How do I keep my pinion angle from changing? - Impala Tech
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post #1 of 15 (permalink) Old 06-07-2013, 11:38 PM Thread Starter
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How do I keep my pinion angle from changing?

Ugh! I caused a problem to apparently re-appear tonight after doing a satisfying burnout. I don't mind breaking stuff, but I do prefer to FIX it for GOOD. Sheesh!

When I got home, I noticed my differential/pinion was pointing way up high again, making my drive-shaft hit the tunnel on the slightest bump. Also, the rubber pinion bumper was popped out again as noted in my previous thread. A quick glance underneath and it looked as if everything was in it's place, nothing broken. I'll look closer tomorrow.

This occurred even after replacing rear control arm bushings, boxing the stockers and the new single Upper is now a Hotchkis adjustable unit. Still on the stock track bar, but with poly bushings now.
After the upgrades, I adjusted the pinion angle per the book at about 1.5 degrees as the manual shows it.

A month ago, the pinion was noted to be wrong and I thought it was just all my obviously worn out control arm bushings. I guess I was wrong.

Is this just something the 3-link will do when abused with clutch dumping burnouts? How do I fix/prevent it?
Would it happen if I had the 12-bolt and the 2nd Upper arm?
Am I missing something else? I dont' think my Hotchkis Upper will adjust any shorter!!

Arrrgh.

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post #2 of 15 (permalink) Old 06-08-2013, 10:55 AM
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Two is better than one.

The factory installed two upper control arms on any engine that was factory rated at over three hundred horsepower. It not only halves the amount of force (engine torque) that the upper control arms has to deal with, but it distributes the load evenly instead of it being applied off center; which creates a torque arm to further multiply the force trying to knock it out of alignment.

Since you are still using the ten bolt rear end the even distribution will help it live longer as the tires are not held perpendicular to the frame with only one arm. If the axle is out of alignment you introduce an additional force that is being applied to the side of the components (where the factory didn't intend it to be applied) which can accelerate wheel bearing failure or a broken axle.

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post #3 of 15 (permalink) Old 06-08-2013, 12:39 PM Thread Starter
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A closer inspection today noted that the passenger side wheel/tire is moved forward (off center).
Still nothing looks broke underneath. Not sure what the temp-fix is here!
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post #4 of 15 (permalink) Old 06-08-2013, 02:55 PM
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I'd start with new aftermarket lower control arms. Tubular or box construction. Forget the old stamped steel ones, even if boxed.

Two doors, four doors, wagons, and ragtops.
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post #5 of 15 (permalink) Old 06-08-2013, 04:10 PM Thread Starter
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I wish I had the money to spend on that, that's why I had gone with the boxing......but I am missing how that would address this issue.


I may have just figured this out for both instances of when this issue has happened.

I think the axle tube has rotated as compared to the differential. That makes sense, right? I mean, it's a stock 10-bolt, people usually weld the tubes to the diff., it happened both times after clutch-popping little burnouts. 275 series tires, 4100lb, 46 yr old car with a 383 crate motor and Muncie. j
The Drivers side LCA bracket is angled 15 degrees to the front of the car, the Passenger side LCA bracket is angled 9 degrees to the REAR of the car. That can't be right! Axle tube rotation would do that, right?

I think I just found the next Weakest Link. I think this also means there's no easy fix this time to get me on the road again.

Sound plausible? Could I leverage this back in place and then weld the tubes? That sounds tricky, not sure how I'd move the axle tube.

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Last edited by BA.; 06-09-2013 at 10:33 AM. Reason: clarity
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post #6 of 15 (permalink) Old 06-08-2013, 04:13 PM Thread Starter
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Anybody got an angle checker to measure their LCA mounts are different, or at least eyeball them to see if your passenger side is angled to the rear, whilst the Drivers side is angled to the front?

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post #7 of 15 (permalink) Old 06-08-2013, 04:14 PM
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Bolts in the backing plate holes, and a big bar between them would give you leverage. Axles and backing plates off, off course. If you twisted them out, you can twist them back. Just have to get innovative.

Two doors, four doors, wagons, and ragtops.
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post #8 of 15 (permalink) Old 06-08-2013, 04:50 PM Thread Starter
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Good tip Jason!

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post #9 of 15 (permalink) Old 06-09-2013, 07:15 AM
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Check that the frame area where the upper control arm bolts is not
distorting.

Donnie PhD- Mech engr
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post #10 of 15 (permalink) Old 06-09-2013, 09:04 AM
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Quote:
Originally Posted by BA. View Post
The Drivers side LCA bracket is angled 15 degrees to the front of the car, the Passenger side LCA bracket is angled 9 degrees to the REAR of the car. That can't be right! Axle tube rotation would do that, right?

I think I just found the next Weakest Link. I think this also means there's no easy fix this time to get me on the road again.

Sound plausible? Could I leverage this back in place and then weld the tubes? That sounds tricky, not sure how I'd move the axle tube.
Yes that is plausible. The lower mounts should be even. If it was my car I would pull the rear end and take it to someone that knows what they are doing. If the tube has moved that much, just twisting back does not seem like a good fix because the tube may be pulling out or the axle may no longer be perpendicular to the diff.
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post #11 of 15 (permalink) Old 06-09-2013, 10:33 AM
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The plug welds are the weakest link with holding the axle tubes in place. The axle frequently bends in rear end collisions because the axle tubes are held in only one spot allowing the case to twist on impact. All HD race oriented rears are fully welded. The tube walls are also thicker.
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post #12 of 15 (permalink) Old 06-09-2013, 10:03 PM Thread Starter
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The UCA mount area is still solid, thanks for the tip Donnie.


If anyone happens to still be reading the thread,.....I'm wondering what those other rear-ends are that would fit. While I CAN weld if necessary, I have some doubts about accurately welding on any UCA/LCA brackets since I'm just on jack-stands in a garage.
The 65-70 Impala rear's are the ones I'm sure of from everyone's feedback. Is anything else the right width?

In my web searching for a used/rebuilt rear-end, I'm seeing some mid-60's Chevelle's and mid-80's Grand Nationals. I remember someone mentioning the mid 90's Impala SS but I think it the deal there was that it had disc-brakes which would be some extra conversion work.
I've also seen some 79 T/A rear-end parts, but, I might be mis-remembering those desireable parts from my Camaro background. The traditional reference to "8.5" ring gears got me to wondering what the Impala's rear is referred to as.

Also, if anyone has the measurements handy to cut/paste, that might come in handy.

HOW A NOVICE REBUILDS A 66 IMPALA CONVERTIBLE:
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Last edited by BA.; 06-09-2013 at 10:36 PM.
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post #13 of 15 (permalink) Old 06-09-2013, 10:59 PM Thread Starter
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Found a 12 bolt from a 65 Impala, single UCA, reportedly working when removed and not making noise. Asking $625.
Right part but a little more than I was expecting. I figured I'll be putting in fresh bearings and maybe a posi center, and may have to spring for new gears in rear-end I find.

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post #14 of 15 (permalink) Old 06-16-2013, 11:10 AM Thread Starter
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Listed here are backing plate to backing plate rearend lengths for some of the donor Chevrolet vehicles:
  • 1967-'69 Camaro: 60 inches
  • 1964-'67 Chevelle: 61 inches
  • 1968-'72 Chevelle: 62 inches
  • 1965-'70 Chevrolet: 62.4 inches

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post #15 of 15 (permalink) Old 06-16-2013, 11:11 AM Thread Starter
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You can identify the truck differentials by the smaller 1.438-inch diameter pinion shaft and the size of the rear cover. The truck covers are larger and more irregularly shaped, measuring 10-7/8-inches by 10-7/8-inches. The easiest way to identify a 12-bolt rearend is obviously by the 12 bolts holding the rear cover onto the axle housing. The pinion shaft on passenger-car differentials is 1-5/8-inch in diameter and the cover is oval, measuring 10-15/16-inches wide by 10-5/8-inches tall.

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