I'm replacing my upper a-arm bushings ('70 Chevelle). When re-assembling, should I go back with the original shafts (has the type with the large nut securing the bushings) or should I use a new set of offset shafts? For what it's worth, there were no shims under two of the bolts, one shim under one bolt, and two shims under the other bolt.

Thanks!

sounds like you're a candidate for the offset shafts. Another approach is fix the root cause of the problem. If you're near a decent frame shop you can have the frame problem fixed. Essentially, they chain the frame down on both sides and jack it up up under the center, spreading it back to where it was when it was new. Some shops will just do this, others will insist on pulling all the front suspension off, etc, to run up the hours. You might check around a little.

Otherwise, get the offset shafts. You don't want to put it all back together just to find it can't be aligned properly.

sounds like you're a candidate for the offset shafts. Another approach is fix the root cause of the problem. If you're near a decent frame shop you can have the frame problem fixed. Essentially, they chain the frame down on both sides and jack it up up under the center, spreading it back to where it was when it was new. Some shops will just do this, others will insist on pulling all the front suspension off, etc, to run up the hours. You might check around a little.

Otherwise, get the offset shafts. You don't want to put it all back together just to find it can't be aligned properly.


Thanks Tom!

I was reading some of the previous posts & ran across a couple where it was suggested that the offset shafts be installed 'backwards' to reduce the amount of shims needed. Does this make sense? How would I know whether to install them 'correctly' or 'backwards'?

Tom describes the exact operation that was done on our 396 Chevelle. It was to the point where, with all the shim out there still was not enough adjustment. When done, I could drive the car down the highway with one finger and I didn't have power steering. It does cost a few dollars but at least you know that the car is right.

Go the offset route. You can shim the offset arms back to stock if you wish. Once the stock pivot arms has no shims left you are forced into the frame $hop.:cool:

Go the offset route. You can shim the offset arms back to stock if you wish. Once the stock pivot arms has no shims left you are forced into the frame $hop.:cool:

I'm somewhat confused as to how offsets relate to the shim pack & I'm seeing differing opinions as to how the arms should be installed. Should the offset arms be installed 'correctly' or 'backwards'.

Thanks to all!

look at the way the arm/shaft assembly mounts. it's on the inside of the ears sticking up out of the frame. when the frame folds up a little it pulls the mounts inward, pulling the top of the tire inward, giving negative camber. It will also screw up the caster. as the frame gets narrower the shim packs get smaller until you can't get correct alignment even with all the shims removed.

installing the offset shaft with the offset ends to the outside gets back some of this room. Or, you can have the frame fixed.

I don't know what those guys are talking about installing them backwards to eliminate the stacks of shims. These guys must be working on some pretty strange Chevelles.

One clarification: Negative camber is not a Bad Thing in itself, but not being able to align the front end is.

look at the way the arm/shaft assembly mounts. it's on the inside of the ears sticking up out of the frame. when the frame folds up a little it pulls the mounts inward, pulling the top of the tire inward, giving negative camber. It will also screw up the caster. as the frame gets narrower the shim packs get smaller until you can't get correct alignment even with all the shims removed.

installing the offset shaft with the offset ends to the outside gets back some of this room. Or, you can have the frame fixed.

I don't know what those guys are talking about installing them backwards to eliminate the stacks of shims. These guys must be working on some pretty strange Chevelles.

One clarification: Negative camber is not a Bad Thing in itself, but not being able to align the front end is.

Thanks Tom...I get the picture now!

Thanks Tom!

How would I know whether to install them 'correctly' or 'backwards'?

They are marked as to how to install. pete

Don't the A-Arm shafts install on the inside of the ears closer to the engine??

Then you put shims between the ears and the shafts to adjust them so if they are offset towards in less shims to pull her in and offset towards out, more shims...

Right???

pdq67

Yes, that is correct.

I recently did a search for upper control arm shafts at Autozone, Checker and NAPA and it seems that the standard shafts are becoming scarce. The offset shaft seems to be the norm on those sites.

The question has been posed…..

“I'm replacing my upper a-arm bushings ('70 Chevelle). When re-assembling, should I go back with the original shafts (has the type with the large nut securing the bushings) or should I use a new set of offset shafts? For what it's worth, there were no shims under two of the bolts, one shim under one bolt, and two shims under the other bolt.”

To answer this question you need to know what the shims do. They are used to adjust both caster and camber. Ok, what is caster and camber?

CASTER

Caster is the angle to which the steering pivot axis (a line drawn through the upper and lower ball joints) is tilted forward or rearward from vertical, as viewed from the side.

If the pivot axis is tilted backward (that is, the top pivot is positioned farther rearward than the bottom pivot), then the caster is positive; if it's tilted forward, then the caster is negative.

This is adjusted by either adding shims to the front or rear mounting point of the upper control arm pivot shaft. If you add to the front and remove from the rear you tilt the pivot axis to the rear or you add positive caster.

CAMBER

Camber is the angle of the wheel relative to vertical (a line that passes through the center of the spindle), as viewed from the front or the rear of the car.

If the wheel leans in towards the chassis, it has negative camber; if it leans away from the car, it has positive camber.

So by adding or removing an equal number of shims on both the front and rear mounting points of the upper control arm pivot shaft you can adjust camber.

By adding shims you are adding more negative camber. By taking away shims you are adding positive camber.

SO
If you have no shims you can see that you cannot adjust the front-end alignment unless you do something so that you can play with the caster and camber angles. You can go to a frame shop and have the frame twisted so that you can add shims (twist the frame horn towards the outside of the chassis or use an offset shaft in the upper control arm to give you back some adjustment. Both do the same thing.

I hope this helps. :cool: