Rear Axle Trust Angle

[DonaldSmith]

 

In September of 2019, I took my '47 DeSoto Suburban to an alignment shop for a wheel alignment.  They found that the rear axle thrust angle was negative 0.94 degrees.  Maximum should not exceed 0.75 degrees.  That means that the car was trying to steer to the right.  The adjusted the steering centering to compensate.  They suspected that my extruded aluminum lowering blocks were damaged at the locating pins, and offered to make billet lowering blocks. 

 

This month I ordered some billet aluminum lowering blocks from a speed shop.  I removed one of my existing blocks and discovered that the locating pin in the new blocks is too fat, 5/8" rather than a fat 1/2".  What to do?  I removed the other existing block.  I found no damage in either block.  So I'll return the billet blocks. 

 

I spent the last few days reassembling the rear suspension, a difficult task at my age,  But why the mis-aligned axle?  Then a Duh! moment. Suddenly it all came back to me.   In the Summer of  2018, while marshaling for a car show, I backed quite forcibly into a power pole.  It left bumper distortion and a dent in the side of the fender.   I suspect frame damage; that would explain the misalignment of the axle. 

 

Now I have to think about about having a frame and body shop inspect frame and correct the condition.   Or maybe I'll just let it ride.   Maybe his car is too much for me.  

[Tooljunkie]

.19 degrees? Could be factory. 
if it drives normal and no unusual tire wear i wouldnt think twice about it. 
spring mounts could be another thing to look at. Worn bushings. 
Dont know how precise the alignments were back in 1947. 

Edited June 26, 2020 by Tooljunkie

[Plymouthy Adams]

did you check the forward silent block on the vehicle  also the rear shackle bushing are notorious for wear to the point they knock the driveline out of phase......in this era the SB mount is a riveted mount...and not tweakable with shims as is later style....bushing are replaceable big box store item and are inexpensive Mopar A-body units...you will have to trim a bit as the older springs are a bit narrow.

Edited June 26, 2020 by Plymouthy Adams