Understanding suspension and steering
Posted: Thu Apr 30, 2015 1:39 pm
I thought this may be useful info to some people.
Let's start with caster. What is caster? To keep it simple all you need to remember is caster is the angle the the steering arms are at on the knuckle. If you take an angle finder and place it on top of the knuckle you will get a reading. On Patrols I find this to be 2 degrees (2*) with decent but old suspension. Now 0* would be totally level. Keep that in mind. Forward of the 0* is called negative caster. That is bad. Back from 0* is called positive caster and is what you want. When you lift a truck or the suspension is very old and sagged it changes caster. This applies to both leaf spring and coil spring trucks. Lifting the truck rolls the axle forward reducing caster. Lowering it rolls the axle back increasing caster.
I have looked in the manuals and they only talk about caster in terms of how it is designed. The manuals only mention how to figure caster using a very old school (but very sound) method that is complicated. These days an angle finder or digital level does the trick easily. Point is though, there is no reference to caster in the books as far as what it should be for a stock Patrol. Again, my best estimates are 2*, that is 2* positive as anything in the negative range is a big nono.
For more reading on caster go here
http://en.wikipedia.org/wiki/Caster_angle
Now what happens to a truck when the caster is off? Lets say it is 2* negative or -2*. Going down the road the truck is going to be squirrelly, wander a lot and not corner well. You will notice this most at speeds above 40mph. If caster is way out, let's say -5* the truck will be almost un-drive-able and dangerous. So caster is very important in how the truck handles and drives.
Caster is really only going to be an issue on an old Patrol if you lift the truck. On a leaf sprung truck generally shims are used between the leaf spring and the axle housing to bring the angle back into specs. I personally really dislike shims. What I do is called a "cut & turn". I think a C&T is a bit advanced though for 90% of Patrollers and only needed if lifting over 3" or doing a spring over axle conversion. So I think I will skip describing it and what it does for now. One thing to remember though is the bigger the tire you run the more caster you want. For example, if stock caster on a Patrol is 2* with a 31" stock tire I would want my caster at 4-5* with a 35" tire. Increasing caster with a large tire makes it drive like the tires are small.
One last thing about caster. I am not sure it applies to a Patrol but it does apply for any more modern vehicle, let's say from 1980 onward. Caster is different side to side from the factory. It can be different by as much as 1-2* but generally .5* or there abouts is normal. Now why would caster be 2* on one side and 2.5* on the other from the factory!? Simple, it accounts for the crown in the road. If caster is the same on both sides and the road has a good crown on it the crown will push the truck to the shoulder. If the caster is off a bit like .5* it makes the truck push into the crown (not noticeable) which in turn makes the truck track straight down the road.
Camber does not apply on a solid axle truck like the Patrol. Camber is the angle left to right if looking at the front of the truck that the tires sit on. This is built into a Patrol and can not be changed. Lifting the truck or anything you do to it will not change camber.
Ackerman angle is another thing that is important. Ackerman angle is how far each tire turns in a corner. If you move the steering wheel full lock to right or left and look at the tires or take a reading using an angle finder you will see one tire is turned inward more than the other. This is ackerman angle. This is important in corners as one tire needs to turn more inward for the truck to track correctly.
Ackerman angle is relatively simple to understand but is also complex by design. For more reading on ackerman angle go here
http://en.wikipedia.org/wiki/Ackermann_ ... g_geometry
Toe in is another steering angle that is good to understand. All vehicles generally have a small bit of toe in. When you go get an alignment of the front end this is one of the things they adjust. A slight toe in of the tires is ideal because it allows the truck to track straight and true, gives even tire wear and keeps the front tires from fighting each other if the surface is not perfectly smooth. Usually after I work on a front end I set the toe in using a tape measure in the shop. Give it a good guess, adjust, check and so forth. Once done I take it in for an alignment since they have the tech machine and equipment. Nine times out of ten I am very close on my shop adjustment with a tape measure. It is very easy to do, don't be intimidated by it! Always get it professionally aligned though, if nothing else you get a print out of the specs on your truck showing toe in, caster, camber and so forth. More on toe (in) here, http://en.wikipedia.org/wiki/Toe_(automotive)
Lifting a truck also changes pinion angle. As you lift the truck the axles rotate. That changes pinion angle. Without a double cardan or CV style driveline and pinion angle out of specs you will get driveline vibrations. Patrols use a standard driveline but you can easily fit a DC shaft, it just has to be custom built. Outputs on the t-case and the pinion on the axle with a standard driveline need to match. Meaning, at the same angle. Pinion angle can be changed by cutting off the leaf spring perches on the axle and rotating them but you can not change the output angle on the t-case. So unless you were to run a DC shaft the angles need to remain the same.
Here is a good video explaining drivelines and how they work in relation to angles.
https://www.youtube.com/watch?v=gmV4qwLfOMY
Now how about steering? First, the design of the Patrols steering is known as "cross over" steering. It is a tired and true design that goes way back in automotive history. Cross over steering simply means the tie rod and drag link are located in front of the axle. Technically it is often called "T" steering since true crossover means the drag link attaches to the knuckle arm not the tie rod. But if you just call it crossover you are right unless somebody wants to get anal on you! What the Patrol has is actually just like a GM style, known as a "y-link". All this means is the drag link connects to the tie rod rather than directly to a steering arm on the knuckle. Two different principles apply and are important depending on the type of suspension, ie leaf sprung or coil sprung. Since Patrols are leaf sprung let's just talk about that. What you need on a leaf sprung truck and how they are designed is with a flat or relatively flat drag link. That means left to right when you are looking at the front of the truck the drag link is level. As you lift a truck this obviously increases the angle. What that does is cause what is known as "bump steer". With a heavy angle on your drag link going down the road, you hit a bump, even can be a small one, and the truck will swerve side to side even though you are firmly holding the wheel straight. That is bump steer, it is no good.
While I don't think all this stuff will help many Patrollers because you need to lift your truck 3 or more inches before things get to far out of specs and problems are encountered. What this does do is give you a basic understanding on how it all works and why things are important. That is solid info very useful to any hobby mechanic. The more you understand a Patrol and how things all work, the better off you are! Even if you take your truck to a mechanic for work, being educated means they can't pull a fast one on ya!
Other problems can be encountered in an old truck that will give similar results to bad caster, bad drag link angle and so forth. But that is all going to be from worn out parts. Worn out and shot leaf spring bushings or badly worn pins will give wandering and bad handling results. That has nothing to do with caster though, simply that the parts are worn out causing poor handling.
Cheers
Let's start with caster. What is caster? To keep it simple all you need to remember is caster is the angle the the steering arms are at on the knuckle. If you take an angle finder and place it on top of the knuckle you will get a reading. On Patrols I find this to be 2 degrees (2*) with decent but old suspension. Now 0* would be totally level. Keep that in mind. Forward of the 0* is called negative caster. That is bad. Back from 0* is called positive caster and is what you want. When you lift a truck or the suspension is very old and sagged it changes caster. This applies to both leaf spring and coil spring trucks. Lifting the truck rolls the axle forward reducing caster. Lowering it rolls the axle back increasing caster.
I have looked in the manuals and they only talk about caster in terms of how it is designed. The manuals only mention how to figure caster using a very old school (but very sound) method that is complicated. These days an angle finder or digital level does the trick easily. Point is though, there is no reference to caster in the books as far as what it should be for a stock Patrol. Again, my best estimates are 2*, that is 2* positive as anything in the negative range is a big nono.
For more reading on caster go here
http://en.wikipedia.org/wiki/Caster_angle
Now what happens to a truck when the caster is off? Lets say it is 2* negative or -2*. Going down the road the truck is going to be squirrelly, wander a lot and not corner well. You will notice this most at speeds above 40mph. If caster is way out, let's say -5* the truck will be almost un-drive-able and dangerous. So caster is very important in how the truck handles and drives.
Caster is really only going to be an issue on an old Patrol if you lift the truck. On a leaf sprung truck generally shims are used between the leaf spring and the axle housing to bring the angle back into specs. I personally really dislike shims. What I do is called a "cut & turn". I think a C&T is a bit advanced though for 90% of Patrollers and only needed if lifting over 3" or doing a spring over axle conversion. So I think I will skip describing it and what it does for now. One thing to remember though is the bigger the tire you run the more caster you want. For example, if stock caster on a Patrol is 2* with a 31" stock tire I would want my caster at 4-5* with a 35" tire. Increasing caster with a large tire makes it drive like the tires are small.
One last thing about caster. I am not sure it applies to a Patrol but it does apply for any more modern vehicle, let's say from 1980 onward. Caster is different side to side from the factory. It can be different by as much as 1-2* but generally .5* or there abouts is normal. Now why would caster be 2* on one side and 2.5* on the other from the factory!? Simple, it accounts for the crown in the road. If caster is the same on both sides and the road has a good crown on it the crown will push the truck to the shoulder. If the caster is off a bit like .5* it makes the truck push into the crown (not noticeable) which in turn makes the truck track straight down the road.
Camber does not apply on a solid axle truck like the Patrol. Camber is the angle left to right if looking at the front of the truck that the tires sit on. This is built into a Patrol and can not be changed. Lifting the truck or anything you do to it will not change camber.
Ackerman angle is another thing that is important. Ackerman angle is how far each tire turns in a corner. If you move the steering wheel full lock to right or left and look at the tires or take a reading using an angle finder you will see one tire is turned inward more than the other. This is ackerman angle. This is important in corners as one tire needs to turn more inward for the truck to track correctly.
Ackerman angle is relatively simple to understand but is also complex by design. For more reading on ackerman angle go here
http://en.wikipedia.org/wiki/Ackermann_ ... g_geometry
Toe in is another steering angle that is good to understand. All vehicles generally have a small bit of toe in. When you go get an alignment of the front end this is one of the things they adjust. A slight toe in of the tires is ideal because it allows the truck to track straight and true, gives even tire wear and keeps the front tires from fighting each other if the surface is not perfectly smooth. Usually after I work on a front end I set the toe in using a tape measure in the shop. Give it a good guess, adjust, check and so forth. Once done I take it in for an alignment since they have the tech machine and equipment. Nine times out of ten I am very close on my shop adjustment with a tape measure. It is very easy to do, don't be intimidated by it! Always get it professionally aligned though, if nothing else you get a print out of the specs on your truck showing toe in, caster, camber and so forth. More on toe (in) here, http://en.wikipedia.org/wiki/Toe_(automotive)
Lifting a truck also changes pinion angle. As you lift the truck the axles rotate. That changes pinion angle. Without a double cardan or CV style driveline and pinion angle out of specs you will get driveline vibrations. Patrols use a standard driveline but you can easily fit a DC shaft, it just has to be custom built. Outputs on the t-case and the pinion on the axle with a standard driveline need to match. Meaning, at the same angle. Pinion angle can be changed by cutting off the leaf spring perches on the axle and rotating them but you can not change the output angle on the t-case. So unless you were to run a DC shaft the angles need to remain the same.
Here is a good video explaining drivelines and how they work in relation to angles.
https://www.youtube.com/watch?v=gmV4qwLfOMY
Now how about steering? First, the design of the Patrols steering is known as "cross over" steering. It is a tired and true design that goes way back in automotive history. Cross over steering simply means the tie rod and drag link are located in front of the axle. Technically it is often called "T" steering since true crossover means the drag link attaches to the knuckle arm not the tie rod. But if you just call it crossover you are right unless somebody wants to get anal on you! What the Patrol has is actually just like a GM style, known as a "y-link". All this means is the drag link connects to the tie rod rather than directly to a steering arm on the knuckle. Two different principles apply and are important depending on the type of suspension, ie leaf sprung or coil sprung. Since Patrols are leaf sprung let's just talk about that. What you need on a leaf sprung truck and how they are designed is with a flat or relatively flat drag link. That means left to right when you are looking at the front of the truck the drag link is level. As you lift a truck this obviously increases the angle. What that does is cause what is known as "bump steer". With a heavy angle on your drag link going down the road, you hit a bump, even can be a small one, and the truck will swerve side to side even though you are firmly holding the wheel straight. That is bump steer, it is no good.
While I don't think all this stuff will help many Patrollers because you need to lift your truck 3 or more inches before things get to far out of specs and problems are encountered. What this does do is give you a basic understanding on how it all works and why things are important. That is solid info very useful to any hobby mechanic. The more you understand a Patrol and how things all work, the better off you are! Even if you take your truck to a mechanic for work, being educated means they can't pull a fast one on ya!
Other problems can be encountered in an old truck that will give similar results to bad caster, bad drag link angle and so forth. But that is all going to be from worn out parts. Worn out and shot leaf spring bushings or badly worn pins will give wandering and bad handling results. That has nothing to do with caster though, simply that the parts are worn out causing poor handling.
Cheers
) 
that means that a basic 2 inch lift, and 2 inch guard/fender trim will see 35s fit without any hassle and even 37s dependant on rim offset......not that im suggesting that stock c216 diffs and cvs would handle 37s in any case......
well sort of, the back end has a bolt on add a coil sus kit/load leveler. Hermit will end up with this kit soon......