triangulated lower links? parallel upper links? No panhard? (1 Viewer)

[workingdog]

So, My son had me watching FabRats on youtube. And he's working on an older dodge and he's putting triangulated lower link, parallel upper links (outside the frame rails) and no panhard in the front. And I'm thinking, WTF? That's not supposed to work. So, he also has an fj45 (ultimate rock crawler) that he's built the same way. I'm trying to get a better look at the thing, they are always moving around and can't find the episode where he actually does the front suspension on the the thing.

I've always assume you couldn't do that because of front driveshaft interference and you have to use a panhard. But, looking at what he's done - I'm hoping someone here will tell me why it's a bad idea before I rip apart my EV project - Builds - fj60 going to EV FJ45 - https://forum.ih8mud.com/threads/fj60-going-to-ev-fj45.1234095/ - and do it that way.

My guess is that, since the lower links more or less parallel the driveline as the front axle goes up and down, if you get the front link mounts right, you won't get any contact. His other trick is to move the upper mounts outside the frame and have the uppers entirely outside the frame. That means you have a to run a pretty wide axle (I'm running Dana 44 out of a 2020 Jeep Rubicon Gladiator), but there's lots of room out there. Now, on his dodge at least, he runs the Johnny Joints the wrong way on the frame side (90 degrees rotated from where they should be) to make it easier to build the mounts. But, if you can make all that work - no panhard, not lateral movement of the axle, no bump steer.

Tell me why this won't work.

 

[gnob]

The tow rig is a sorta chevy.
The reason you are questioning this is because of years of reading "internet experts" opinions.

 

[matzell]

4 link and full hydro steering does not need panhard. No bump steer like a gearbox would have. Jimmys4x4 builds a lot of cars like this, more so in the rear. Proper 4 link, double triangle the axle will not have much if any roll steer or side to side movement. Just cause it works at low speed off road does not mean it will work on the road at highway speeds.

 

[peesalot]

As above, the hydro makes no panhard possible. The parallel uppers is a good set up, An old ultra4 racer once told me that he prefered the parallel uppers and that it worked better. Easier on packaging as well.

 

[mtweller]

Just curious, if full hydro steering, will CA allow that to be tagged and registered?

 

[workingdog]

@mtweller - huge debate about that. If you took a homemade rig to CHP for safety, I'd bet they'd deny it, but otherwise I'm unaware of anyone ever getting in trouble for it.

@peesalot - You can't get parallel uppers inside the frame to get clearance, and it never occurred to me to put them outside the frame rail. It also never occurred to me to triangulate the lowers in front. I've got to look at my rigs and see if I can make that work.

 

[workingdog]

Okay, is it the full hydro that allows you to go four link? Or is it packaging. If you do true triangulated 4 link on the front without panhard and still have a drag link, will the front end tear itself up???

 

[matzell]

Okay, is it the full hydro that allows you to go four link? Or is it packaging. If you do true triangulated 4 link on the front without panhard and still have a drag link, will the front end tear itself up???

Gotta have a panhard with a draglink. IF NOT the bump steer would be all over...Not sure you could even drive it.

 

[Firemedic831]

Full Hydro you are pushing and pulling from the center of the axle . Drag link you are pushing and pulling from the frame / Steering box

 

[peesalot]

FWIW, IMO it's a job either way, I will say I have seen a fair shake of drag link, panhard failures, not so many full hydro failures. If you want street legal then you know what you gotta do, if its trail only then I would say go hydro and have more fun.

 

[GLTHFJ60]

Gotta have a panhard with a draglink. IF NOT the bump steer would be all over...Not sure you could even drive it.

Totally trust and believe that you're correct, but help me understand more. Is it because a triangulated 4-link up front allows a ton of vertical travel and moves in line with the centerline of the truck, not in relation to the frame rail where the steering box is or would be?

If so, wouldn't a "long travel" leaf spring front suspension with drag link (obv no panhard) have a similar bump steer problem?

 

[cruisermatt]

Gotta have a panhard with a draglink. IF NOT the bump steer would be all over...Not sure you could even drive it.

I have driven a 4 link with traditional steering box and no panhard. It was bad but not completely undrivable. Basically comparable to a SOA without high steer.

Totally trust and believe that you're correct, but help me understand more. Is it because a triangulated 4-link up front allows a ton of vertical travel and moves in line with the centerline of the truck, not in relation to the frame rail where the steering box is or would be?

If so, wouldn't a "long travel" leaf spring front suspension with drag link (obv no panhard) have a similar bump steer problem?

Depends on how much angle... on trucks like ours where they are actually set up correctly (flat panhard or close to it) it is a non issue since the horizontal displacement is minimized.
If you do the math even with high travel the axle end of a panhard/draglink barely moves when it's flat. It's something like less then 1/4" on a 36" panhard.
Plus leaf springs have high compliance naturally, due to the bushings, shackles, etc that's putting a big damper on everything

 

[GLTHFJ60]

Depends on how much angle... on trucks like ours where they are actually set up correctly (flat panhard or close to it) it is a non issue since the horizontal displacement is minimized.
If you do the math even with high travel the axle end of a panhard/draglink barely moves when it's flat. It's something like less then 1/4" on a 36" panhard.
Plus leaf springs have high compliance naturally, due to the bushings, shackles, etc that's putting a big damper on everything

Totally get the drag link angle thing. Could be set up the same on a triangulated 4-link, and is why I'm asking.

Aside from the compliance in the leaf spring bushings, I'd expect a SOA truck to have the same bumpsteer as a triangulated 4 link, assuming the drag link is parallel to the housing at ride height in both setups. That's the basis of my question. If the 4-link is worse, what elements make it worse?

 

[matzell]

Totally trust and believe that you're correct, but help me understand more. Is it because a triangulated 4-link up front allows a ton of vertical travel and moves in line with the centerline of the truck, not in relation to the frame rail where the steering box is or would be?

If so, wouldn't a "long travel" leaf spring front suspension with drag link (obv no panhard) have a similar bump steer problem?

If the axle moves straight up and down the steering has to do something to move one way or the other with a drag link. The longer the drag link the less noticeable. With a panhard the steering and axle travel the same arch and it does not move (much).

 

[GLTHFJ60]

If the axle moves straight up and down the steering has to do something to move one way or the other with a drag link. The longer the drag link the less noticeable. With a panhard the steering and axle travel the same arch and it does not move (much).

Cool, that's what I figured. Wonder why (or if I guess) it's a bigger problem with 4-links than it is with leaf spring SOA trucks.

Maybe it's just a problem with speed? Most SOA trucks don't do speed, mine certainly doesn't, but 4-link trucks with big shocks I could see hitting the whoops at 40+. Bump steer would be crippling at that speed I bet.

 

[cruisermatt]

Cool, that's what I figured. Wonder why (or if I guess) it's a bigger problem with 4-links than it is with leaf spring SOA trucks.

What I was trying to say is that it shouldn’t be a serious problem, if the drag link is flat-ish.

The truck I drove had a 6” lift and stock steering knuckle, so quite a bit of drag link angle. I drove it 40-45mph…

 

[matzell]

What I was trying to say is that it shouldn’t be a serious problem, if the drag link is flat-ish.

The truck I drove had a 6” lift and stock steering knuckle, so quite a bit of drag link angle. I drove it 40-45mph…

Over bumps? It was really bad on old SA Toyota trucks 84-85. my steering wheel would turn 60 deg or so on big bumps, you just had to know how to it with the push pull steering. Cross over really helped out.

 

[GLTHFJ60]

Over bumps? It was really bad on old SA Toyota trucks 84-85. my steering wheel would turn 60 deg or so on big bumps, you just had to know how to it with the push pull steering. Cross over really helped out.

Yeah, that's pretty much it right there. It's about speed, and it makes complete sense.

Going over whoops embarrassingly slow at Uwharrie or whatever, my steering wheel rows quite a bit. This makes sense, my front axle is moving up and down, and the distance from the steering arm to the box is changing as I do that. Impact is minimal at slow speed, or on flat ground.

You start going fast, which is a large part of the reason to go to links, then this affect is magnified. Your wheel would go all over the damn place.

Totally get it. Thanks matzell for clarifying.

 

[workingdog]

So, I'm guessing I have too much draglink and panhard angle here. Because the front of the truck walks 2" to the side when I have it on the lift and lower it to the ground. But that's from full drop, which is max angle.

 

[GLTHFJ60]

So, I'm guessing I have too much draglink and panhard angle here. Because the front of the truck walks 2" to the side when I have it on the lift and lower it to the ground. But that's from full drop, which is max angle.

It is ideal to have the relay rod and drag link parallel at ride height.