caster effects on handling

[bad_religion_au]

ok, i got my castor shims in the front axle, the wheel self centers well, a little heavier to steer, but hey.

but in corners it's 100% better... no understeer, no feeling of the tire rolling under itself. are these all expected outcomes of having castor closer to factory specs? or is it blind luck...

i guess what i'm asking is what effects on handling dynamics does changing the castor have?

 

[CruisinGA]

Yes, those are all effects related to a proper caster angle.

Good caster is also required to safely flat tow.

With very large tires, caster somewhat over stock is good too.

 

[Klunky Chris]

I've got a 4" SU lift on mine with 35x12.5 Truxus and a mini PS conversion.

when I first drove it with the new lift it was down right SCARY!

I had it laser alligned and found out I was -1 deg caster on one side and -1.5 on the other. stock for the 40's was +1 deg.
I put 2.5 deg shims in and it made a big difference because it took me to +1.5 and +1 deg.

however..... with the big tires I didn't feel it was enough. Also keep in mind that new vehicle design gives much more caster. for example my 93 FZJ80 has +3 deg caster stock! (and I think the FJ60's have +3 deg also, but not sure...)

therefore.... I recently put 6 deg shims in. this gives me +5 and +4.5deg

this has made a big difference over the 2.5deg shims and I am now MUCH happier with the handling. drives straight/ holds turns steady over real rough potholes and bumps, doesn't jumps around and wander etc...
it is harder to turn, but this is an easy trade IMO.

I highly reccomend the 6 deg shims. the only issue is that your pinion angle will change, so you need to make sure it won't be a problem.

 

[dgangle]

I had +1* caster with the MAF steering correction kit and their cheesy aluminum shims. This arrangement pointed the pinion 1* down which caused d-shaft U-joint to bind compounded by my V8 conv which moved the TC forward 3". I did a cut and turn which was relatively easy pointing the pinion up at 12* to get good d-shaft angle and turning knuckles back to get +5* caster. It steers and flat-towes like a dream. The outside tire seams to scrub more on tight asphalt turns but that is another issue.

In my research I found +3-6* caster is typical, on the higher end with larger tires. I measured by setting a Home Debit angle guage across the top trunion bearing outter race, with the knuckle off the axle housing , obviously. Some say you can measure caster flat across the top of the steering arms but my studs were slight different lengths giving unrepeatable measurements. I love the way it steers/tracks now and wish I had done the cut and turn years ago. I am not trying to turn this into another to cut or not to cut & turn discussion but if you want more + caster it causes d-shaft problems and the only way to fix right is with a cut and turn of the front axle housing.

 

[bad_religion_au]

thanks for that...

cut and turn is abit excessive for my situation given the modest amount of lift. i can't believe it's the same truck

i actually have driven it over a particular windy mountain pass for fun 3 times in the last 24 hours (a good 100 k's worth).... it's fun.

i was given some advice to drop the spring hanger (solid mount end) to improve castor... i may have to look into that considering my shackles need a little more length, potentially undoing the good i have done with shims.

any thoughts on this

 

[dgangle]

I thought a cut and turn was only for the SOA guys...but my situation gave no other alternative. I am SUA with a spring reversal, 2.5" springs in the front and 4" springs in the rear. Add a V8 which moved the TC forward 3-4".

Shims used to increase caster = pointing the pinion down no matter how one rationalizes it. It "may" not be an issue with your arrangement. Adding shackel length (assuming you have a spring reversal) increases caster which rotates the pinion clockwise looking at the driver's side wheel. Adding shackel length if you do not have a SR decreases caster but will improve front U-joint angle.

 

[66fj40x2]

Stupid NOOB Question - Sorry

Using an angle finder across the top of the knuckle housing (bearing race) the back of my axle is about 4* lower then the front. I've search about all the threads and have only managed to confuse myself on the topic.

Is my measurement positive or negative caster?

Again, sorry for the dumb question

 

[Devils Paw 80]

66FJ40x2,
I believe your measurements indicate a postive caster angle, which is what you want with larger tires according to the guys with experience here. Extended shackles move the axle more towards a negative angle. Spector offroad lists stock angle as -1 degree. They don't specify model, so I'm assuming they're referring to the 40. Maybe the 60 is also the same? I've run Spector 1-2" lift shackles (without shims) for over a year now without any steering problems noted. I would imagine that it's more important to have both wheels with nearly identical castor than it is to have your axle on exact stock specs.

 

[Fireman]

I'm going to do a SR with extended shackles and use shims to hopefully get the caster back to where is should be. Don't know if it'll work, bu will find out.

 

[mr_manny]

I found the following procedure online, and was wondering if anyone ever used a digital level to determine caster?

http://www.tru-line.net/pdf/smartlevelprocedure.pdf

thanks,
manny


Using a Smart Level (Digital Protractor) to Measure Caster

There is another way to read Caster on Heavy Duty Truck with a solid front (steer) axle.

This method provides an accurate caster reading and gives the user the ability to make

caster measurements and adjustments with out having to purchase turn tables which

can be heavy and costly. To measure caster using a smart level use the following

procedure.


1.) Calibrate the smart level by following the directions on the back of the smart level.

2.) Clean the flat area on the axle where the u-bolts mount to the axle and spring assembly
of any built up grease & dirt.

3.) Place the smart level on the flat area next to the u-bolt assembly. Making sure that
all of the levels flat surface is touching the axle.
In some cases this might require the technician to crawl underneath the truck to access the axle.

3.) Read the digital scale on the smart level. Smart levels always have arrows that point which direction goes to zero degrees.
If the arrow on the side of the scale window that is near the front bumper of the truck
is pointing down to the ground and the arrow on the other side of the scale window is pointing up. Then the reading would be positive caster.

4.) After taking the caster reading on one side of the truck,
please proceed to read caster on the other side by using the same procedure starting at step 2.