‘68 Polara Alignment by the book

Brakes, Suspension, Rims and Tires

  1. HWYCRZR

    HWYCRZR Senior Member FCBO Gold Member

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    Good question. At zero it will not make a difference. But I could see where on a larger diameter tire it could make some difference if measured on the most forward and rearward portions of the tire.
    The manual description is up for interpretation:
    "Tow- in is measured in inches and is the distance the leading edges of the tires are closer than the trailing edges."
    So what is the leading edge? They could be talking the the actual tire leading edge on the ground, or are they talking the leading edge measured at the largest diameter of the tire?
    I need to find my old college suspension book.

    This is an interesting exercise to break up the afternoon.

    Without a special fixture like you described it would be difficult to measure the outer edges.

    The fixture I used was for 13 - 18" tires and measure point was 13 inch from center-line. I am running 14 inch tires. My tires measure close to 28" diameter (front to back)
    I couldn't do the math in my head so I laid it out on my work bench.
    Using the 1/8" spec in the manual, I set my bars so that they had an 1/8" difference between fore and aft (1/8" difference at 26"). Crap now that I laid it out and am writing it down I could have done the math.
    Maybe I will come back to the math, but first the visual.
    I then extended the lines on my bar and measured at 14" (28" diameter) and at 15" (30" diameter).
    At 13 inches each direction of center-line (the length of my bars) I had 1/8" (4/32")difference, at 14 inches I had about 5/32" inch difference, and at 15 inches I had about 3/16 (6/32").
    So for this set up and with my 14 inch tires, if I was to set to factory specs and the leading edge of the tire (largest diameter) is where I should measure, then I should have set my toe-in toe to 3/32" (1/8" - 1/32).
    I can live with less than 1/32" of tolerance, (actually the tape measure the sent in the kit only goes down to 1/16".
    I think the math is much less than that, but my lines are about 1/16" wide and my tap measure measure is not that accurate.

    Now the math model. I am not a math scholar or geometry expert. (So I could be wrong, but I am assuming the same rate of change throughout the distance)
    per spec 1/8" I have a 14" tire that is about 28" diameter
    1/8 of difference in 28"
    .125 / 28 = .00446429 This is the factor I should be able to use for every inch difference of tire diameter.
    13" from center line (26 x .00446429 = .11607143). At 14" from center-line (28" dia) the spec is .125 (1/8). .125 - .11607143 = .00893 or just a little over 1/128".
    So in theory I should have subtracted 1/128" off the 1/8" measurement to compensate for my 13" fixture. 16/128" down to 15/128"
    So in my case it is not a measurable difference.

    How about a 40" dia tire with my alignment set up (13" bar from center-line)
    Say the spec was still 1/8" (.125) but now on a 40" dia
    .125 / 40 = .003125 My bar is 13" from center, so 26" long. (26 x .003125 = .08125) .125 - .08125 = .04375" This means I would have to subtract about 3/64" from the spec using my bar . So somewhere between 1/16 and 1/32 of an inch difference.
    So I don't know if it really matters that much.
    Also as you get larger tires you need larger fixtures. I would guess that the larger fixture comes with a longer bar.

    Thanks for the afternoon brain teaser. For disclosure made me second guess my accuracy so I had to prove to myself whether it makes a difference or not.

    It does not with standard measurement tools.
    My visual experiment was not as accurate as my math calculation.
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  2. Gerald Morris

    Gerald Morris Well-Known Member

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    I used a brass wire brush in a drill motor to clean the jack screw threads the 1st time in Mathilda (66 Newport) a couple yrs ago before oiling the threads and relaxing them. Tires/wheels are in the air for the entirety of this work. Later, I used a shot of penetrant to soak down into the retainer as well as the threads. Last week, I flicked what little dirt and rust had accrued on them off, then repeated the procedure, but I DO use an impact wrench to save time unwinding and winding the threads until they reach the point where they actually are pushing against the torsion bar some. Then, I use the ratchet.
     
  3. 3175375

    3175375 Member FCBO Gold Member

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    Good work.

    I too am unsure of what the real measurement should be. I will dig into this a bit.
    From a pragmatic viewpoint, I think that you are good to go.
     
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  4. Jeff55

    Jeff55 New Member

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    As a 40 year certified master technician I was impressed with this post. I thought that you did an excellent job with the explanation of angles and adjustments. As far as tow with radial tires, when I was doing alignments just about every vehicle with them had 0 for tow. If I can make one suggestion it would be to call the suspension arms by their technical names ( control arms). As my suspension instructor said when I was in technical school, an A frame is a house. Very good job!
     
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  5. HWYCRZR

    HWYCRZR Senior Member FCBO Gold Member

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    Went for a drive tonight to check out my alignment. Roads were dry and about 26 degrees out, so no splashing.
    I didn’t get the steering wheel quite as straight as I wanted it so had to adjust the steering rod sleeves. I drove it in the garage straight leaving the wheel off center. (Tires were centered). Marked the turning plates with the wheels straight and then centered the wheel. Turned One in and turned one out. Until my lines on each plate were straight again with the steering wheel centered. Technically I should have put m alignment bracket on the rear wheel and run a string line to the front bracket. But on a C- body there is not much room on the rear wheel for the bracket. Any some beauty shots on my test drive.
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  6. Polara_500

    Polara_500 Senior Member FCBO Gold Member

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    River's up.
     
  7. HWYCRZR

    HWYCRZR Senior Member FCBO Gold Member

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    Yep, one of my reasons for driving that way. It broke flood stage here in Fargo yesterday and will go up more as soon as the 40’s hit. Nothing too out of control. Thankfully it quit snowing after January.
     
  8. Polara_500

    Polara_500 Senior Member FCBO Gold Member

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    Has to be south of town, I'm not recognizing the area. Stay dry (although it looks to be headed thataway).
     
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  9. 3175375

    3175375 Member FCBO Gold Member

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    Good work.

    I did some digging and found these links:

    Toe-in How to measure:
    How to measure toe yourself (with pictures)
    Adjusting toe alignment on wheels
    http://www.longacreracing.com/userfiles/articles/text/Set_Toe_Properly.pdf

    DIY Precise Alignment (Toe-in)

    Best:
    How To Measure Toe In/OUt? - Pelican Parts Forums

    The key is to measure (when the spec is in inches, not degrees is to measure the toe at the front and back of the rim.

    I hope that this helps...
     
  10. HWYCRZR

    HWYCRZR Senior Member FCBO Gold Member

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    Yes just south of Wild Rice by the Governors Country house, North of Oxbow.
    I used to live on the river. At 30 ft above flood stage it would come out of the trees and start flooding the flats between the trees and my house. Between 32 and 35 you would start to prep.
    Now I am off the river and built high enough that Casselton will have to flood before I get water to my house.
     
  11. HWYCRZR

    HWYCRZR Senior Member FCBO Gold Member

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    Thanks. I went back in and did some editing, I prefer to be accurate. Control Arm instead of A- Arm. I even used upper control arm a couple of times.