My caster mod (with pictures)

[chevyrestoguy]

Originally Posted by Ackattack

Nice work! I'm planning on doing either this, or moving the ball joint on the LCA.

One thing, IMO the locating pin is most likely only there to aid in installation. Once you get the LCA u-bolts tight, I think they hold the shaft from moving front to back. So I don't think modifying the saddles is necessary, but it won't hurt anything either.

Thanks. I had a co-worker tell me the same thing about the saddles, and although I can see where he's coming from, I had to disagree. To me, the locating pins serve a few purposes. First, they index the control arm at a certain location in relation to the center crossmember, which in turn, helps establish the factory-spec'd caster angle. Plus, they ensure that the rotation of the control arm occurs at the control arm bushing and not on the circumference of the shaft. If the rotation occurs at the circumference of the shaft instead of the control arm bushing, it will wear grooves in the shaft at the contact point with the saddles. If it wears excessively, then the shaft will become sloppy and wear out the other suspension components prematurely . True, the saddles/U-bolts hold the shafts tightly, but during the constant abuse that the suspension sees during normal use, they help to keep the lower control arms from moving from front to aft. If the control arm was only secured using the u-bolts/saddles and hit something hard directly on the forward face of the control arm, it could move the arm back slightly, changing the alignment. I may be over-thinking it, but I think the locating pins serve a very important function.

[SCOTI]

Originally Posted by chevyrestoguy

Thanks. I had a co-worker tell me the same thing about the saddles, and although I can see where he's coming from, I had to disagree. To me, the locating pins serve a few purposes. First, they index the control arm at a certain location in relation to the center crossmember, which in turn, helps establish the factory-spec'd caster angle. Plus, they ensure that the rotation of the control arm occurs at the control arm bushing and not on the circumference of the shaft. If the rotation occurs at the circumference of the shaft instead of the control arm bushing, it will wear grooves in the shaft at the contact point with the saddles. If it wears excessively, then the shaft will become sloppy and wear out the other suspension components prematurely . True, the saddles/U-bolts hold the shafts tightly, but during the constant abuse that the suspension sees during normal use, they help to keep the lower control arms from moving from front to aft. If the control arm was only secured using the u-bolts/saddles and hit something hard directly on the forward face of the control arm, it could move the arm back slightly, changing the alignment. I may be over-thinking it, but I think the locating pins serve a very important function.

I think you're 100% correct on all counts.

[usmcchevy]

Thanks for the write up!

[Painter D]

Originally Posted by SCOTI

I think you're 100% correct on all counts.

Agreed



Great write up, and great mod. Be sure to keep us posted with results.

[Mike_82_Shortbox]

Originally Posted by chevyrestoguy

Thanks. I had a co-worker tell me the same thing about the saddles, and although I can see where he's coming from, I had to disagree. To me, the locating pins serve a few purposes. First, they index the control arm at a certain location in relation to the center crossmember, which in turn, helps establish the factory-spec'd caster angle. Plus, they ensure that the rotation of the control arm occurs at the control arm bushing and not on the circumference of the shaft. If the rotation occurs at the circumference of the shaft instead of the control arm bushing, it will wear grooves in the shaft at the contact point with the saddles. If it wears excessively, then the shaft will become sloppy and wear out the other suspension components prematurely . True, the saddles/U-bolts hold the shafts tightly, but during the constant abuse that the suspension sees during normal use, they help to keep the lower control arms from moving from front to aft. If the control arm was only secured using the u-bolts/saddles and hit something hard directly on the forward face of the control arm, it could move the arm back slightly, changing the alignment. I may be over-thinking it, but I think the locating pins serve a very important function.

I think you are right. Friction joints are only as strong as the suface tension of the material and the clamping force of the bolts that hold them. So the pins obviously serve the triple function of positively locating the arm/rod assembly for steering geometry, and giving the rod a positive mechanical connection to the frame to prevent the rod from rotating, and to help it withstand logitudinal stresses.

My question is, will we experience undesirable toe-out on turns readings by taking the steering arm on the spindle out of alignment with the pitman arm/center link/idler arm assembly?

It seems to me that given the triangular geometry we will create by doing this, the outer wheel will want to turn at a greater angle than design, while the inner wheel will want to turn at a lesser angle.

The setup of my 1982 C10 is shown, with the steering linkage in front of the wheel center axis.



Your thoughts?

Mike

[chevyrestoguy]

Mike-
That's a great question. I'm going to have to draw this out on paper and visualize the linkage. Moving the arm back .75" will effectively move the tie rod attach point on the spindle up slightly and slightly to the rear. Because the change is occuring at an arc, the collective position change in the upward and rearward direction is very small. What I need to do is to install the linkage completely on the truck and see if I have an ackerman condition. If so, I could probably shift the idler arm on the passenger side frame rail to compensate, but the pitman arm on the steering box determines the position on the driver side, and that could get tricky.

I believe that the combination of the ball-joint unions on the tie rods and the idler can compensate for the slight alignment change, but until I put the linkage together and see for myself, I'm not 100% convinced.

I'm very interested to get more opinions on this, so feel free to post up any opinions, theory, or data.

[D13]

Originally Posted by chevyrestoguy

Mike-
Moving the arm back .75" will effectively move the tie rod attach point on the spindle up slightly and slightly to the rear.

Didn't you move the LCA forward? That would move the tie rod attachment forward?

[SCOTI]

Originally Posted by D13

Didn't you move the LCA forward? That would move the tie rod attachment forward?

No.... He just moved the lower forward.

[chevyrestoguy]

Originally Posted by chevyrestoguy

Mike-
....Moving the arm forward .75" will effectively move the tie rod attach point on the spindle up slightly and slightly to the rear. Because the change is occuring at an arc, the collective position change in the upward and rearward direction is very small.

Yeah, that was a typo on my part. I meant to say forward instead of aft.

Originally Posted by D13

Didn't you move the LCA forward? That would move the tie rod attachment forward?

Only the lower arm was moved forward, so it rolled the tie rod attach point on the spindle slightly up and back. To visualize this, get two pencils and tape them together like a cross. Then, place them between your two index fingers and then move the lower finger slightly forward. If I moved both lower and upper control arms forward an equal distance, the tie rod attach point would be moved forward because the spindle moved the same distance.