The Stovebolt Site Forums The Shop Area Driveline Camber, Toe in/out, and caster on a stock 3600

BZTGUY, I'm betting your problem is wheel offset, though,it could also be a combination of alignment and misassembly.

For example: If the drag link in not assembled correctly or has weak springs it will not be the correct length. So if you adjust the steering box with the wheels straight ahead rather than with the pitman arm disconnected you may not be on the high point when you make the adjustment. In which case, the steering gear will bind when it goes past the high point and not return to center automatically. Also, if the tapered caster shims were installed backwards there would be negative caster rather than positive and the steering would not return to straight very well if at all. It would also hunt all over the road and require much steering correction. The spec for caster is + 2-1/2 degrees plus or minus 1/2. Camber is +1 degree plus or minus 1/2. With radial tires camber can be reduced along with toe in.

Caster impacts another dimension known as trail, which is the distance the king pin line leads or trails the contact patch center. The more trail, the heavier the steering will feel. Trail is directly affected by caster and indirectly by tire rolled radius. As tire rolled radius increases, the distance between the kin pin contact point and a vertical line dropped to the center of the contact patch will increase. So larger diameter tires will make steering feel heavier with no change in caster. Thus, even though the big trucks with 20" wheels have only 1/4 degree more caster they have a great deal more trail and of course will have heavier feeling steering. With zero caster there will be no change in trail with larger diameter tires. The commonly used 235/85X16 tire at a measured 15.5" RR is a great deal larger than the original 15 inch tires supplied on 3/4 tons with specified rolled radius of 14.1". So you can see that the trail will have increased with the larger tire making for heavier steering.

I stated incorrectly in my last post that the king-pin line goes to the center of the tire. That is not the case. It will go slightly inboard of outboard of center (depending on the design) so the wheel/tire assembly will roll slightly, rather than scrubbing, when the steering wheel is turned greatly reducing steering effort at low speed.This is a function of king-pin inclination and is set at the factory when the steering knuckle is forged and machined. The intersect point is also affected by wheel offset. If a spindle is bent that point will move with the degree of the bend.

The further the intersect point is from the tire's contact-patch center, the more steering effort is affected by caster. If it's too far away you simply can't hold a straight line on a rough road with no power steering. There was a design used on heavy trucks that I'm familiar with called center-point steering. This put the contact point of the king pin line exactly at the center of the tire's contact patch and used hubs that mounted the wheel further inboard. In the days before power steering on heavy trucks (1970s and before) this was used to reduce driver fatigue and was not affect by caster angle. I did not like it as the steering required too much correction.

If you still have the original wheel/tire combo, you might try putting them on to see if the problem goes away. Failing that figure out what the offset is on your wheels. Remember, offset is not the same as backspacing and if you have wide wheels the proper offset will not give you enough backspacing to clear the tie-rod ends. With 17 inch wheels on a 1-ton the tie rod ends isn't such a problem but it is with 16" wheels.

I have looked high and low for alloy wheels with positive offset and I don't think the aftermarket supplies them. I did find 6", zero offset alloy trailer wheels and have used those on my 1-ton and it steers fine. I cannot use 25mm positive offset Chevrolet steel wheels because of the tie rod end issue. I tried.