The Stovebolt Site Forums The Shop Area Driveline Front end problems

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.

Hi Bill, outside tire wear is indicative of too much "toe in" as was found at the shop. The truck can have left and right toe adjusted separately in relation to the center point of the steering gear, total toe is the left toe and right toe added together. It is possible for the total toe to be correct but not on center of the steering gear, this would result in one side being less toe than the other side and would easily show up in the steering wheel being cocked. The first thing they need to do is confirm the center point of the steering gear, then check caster, camber, and adjust the toe. If they are 100% sure of the center point, the steering wheel then can be re-clocked. Are all four tires and wheels the same diameter? are the springs in good shape or does the truck sit higher in the front or rear? If it is high in the rear, there will be too little caster IF everything else is stock. SAI is similar to the camber angle, in our case with solid front axles, it is the angle through the king pin as viewed from the front of the vehicle. The combination of king pin inclination and spindle angle will determine the camber on our trucks.

I beam axle camber is adjustable- - -but most shops don't have the equipment, or the knowledge to do it. It's done by bending the axle between the spring mount and the spindle. A piece of HEAVY chain, a piece of 6 inch or bigger H beam longer than the axle, and a 30 ton bottle jack is all that's needed. Any shop that does heavy truck (like 18 wheeler) alignment can tie that flimsy little axle into a knot. Caster correction is easy, as long as both sides need the same amount of correction- - - -just use a shim that increases the angle appropriately. Changing caster on one side involves twisting the end of the axle- - - -something a big rig shop can probably do, but it's usually not necessary. Ignore all the specifications like "total toe" etc.- - - - -just adjust the tread centerline measurement 1/8" less in the front than the measurement at the back, measured at spindle height. Correcting the steering wheel off center situation will require a drag link that's adjustable for length- - - -something Chevy chose not to do at the factory. There is a tech tip somewhere on this site, I think, that explains how to do that. Good luck!
Jerry

31.5" tires. What are the specs for these tires? (Numbers and letters).
Those are pretty tall tires. If they are also significantly wider than stock, you are risking upsetting everything engineered into the front axle assembly. That assembly was designed for stock tires and rims.
Can this be overcome? I don't know. I am not an engineer. You need an engineer.
Do you happen to have access to a stock set of rims and tires to throw on there and see if all of your problems disappear?

When I rebuilt the king pins, tie rod ends, and drag link on mine, I opted to use an adjustable drag link. The truck tracks straight, I do need to add more caster angle since my drive tires are about 2 inches bigger than my steers.

I am assuming you have radials. Radials need a lot less toe in than bias. We went to almost zero toe in on our trucks when we switched to radials about 40 years ago. General Brake in San Antonio used to do aliments for us, but we use an old fashioned Wheel a Matic gauge. General brake has anchors in their floor to bend I beam axles. We have had some I beam as well as trailer axles bent there. We have taken axles out and bent them with our hydraulic press. 25,000 trailer axles yield at 38 tons. They are still in business, but I'm not sure if they have any competent people down thee. Also radials need more caster. Since everything we do is I beam we call it king pin inclination instead of caster. That is also simple to measure with a magnetic gauge on an I beam. Over the years we have had a few aliments done with laser setups, but we always wound up re-doing them. I really don't have anyone at the shop that understands alignment any more. Where did you get an alignment. I hope it wasn't a deal like my daughter fell into when she was in college in Seguin between 1990 and 1994, I got my BBA in accounting and pre law down there in the 1960's. She drove a 71 AMC Hornet and was having problems so I told her to take it to an old AMC dealer in New Braunfels. I didn't know they had sold out. They charged her big bucks to run diagnostics and found nothing. I'm not sure where they found a diagnostics port. I drove there and filed the points and the next time she came home I installed a new set of points.

Could this be done without completely removing the tie rod from both ends, threading it back into one end a few turns and then continue threading both ends of the tie rod into their respective ends? I can't think of any other way to mess this up other than bending the tie rod.


When you say "confirm the center point of the steering gear" are you speaking of the center point found by measuring the increased "pull over center" when adjusting the sector gear lash (done with the Pitman arm disconnected) or the center point found by slowly turning the steering wheel all the way in one direction, counting turns to the opposite direction stop and then dividing the count by 2 to find the center?



Tires are all 215R85x16 which are 31.5" tall. I'll try to determine if any springs are out of spec in the next few days. I guess by measuring bottom of the frame to ground near where the tires are???


There doesn't seem to be any specs in my manuals for spindle angle. Would C + D in the drawing below be the same thing?

One thing I think it is important to keep in mind is that this condition happened suddenly.

Jerry:

I tried the only big truck shop in town a couple of weeks ago. They said they knew how to bend the axle, but their alignment testing equipment was physically to large to fit my small truck.

I've done caster shims on my '57 half ton in the far past. Got them at an offroad truck store. Had to make them narrower and not quite as long, but that was easily done with a hack saw. Should be the same on this truck.

Carl, the tires are 215/85R16. I know they are wider than the stock tires, but they've been on the truck for a lot of years with no problems.

I do not have access to stock rims and tires. Stock rims (8 lug) will no longer bolt on as all hubs are now (and have been for 11+ years) 5 on 4 3/4".

Again, this problem has occurred recently. While I'd love to have an adjustable drag link, I think adjusting the drag link to center the steering wheel would just be hiding the actual problem.

I have the stock ball, cups and spring ends on my drag link and tie rod. Does anyone make an adjustable drag link with these ends, or would I also have to convert to the newer type ends?

I have a set of Snap-On magnetic caster/camber gauges that attach to the hub, and all you have to do to read caster is turn the wheel in and out 20 degrees each way and read the gauge. Camber reads directly, as long as the vehicle is on a level floor. Any alignment man who understands basic geometry should be able to get an accurate reading, while they're set up to do the bending. Want me to send them to you as a loaner?
Jerry

Kenneth:

I got the alignment at the place you pointed me to, American Muffler and Brake on 16 South. Fritztown Diesel and Truck Services on Tivydale Road was the big truck shop that said they could bend the axle, but their alignment equipment wouldn't fit my small truck.

Jerry, I might just take you up on that offer. Let me see how flat my garage floor is.

So the bending of the axle takes place while the axle is still on the truck???

I have heard good things about those guys with independent front suspension. But they may be trying to make an I beam suspension more complicated than it is. We remove trailer axle to bend them for camber because they yield at 38 tons. We don't have D rings in the floor so we can't bend axles on the truck. But we have never had reason to do that. Usually if we discover a camber problem in steer axles we we check the king pin inclination on both sides. A difference indicates a twist in the I beam that is not feasible to try to straighten. Since I was a licensed salvage dealer for many years I have a lot of steer axles on hand. We just replace the whole axle. The Wheel a Matic magnetic gauge is the same thing as Snap On. In fact they may make them for Snap On. On a pickup we could probably bend an axle by using an old truck frame to anchor to. But before worrying about camber, check the camber. All incorrect camber does is wear tires on the edge like worn out king pins. Having almost zero toe in on radials is very important. If the king pin inclination is off, that can be corrected with shims between the axle and the spring.

I use a piece of H beam a little wider than the axle, chain the axle down around the spring, and jack up under the spindle area with a big bottle jack. A steel block supports the axle just inboard of the spring, so the bending force is applied under the spindle. That is to move the camber in the negative direction. To make the camber more positive, chain the axle to the H beam at the spindle area and inboard of the spring, and jack up on the spring seat. It's all simple geometry. It's usually necessary to move the axle a little beyond the desired correction to allow for spring-back when the load is removed. Yes, on a pickup sized axle, it's all done on the vehicle.
Jerry

Bill, are you wheel bearings tapered? If so, are you adjusting them as you would ball bearings?
I converted my original ball bearings to tapered roller bearings and adjusted them like one would adjust ball bearings, leaving a tiny bit of slop. That created a slight shimmy so I broke out my 1966 Buick Factory manual and found out they used the same type of roller bearings and the adjustment procedure was vastly different.
The instructions state that, as you are spinning the wheel, tighten the nut to 19 foot pounds, then loosen the nut, resume spinning the wheel and tighten to 5 foot pounds. This indicates to me that these types of bearings require 5 pounds of preload. That is quite different that what ball bearing call for, which is a specific range of a little 'slop'.

Carl:

The set of tapered wheel bearings I wrecked in less than 500 miles by following the instructions for ball bearings were on my '57 GMC 102. The GMC Maintenance Manual routine for adjusting the ball bearings says after cleaning, lubing and reinstalling, tighten the nut to 33 ft/lbs while spinning the wheel. Then back off the nut no more that 1/6 (one nut flat) of a turn and install the cotter pin. In my case (with either ball or roller bearings) there was no "slop" using either bearing type.

I had changed to roller bearings when I installed disk front brakes using the original hubs. After the bearing failure I went back to ball bearings and drove the truck over 100,000 miles in 12 years.

Thank you all for your suggestions. I think I'm going to put this problem on the back burner for a couple of weeks until my neighbor gets home. He has an accurate 8' long straight edge that I will borrow to check the "level" of my garage floor and the slab of my carport. If either are acceptable I will use the procedures in the GMC Maintenance Manual to at least test some of the front end measurements.

In the mean time, I'll try to stop by Kenneth Crenwelge's house to get a better understanding of how one "bends" a front axle into spec. Not that I would try to bend mine myself. I just cannot envision how it is done from comments in the posts above.

Thanks,

Bill

Often suitable I beams can be found around construction sites, overhead garage door beams are one use.

Ed

Bill:

Back in the day I worked in a general truck shop that did frame and axle work too. I spent most of a year on the frame rack where even the tools weighed 100 pounds. I spent part of each paycheck at the chriopractor. Anyhow, we straightened steel and aluminum frames with chains, steel blocks and port-a-powers, and aligned axles the same way. I did the boss's nearly new '76 4x4 Scout II with the same chains, blocks and port-a-powers with the addition of a little heat. It had come from the factory with too much camber on the short-axle side and it wore the tire badly. The dealer couldn't or wouldn't do anything about it, so our shop did.

I think with some basic geometry, a port-a-power and Jerry's alignment gauges you could align the axle on your pickup. You could even twist it if necessary.