Van front suspension thoughts

[Photog]

This is a long one. By the way, is Mike following this, or is this just an interesting discussion on suspension design?

From a design and performance point of view; what is the weight of one of these vans, when loaded for a trip? The Dana 44 & Dana 60 are designed for two different load and torque ratings.

Judging by the photographs, UJoint's van uses the 4X4 function in severe conditions. Per Mike's requirements, it does not seem like his van will be used in such a severe fashion. Unless the weight on the front axle is to high for the Dana44, I'm sure it will do a fine job, as a front axle. A Dana 60 might be necessary for the rear axle.

As for leaf spring ride quality: the long leaves definitely improve the ride quality. The soft springs are not usually suitable for carrying a load. This would bring us back to weight on the front axle. How much does the front axle load change, when the van is empty or loaded for a trip? If the weight is fairly stable, then design the leaf system for comfort, at the typical load. If it were a sports car, off-road racer, or luxury car, I would NOT want a leaf spring front suspension. This van is not in these catagories; so I think it could be set up to be comfortable and functional, either way. The off-road racers that use a straight axle, do use coil spring systems; but they did use leaf spring systems for many, many years. I suspect these van frames were not made for any type of off-road pounding, and the frame should be reinforced, with either suspension type. There are other issues with the leaf setup; such as eliminating the crush can section of the frame, and applying over 1/2 the suspension load to the forward section of the frame. The frame may need reinforced all the way back to the other end of the leaf spring.

Trac-bar angle being flat is usually a good thing, and so are steering-linkage angles. Unfortunately this probably can not be achieved with this van. Trac-bar and steering linkage lengths and angles work well when they are matched to each other. The suspension may move in a slight arc; but the bump steer can be minimized.

:arabia:

 

[ntsqd]

Just a note on trac-bar & drag link angles; I prefer to set them slightly down towards the axle end. The logic being that if they are flat that you are giving up some of the prime bump-steer free travel. Note that it's usually refered to as "bump-steer" and not "droop-steer".
With the slightly downwards angle the system stays within it's sweet spot for more compression distance.

 

[ujoint]

I've been wondering if Mike's been reading as well. No matter the angle (unless it's really ugly), as long as the trac bar & drag link are at the same angle, there shouldn't be ANY bumpsteer. The trac bar should have NO side to side give. Either way, there are plenty of different ways to build a suspension, depending on the needs of the owner. I use my van for everything: daily driver, mtn bike shuttle, camping rig, wheeler, and it works exactly the way I want it. I built hundreds of trucks when I was @ ORU, and I took what I felt to be the best parts from what I'd seen work over the years. I get calls almost daily on 4x4 van conversions, and I always recommend the same things. Durable, cost effective, realistic suspensions.

 

[ntsqd]

IME it's pretty rare that the drag link and the trac-bar can be both the same length and parallel to each other in both the top view and the side view. Same length & parallel is certainly what you're shooting for, but trying to get textbook perfect alignment btwn them in an existing vehicle is very likely to be difficult at best.

That's not as big of a problem as it might sound like. So long as the travel curves are similar and the starting point of both axle pivots are near the bottom of the region where the curves are the most superimposed, bump steer is not a problem. It is an uncommon driver who can feel a 1/8" divergence in those two arcs, but you can't allow much more than that within the first 3"-4" of up-travel. It's been a while since I looked at it, but I think that Allan Staniforth's "String Computer" technique could probably be used to find the ideal pivot locations of one element given that the other is set.

 

[\\'anderer]

Sorry I have not replied, I am having Internet connection issues at the moment, but I have read the thread carefully.

Now that I have had some time to think about the van's use. Here is what I need:
The van will be used for expeditions and long camping trips towing my trailer, so it will be on the heavy side.

1. load carrying capacity and safe predictable steering are a must (many miles on road as well as off).

2. A more comfortable ride is important but not at the cost of #1

3. Off road worthiness, will not be extreme, but I would rather overbuild than under estimate the trails I would take it on.


I could remove 1 track bar, and with new bushings, it will probably drive better than it does now but, the track bar is too small for comfort. The front axle sits nicely under the cross member, Moving the axle forward will put it dangerously close to hitting the cross member and steering linkage.

The more I look at the front suspension, the more I see that a "patch" is not the best choice. A complete redesign of the front suspension as a system is the only way to go.

I like the coil spring setup, and removing the small track bars, adding 1 larger bar and crossover steering would make a world of difference. The front end would retain some pathfinder specific parts, namely the bushings that I would rather do away with.

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

This is still my most likely choice. I really like the simplicity and durability of a front leaf setup. Getting the correct spring rate for my load would help with the ride quality. I think all the modern van conversions use a leaf spring setup
there must be a reason (besides cost) why the coil setup went away.

Besides ride quality complaints, any reason why leafs would not be a good choice for my application?

 

[ntsqd]

The first big red flag I see is the previously mentioned accordion section of the frame. If you pursue leaves that needs to be torn out and rebuilt since 1/2 the weight of each side will now be carried forward of it and if it doesn't immediately start flexing it soon will.

I can't say how strongly I believe that changing to leaves is not only much more unnecessary work, but also a step backwards in both ulitmate ride quality and in control. And yes, I do think that economics combined with familiarity as being what drives most conversion companies to use leaves.
With cross-over steering and leaf springs it is not all that uncommon to need a trac-bar to counter steering input induced spring deflection. This is more frequent in harder core off road use, but it does happen on the pavement too.

The spring rates you already have must be close to what you need. If not, coil spring rates are much more easily changed than leaf spring rates are. The frame is designed to have the existing load application points, changing to leaves means re-engineering, designing, and modifying the frame.

What I'm reading and seeing tells me that the first step is to address the trac-bar issue and then re-evaluate ride quality and vehicle control. It is my firm belief that a proper trac-bar combined with a quality set of dampers will meet at least 80% of your goals and quite probably do everything you need. I'm not saying that the trac-bar will be easy, but it is fixable for less effort than completely re-designing the front suspension to use leaf springs. If this fabrication is beyond what you're able to do or comfortable with I would suggest contacting a shop that works with Early Broncos, such as West Coast Broncos on Hwy 247 in Yucca Valley, as they work with exactly that front suspension. If you do contact WCB tell Dusty that Thom Singer sent you.
Alternately, Autofab, Spirit Racing, or Camburg Engineering all have extensive history in working with Fords and the TTB and will be familiar with what needs to happen to make it work.

 

[ujoint]

The accordiansection of the frame is a concern, easily cured by boxing it.

Sure, a trac bar is always nice to have, but hard to put in a van unless you go with the 86-97 Ford F350 style, which went from the engine x-member to the pass side, very short. I'm not running a trac bar on mine, nor have I put one in any of the conversions I've done. As long as the lift isn't too high and the drag link is as flat as possible, everything is ok. Another thing we have to consider is that everyone has diferent standards of what they consider a "good" or "bad" ride quality. I've driven trucks that I thought rode great, and the customer complained of a horrible ride. I've also driven trucks that I thought rode like a garbage truck on concrete tires, and the customer had no issues, even though I told them I thought it rode bad. So eveyone has different expectations & standards, that's the way it goes. ---- This has turned out to be an awesome thread, tons of fun!!!!!!!!!!

 

[Photog]

Mike,
Is there any way to get a photo of your suspension from the side (looking straight from one hub to the other)? One of the big issues here is, how much up travel is available for the axle, before it crashes into something?

From the photographs you have already posted, it looks like part of a cross member has been cut out, to make room for the differential, as it rises. This cross member looks to be behind the axle. Is there also one in front of the axle?

The proper photo would clarify this.

Steering linkage can be changed, to make room for the axle to move forward a little. Things like a different pitman arm, etc.

 

[\\'anderer]

This picture shows the axle directly under the crossmember, the track bars and steering linkage routing



This pic. from behind the front axle looking forward and up. Notice how neatly the axle can tuck up into the crossmember. Too far and the axle will hit the oil filter. Available travel upwards is minimal. an inch or so max with with both sides compressed or maybe 3" with just one side compressed. Total suspesnion travel from droop to compression is less than my mountain bike.

 

[Photog]

That looks like a custom crossmember. Probably more beefy than the factory 2WD parts, or mayby a modified 2WD part.

If you modify your coil spring suspension, or go with a leaf system, it looks like you will need to change that crossmember. Replace it with something completely different. Even then, you may need to raise the van an inche or two, to make room for som suspension travel.

You also need to move the axle forward, to make room for the tires. With an A-arm style of axle locator (instead of a trac bar) you would not have any trouble with linkage hitting the axle. It looks like you could move the axle forward a couple inches. Again, this is with a different axle locator (coming from behind the axle), and a modified crossmember.

 

[ntsqd]

The only reason my Sub is lifted 4" is to get something more than 1" of bump travel. I think that the same sort of thing will hold true here too. There isn't much if any room to increase the bump travel without raising the ride height.

Unfortunately you can not use an A-shape locating member in front suspension unless the drag link is a push-pull & has it's frame end adjacent to the A-link's frame end. An A-arm used with the current steering will result in massive bumpsteer.
I've seen a drag link arranged so that an A-link would work. It's under a semi pre-run '57 Chevy truck somewhere in Nor CA and the linkage required to get it there is rather involved.

 

[ujoint]

That x-member is the stock 2wd Ford x-member that got hacked up in the typical Pathfinder fashion. There's no reason to change it, waaaaay too much fabrication, and not needed for a project like this.

 

[Photog]

If the factory crossmember stays, the van will need a suspension lift, to get any type of functional travel.

If the axle gets moved forward, the crossmember will probably need a little more trimming, and maybe a little reinforcement.

Now; as for the axle locator. My thoughts on the A-arm locator are: Mount the A-arm from the rear, attaching to the frame, near the radius arm mounts. The axle already moves through an arc, based on the length of the radius arms; so if the A-arm were designed to match that same arc, it seems like the steering-feel would not be changed from its current condition. The A-arm could come in low, under the driveshaft.

I can see how the there might be some bump steer, because the axle would move through an arc, in a different plane than the steering linkage.

After the lift, you would want to put on a drop-type pitman arm, to reduce the angle of the steering linkage. There would also be less clutter in front of the axle, with the existing trac-bars removed; so other steering changes could be made.

What issues would this type of arrangement cause?

 

[ntsqd]

I've been pondering whether the trac-bar could be in front of the steering linkage. My best estimate is that it would need to be futher fwd at the frame end than at the axle end, but this should be kept to the barest minimum necessary to keep the plane of the lateral location arc as close to the plane of the long tie-rod's arc as is possible.

I abhor drop pitman arms. They introduce a leverage on the steering box that it really wasn't designed for. Some times you can get away with it, other times they kill the box faster than acceptable.

While I've seen exactly this existing system in the past, we weren't asked to improve that aspect, so I put no effort into what would need to happen. And I'm more and more thinking that it's really going to take a physical inspection to move down the road to improvement.
So I'll repeat my suggestion that WCB is the most local fab shop that I am willing to suggest as capable of handling this mod. Early Broncos and F-100's have this proposed suspension layout, so WCB is well versed in the intricacies of making them behave as they should. They also have the ability to supply the cross-over type steering in wear parts of suitable size should that still be desired.

 

[Photog]

I was just thinking about, "If this were my vehicle, what would I do?"

I would take the info put forth in this thread, spend some time under the rig, to understand how it is supposed to work, and then take it to a shop that really knows this type of system, such as WCB. I really have to agree with Thom on this one.

Also, while at the specialty shop (WCB), ask their opinion on a leaf spring system. Maybe the coil system will be straight forward, and meet all the needs, maybe not.