I hope you people will help educate me a little about front end alignment. I understand the concepts of toe, caster and chamber, but a recent trip to an alignment shop with my ’52 GMC 152 ¾ ton truck has me scratching my head. The last time I used front end alignment tools was in my Auto Shop class in 1964. Things have changed a bit since then.
This all started with the failure of my right front wheel a few weeks ago. Check
here if you are interested. I didn’t find anything loose or bent after this episode.
Prior to the wheel failure the steering on the truck was stable (no pulling, little vibration, steering wheel properly centered), but was exhibiting wear on the outside edges of the front tires.
After the wheel failure the truck had a fairly strong pull to the right. The only nearby shop that was willing to do an alignment stated that they could check toe, caster and chamber, but could only adjust toe. They said that they would report caster and chamber. I left the truck with them along with alignment pages from the GMC Maintenance Manual.
King pins and their bushings were new less than 2 years and 5000 miles ago. I checked the tie rod and drag link ends for wear after the wheel failure and they looked OK.
The report they gave is shown below, along with the alignment specs from the Maintenance Manual. I’ve made comments in blue on the report. First, they used Chevrolet 3100 (half ton) specs instead of 3600 (3/4 ton) specs. Comparing the Maintenance Manual specs from ½ to ¾ tons, chamber and king pin inclination are identical and caster is only .5 degrees different. So I don’t feel too bad about using the ½ ton specs.
If it makes a difference to any calculations, the tires are 31.5” tall.
My questions reference items on the report.
1. Caster is below spec on both sides. The alignment shop’s spec is for ½ to 1 degree, but the Maintenance Manual calls out 2.5 degrees. Should I get an additional set of caster wedges?
2. Camber is below spec on both sides, with driver’s side worse. The Maintenance Manual calls out 1.5 degrees. Wheel bearings are roller, not the original ball type. I know (learned the hard way on a previous truck) that you can’t adjust roller bearings the same way you do ball bearings. I have them adjusted with the smallest bit of slop that I can detect. Bearings and kingpins/bushings are the first 2 items in the “what to do to correct camber” list in the maintenance manual. Next item in the list involves bent steering knuckles and bent axles. Detecting either involves access to front end alignment equipment, which is outside of my abilities.
3. What is SAI?
4. What is Included Angle? Do I care? Repair in item 2 above references “Included Angle” as Camber plus King Pin inclination.
5. What is Front Cross Camber, what should it be and do I care?
6. What is Front Cross Caster, what should it be and do I care?
7. What is Front Cross SIA, what should it be and do I care?
8. What is Front Total Toe? My guess is this is the difference between a toe measurement taken at the front side of the tire tread half way from the ground to the top of the tire and the same point at the back side of the tire. I think this is the 1/8” Toe In measurement from the Maintenance Manual. Back in ancient times we measured this with a string.
9. Unless you have an independent rear suspension (my truck has a solid rear axle) I can’t imagine what use what the three “rear” readouts on the reports are good for.
It looks to me like the truck as delivered to the shop had way to much toe IN (1.1 degrees, about ½”), which they adjusted to the factory spec of 0.25 degrees (about 1/8”). Their comment “the steering wheel is currently level” is not correct. On the flattest road I could find the wheel needs to be held at about 15 degrees CCW to make the truck track straight.
I can use all the good help and hints I can get from our forum to educate me.
