My experiment with adding caster

[rusty_tlc]

I'm thinking I will need to add some caster to my rig as it wanders a decent amount. No bump steer, but plenty of wander.

ntsqd, perfect explanation as usual.

Wonder can be the result of many things other than castor. I'd eliminate those possibilities first.

The usual suspects;
Spring bushings
Tie rod ends
Bad/missing steering dampener.

 

[Moby]

I'm not sure rotating the pinion down would result in DL vibrations. What it will do is add stress to the pinion gear splines, increasing the chance of breaking the gear at the splines. This is the notorious weak link in the Land Cruiser axle. It's my understanding that's why most of the SOA guys do the cut and turn.

My understanding, and again, this could be wrong, is that the output of the t-case and the pinion need to be in the same plane, give or take some. If these two are too far out of alignment you may get driveline vibration. Again, my understanding here is limited, this is really my first foray into driveline and steering tech. Please correct me if this is not accurate or is too limited.

Interesting about the pinion gear splines, I was not aware of that. I'm not too worried about this though for my scenario. The face of my pinion flange is pointed 7 degrees towards my t-case with weight on the springs, I'm only running ~2" and I don't wheel this truck hard. For others with more lift or more horsepower this might be an issue.

 

[Moby]

I had the opportunity to take an hour long drive in the cruiser over the weekend, mostly on the sometime significantly rutted freeway around Seattle that we like to call I-5.

Previously changing lanes at high speed could sometimes be a little unnerving if the road was highly rutted. The wheels wanted to stay in the original grooves and then wanted to "grab" the new ruts. Not a big deal but one of those little things. While the truck still exhibited some of this behavior it was definitely improved.

 

[Moby]

Great thread! I've wondered about doing the same, but I'm so far from thinking about fine tuning at the moment. Have to finish the engine swap first.....

Caster changing the toe setting:
See if I can make it clearer;
Picture the axle having no caster. Now give the tires some toe-in. Think of the tires as being very, very thin.
OK, now rotate the whole axle top toward the rear. Think of how those thin tire "discs" rotate with the axle housing rotation. Exaggerate the toe-in, the OD of the tire "discs", and the amount of rotation in your mind. Note that the place where toe is measured does not rotate with the axle housing.
As you rotate the housing to gain Caster you will lose toe-in.


This is a good reason for running a lot of Scrub Radius on a serious crawler. That lifting can load a tire and find traction.

Thanks for this explanation! I will get the truck to an alignment shop to have them check toe-in.

 

[ntsqd]

Good, I'm glad that helped!

 

[rusty_tlc]

My understanding, and again, this could be wrong, is that the output of the t-case and the pinion need to be in the same plane, give or take some. If these two are too far out of alignment you may get driveline vibration. Again, my understanding here is limited, this is really my first foray into driveline and steering tech. Please correct me if this is not accurate or is too limited.

Interesting about the pinion gear splines, I was not aware of that. I'm not too worried about this though for my scenario. The face of my pinion flange is pointed 7 degrees towards my t-case with weight on the springs, I'm only running ~2" and I don't wheel this truck hard. For others with more lift or more horsepower this might be an issue.

Is the plane on a conveyor belt?

 

[GLTHFJ60]

Wonder can be the result of many things other than castor. I'd eliminate those possibilities first.

The usual suspects;
Spring bushings
Tie rod ends
Bad/missing steering dampener.

Not to hijak a thread, but bushings are brand new and TRE's are a year old but I have no steering dampener. I thought that just decreased wobble vibes as opposed to reducing wander?

 

[Spook50]

I had the opportunity to take an hour long drive in the cruiser over the weekend, mostly on the sometime significantly rutted freeway around Seattle that we like to call I-5.

Previously changing lanes at high speed could sometimes be a little unnerving if the road was highly rutted. The wheels wanted to stay in the original grooves and then wanted to "grab" the new ruts. Not a big deal but one of those little things. While the truck still exhibited some of this behavior it was definitely improved.

Great to hear. That's a huge annoyance for me since I-90 here has some nasty ruts in areas and my 62 likes to jump right the hell into them.

I'm going to give a pair of 2-degree shims a try.

 

[Moby]

Is the plane on a conveyor belt?

I'm not following that question... but if my understanding isn't correct, which wouldn't surprise me, what does cause driveline vibrations (other than an out of balance driveshaft)?

 

[RockDoc]

It's a chat reference, don't sweat it.

 

[Moby]

Great to hear. That's a huge annoyance for me since I-90 here has some nasty ruts in areas and my 62 likes to jump right the hell into them.

I'm going to give a pair of 2-degree shims a try.

You might consider measuring your existing caster first so that you know where you are starting and how much to add (maybe you've already done this). You can do this measurement yourself, you can buy a caster/camber tool for $75-$200 or you can go to an alignment shop. I paid $30 at my local Sears with a Hunter machine. Took about 30 minutes. For example if you're currently within specs at 1 degree negative and you buy a 2 degree angle you'll be at 1 degree positive, which is where I started and which isn't much caster.

 

[rusty_tlc]

Not to hijak a thread, but bushings are brand new and TRE's are a year old but I have no steering dampener. I thought that just decreased wobble vibes as opposed to reducing wander?

Maybe not wonder so much as jerky steering. It is my understanding that the damper reduces the tendency to grab cracks and follow them.

Another place for you to look is the upper steering linkage. I had some u-joint issues once, I had to constantly steer the truck to keep it straight.

 

[rusty_tlc]

I'm not following that question... but if my understanding isn't correct, which wouldn't surprise me, what does cause driveline vibrations (other than an out of balance driveshaft)?

It was an oblique reference to a thread in chat, it's kind of a running joke.

To answer your question, partially anyway, an out of phase drive shaft is a common cause of DL vibrations. I'm pretty sure you can search on "drive line phasing" and find volumes to read on the topic.

 

[Spook50]

You might consider measuring your existing caster first so that you know where you are starting and how much to add (maybe you've already done this). You can do this measurement yourself, you can buy a caster/camber tool for $75-$200 or you can go to an alignment shop. I paid $30 at my local Sears with a Hunter machine. Took about 30 minutes. For example if you're currently within specs at 1 degree negative and you buy a 2 degree angle you'll be at 1 degree positive, which is where I started and which isn't much caster.

I just had my alignment done a couple days ago (yay severe wobble and wandering are gone. I was way toe out) and got the full before/after specs list from 'em, and they measured my caster at 1 degree positive. So I'm thinking 2-degree shims might put me right where I would want to be ideally. My shackles are stock length, but my truck sits maybe 1.5-2" higher than stock with the AALs installed. I'm going to take a close look at my front diff and see if my pinion angle is going to be too drastic with an extra 2 degrees of caster.