Alignment Question

[dpson]

Does anyone know how much one rotation (360 deg.) of the tie rod changes the toe in/out?

[dpson]

Okay lets try this: if the tie rod has 14 threads per inch (assumed, based on similar diameter fine thread bolts), then each revolution should move the rod 1/14 of an inch, however there are two ends turning so the result would be doubled, 2/14 or 1/7 (0.143) of an inch per revolution. Does that sound reasonable? (I'm a civil engineer, not a mechanical engineer).

Mechanical engineers build weapons, civil engineers build targets.

[Synchro909]

Originally Posted by dpson

Okay lets try this: if the tie rod has 14 threads per inch (assumed, based on similar diameter fine thread bolts), then each revolution should move the rod 1/14 of an inch, however there are two ends turning so the result would be doubled, 2/14 or 1/7 (0.143) of an inch per revolution. Does that sound reasonable? (I'm a civil engineer, not a mechanical engineer).

Mechanical engineers build weapons, civil engineers build targets.

While I agree with your reasoning, I don't think you went far enough. The steerig arms are much shorter than the diameter of the wheels. We need to consider the diameter rather than the radius because as you screw the tie rod, the front of the wheels might (say) come closer together and the back of them get further apart, thus doubling the effect. The short steering arms exagerate things even more.
To answer the OP's question, I don't know but with a thread gauge and a tape measure, you should be able to get close.

[daveymc29]

Along with that, do you mark your tires then push the car forward to get the next measurement or can you mark them and move the car backward to get the measurement. I'm serious, does it make a difference which way you roll the car for the second measurement? I have been told it does.

I have had good luck with a measuring stick I made from some tube, JB Weld, two nuts and two carriage bolts. I affixed one carriage bolt into the tube with JB Weld. (Tube is an inch of short of the inside width, between the tires.) Then I put two nuts on the other carriage bolt and put that bit into the other end of the tube, secure the first nut in place with the JB weld or you could weld them, I don't have the welder. Now you have a stick just less than the distance between the wheels with an adjustable carriage bolt and lock nut on one end. I set this up onto two 2" X 6" inch boards I created, That gets the measure point 6" up and there I mark the front of the tires with the stick just touching. Now I push the car forward until I can set my stick on top of the two wood blocks up to the chalk marks 6" off the floor. Should be about an eighth of an inch short of touching the chalk marks on one end . Seems to work for me. No death wobble since I made this tool and used it unless there is serious troubles in the steering system. I have has that also and commented on it in the past. PM me if interested.

[denniskliesen]

Just a guess from the last time I did one, a 1/16" with about 45 degree turn of the tie rod. I made some tools to check toe-in. I jack up each front wheel and scribe a line in the middle of the tire rotating it at least one full turn. Set it back on the ground and roll it back and then forward on level ground. Set the pointers on the front and then take the tool around to the rear. Look at difference and turn tie rod about a 1/4 of a turn. Roll the car back and forward again. This lets the tires adjust without pulling on the tread. Reset the pointers on the front and then repeat steps above until toe-in is achieved. I try for 0-1/16" toe-in. My car drives down the road straight as an arrow and does not wander from side to side.

[Tom Wesenberg]

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Originally Posted by Synchro909

While I agree with your reasoning, I don't think you went far enough. The steerig arms are much shorter than the diameter of the wheels. We need to consider the diameter rather than the radius because as you screw the tie rod, the front of the wheels might (say) come closer together and the back of them get further apart, thus doubling the effect. The short steering arms exagerate things even more.
To answer the OP's question, I don't know but with a thread gauge and a tape measure, you should be able to get close.

I'm not aware of any short steering arms, but only the shorter pitman arm, which doesn't affect the tow in.


This is an interesting question, and someone should set the tires to 0 toe in, then turn the tie rod one turn and measure the toe in. If no one does, then I may do it some day.


I just did a similar thing on my 1950 Studebaker, and posted the results on the Studebaker website to help others with the same problem. My steering wheel was at 1 o'clock while driving straight ahead, and my toe in was perfect, so I had to turn each tie rod the same amount to set the steering wheel straight up at 12 o'clock.

[WHN]

Front end shop. $49.95, no problems. Your local Ford Dealer might do it for free just to have your car there. The young guys like to poke around Model A’s. Enjoy.

[duke36]

The Ford Service Bulletins and other publications don't address how many turns but show conflicting alignment photos. Dennis' post 5 shows the marking point at the vertical centerline of the axle which we try to achieve, (as in the Bulletins) not 6-8" or whatever chains length are in some of the alignment photos from ground to tire. The problem is some jigs can be blocked on the tire back side by the radius rods, etc. Also, the wheels should be straight ahead for proper adjustment.

[Synchro909]

Originally Posted by Tom Wesenberg

I'm not aware of any short steering arms, but only the shorter pitman arm, which doesn't affect the tow in.


This is an interesting question, and someone should set the tires to 0 toe in, then turn the tie rod one turn and measure the toe in. If no one does, then I may do it some day.


I just did a similar thing on my 1950 Studebaker, and posted the results on the Studebaker website to help others with the same problem. My steering wheel was at 1 o'clock while driving straight ahead, and my toe in was perfect, so I had to turn each tie rod the same amount to set the steering wheel straight up at 12 o'clock.

Bill, I was referring to the relative legth of the steering arms in relation to the size of the wheels. The ball joints are much closer to the king pin than the tyres.

[dpson]

Update: I just got a new tie-rod from Snyders and the threaded ends are 24 tpi (actual measurement), so to follow up on the previous discussion it appears that each full turn (360 degrees) of the tie rod would change the length by 2/24 or 1/12 (0.083) inches.