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Pulling my hair out on my '49 Desoto


James_Douglas
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I am running out of ideas on my restored 1949 Desoto Convertible. The steering sucks. I have never had such trouble with the steering in a car.

 

To sum up. Everything is new or rebuilt. The car darts or wanders and does not self center after a turn. As you know if you have been following my posts, I have checked to make sure I have vertical end play on the king pin thrust bearings. I have made sure that the pin bores are correct. I have checked that the center bearing is correct and not binding. The steering box has all new gears and is properly adjusted.

 

On advise of a suspension engineer, he suggested that I crank in all the Castor I could get taking it from the book (-3 to -1 with -2 preferred) up to positive 4 and see if I could still turn the steering on the street. Basically he said to add in all Castor I could until the steering was too hard then back down until the steering was acceptable. That would give me the most "Castor Effect" that this car is capable of.

I tried yesterday to get the Castor to plus four. I could not. With the adjuster all the way back the best I could do was -0.5 on the drivers side and -1 on the passenger side. The cam was up against the control arm. I did back it off a little so it would not rub.

 

I am at a loss. Did they design the 1949 with so little adjustment range? If I go the other way, the best I can get is perhaps -3 and that is it.  I checked the King Pin Inclination and it is within specification and within a half a degree side to side. So, I do not think anything is bent. The car was never in a wreck.

 

At this point in time, I am thinking that I may have to tear out the front end and diverge from the factory service manual. The book warns you in italicized lettering to make sure you do not turn the control arm pivot bars or you will screw up the Castor settings. I was very care full to make sure the center-line of the bar bolt holes were equal distance from the inner machined edge of the control arm bushings. What I now think I may have to consider is to get "more Castor" I will have to move the upper bar forward so the upper control arm is further to the rear and do the opposite to the lower so it moves forward.

 

That will tilt the steering knuckle support top to the rear and bottom to the front. The question is when I do it, how many turns of the bar will equal how much of a Castor range change.  Of course you cannot go too much or the control arms will bind.

 

Interesting in that the second series 1949 Desoto uses the same spindles as the 1946 to 1948. They changed to a new spindle part number in 1950 although the steering knuckle support stayed the same from second series 1949 to 1953. I am starting to wonder if they had a production delivery problem with the new spindles and so they just used the older one and then made the switch six months later when the 1950 models came out.

 

The only other suggestion was to take out the upper control arms and give the lips on either side a slight reduction with a grinder to give the steering knuckle support a little more room to move. Also, it was suggested to take a little bit (a few thousands) off of the face of the steering knuckle support and machine a little off of the end of the bushing. All to make the eccentric bushing have more room to be adjusted. Of course how much one would get would be a very laborious effort.

 

I would ask that anyone with a second Series 1949 or 1950 Desoto or Chrysler six that has had a front end alignment and knows what the final numbers are please share them with me and your qualitative assessment of how the drives at freeway speed and on self centering.

 

No doubt I am missing something or it may be that this car was crap steering from the factory. My older brother, 15 years older, said that "the car never really did steer good". But, his memory is often not that good...

 

Any suggestions would be helpful.

 

James.

 

 

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Guys,

 

I am well aware of the issues with radial tires. The car is a concourse restoration. All the tires are new. They are Diamond Back Radials 700R15's (AKA Yokohama) the same ones I use on my 1947 Desoto. I have tried them from 40 to 60 PSI. No difference.

 

The problems is on perfectly flat roads on asphalt. The lack of centering after a turn is not generally related to type of tires.

 

What I find interesting is that I am getting only three degrees of total change on the eccentrics. I am wondering if the rubber seals are for some reason too thick and not allowing the thing to screw all the way forward or aft.

 

James

 

 

Edited by James_Douglas
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Just out of curiosity. What are your toe in settings and is your steering centered?

The reason I ask is that on my 1948 P15 the steering was not centered and my toe in was excessive. This made it very hard to steer and the steering did not want to return to center after making a turn.

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Also remember that in the old days when these cars were produced our roads were designed with a high berm. So the middle of the road was higher than the endge of the road. This was also done to help with rain water being pushed to the edge of the road and into the curb or cutter for drainage.

 

So you will have some built in slop in the steering wheel to compensate for this, But in our newer road construction we have now gone to a more flat road surface becasue of the use of power steering and the use or radials and rack and pinion steering linkages.

 

So are you sure that you really have a problem and are you expecting the steering wheel to always come back automatically to a centered position with out any help from you?  Not sure if these car are setup to always do that. 

 

Rich HArtung

Desoto1939@aol.com

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55 minutes ago, desoto1939 said:

Also remember that in the old days when these cars were produced our roads were designed with a high berm. So the middle of the road was higher than the endge of the road. This was also done to help with rain water being pushed to the edge of the road and into the curb or cutter for drainage. . .

 

It is called crown and they still make roads that way. They just use less crown than they used to, I guess experience has shown that they did not need as much crown for drainage to work as they once thought.

 

Sorry, but I can't be of help for James’ issue: I've found he knows more about this type of thing than I. If he is stumped that it is unlikely that any suggestion of mine will be useful.

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James what happens when you put the original bias ply tires back onthe car? Is there any difference.  I do know that the AACA does not promote the use of radial tires onthe older cars that were designed for bias ply tires. The reason that I was told at a judging seminar is that the car steering and chasis is not made to handle the rolling action of the radial tire as compared to the what the car was designed to steer and turn with the bias ply tire.

 

Rich Hartung

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HMM,   After rebuilding my 47 I took it to a shop that only works on old or high performance cars. He four wheel aligned, reset everything.  When you say it wont re center could there be a little binding?  Believe it or not, one thing he did notice and we changed was the relation of the angles of the tie rod ends to the spindles and other connections points. His reasoning was that the car under load, turning bumps parts are moving around. What its worth department. 

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A long shot- what about bump steer from bent or  parts installed wrongly somewhere, maybe years back and repeated on rebuild?

 

Most full service Hot Rod shops have to use that tool to design and built front and sometimes rear suspensions.

 

I know one one in South San Francisco and one in the East Bay area.

 

DJ

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Is this the same 49 convertible with esi disc conversion? That required spindle spacers that pushed the hub out 3/8"?

I would think it's possible that altered scrub radius on a car with negative caster could give this effect.

Particularly if it made it come up to or across the zero line.

 

I haven't fooled around on these cars with rim offsets or anything else that would change the scrub radius enough to know from experience though so........

Edited by 50mech
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To answer some more of the questions...

 

* As far as I can tell when I rebuilt the front end, none of the parts appeared bent. When I did the King Pin Inclination check there were within 1/2 of a degree so it is not likely that the spindles are bent.

 

* I checked all the tie rods to make sure none were binding.

 

* The steering box has all new parts in it, including the worm and sector gears. I set it up according to the MOPAR service manual using the spring gauge at the wheel rim. Just like in the little service books on the Chrysler Imperial Site.

 

* 50Mech has his thinking cap on. I did use and ECI disc brake on the front which included their hubs. Their hubs moved the bolt face of the wheels out about a 1/4 inch on each side.  When I had the rims built with the back space for the calipers, we were able to move the outer rim of the wheel back enough so that the center-line of the tire is back to where it should be with the stock rims. I have tried to visualize in my head if there could still be an issue anyway. So far, I cannot "see it".

 

The only other thing we did was to cut a 1/2 turn off the springs.  The car sat up terribly high in from and my photos from 1963 show that is how it was at age 14.  It is possible that by lowering the car a bit that upper control arm line would "grow" and pull back on the support upright and thus pull the top of the spindle a little more inboard.  But this would effect Camber and not Castor, so I do not think that is the issue.

 

I guess we will have to wait until I get up there next week to test drive it. I would be pleasantly surprised if the change from an upper bushing to a torrington needle bearing and 1.5 degrees more Castor made a large difference. One can hope!

 

Other than that I am at something of a loss on this one. I may have to tear out the entire suspension and go through each item one by one to make sure they are ok.

 

So much fun on a car one thought of "done".

 

James.

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Could compare the steering effort for both of your cars sitting on turn plates. ( Even home brews like vinyl tiles and grease)

That way you could positively eliminate or confirm whether any binding exists with the weight on the wheels. If not then you could confidently focus on certain aspects of the geometry.

Edited by 50mech
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Having a hard time putting concours restoration and ECI disc brakes with the same car.

 

We now know the rims and front springs aren't concours as well. 

 

What else's isn't "concours" because the info you give is misleading and it's hard to offer any help when it's not what we think it is.

 

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Upper or lower A-arms possibly could be moved forward or backwards for more caster.

Tiny amount of pivot shaft adjustment.

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3 hours ago, Sniper said:

Having a hard time putting concours restoration and ECI disc brakes with the same car.

 

We now know the rims and front springs aren't concours as well. 

 

What else's isn't "concours" because the info you give is misleading and it's hard to offer any help when it's not what we think it is.

 

That's why I thought it wasn't the same car. 

I think myself and everyone else answering envisioned something  entirely factory.

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Ok so looking through any post I could find about this car a few things stand out.

Just thinking out loud here.

 

1. The car mysteriously rode too high in the front.

2. It won't steer correctly with anything close to factory adjustments and geometry

3. The spindle spacers esi made to fit a 49 DeSoto convertible didn't fit.

4. The rear section of the frame was bent for a not completely clear reason.

 

Given it seems you've gone to great lengths to check and correct everything else. Mysteriously bad steering and mysteriously high ride height and some sort of odd deviation in parts fitting just seems to really point to it wearing the wrong parts.

 

If it were me I would concentrate on that, even to the point of getting all components from another car rather than deviating wildly from factory settings.

Edited by 50mech
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When I say a concourse restoration, I use the term to mean every single part was taken down and repaired or replaced. I did change the car over to disc brakes. The frame was not "bent" at some point in its life the rear cross member was bent when someone put cinches on it. If you look at all the Chrysler-Desoto rear frame cross members they are a thin item that does noting bu keep the side rails apart. I took out that member and put in one that is stronger and  is set up in the event I want to tow a tear drop with it at some point. I am going to do the same thing to the 1947 Desoto next year when I take it apart.

 

Other then that it is stock.

 

I looked at 4 different 1949 Convertibles and they all had the front end up in the air. I wanted to get the rake level. The stock factory photos show the front end way up in the air as well.  It is possible that lowering a car can effect camber, but I have not see any information to show that it would affect Castor. It is castor effect that I am dealing with or something preventing the Castor Effect from doing its job like binding.

 

The ECI hub spacers as I remember moved each hub out about a 1/4 inch or less. I had Stockton Wheel, when they made the new wheels, make that 1/4 inch back up so the tire center line  is the same as it was with the drums. So, unless I am missing something, and if I am someone explain it to me, how would that affect the Castor Effect? With the King Pin Inclination within specification and the center line of the tire in the same place the scrub radius is the same regardless of what hubs are used.

 

James.

 

 

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Well, hopefully the needle bearings do the trick.

 

As best I understand the negative caster setup in these is to make manual steering easier while the wheel return is derived entirely from kingpin inclination.

 

Supposedly the camber does change caster on them, but only very little.

 

Assuming measurements and binding checks you did were with it jacked up on the control arms, it really only leaves the kingpins binding under weight......

 

Again I'm just tossing around ideas... hoping maybe something will click.

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Right now I have:

 

King Pin: Pax=5.75 Driver=6.25  (4-3/4 to 6 is the spread) So in theory I am over on the right by 1/4 degree

 

Camber: Pax = +0.25 Driver +0.25

 

Castor: Pax = -1.0 Driver -1.0

 

Toe is set to Positive 1/16 inch

 

I did not do toe out on turns this last time I was up there working on it. Last year as I remember it was within spec. I do not have the tools to do a thrust angle.

 

What I do not get is that with eh King Pin Inclination at the upper end of the range...I should be getting more castor effect and a little bit of a hard to turn wheel.

 

I can tell you that when I pulled the kin pins the first time which had been line honed on a Sunnen machine that the bushings galled on the pin. I opened them up some with my correct reamer and again when I pulled them 2 weeks ago to put in the needle bearings there was galling of the bronze bushing onto the upper outer of the king pins.  So, even with grease and new bushings and new pins that is a lot of load at that point.

 

Middle of next week I will pull it off the rack at the house and drive it and pray that the needle bearings are the issue.

 

 

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Hello James,

 

Some suggestions....  Rip out the page in your service manual with factory alignment specs and throw it away, we're going to get it as close to accepted / basic RWD specs as we can and see how it drives?  

- Caster is the easiest way to bring stability and you are at the wrong end.  We already know this...  Can you get it into + territory at all?

- Adjust you camber to -1.0 to -1.25 on both sides, this will help with stability.  I don't have the factory specs but I can't believe + camber would be call for.  If it is specified in the positive, the engineers made a mistake, I don't care what type of tires you run.  

- Adjust your toe in to 1/8 inch.

We keep focusing on caster only, but these other specs are almost as important.

Give this a try.  Was your set back or thrust angle in spec?

 

P.S.  Optimal specs are 

3-7 degrees positive caster (I got 2 out of my 49)

1 to 1.5 degrees negative camber (I'm at 1.?) 

1/8 toe in  (I'm there)

Drives good, wheel returns to center and is fairly stable at freeway speeds. so good enough...

 

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