Strange rear axle height & angle issues after UMI upgrades - Chevelle Tech
Brakes, Suspension & Steering Conversion questions & more.

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post #1 of 25 (permalink) Old Jun 24th, 19, 9:11 PM Thread Starter
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Tom
 
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Strange rear axle height & angle issues after UMI upgrades

So I have spent the better part of a year now upgrading the entire rear end of my '66 Chevelle. The Right Stuff rear big brake disc conversion, new UMI lower tubular and adjustable upper control arms. New KYB KG5507 shocks. Same springs.

When I set the length of the adjustable upper control arms, I made it the same center-to-center bolt dimension as the old stock original ones, to start. The lowers are tubular, non-adjustable.

I had completely removed the rear axle to do the other upgrades, but re-installation was a non-issue. Until I tried to connect the driveshaft. My exhaust has an H-pipe configuration with a cross-pipe running under the driveshaft. When trying to connect it to the rear differential, it was very difficult. It turns out, it was severely rubbing on this exhaust pipe. I finally got it, but figured I am going to have to remove this H-pipe to set the proper pinion angle. I wouldn't have thought it would be any different, since I set the upper arms to the same length. I also verified the lower arms were the same length as original. All new bolts are still not tightened yet on the control arms.

Then, the second thing I noticed was the the coil springs didn't seem to be compressing as much when I placed the jack under the differential and raised the frame off the jack stands. I thought at first it was the shocks, so I removed the lower bolts from the axle, leaving the shocks to just dangle, but not much of a change to ride height.

When I installed the wheels is when I knew 100% something is off. There is now about a 3-1/2" vertical distance between the top of the tire and the wheel well opening. It's like I have air shocks from the '80's on Before, the tires sat just up inside of the wheel well.

Any thoughts? I know, everything is new except the springs. So lots of things have changed. But I can't explain it. My springs are well oriented and seated in their upper and lower pockets nicely. Everything else looks good. So I can't figure why the rear won't tuck up in the car better. If I could remove that 3-1/2 inches (!), I bet my pinion angle would be much closer to where it was before too.

Thanks for any info you can throw at me.

Tom

1966 Chevelle SS, 355 V-8, TH-350.

Last edited by Gunn317; Jun 24th, 19 at 9:39 PM.
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post #2 of 25 (permalink) Old Jun 24th, 19, 9:23 PM
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Jason
 
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Suspension bushings need to be tightened at ride height. Especially the rubber ones. I think poly not so much, but it wouldn’t hurt to with the poly. The adjustable uppers are used to set the pinion angle.
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post #3 of 25 (permalink) Old Jun 24th, 19, 9:55 PM
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Steve
 
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Re: Strange rear axle height & angle issues after UMI upgrades

All the bolts are still loose, so you shouldn't have much binding.

Try this - remove the springs and leave the shocks unbolted, then jack up the rear end at the pumpkin and see if you can notice any binding of anything anywhere.

It should just go straight up with no springs or shocks to stop it.

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post #4 of 25 (permalink) Old Jun 24th, 19, 10:50 PM
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Jason
 
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Well if everything is loose like you say there is no reason the car would be setting higher with the same springs unless the springs perch’s are higher on the axle tubes.
Also is the upper control arms mounted to the center set of holes on the frame?
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post #5 of 25 (permalink) Old Jun 25th, 19, 9:36 PM Thread Starter
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Tom
 
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Thanks guys. Tonight (before reading your suggestions) I removed the lower bolts from the shocks and let them dangle. I could push and pull the body up and down and everything seemed to move smoothly without binding.

I will remove the springs and see what how that works out, but I expect it to be ok.

Any chance these springs, after sitting out of the car for a year, expanded without any weight on them?! And I have a brand new fuel tank with no fuel. So no extra weight.

I will also check to be sure I mounted the upper control arms correctly to the frame. Can't recall there being any decisions to be made there but...maybe I did something wrong.

Thanks!

Tom
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post #6 of 25 (permalink) Old Jun 30th, 19, 8:19 PM
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Russ
 
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Re: Strange rear axle height & angle issues after UMI upgrades

Are you sure the springs are correctly seated in their pockets? Try rotating them to see if the drop a bit when they fit into the pockets for the spring ends.
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post #7 of 25 (permalink) Old Jul 1st, 19, 9:07 PM Thread Starter
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Tom
 
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Re: Strange rear axle height & angle issues after UMI upgrades

Ok, finally got around to removing the springs. I also removed the driveshaft.

With the springs removed I can jack the rear axle from hanging low to way up high into the car. So the control arms are not binding at all and I have a free range of motion up and down.

With the springs removed from the car, they measure 15-1/2" free standing (with rubber isolator installed on spring).

I jacked up the axle until I had the previous original ride height that I used to have. The distance between spring mount locations was about 9".

So then I put the springs back in. No driveshaft. As I compressed them with the jack under the differential I made 100% sure the springs were seated in their upper locations...and rotated to fit in the correct spot. They look good. But when I jack it up under the differential, once the frame leaves the jack stands I measure ~12" between spring mount locations. So it seems I'm about 3" from where (I swear) it used to be!

Don't know what to make of it. Can the springs have expanded from being outside the car?

Does anyone know the length of new or old uncompressed stock springs? Or their length under the car compressed under the full weight of the body? Just trying to figure out where to go from here.

I guess I could bite the bullet and spend another grand on a coilover setup...IF that would fix the problem!

Tom
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post #8 of 25 (permalink) Old Jul 1st, 19, 9:21 PM
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Re: Strange rear axle height & angle issues after UMI upgrades

Tom,
The Southern Maryland gravity factor has changed since you took it apart Have you tried letting it sit on the ground for a few days with weight on it and see if it settles down any ? Maybe put a few bags of sand in the trunk.

Just thinking out loud.
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post #9 of 25 (permalink) Old Jul 1st, 19, 10:01 PM
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Re: Strange rear axle height & angle issues after UMI upgrades

Look up inside the frame where the upper part of the spring sits.Find where the upper end of the spring used to sit.There will be witness marks where it used to sit.Spin the spring around till it sits where the end of the spring used to sit and try that.

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post #10 of 25 (permalink) Old Jul 1st, 19, 10:09 PM
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Steve
 
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Re: Strange rear axle height & angle issues after UMI upgrades

Something goofy going on. I used the Google and found this link:

https://www.speedwaymotors.com/1964-...t-,115414.html

Shows 15" uninstalled height, 9.78" installed height.

Yours don't seem to be compressing fully?

1972 Chevelle, 454, 2004r, 3.08
1981 Camaro Z28, 355, TH350, 3.73
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post #11 of 25 (permalink) Old Jul 1st, 19, 10:34 PM
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Re: Strange rear axle height & angle issues after UMI upgrades

Tom,

Here is a pic of my BMI 1" rear lowering springs.

I have a 67 convertible; should be the same for a 66.

I am installing a S60 rear from Strange so I should know in a few days if I have height problems too
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67 Chevelle convertible, 138 vin, original 4 speed, bucket seats, 12 bolt, Marina Blue with black interior
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post #12 of 25 (permalink) Old Jul 2nd, 19, 4:17 AM
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Re: Strange rear axle height & angle issues after UMI upgrades

Quote:
Originally Posted by Gunn317 View Post
Ok, finally got around to removing the springs. I also removed the driveshaft.

With the springs removed I can jack the rear axle from hanging low to way up high into the car. So the control arms are not binding at all and I have a free range of motion up and down.

With the springs removed from the car, they measure 15-1/2" free standing (with rubber isolator installed on spring).

I jacked up the axle until I had the previous original ride height that I used to have. The distance between spring mount locations was about 9".

So then I put the springs back in. No driveshaft. As I compressed them with the jack under the differential I made 100% sure the springs were seated in their upper locations...and rotated to fit in the correct spot. They look good. But when I jack it up under the differential, once the frame leaves the jack stands I measure ~12" between spring mount locations. So it seems I'm about 3" from where (I swear) it used to be!

Don't know what to make of it. Can the springs have expanded from being outside the car?

Does anyone know the length of new or old uncompressed stock springs? Or their length under the car compressed under the full weight of the body? Just trying to figure out where to go from here.

I guess I could bite the bullet and spend another grand on a coilover setup...IF that would fix the problem!

Tom
This is what Moog spec the three different springs they offer for 64-66

p/n 5235 (wagon listing) is 16.05" free height, 8.50" compressed, load 1104.0, 146.0 lbs/in. p/n 6197 (hd listing) is 15.06" free height, 8.50" compressed, 878.0 load, 138.0 lbs/in p/n 6201 (reg listing) is 15.44" free, 9.78 compressed, 628.0 load and 112.0 lbs/in

Since 64-66 only use pigtail in the end that sits on the rearends spring perch you can cut them if you are sure there are no other problem even though it may not be the best solution.

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post #13 of 25 (permalink) Old Jul 2nd, 19, 4:13 PM Thread Starter
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Tom
 
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Re: Strange rear axle height & angle issues after UMI upgrades

Quote:
Originally Posted by lucifershammer View Post
Something goofy going on. I used the Google and found this link:

https://www.speedwaymotors.com/1964-...t-,115414.html

Shows 15" uninstalled height, 9.78" installed height.

Yours don't seem to be compressing fully?
Quote:
Originally Posted by Malibu ss 64 View Post
This is what Moog spec the three different springs they offer for 64-66

p/n 5235 (wagon listing) is 16.05" free height, 8.50" compressed, load 1104.0, 146.0 lbs/in. p/n 6197 (hd listing) is 15.06" free height, 8.50" compressed, 878.0 load, 138.0 lbs/in p/n 6201 (reg listing) is 15.44" free, 9.78 compressed, 628.0 load and 112.0 lbs/in

Since 64-66 only use pigtail in the end that sits on the rearends spring perch you can cut them if you are sure there are no other problem even though it may not be the best solution.
Wow thanks everyone for the detailed specs! So from where I thought the original wheel location within the wheel well (and measured ~9" between upper/lower spring locations in my post above) is very close to these stock spring heights. Man, this is strange! I have no idea why mine won't compress. With the springs out, I have plenty of travel with the new control arms; the rear will go way up in there... Put the springs in and it sits way too high.

I ended up doing a lot of painting and cleanup in that area, so there are no old witness marks where the springs used to set. But when I am installing them now, I am making sure the end of the coil spring is butted up against the little stop formed in the perch in the frame, so I assume I'm doing that right.

Right now the car is lifted with jack under the differential, off the frame jack stands so we'll see if any settling occurs.

If I can't figure this out, I'm going to start cutting the top of these springs, or maybe try the inexpensive Moog 6197 spring (8-1/2" compressed, $46.99/pr at Summit) just to trial-and-error and figure this out.

I'm beginning to think the Southern Maryland gravity factor is indeed at play here...

Thanks again for the suggestions.

Tom

1966 Chevelle SS, 355 V-8, TH-350.
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post #14 of 25 (permalink) Old Jul 2nd, 19, 5:30 PM
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Steve
 
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Re: Strange rear axle height & angle issues after UMI upgrades

Silly question.

Do you have more than one set of springs laying around that you might have gathered up?

Any chance you put the wrong ones back in the car?

(Probably not, but had to ask. )

1972 Chevelle, 454, 2004r, 3.08
1981 Camaro Z28, 355, TH350, 3.73
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post #15 of 25 (permalink) Old Jul 2nd, 19, 5:43 PM
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Re: Strange rear axle height & angle issues after UMI upgrades

Do you still have the old springs to put back in the car and measure?
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