Rear axle shifted

[Guest Blackpack]

My story starts when I developed a severe shaking in the front end of my 48 Super convertible. Upon looking at the tires, I noticed that all 4 tires were wearing unevenly with the inside tread going bald. I decided to have the alignment checked and the right front was way out of adjustment. With that problem fixed, I ordered new tires for the car and soon discovered a couple of new issues. For some reason, the car had 5.5" wide rims on the left front and right rear and 6.5" wide rims on the right front and left rear. I instructed the technician to put both 5.5" rims on the front and the 6.5" rims on the rear. We we did that, another issue arose. The right rear tire clears the fender skirt by only 1/4" and the left rear tire clears by a good 2". My questions are, how could the axle get shifted this far to the right and is there an adjustment to move it back to center without pounding on the axle? Thank you

[Ben Bruce aka First Born]

 

 Since the car has coil springs, it has a panhard bar to hold the "axle" in place, side to side.. The bar is either bent or the bushings are shot.     The panhard bar attaches to the frame , behind and above the axle housing on the driver side and to the lower spring mount  on the passenger side. No adjustments.

 

  Ben

[Bhigdog]

1 hour ago, First Born said:

The bar is either bent or the bushings are shot.  

Or the body mounts are rotted and the body shifted, or the body was mounted a bit askew from new, or a combination of all of the above..........Bob

[Guest Blackpack]

These are good suggestions. I'm pretty sure the body mount busings need attention, but I will check the bar bushings as well. The coil springs are not setting straight either

[95Cardinal]

It's probably the Panhard bushings, but you should also verify that the Panhard bar is the proper length for your Super.

The bar that was installed on my 58 had obviously been broken in the past. When they repaired it, it was not the correct length.

Parts car to the rescue!

[old-tank]

It should be pretty much centered with the full weight on the axle.  If lifted or excessive weight in the trunk it will shift to one side or the other.  Also check the distances with the frame as a reference; a quarter panel may have been replaced or body damage repaired incorrectly.

[Ben Bruce aka First Born]

2 hours ago, Blackpack said:

 The coil springs are not setting straight either

 

  The top of the springs fit into a pocket in the frame. In the event the panhard bar is the problem, this fits.   I think.

 

  Ben

[Smartin]

Yes, with the weight of the car completely off the suspension, the entire rear assembly will be shifted significantly.  I noticed this on my 58 when it was nothing but a chassis.  I thought something was bent, but it became clear that when a load was put on it, everything came back to center.

[jscheib]

To me, this raises one question - how long and miles have you owned this car before this came to your attention?  Seems possible not long, if you did not notice the different wheel sizes.

 

John

[buick5563]

3 hours ago, old-tank said:

It should be pretty much centered with the full weight on the axle.  If lifted or excessive weight in the trunk it will shift to one side or the other.  Also check the distances with the frame as a reference; a quarter panel may have been replaced or body damage repaired incorrectly.

 

You HAVE to check it on the ground or you WILL freak out. I doubt it is anything but the panhard shift. (Guessing) 

[Ben Bruce aka First Born]

11 hours ago, buick5563 said:

 

You HAVE to check it on the ground or you WILL freak out. I doubt it is anything but the panhard shift. (Guessing) 

 

  Mike is right, check on the ground. I just ass u me ed that was the case.  It WILL be off centered due to the geometry of things otherwise. 

 

  Ben

[Guest Blackpack]

The measurements that I stated above were with the car sitting on the ground. However, the mechanic told me the coil spring was skewed and may have been looking with the car in the air. Another thing to check. As far as the size of the wheels go...I only learned that two of the rims were 1" narrower when I had new tires installed. Otherwise, they all look identical and you can't really tell with the tires mounted. I did have wider tires than what was called for put on the car, but they were the same size that were previously put on the car

[EmTee]

6 hours ago, Blackpack said:

The measurements that I stated above were with the car sitting on the ground. However, the mechanic told me the coil spring was skewed and may have been looking with the car in the air. Another thing to check. As far as the size of the wheels go...I only learned that two of the rims were 1" narrower when I had new tires installed. Otherwise, they all look identical and you can't really tell with the tires mounted. I did have wider tires than what was called for put on the car, but they were the same size that were previously put on the car

 

Do the pairs of wheels having the same width also share the same backspacing/offset...?

[NTX5467]

With one end of the Panhard bar anchored to the frame, as the suspension moves though it's total travel, the lateral location of the rear axle will move from its centerpoint, which would be a factory "ride height".  The length of the bar will determine the radius of the arc.  When the rear suspension is at full compression, or full extension, the lateral position should be similar, but when at the middle of travel, it should be basically centered between the frame rails.  That's the "geometry" issue First Born mentioned.  This is also why having the car at CORRECT ride height is important.

 

NTX5467

[Tomaapilot]

If I might suggest, one can learn lots from making a few measurements with the car on jack stands, tires removed.  With the car loaded and level as though it were on the ground, measure the wheelbase side vs side, and also the diagonal dimensions.  Be sure you pick a good 'fixed' spot, like immediately under the rear axle on the face of the brake drum as a reference.  Likewise, on the front, under the ball joints might be a good spot.  I use a plumb bob on a string, and simple mark a spot on a piece of tape on the ground.  Armed with these numbers you'll be able to immediately tell if something is cattywhompus or not.  I'm not certain how to spell cattywhompus, but you know what I mean.  Based on your report though, I'd be shocked if the car wasn't also handling quite rudely.

 

Respectfully,

Tom

[Beemon]

I don't know what suspension information is detailed in your shop manual, but in the 56 manual, it shows you how to tell whether or not your springs are good or bad. Most notably, if your rear springs are sagging, then as others have stated, the panhard bar will be anchored in an unusual spot. If the springs are skewed, make sure someone didn't remove an insulator from one side and forgot to install it.