Van front suspension thoughts

[ujoint]

If you move the axle forward with the current steering, I'm afraid it's going to bind up & possibly hit the diff cover. Also, there isn't much room to fab a single trac bar from the drivers side frame rail to the pass side of the axle. If you just remove the drivers side trac bar, the van is gonna handle really weird, I know this because I did it on my Pathfinder. The solution to that is to install a stronger joint @ the axle end, something that doesn't have the "give" of the current bushing. You can see what I mean with about 10 minutes of work (remove the drivers side trac bar).

 

[Photog]

You could be correct about the steering hitting the diff-cover. The photos don't show how much/little space there is availble. I would change the steering linkage design, to a cross over style, with the steering-rod connecting into the tierod on the passenger side.

As for making one of the trac-bar bushing into a stronger joint; the current design won't work, without a fair amount of flex in the joints. When the axle rises straight up, those joints need to collapse. If one is stronger, the axle will move sideways, as it comes up. If they are both stronger, the axle won't move up. It is triangulated.

Other options: Take out the track-bars, put a bumpstop on the cross-member for the axle/pumpkin stop. Build a longer, single, trac-bar, probably requiring a coupl custom brackets for the ends (frame & axle). Make the trac-bar the same length as the new steering-rod, to reduce bump-steer. The track bar would need to be attached to the frame on the driver's side, and axle on the passenger side.

edit: A bumpstop on the cross member might cause the axle to be bent, with a hard hit. Might not be an option.

 

[ntsqd]

Do those rubber donuts on the axle ends of the trac-bars have a center sleave, or can you tighten them to where ever you want?

If no sleave I would suggest, as others have, removing the driver's side bar, and then tighten that passenger side trac-bar nut. Try that as an experiment and see how it rides. For the moment ignore how it steers.
Even if there is a limiting sleave I'd still do the experiment.

FWIW I'd leave that steering design alone. Ford spent a lot of time & money to come up with that design to achieve at least one worthwhile goal, toe-in in droop. Besides, the steering isn't the issue and going to conventional cross-over steering isn't going to buy you much.

Not sure how possible it would be, but if in search of wheel travel I'd be eyeing that cross member with the intent to replace it with a fabricated unit of more differential clearance.

 

[ujoint]

That steering is from a TTB ford, Pathfinder probably only used it because it was available off the shelf & cheap at the time. A true "crossover" will bring the drag link up high, not needed for this rig, and would require custom machining to the pass side steering knuckle. A straight tie rod with the drag link attached would be better, as stated above, but good luck finding a good donor application. ---The bushings at the ends of the trac bars are basically the same as the radius arms, there isn't a sleeve. You can tighten them until they bust, and the axle would be off centered. Clearance is very very tight near the steering box, so a trac bar mount there will be hard, and you also have to worry about the stress on the accordian section of the frame. An additional brace to the pass side frame rail would be needed. Pathfinders are known to already have frame cracking issues near the gearbox, so the whole area will need some bracing. Just bite the bullet and go leaf spring dana 60!!!!!!!!!!!!!!!! You know that's what you want!!!!!!!!!!!!!!!!!!!!

 

[ujoint]

Photog----

When the axle rises straight up, those joints need to collapse.


what do you mean?

 

[ntsqd]

snippage......
A straight tie rod with the drag link attached would be better, as stated above,

Why do you think that? Rock-crawlers seem to be the only folks who have on-going troubles with that system and it has some decided pluses for other applications.

The bushings at the ends of the trac bars are basically the same as the radius arms, there isn't a sleeve. You can tighten them until they bust, and the axle would be off centered.

Presumably then one could drive the vehicle with these overly tight as test of what loosing one of the trac-bars would do for ride quality. Surely wouldn't suggest it a permanent fix.

Just bite the bullet and go leaf spring dana 60!!!!!!!!!!!!!!!! You know that's what you want!!!!!!!!!!!!!!!!!!!!

I sure don't want the extra unsprung mass of a D60 when I'm not rock-crawling the truck and a well set-up coil system can't be touched for ride quality by the best of a leaf sprung system, particularly in a Van where you're sitting right on top of the axle. I have leaves under the front of the Sub right now. They are an obscure Rancho Pre-Runner K5 spring that work very well, but I know that I can't run with a coil sprung truck. It just isn't going to happen. If I ever go to a bigger front diff or tire of the ride of the leaves it will be an F-250 TTB on coils & radius arms that gets stuffed under there.

 

[Photog]

Looking at how everything is connected, the axle and two trac-bars makes a triangle. If the trac-bars had bearings on both ends, the triangle would be solid, and the axle could not rise straight up. It would piviot around the point on the cross-member, where the trac-bars connect.

As it is built now, the ends of the trac-bars have bushings (like the radius arms). As the front end rises or falls, these bushings are compressed. If they could not compress, the axle would not move up & down; but only pivot. These bushings probably need to be fairly soft, to function properly. I suspect they should not be tightened down too much, either.

For a rock crawler, the axle may not need to move up & down much; but it would need to pivot, and articulate. On a street and off-road vehicle, the axle must not only articulate; but also move straight up & down. Consider driving through a "Dip". The whole suspension needs to move up, as a unit.

Does this make more sense?

 

[Photog]

There certainly isn't much room under that van, to build up the suspension; but I would make an attempt at improving the existing coil system.

Modify the steering, and trac-bar, to eliminate the issues with the existing system.
A) The trac bars could be replaced with an "A-arm axle locator" coming from behind the front axle. Many folks have used these on rear suspensions.
B) The existing steering linkage causes bump steer, and the toe angle changes as the axle moves up and down. That is why I like the single tie-rod between the knuckles, on a straight axle suspension.

The remaining problem, is how to prevent the axle from rising up and hitting the cross-member, and still allow for articulation.

 

[Photog]

Solutions for the cross-member problem.

A) Replace the cross-member with a custom piece, that is behind the front axle. Might have to add a small cross-member in front also.

or

B) Put enough lift into the suspension, to give the axle more room to move.

or

C) Move the axle forward, away from the cross-member, and work around the steering linkage issues this causes.

or

D) a combination of a little of each.

 

[ntsqd]

The toe-in in droop is an intentional result. It promotes stability and a desire for the vehicle to want to go straight when the front end is light. I would not eliminate this just 'because'.

Bump-steer isn't necessarily a villain. Depending on when & where it can be beneficial. What happens is that the steering geometry is developed for a specific ride height and all is good. Then we come along and want more ride height. Suddenly the steering is out of it's design envelope and the design, rather than the modifier, is the villain. Not easily done, but were the ride height change properly done the stock steering design's traits would be maintained.

The way I see it the first thing is to determine what the ride quality is w/o the left side trac-bar. It is the villain. Obviously the trac-bar will need to have a similar arc as whatever the eventual draglink's arc of travel is, but for the immediate future I think identifying the villains and removing them for testing is the priority. Then how to fix it within the desired goals and fabrication skills available can be discussed.

 

[Photog]

I like your thinking process. Most folks don't think that far down the trail. You are correct about changing ride-height that then changes suspension geometry. It isn't a design problem, unless you need massive travel (off-road racer). As for toe settings, you normally want a slight toe-in. Toe out almost always causes steering problems such as: hunting, wandering, wind steering, etc. A stable toe setting seems more desireable.

So; what is the desired set-up with this rig? Axle forward (fender well room), stable on the freeway, stable off road. How do we get there from here?:rappel:

In making the necessary modifications to do this, do they want to improve on some of the issues of the existing system?:Mechanic:

The steering could be improved with a lowered pitman arm, and still function within the suspension travel envelope. 1" longer radius arms to improve tire space in fender well (this may cause secondary issues). There must be a better way of locating the axle than those two trac-bars, above the axle. AND NEW BUSHINGS AND BUMPSTOPS.:shakin:

 

[ntsqd]

My goals would be:

1) Ride Quality. Trac-bar design appears to be the villain. Testing should prove or disprove this.

2) Tire Clearance. Slightly longer radius arms or moving radius arm brackets or spacing the existing arms forwards depending on fab skills available & desired level of involvement.

3) Optimize wheel travel. Could be part of 1).

Order of Events:

1) Move/change/build radius arms. Everything else hinges on where the axle is.

2) Decide on steering design type. Fab as necessary. Reinforce steering box mounting, to opposite frame rail and/or engine x-member if deemed necessary.

3) Single Trac-bar system fabrication.

4) Damper mounts, if needed, to employ quality dampers. The closer you are to an axle the more pronounced it's bad ride qualities will be.

 

[ujoint]

I've done the trac bar test!! The van will be all over the road, the bushings have too much give. It may be better with a sway bar. --- Also, I love how everyone bases all leaf spring suspension on the 73-87 GM's. Those springs are so short they will never ride good. I invite anyone to ride in my van and tell me it rides like crap. A straight tie rod is better because there are less joints to wear and cause steering slop/shakes. ---Ford TTB's are horrible for keeping alignment, causing nothing but headaches & bad tire wear. I also want the assurance that I have a Dana 60 under the front end so I know that I'll get home. What's the weight savings over a Dana 44? Is it really worth it?

Why do you think that? Rock-crawlers seem to be the only folks who have on-going troubles with that system and it has some decided pluses for other applications.


Presumably then one could drive the vehicle with these overly tight as test of what loosing one of the trac-bars would do for ride quality. Surely wouldn't suggest it a permanent fix.


I sure don't want the extra unsprung mass of a D60 when I'm not rock-crawling the truck and a well set-up coil system can't be touched for ride quality by the best of a leaf sprung system, particularly in a Van where you're sitting right on top of the axle. I have leaves under the front of the Sub right now. They are an obscure Rancho Pre-Runner K5 spring that work very well, but I know that I can't run with a coil sprung truck. It just isn't going to happen. If I ever go to a bigger front diff or tire of the ride of the leaves it will be an F-250 TTB on coils & radius arms that gets stuffed under there.

 

[ujoint]

Any vehicle with a trac bar has an arc that the axle moves under articulation. The flatter the trac bar angle, the less the arc. I thought that you were saying the trac bar needs to have some sort of slip in it.?.

Looking at how everything is connected, the axle and two trac-bars makes a triangle. If the trac-bars had bearings on both ends, the triangle would be solid, and the axle could not rise straight up. It would piviot around the point on the cross-member, where the trac-bars connect.

As it is built now, the ends of the trac-bars have bushings (like the radius arms). As the front end rises or falls, these bushings are compressed. If they could not compress, the axle would not move up & down; but only pivot. These bushings probably need to be fairly soft, to function properly. I suspect they should not be tightened down too much, either.

For a rock crawler, the axle may not need to move up & down much; but it would need to pivot, and articulate. On a street and off-road vehicle, the axle must not only articulate; but also move straight up & down. Consider driving through a "Dip". The whole suspension needs to move up, as a unit.

Does this make more sense?

 

[ntsqd]

I've done the trac bar test!! The van will be all over the road, the bushings have too much give.

Which is why I was suggesting that the nut be tightened more and was specific about stating that this is a test and not a cure.

Also, I love how everyone bases all leaf spring suspension on the 73-87 GM's. Those springs are so short they will never ride good. I invite anyone to ride in my van and tell me it rides like crap.

Not based of off, used as a point of reference. BTW, mine is a '91
I also have an '84 yota 4x4. It works exceptionally well. Most who ride in it comment on how smooth those leaves work.
Still, there is no way, NONE, that I can keep up with a coil sprung or torsion bar sprung truck for very long w/o really beating on the truck. BT, DT, have the cracks to prove it.

A straight tie rod is better because there are less joints to wear and cause steering slop/shakes.

There is no difference in the total number of TRE's in the system. There is a considerable difference in each system's road behavior.
No argument that a straight drag link and tie rod are preferable, however keep in mind that the Ford design is primarily in tension and tension wants to straighten out those bends, not permanently bend the member. Compression only really happens when rock crawling and a tire is forced to turn into something, or when backing up.

---Ford TTB's are horrible for keeping alignment, causing nothing but headaches & bad tire wear.

That bad tire wear is b/c Ford never put enough damping on the system not necessarily b/c the alignment was off. Too many desert race trucks have been successful to outright dominating of their class to say the design is poor. The execution of the design can be fixed, and he's not considering such a thing - I am.

I also want the assurance that I have a Dana 60 under the front end so I know that I'll get home. What's the weight savings over a Dana 44? Is it really worth it?

Yes, it is to me. One pound of unsprung is roughly equal to ten pounds of sprung weight in vehicle performance. So that 100 lbs difference is too much to me.

We're probably going to have to agree to disagree.