'm considering is this: just for fun i did some maths. I made up some numbers, i said lets say i measure 2 points that are on opposite corners of a rectangle and measure the diagonal btw them. I used a rectangle of dimensions 40"x25" for the sake of guesstimating the subframe size. If not diamoned, this would have a diagonal of ~47.17" [ sqrt(40^2 + 25^2) ]. Let's say their measurement of a 1.5" setback is correct, this would now make the diagonal ~48.44" [ sqrt(41.5^2 + 25^2) ], about 1.3" difference OR ~45.90" [ sqrt(38.5^2 + 25^2) ] difference of 1.27" (diamoned the other direction) .. seems like this should be detectable, just thinking out loud here. just wondering if by transforming the points onto the plane of the ground some accuracy will be lost if the car doesn't sit level and the ground isn't perfectly level. Also, this would only detect a single plane variation.. if something is off a small amount horizontally but some amount vertically.. this would be missed or at the very least minimized by this measurement method.
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Re: Rear axle "alignment" and rear tire wear

Postby MechBob » November 25th 2020, 7:26pm

Not gonna get into your measurement stuff.Seems you are pretty sure it is simply rear end has shifted.Any competent mechanic,in the old days could tell you in 5 minutes or less,on a drive on hoist,where the wheels are not lowered.You have to measure the axle housing to the body measuring points.What usually causes this is broken spring centering pins/bolts.
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