Can anyone explain to me what the importance of caster is on our trucks?

Is it for driveability, wearability or both?

I just picked up my truck from a "reputable" alignment shop (and please not my quotation marks around reputable) and thought since I just replaced all the front end components I should get a full and thorough alignment done.

It looks as though they only aligned the toe and camber, not the caster. When I took the truck apart the old passenger side leaf spring had a 1* caster shim underneath it. Looking at the paperwork I received the Driver caster is 2.4 degrees and the pass. side is 3.6 degrees. It seems to me that 1 degree shim was there to make the pass side 2.6 degrees (being much closer to the driver side reading).

SO is this something I should be concerned about? I have to take the truck back anyway. I notice that I have to hold the wheel slightly to the left in order to go straight.....they obviously did a mediocre job on centering the wheel. Makes me wonder what else they skimped on.

Also, anyone know how to find a truly reputable 4x4 alignment shop? I mean is the dealer reputable? Or are they just as bad? I know this truck did not come off the assembly line like this...and it can certainly be re-aligned to factory spec its just a matter of getting someone who can and will do it right.

Thanks for any input. I'm a bit beside myself. If I could do the alignment myself I would have.

Thanks,

 

Caster is the angle of the steering knuckle when you look at the wheel face on. If this sounds confusing, look at a "caster wheel" on a shopping cart. You will notice the center of the wheel is offset from its mounting location to the cart. This forces the wheel to always center itself. The same is true for your vehicle. The difference, however, is the caster wheel freely follows and defaults to negative caster, rather than positive.

The more positive caster you give the wheels, the snugger the steering will feel because the weight pushes the the wheels into the straight ahead position. If they were at dead zero, they would not be as loaded and you will have to steer more often as if it were sloppy. Negative caster might give an unpredictable funny handling/steering characteristics when you turn. Back up at 40mph with your basic RWD Volvo, turn suddenly back and forth and you'll know what i mean.

What should concern you most at the alignment shop is that caster is no more than 1/2 a degree different from side to side. I'm getting that number from a Hunter video, if memory serves. Any more and the steering will pull. It won't really wear tires like toe or camber, but you'll be hanging on to the wheel all the time and the increased work to keep it straight will wear your tires faster than normal. We're talking quite a lot of miles, here, so if you do have a pull, don't panic, you have time to fool with it. The question is, is just your steering wheel off center? If you let it go, will the truck pull to one side on flat pavement? If you get a strong pull, id say that shim needs to be back under the spring.

I have not had the pleasure of playing much with a leaf sprung ttb, but just seeing a 1 deg shim in there, i wouldn't consider anything bent or broken. Just as long as the wheel wants to hold straight, you're probably fine. Try turning all the way to lock and accelerate forward. Do the wheels skip along on the corners of the tread? I have that problem now that i've lifted things a bit over an inch and i have to compensate by bringing the radius arms down to correct the negative caster. My guess is you're probably at stock height with nothing like this to worry about. If you experience this, you'll want to get the caster more positive, but 2.6 deg sounds okay. I don't have the exact spec on hand, but hey, you're well positive so its a good place to be.

 

BBBTruck, thanks for the input. I've become well educated over the past month on the effect of caster, camber, et. al. I was even debating doing the alignment myself (thanks to the above replies). The cross caster currently being 1.2 degrees difference is making the truck ride like absolute garbage; so much to the point I dread driving it and only will when I really have to.

I found a heavy duty truck shop that services diesels/tow trucks/plow trucks/box trucks/etc. They have a pretty good rep and I'm almost certain if I tell them what I want they'll make it happen. :::Fingers crossed:::

Since the pass side has the lower caster angle (and that's where I originally had a 1 degree shim) I'm going to have them install it or a new one and then re-align. I was going to forego the TTB bushings but I think I'm going to have them done too then everything up front will be tight with the exception of the ball joint that have about 10,000 miles on them. Steery box is a new red head too.

If I get my butt in gear hopefully I can have her going straight before the end of the year. YIKES....what a thought!