Caster

Eddie 70 · May 14, 2017

I searched and saw Caster mentioned several times. I had an alignment done on my truck several months back and they said they were unable to get Caster in spec. On the drivers side it is in at 2.7 degrees. On the passengers side it is out at 4.1 degrees. It has not caused any wear on the tires as you would expect. The truck centers like it should when coming out of a turn. Right now I am not worried about it but was just wondering why there is no adjustment on Caster on our trucks? Anyone have any idea?

I am stock height with stock suspension. Two wheel drive.

Eddie 70 · May 14, 2017

Remainder of specs

Camber

.4 and .3

Caster

2.7 and 4.1

Toe

.04 and .06

slee3247 · May 14, 2017

There is caster adjustment on our trucks and it is very simple.

Before we start, caster is not a tire-wearing measurement. Toe and camber will wear tires, whereas caster will only mess with steering feel and handling.

Caster is the relationship of your upper steering locator (upper ball joint) to your lower steering locator (lower ball joint), measured as though you're looking at the tire. Positive caster means your upper steering locator is located further back than the lower, meaning your upper ball joint is further towards the rear of the truck. Negative caster would be exactly the opposite. The upper locator would be located forward of the lower locator, hence why a vehicle will handle so well going forwards but so poorly in reverse (at speed).

The upper control arms on our trucks (and GM trucks since the 90s) come with eccentric bolts where they mount to the frame. This simply means the bolts have an egg-shape where they pass through the control arm bushings. Using this design, alignment can easily be corrected if your mechanic knows what to do. Say you want to add positive caster, you could loosen the front-most mounting nut, and turn the bolt to a point where it pushes the arm outwards. This in turn moves the entire UCA slightly rearward, therefore increasing caster.

While adjusting caster, you should know that it's also going to rapidly change your camber measurements. Unless your truck has been in an accident and something is tweaked, there's no reason you cannot get a proper alignment.

Attached is a picture of my alignment with my truck lowered 4" in the front, and 7" in the rear. Positive caster isn't going to hurt anything as far as tires are concerned, I was more worried about my toe and camber. If anything, more positive caster should make steering effort slightly increased, and it can also help in high-speed handling, as the tires will be able to "lean" over further, and more readily return to their straight-ahead position.

DM if you have any questions!

Toe is on the bottom, camber in the middle, and caster on the outer edges.

Eddie 70 · May 14, 2017

There is caster adjustment on our trucks and it is very simple.

Before we start, caster is not a tire-wearing measurement. Toe and camber will wear tires, whereas caster will only mess with steering feel and handling.

Caster is the relationship of your upper steering locator (upper ball joint) to your lower steering locator (lower ball joint), measured as though you're looking at the tire. Positive caster means your upper steering locator is located further back than the lower, meaning your upper ball joint is further towards the rear of the truck. Negative caster would be exactly the opposite. The upper locator would be located forward of the lower locator, hence why a vehicle will handle so well going forwards but so poorly in reverse (at speed).

The upper control arms on our trucks (and GM trucks since the 90s) come with eccentric bolts where they mount to the frame. This simply means the bolts have an egg-shape where they pass through the control arm bearings. Using this design, alignment can easily be corrected if your mechanic knows what to do. Say you want to add positive caster, you could loosen the front-most mounting nut, and turn the bolt to a point where it pushes the arm outwards. This in turn moves the entire UCA slightly rearward, therefore increasing caster.

While adjusting caster, you should know that it's also going to rapidly change your camber measurements. Unless your truck has been in an accident and something is tweaked, there's no reason you cannot get a proper alignment.

Attached is a picture of my alignment with my truck lowered 4" in the front, and 7" in the rear. Positive caster isn't going to hurt anything as far as tires are concerned, I was more worried about my toe and camber. If anything, more positive caster should make steering effort slightly increased, and it can also help in high-speed handling, as the tires will be able to "lean" over further, and more readily return to their straight-ahead position.

DM if you have any questions!

Toe is on the bottom, camber in the middle, and caster on the outer edges.

Thanks for the great response. My truck was bought used so there may have been a wreck at sometime. I have been under it changing oil and checking around and can see no signs of damage or where it may have been pulled. It drives straight and shows no signs of abnormal tire wear. I do keep the tires rotated every 10K and do about 85 miles roundtrip everyday to work and back.

slee3247 · May 14, 2017

You're very welcome! If I wasn't a mechanic, I'd look for a shop that specializes in high performance vehicles. The guys and gals that do alignments at these shops should know exactly what to do. Just make sure to assert that you want them to make the proper adjustments on the upper control arms!

-Shaun

Eddie 70 · May 14, 2017

I was looking at Rockauto and noticed they have a specific set of upper control arms for trucks with Z60 suspension. They were cheap enough and I ordered them from Advance Auto. The control arms look the same but the ball joints came loose in the box and are offset to correct caster.. I have been hesitant to install them and they have been on the shelf.