Advice for Aligning Rear Upper Control Arms
 

Been working on refreshing the tired rear controls arms and bushing on my 72 GP.

Swapping them in and out, but even one at a time, it does indeed cause the rear axle to twist a little, so my rear upper control arm holes aren't aligning too easily with the new axle bushing's hole.

Any tricks to getting this axle to rotate counterclockwise a little to get hole alignment? I do have a jack with wooden block pushing up at the front of the axle housing, and that gets it in the ballpark, but right now there's no way to run the bolt through that connection easily. I need a little more rotation of the axle...

Harvey

take the lower control arm bolt out of one side of the differential
and
see if that helps

I'm assuming you have the car blocked up and are working underneath.

Next time just pull the entire rear end and do them all at once, much easier.

If you have the shocks mounted, unbolt them both at the bottom.

Edit - If they are close to going through and they are the correct bolts,

they are pointed, most times you can screw them through, good luck.


Frank

Try some pull-aways on a straight LEVEL road, with steering wheel basically light-fingered. Don't lose traction but surely have the posi working or a working posi.

If the car wants to dart left or right then the frame is jot square, making a lower arm appear too short. Offset bushings are avail, or if you can dig it, like i did, you can offset the sleeve in a lower bushing (rattail the urethane & shim with copper, or similar). Upper arm will likely need a tweak, so if adjustable, then you will know the correct length.

I used the " long-string method " to measure the front alignment and rear track. The string method confirmed the rear track was off, then corrected.

Yes, up on jackstands. I'll undo the shock absorber bolts to see if I can buy enough CC rotation via the two hydraulic jacks I'm employing to get the holes to align. Holes aren't far off, but not yet good enough to get the bolts started.

Thanks for the ideas so far, PY'ers.

Shows what happens when ya don't read Post#1 ;)

Lol, happens... :noidea:

None the less a nice post. :)



Frank

Could you throw a ratchet strap over the housing and hook it over the lower arm where it meets the rear? Go forward to a hole in the side rail or trans cross member and ratchet the rear forward (hoping it may rotate on the lower arm bolt) and bring the upper arm location forward.

When these cars were our everyday drivers, my buddies and I could swap out a blown housing in about and hour. I believe back in the day we would shove a Phillips screwdriver in one end to align the inner sleeve and start the bolt from the other end, the a few whacks with a hammer to drive it in.

Later on when we had access to real tools, a tapered drift would be used in lieu of the screwdriver.

Very Sloppy Rear Control Arms
 

This is what worked. A bit of hydraulic jack maneuvering, enough to where the holes partly lined up, and a sharp-pointed driver to bring the holes into closer alignment.

Once it was close enough, a large Philips driver aligned it enough to get the bolt started in the opposite side of the bushing.

Interestingly, when I was able to pry in that hole and gently move the rear axle, I could see my upper and lower driver's side control arms moving a bit too freely. A bit shocking actually to watch those arms and the axle move separately.

Upon closer inspection, one of the upper arm nuts was backed off about 1/8", and the lower control arm is worn out.

I think I may have found the answer as to why this SSJ has wandered and steered funny under acceleration. Rear axle is trying to go one way, the front end another. So far, all of the bushings have been split, cracked, or are missing rubber.

I'll report back once all 4 control arms and bushing are properly mounted and torqued.

Back in the late 70s I had customer bring his Lincoln to my garage, he had a rather strange condition the same as you're describing. Under acceleration you had to steer the car to keep it going straight, a parts changer (I discern parts changers from mechanics, as they have low diagnostic skills) had put motor mounts in the car, and obviously that cured nothing.

On the lift I inspected the rear lower control arms, and found the drivers side found the bushing was deteriorated causing the rear axle to steer under acceleration. After replacing the rear lower control arm the car drove like new, customer paid a lot of money to have the motor mounts installed for zero improvement. He was very pleased we found the problem, and became a very good customer from that point forward.

Doing the driver's side upper and lower rear control arms right now.

I noticed the driver's upper has a small squared plate attached to it from the factory, and it looks like the arm itself is chamfered by GM for a little bit of 12-bolt housing clearance.

Has anyone else seen this before, and what's the solution to my replacement arm that has neither of those features?

Harvey

Normal for a Chevy 12 bolt. 10 bolt doesn't need it.

https://www.lever-family-racing.com/...olt-difference

And that confirms it. That's exactly what I'm seeing.

Looks like Inline Tube has this specific-to-12 bolt design for the driver's side.

Thanks 68!

Harvey, Just a note, It is best the do your final tightening of any control arm bolts with the suspension on the ground at normal ride height so that the bushings are not pre-loaded.

Does having the rear axle on jackstands with the full weight of the frame and body loaded accomplish the same thing?

Yes, it does.
 

Just bounce the rear a few times before you torque.

The torque is showing as 110 ft-lbs on the bolt side of the joint in the service manual.

When torqueing down on these bolts, it's obviously squeezing down on the bushing's center metal sleeve.

Is the travel of any of the trailing arms simply dependent on the flexibility of the rubber bushing, or is that center sleeve actually rotating inside the bushing?

I'm not sure I understand the concept of how these actually work to allow travel. This trailing arm work is somewhat new to me.

I have one of these

The bushing will twist flexing the rubber. The rubber does not rotate. That's why you torque with the bushings centered. If you were to tighten under a hanging axle condition, you can see how the bushing would be stressed when the axle rises.
.