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P15 upper control arm repair


Oldguy48
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My mechanic tells me that my upper control arm bushings are in need of replacement to pass PA state inspection.  It doesn't look like a job I want to tackle myself.  I know that replacement parts are available, but my repair manual shows some special tools being used.  Are those special tools required for this work?  I'm sure my mechanic doesn't have them.  I'm not certain which direction to go from here.  Must I acquire those special tools?  Any tips or thoughts would be appreciated.  Thank you!

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First question that I have for you, Is your car tagged as an antique car or with a regular Pa Tag or classic tag?

 

reguar tags and classic tags require Pa inspections.

 

The cars that have the real antique tags do not need to go through Pa annual inspection. I have a 39 Desoto and my car does not go throught PA inspection and or Emissions testing it is grand fathered with the Antique tag on the car.

 

Yes the two special tools do make it easier to put in and adjust the upper an lower control arms. If you are going to be doing the upper might as well do the lower and also the tie rod ends at the same time since the car willbe up in the air and also kingpins at the same time unless you are tight for spending money at this time.

 

 

Rich HArtung

Desoto1939@aol.com 

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The car is titled as a Street Rod, so it requires a normal vehicle inspection.  I'm hoping minimal repairs will be needed, as my driving it is mainly to local car shows or parades.  My odometer shows only about 100 miles since last year, mainly due to the Covid issue.  Are these special tools a must for this repair?

 

Wayne Varner

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Be very careful. You may need to "educate" the inspector. Odds are her or she has no idea of that they are looking at. Let me explain.

 

The 1930 to early 1950's MOPAR's used a "nut and bolt" bearing design. There are no rubber bushings and there are no smooth wall bearings-bushings. The center block of the control arms pivots are in essence a threaded rod. The "nuts" which go into the control arms are threaded on the inside to thread onto those threaded rods and the outside is designed to cut into the control arm like a self tapping bolt.

 

When UNLOADED there is a LOT of play in these type of designs. It was engineered that way.

 

Time and time again I see people pulling the front end apart thinking they have "worn" control arm bushing. When in fact they did not.

 

The bushings are "out of specification" when they have more than 20 thousands of clearance. That is a lot. See the attached PDF and the attached image.

 

Check them yourself and if they are equal to or less than 20 Thousands then educate the inspector.

 

James

control_arm_bushing1.JPG

Control_arm_bushing_clearnace.pdf

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The second thing to be VERY careful about is when replacing a bushing if it is off as little as one rotation you can toss out the Castor Alignment and may not be able to get it back no matter how far you turn the eccentric adjuster.

 

Why?

 

Because the placement of the control arms sets the inclination of the arm that hold the kind pins. If the relative distance between the lower control arm and the upper control arm is moved then that changes the inclination. 

 

On my 1949 Desoto, either the factory screwed up and did not get it right (only six months production on those and it was running very late) or I screwed up when I did mine.

 

I have the castor adjusted with the eccentric all the way to the rear and I just get -1%. Technically just within spec but I noticed I really need more for it to be stable.  I am going to pull the nuts on the lower at some point and move the lower control arm one turn forward so that I can get more castor and get the eccentric to be in the middle of that rather small adjustment range. You do not want the eccentric rubbing on one side or the other of the control arm.

 

See the manual or the Imperial Club Lit on this subject and you will see what I am talking about. That is why if they are ok it is beast to leave well enough alone. I doubt your mechanic, unless he/she is 70 years old has any idea what they are getting into with this suspension. It takes a lot more detail than a modern rubber bushing suspension to do correctly.

 

James

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I'm thankful for the replys to my question.  I intend to pay a visit to the inspection shop, armed with this information.  Perhaps the old girl will be on the road again soon!!

Thank you again for the responses!

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Oldguy48.....what the others have said is correct...the inner & outer, upper & lower control arm bushings on mopars up to 1956 do have more "play" than the modern car & if the mechanic is not familiar with the design will assume the bushings are worn.......they maybe BUT they also are designed to have more play than a modern car.........I too have a "hotrod'.......actually has been that way since 1973 when the 318 Poly was installed in the 1940 Dodge.........each year I have to have an annual safety inspection and always come prepared to argue the merit or not of the stock style front suspension...........hopefully your inspector will believe your presentation.........lol..........andyd  

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My mechanic is still convinced there is too much play in the upper control arm bushings,  He didn't actually measure anything, hence I'm skeptical of his opinion.  I have a difficult time physically with crawlling under the car, so I'm going to enlist my son-in-law to take a look.  I may ultimately take the car to another shop that is more familiar with these vehicles.  Kinda lilke getting a second opinion from your doctor!  There could possibly be too much wear in those bushings, but I need it to be checked out more thoroughly.  I'm just really frustrated that I'm unable to legally drive the car right now.  I honestly do not believe that the car has any safety issues whatsoever, but we'll see!!  Depending on the outcome, I may not be a customer of my current shop ever again.(But I'll reserve judgement pending further investigation!)

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