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A very odd and interesting case...front end - steering issue.


James_Douglas

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Every since I restored the 1949 Desoto the steering has not been correct. When driving the wheel did not come back to center as it should. One would have to help it along. Also, out of the freeway the car felt twitchy.

 

At one point, due to things not related, we had the engine out. I added a shim to the worm bearing pre-load plate and that helped a very little bit, but the problem did not go away.

 

Because in 1949 they mounted the steering box on top of the frame, you have to pull the whole thing out to get to the end plate and the shims. You can pull the inner fender but that is even more work.

 

The other day I decided to bite the bullet and pull the steering box and column out and checked the worm gear pre-load on the bench. It was at the high end of the specification of two pounds pull through the center of the worm. The range in 1 to 2 pounds with the Sector (cross) shaft in the box.

 

I added some shims and dropped it down to 1.5 pounds of pull. The wheel drag through the center point felt a little better, but not enough to explain the problem.

 

Since the steering was out, I jacked up the front end and tried turning the wheels left to right to see if the king pins felt like they were binding. The front end did not swivel as one would think. A lot of drag. I suspected that I got too greedy with the king pins. However, the pins were line honed on a sunnen machine and spun like a fine bearing. Perhaps I got the thrust washer shims too tight?

 

Before digging into the king pins, I pulled the outer tie rods and tired each wheel independently. They were both fine and flopped around like a fish..  Hummmm.

 

The tire rods are all NOS or NORS. They all took grease.  When I got them, some of them did not have dust boots or the boots were very bad leather ones.  When I had put them in I had used a set of urethane ones I purchased at the local speed shop.  Hummmmm.

 

I took a knife and cut them all away from the 4 tie rods and the two on the drag link.  Everything moved MUCH better. The center bearing has no drag at all.

 

The modern urethane dust boots were binding on the tie rods.  I now have to see if I can find some old style leather tie rod boots.

 

I suspect that the problem is one of "staked tolerances" where one item itself does not cause and issue, but the sum of a lot of little problems added up to more drag than the geometry could overcome and pull the wheel back to straight line with hold from the driver.  I will finish putting it back together next weekend and see what I get.

 

Just when you thought you had seen everything, something new.

 

James.

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That sounds more like an alignment issue.  The steering not returning to center while driving can be because the caster (king pin angle to front/rear of the car) of the front wheels are not set right. I don't have the specs for DeSoto, but a '48 D24 is 0 to +1 degree (positive being towards the rear of the car).  Improper camber angle would cause the car to pull to one side or the other, rather than go straight down the road.       

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I agree with Dan that it sounds more like caster issue. The original specs for alignment are for the bias ply tires used back in the hey day of these vehicles. Some things to consider:

  • If you are running bias ply tires then the original specs can be used but I would lean alignment settings toward the highest positive caster setting the spec calls out. With zero caster the car would not have much influence to center on it's own and at speed could be your twitchy issue.
  • If you are running radials then you need modern alignment specs which include negative camber and additional positive caster. Below is what I use for my old cars now running radial tires. 

image.png

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I also like more caster, helps with wander and aids return to center.  Also be sure the wheels are straight ahead when the gear is centered.  Things can be assembled so that is not true and will cause the return to center problem.  Wheels straight ahead and gear offcenter will really feel wonky.

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The front end alignment is spot on. One could feel the difference in the front end when turning the wheels by hand before and after I cut off the boots.

 

Once I get time to finish putting everything together I will take it for a drive and see what the difference is if any. If it still does not come to center, then I will check for the 4th time the alignment.

 

Basically, I went through the MOPAR service diagnosis that is in the "Tech" series (Vol.# No.4) on the subject.

 

The specifications for second series 1949 are:

 

Camber: 0 to +3/4 degrees with +1/4 Preferred.

Castor: -1 to -3 degrees with -2 Preferred.

Toe-In: 0 to 1/16 inch with 0 Preferred.

Toe-Out: 21-1/2 degrees plus or minus 1 degree.

King Pin Angle: 4-3/4 degrees to 6 degrees.

 

James. 

 

Edited by James_Douglas
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