P-18 Alignment

[woodie49]

I am replacing the king pins in my '49 Woodie.  I am not disassembling the A-Arms or replacing the bushings/seals.  While cleaning the lower A-Arm, I might have allowed the pivot bar to rotate.  I am not sure, but I used a small guage wire through the pivot bar to attach to the A-Arm to maintain the orientation and one came off during the cleaning/painting process. My manual has the attached diagram showing the correct positioning of the pivot to the A-Arm.  I have a couple laser tools that I  am using try to check that my readings are as desired from the layout.

I have a couple problems.  First, the actual width of my A-Arm (measurement "A" in the diagram), which the diagram shows should be 11 9/16 inches is actually 11 3/4 inches, so 3/16 off. Second, trying to get measurement B, which looks like the key measure to determine the correct position of the pivot, can be either 2 13/64 or 2 8/64.  I can not land exactly on the measurement.

I think the goal of this is to get the pivot bar centered as much as possible between the forks of the A-Arm.  In other words, to align the center of the pivot bar to exactly the halfway point of measurement A.  Is that correct? would that mean that measurement "B" (shown here to be 2 5/32) should simply be made to be as equal as possible on both sides of the A-Arm? 

I am assuming if this is off, it might affect the Caster? If that is the case, and i can not get these to be exactly where the manual says they should be, I probably want to err of the side of moving the lower A-Arm to the front, supplying a bit more positive caster?

[dpollo]

I think you are correct.  

 

The only caster adjustments I have ever seen, is a shim placed under the leading edge  of the pivot.

[woodie49]

This is where someone who really understands the front end architecture of these cars would be really helpful. Because i am not sure of the original position of the pivot bar in the A-Arm, I wanted to use the diagram in the repair manual. The manual provides measurement B, but I can not arrive exactly at that value.  Rotating the pivot  increases or decreases the value of B.  

It looks to me as though this would ultimately affect the position of the kingpin, moving the bottom of the steering knuckle forward or back in relation to the car.  Since the upper A-Arm holds the top of the kingpin in position, it seems like I am affecting the caster by moving the bottom.  Since I can not get the exact measure i want, I believe I am better off with the bottom being slightly forward of desired, as this would create slightly positive caster, compared to having it slightly rearward, creating slightly negative caster. As a teen, I used to do alignments at my gas station, and actually understood what I was doing.  But that is a dim memory. I do recall that it was generally better to have positive caster than negative.  But, I confess, now I am not sure why, whether it was stability, or the tendency of the wheels to return to straight after turning. 

The other question I have is whether anyone knows if the function of the special tool C-594 is to center the pivot in the A-Arm, or to achieve the measurement set forth above. I am leaning toward the centering function.  I assume there must be a few of us left out there who probably have a lot of experience with this and might know.

 

[50mech]

The c594 is for centering.

 

Note the measure b extends toward the outer pivot point to give you measurement c.  So the goal isn't so much centered as it is aligned , if A is off a bit, we still want B and C correct as they will determine caster rather than centering on A.

Edited August 14, 2020 by 50mech

[woodie49]

I understand what your saying.  So, to measure "C" properly, I will need to pre-assemble the steering knuckle to the A-Arm, make my adjustments, then pull it apart and assemble it on the car.  I can do this, but measuring this assembled might be challenging. It looks like the line between "B" and "C" measurement points, perfectly divides the two bolt holes on the pivot. This is how i was measuring the  distance at "B".   I did not try to measure the distance "C" because it is not clear to me what the appropriate reference is.  I am using a laser to establish the line, but that line, in the diagram does not touch the A-Arm.  It looks like it might extent to the end of the bushing in the A-Arm, but that is not clear to me. So, I feel I could establish the cottom of measurement "C" from the diagram, but not the top of the measure. If it is the end of the bushing, i can assemble it without the seal to test the distance, adjust the A-Arm pivot if needed, then put it all back of the car correctly.

It seems to me that the special tool does not know where point "C" is, it just results in the a given relationship at the pivot side, which is why i wonder if the is really just centering the pivot.

[50mech]

Yep, bottom of b extended straight out is the top of c.

Bottom of c is the end of the bushing.

 

It does seem like a hard one to establish accurately.

 

Here's a thread using the tool if it helps any.

https://p15-d24.com/topic/44465-using-miller-tools-c-608-and-c-594/

 

 

I would guess @48ply1stcar could tell you if the tool has to be oriented one way or the other,if not it just centers it.  Which would mean with d correct, hope c is, otherwise the arm is bent.