School Me On Front End Alignment?

[Gary Lewis]

.... Bob - I see you just replied, and Jim replied to your post. But there is a track bar on the back of the axle on the passenger's side, as shown below.

Not seeing the track bar and the drag link at the same time it's hard to picture exactly what will happen as the suspension cycles. It looks like the track bar is probably pretty close to parallel with the drag link. But it also looks to be a lot shorter. So I'm not sure what that will do with bump steer.

The issue (obviously?) is that the drag link will push the tie rod back and forth as the suspension cycles and the track bar will push the axle back and forth. If the tie rod moves the same distance as the axle there won't be any steering input. If they move different amounts there will be bump steer.

With the different lengths the movement can't be the same through the entire range of travel. But is it pretty close in the normal range of travel? That's what I can't wrap my head around without seeing it better.

But this is all talking about bump steer, which is one issue you mentioned. But it won't affect wander which is priobably your bigger concern.

What I don't have on is the factory sway bar, and that's because taking the sway bar off the TTB's helped the ride significantly, and I'm looking for ride quality. Once I get the steering sorted then I could put the sway bar on and see what it does.

I wouldn't think that adding the sway bar would make a lot of difference in the steering unless you feel the truck swaying side to side. If the truck is moving around quite a bit that means you could be getting "bump steer" even if there aren't any bumps. But I'm guessing Big Blue isn't swaying around noticeably. Sure, you could put it on to verify. But I'd be surprised if it would affect your steering, at least in general driving.

I "see" what you are talking about with track bar vs drag link length, suspension "cycling", etc. It is an adjustable track bar, but where I have it puts the front and rear tires in alignment with each other with the truck on the ground. That took a lot of adjustment to do, but it seems to be what you are supposed to do.

However, if the toe-in adjustment doesn't do the trick then I could try adjusting the track bar.

On the sway bar, I'm with you that it won't make much difference in steering. Taking it off didn't, and there's essentially no sway at the present so I'm not seeing the need.

[Nothing Special]

I "see" what you are talking about with track bar vs drag link length, suspension "cycling", etc. It is an adjustable track bar, but where I have it puts the front and rear tires in alignment with each other with the truck on the ground. That took a lot of adjustment to do, but it seems to be what you are supposed to do....

I'm not suggesting you "just" change the length of the track bar. If you made it the same length as the drag link your front axle would stick a couple feet out the right side of the truck! I'm just saying that it's not clear to me what bump steer you might expect, or if there is anything you might do to minimize it. Like I said in my first post, typically adding a drop pitman arm to make the drag link closer to horizontal is a way to reduce bump steer. But I don't know if that would be a good idea here or not.

 

[Gary Lewis]

I "see" what you are talking about with track bar vs drag link length, suspension "cycling", etc. It is an adjustable track bar, but where I have it puts the front and rear tires in alignment with each other with the truck on the ground. That took a lot of adjustment to do, but it seems to be what you are supposed to do....

I'm not suggesting you "just" change the length of the track bar. If you made it the same length as the drag link your front axle would stick a couple feet out the right side of the truck! I'm just saying that it's not clear to me what bump steer you might expect, or if there is anything you might do to minimize it. Like I said in my first post, typically adding a drop pitman arm to make the drag link closer to horizontal is a way to reduce bump steer. But I don't know if that would be a good idea here or not.

Tell you what - if the toe-in adjustment doesn't dial it in close enough for me, or if the wandering is gone and I still have bump-steer, then I'll do some measuring and draw up the suspension. Then I can do what Bill suggested and see what happens when it cycles. (I assume there's a way in TurboCAD to connect parts and have them move in concert.)

[ArdWrknTrk]

Guys - Thanks for all the input. I certainly appreciate it. But I think I may see what the problem is, and it fits with what Steve is saying - toe-in.

The factory specs from the 1995 FSM are below, and I've highlighted the toe-in specs, which are supposed to be between .035 and .085 degrees, with .06 being the center of that. But Big Blue is sitting right on 0.

Using CAD, on 33" tires having both of them toed in at .06 degrees, which I think is what is meant, will put the front inside edges of the tires .060" closer than straight ahead. So basically 1/16". Am I doing that correctly?

That fits with Tire Rack's statement of "Increased toe-in will typically result in reduced oversteer, help steady the car and enhance high-speed stability." And it fits with Steve's statements of "If the toe is set at 0 sitting still, then the toe will be toe out at speed" and "Toe out will cause a wandering feeling and will cause the "bump steer" at speed."

So my plan is to have the toe-in set to .06 degrees and see what that does. But are there other questions that y'all have? Did I miss something?

Bob - I see you just replied, and Jim replied to your post. But there is a track bar on the back of the axle on the passenger's side, as shown below.

What I don't have on is the factory sway bar, and that's because taking the sway bar off the TTB's helped the ride significantly, and I'm looking for ride quality. Once I get the steering sorted then I could put the sway bar on and see what it does.

I hope I didn't misspeak about your SAS RSK Gary.

The wider tires aren't helping any here, and the 'optimum' seems crazy.

.06* +/- .25* ???

Is .31* to -.21* !!!

So the tolerance is more than 4X the actual setting?

[Gary Lewis]

I hope I didn't misspeak about your SAS RSK Gary.

The wider tires aren't helping any here, and the 'optimum' seems crazy.

.06* +/- .25* ???

Is .31* to -.21* !!!

So the tolerance is more than 4X the actual setting?

No Jim, you were spot-on about the front end.

And while you are reading what the FSM says, I wonder if the spec's are wrong. Surely it should have said .025 degree, meaning from .035 to .085 degrees.

But, looking at the spec's on the computer that the alignment shop uses, they show +/- .13 degrees for a total of .26 degrees.

[ArdWrknTrk]

No Jim, you were spot-on about the front end.

And while you are reading what the FSM says, I wonder if the spec's are wrong. Surely it should have said .025 degree, meaning from .035 to .085 degrees.

But, looking at the spec's on the computer that the alignment shop uses, they show +/- .13 degrees for a total of .26 degrees.

.13 is more than still twice .06..

And I can't imagine anyone specifying thousandths of a degree.

It's a truck, not a cyclotron.

[Gary Lewis]

.13 is more than still twice .06..

And I can't imagine anyone specifying thousandths of a degree.

It's a truck, not a cyclotron.

I agree on the thousandths of a degree. I watched Steve play with the adjustments and it took very little to make a difference. So, maybe they really did mean it?

[85lebaront2]

Tell you what - if the toe-in adjustment doesn't dial it in close enough for me, or if the wandering is gone and I still have bump-steer, then I'll do some measuring and draw up the suspension. Then I can do what Bill suggested and see what happens when it cycles. (I assume there's a way in TurboCAD to connect parts and have them move in concert.)

Gary three things on track bars, first, if it doesn't make a handling difference, why do race cars have adjustable ones? Second, when I was helping and crewing an MG Midget for a friend, it had quarter elliptic rear springs, a half length spring that was bolted to the body by what would be the center of a semi elliptic spring and the eye attached to the bottom side of the rear axle, the top had a link that ran to the body above the spring so the axle moved straight up and down. It used a track bar to keep the axle aligned side to side. We had a suspension guy (circle track type) come and look at the suspension one evening. He had the driver, suited up and in the seat with the car supported on jack stands, rear ones under the axle. He had us make an adjustable length track bar and then set it exactly parallel to the axle at static load. Third, 1955-56 Packards had trailing arm torsion bar rear suspension (bars went all the way to the front) and had a Watts linkage rear track bar system so there was no side shift going up or down.

On your steering linkage, from what I remember of the pictures, both tie rods angle down, right side from the pitman arm, left side from the center of the truck. Darth's do also, but Darth being a 2WD means he has twin I Beams that cross pivot so are longer than the tie rods effective length (center to knuckle) so the effect pretty well cancels. On BB since the knuckles are a fixed distance apart, any vertical motion will change from toe in to toe out very easily, further at the present track bar position as the axle comes up toward the frame, it shifts slightly to the right meaning the left front wheel will toe out more than the right one.

I know that a 4WD front end is a compromise in alignment unless it is full time. It has to be able to drive well in both conditions and one of the issues is toe in, under power it will toe in more then it will just rolling in 2WD, hubs unlocked, locked is more drag and ,more tendency to toe out, under power, more tendency to toe in.

Tires, the desired size tire on the proper rim places the center of the contact patch at the center of the king pin axis (even if you don't have true king pins like Darth does). If the contact patch is not centered then you get torque steer under power (ask how I know this) with a live axle you shouldn't get as much as either independent or twin traction beams as a lot of it is caused by the CV joints at the inner end trying to straighten out under power, however if the contact patch is outboard of the king pin axis, and one tire has less or no traction, you better have a good grip on the steering wheel as the side with better traction will want to turn you the opposite way.

[ArdWrknTrk]

Tell you what - if the toe-in adjustment doesn't dial it in close enough for me, or if the wandering is gone and I still have bump-steer, then I'll do some measuring and draw up the suspension. Then I can do what Bill suggested and see what happens when it cycles. (I assume there's a way in TurboCAD to connect parts and have them move in concert.)

Gary three things on track bars, first, if it doesn't make a handling difference, why do race cars have adjustable ones? Second, when I was helping and crewing an MG Midget for a friend, it had quarter elliptic rear springs, a half length spring that was bolted to the body by what would be the center of a semi elliptic spring and the eye attached to the bottom side of the rear axle, the top had a link that ran to the body above the spring so the axle moved straight up and down. It used a track bar to keep the axle aligned side to side. We had a suspension guy (circle track type) come and look at the suspension one evening. He had the driver, suited up and in the seat with the car supported on jack stands, rear ones under the axle. He had us make an adjustable length track bar and then set it exactly parallel to the axle at static load. Third, 1955-56 Packards had trailing arm torsion bar rear suspension (bars went all the way to the front) and had a Watts linkage rear track bar system so there was no side shift going up or down.

On your steering linkage, from what I remember of the pictures, both tie rods angle down, right side from the pitman arm, left side from the center of the truck. Darth's do also, but Darth being a 2WD means he has twin I Beams that cross pivot so are longer than the tie rods effective length (center to knuckle) so the effect pretty well cancels. On BB since the knuckles are a fixed distance apart, any vertical motion will change from toe in to toe out very easily, further at the present track bar position as the axle comes up toward the frame, it shifts slightly to the right meaning the left front wheel will toe out more than the right one.

I know that a 4WD front end is a compromise in alignment unless it is full time. It has to be able to drive well in both conditions and one of the issues is toe in, under power it will toe in more then it will just rolling in 2WD, hubs unlocked, locked is more drag and ,more tendency to toe out, under power, more tendency to toe in.

Tires, the desired size tire on the proper rim places the center of the contact patch at the center of the king pin axis (even if you don't have true king pins like Darth does). If the contact patch is not centered then you get torque steer under power (ask how I know this) with a live axle you shouldn't get as much as either independent or twin traction beams as a lot of it is caused by the CV joints at the inner end trying to straighten out under power, however if the contact patch is outboard of the king pin axis, and one tire has less or no traction, you better have a good grip on the steering wheel as the side with better traction will want to turn you the opposite way.

Remember Bill that this truck has RSK, so any bump is going to tuck the axle back under the steering box.

I'm not sure where this places the axle in relation to the pitman arm joint but I am sure Ackerman is changing quite a bit as suspension cycles.

[Nothing Special]

.... On your steering linkage, from what I remember of the pictures, both tie rods angle down, right side from the pitman arm, left side from the center of the truck. Darth's do also, but Darth being a 2WD means he has twin I Beams that cross pivot so are longer than the tie rods effective length (center to knuckle) so the effect pretty well cancels. On BB since the knuckles are a fixed distance apart, any vertical motion will change from toe in to toe out very easily, further at the present track bar position as the axle comes up toward the frame, it shifts slightly to the right meaning the left front wheel will toe out more than the right one....

I think you're remembering the pictures wrong, or maybe remembering old pictures from when Big Blue had a TTB. I'm pretty sure Gary has essentially a stock F-350 linkage now (albeit lifted). So I'm pretty sure he has a single tie rod going straight from one knuckle to the other. There would be no effect on steering geometry from suspension motion due to the tie rod.

Then he has a single drag link angling down across the truck from the pitman arm pretty high on the driver's side down to either the passenger side knuckle or else it might attach to the tie rod. That's what could cause bump steer, especially since the track bar is such a different length. But it shouldn't cause wandering.

Now if I'm wrong and Gary is still running F-250 steering linkage with the F-350 axle, then yeah, fix that!