Caster (lack of):

Sorta. The caster shim is placed in between the axle and the spring. It is a wedge shape. Between the spring to the axle, or spring to spacer block to axle, each part has a locating center bolt and mating hole to lock each part together with the ubolts. The spring would have a center bolt where the head of the bolt is at the bottom and goes into a hole in the axle to prevent the spring from sliding out of the axle if the ubolts came loose. The caster shim also has a hole that allows the center bolt to pass through it and still penetrate into the axle. Increasing caster means installing a thicker shim. Sometimes the caster shim is too thick to allow the center bolt to properly penetrate the axle. So there is a mechanical limit shim wise. For the most part the hardest part is unseizing or replacing the ubolts to get the shim in there in the first place. You would loosen the ubolts and jack up on the spring somewhere safe to get it up off the axle and take the shim in or out. Caster is not an exact science. I can remove a 1 degree shim, replace with a 3 degree shim so mechanically I have increased caster by 2 degrees. Because the axle is hard to twist and the spring itself will flex that 2 degree caster increase may only actually increase caster by 0.9 degrees. It can be some trial and error.

 

Anyone here noticed a improvement in straight line stability after increasing caster. My truck has 2.5 and 3.3. When i am on the highway its wandering alot and the steering is very sensitive. If its windy the truck is all ober the road. Could it be the caster. Aliment is good

 

Yes, having your caster reset to the trucks maximum positive setting and preferably equal side to side will make a huge difference in how it handles with no downside.

 

yep. minimal caster - less load on PS, easier to drive with faulty ps. Stability issues in Europe are solved with EBS, ESP and RSS.

 

What does EBS, ESP and RSS mean?

Alexhemi7, most highway trucks like to be in the 4 to 5 degree range. Caster on the left should be about 0.7 or so lower than the right to help counter road crown. Your numbers there are ok for a city delivery truck, but low for a highway unit. Low caster and toe out will cause what you are feeling.

 

When you run staggered caster, the truck will steer easier one direction than the other. This will cause over correction issues and the constant need to herd the truck straight down the road constantly correcting. It makes driving a chore rather than a pleasure.

 

Heavyd, I have a 2012 Westenstar that has a Hendrickson airtech steer axle. I got an appointment with my alignment guy next week as it is a chore keeping it straight on the freeway. I told him its needs more caster, and he says the airtech suspension does not respond to the shims. Something about the air bag and one leaf absorbing the angle.
What do you do to put more caster in the airtech front end.
He said their is nothing he can do about caster with that axle.
Is this true??
Thanks and always enjoy your comments. !

 

Bender do you drive truck, or perform truck alignments on a regular basis? I have been doing alignments for years and no one has ever complained about uneven steering effort due to caster stagger. I have never had anyone complain about the constant need to herd the truck straight either. The most common complaint I get is a pull to the right. The crown in the road will cause any truck to pull to the right. You need to have some cross caster to counter this. Pretty much every manufacture allows for cross caster. You don't need much, about 0.8 degrees is the sweet spot around here. It depends on how severe the angle of the road crown is. Every State, county and Province has a different road engineer and therefore a different degree of road crown so it there really is no perfect number, but you do need some. If you do alignments and set your customer's trucks with no cross caster I'll bet you they all pull to the right!

 

Good thread!

I just had toe checked the other week. I was sure it was toeing out since last set.
To my surprise it was + 1/32 right where it should be. Tightened up the gearbox just a hair which helped my problem.

Truck was wanting to wander too much, never staying straight.
Caster was out but I didn't want to stay to pull the U bolts. I am doing new rear spring bushings in Jan. and will bring it back for a three axle align.
I'll pay more attention to the caster specs then and he will definitely be adding more.

I have EFA12. Also the camber was out, always was from factory, but I thought you had to bend the I-beam to change that.

 

These axles are a bit tricky. Your guy is partially correct. You can adjust caster with the Tek series. What you can't do is adjust the cross caster! If your truck is wandering they can certainly increase the caster. The tolerance caster range for your truck can be from 2.75 to 4.75 degrees. The alignment guy just needs to keep the adjustment the same on the left and right side. They can add shims between the axle beam and spring to increase the caster. These axles are a manufactured multi-piece hollow beam, not a solid one piece cast. Cross caster basically puts a twist in the axle. The Hendrickson beams are not designed to twist at all! In fact they are subject to shattering if twisted. Caster is not the easiest or quickest adjustment and alot of alignment techs get lazy and skip this step during an alignment. You kinda have to make sure the tech knows how the truck is driving so he knows you may need a bit more. The problem is the factory sets some pretty wide tolerances for what they say are good. In reality some trucks need to push it a bit to get a good ride. If they won't help you, just take somewhere else.
Here is some literature on your axle;
http://www.hendrickson-intl.com/pdfs/Truck_PDFs/Airtek/Tp_243/Sec_12_13_14_d.pdf