Track bar / drag link geometry

[ksagis]

I'm surprised it doesn't drive better than you describe...lots of folks running similar looking geometries without the unsettled handling characteristics through the bumps...and are we talking pot holes or POT HOLES? Could it be a spring rate or damping rate issue with the coilovers? Just from what you describe, I would suggest checking/replacing the track bar bushings on a more stock-ish setup, but everything looks new under there. Adding ram-assist typically slows steering down if anything, but the Ø1.5" bore ram should be the least offensive in that way so long as your pump is up to the task. I'm adding a Ø1.75x8 PSC ram from WH4x4 to mine, and other than the added diameter being a little tougher to package (things are tight to say the least), function should be similar.

I haven't driven mine yet with the new axles and steering, but I have a similar ~41" drag link length with GM TRE's, and in order to get my track bar length and angle to match, I pushed the frame side mount down and out a bit, though less down since I'm not running a dropped pitman arm. The attached image shows the suspension at full stuff (or within about 1/2"), noting that my track bar just clears the front sump on my double-sump oil pan. If mine looks a little different, it's because it's a HP D44 from an F150 at the 65" width, so I have a little more axle tube to play with than you do.

Is the coilover in the way, or could you just replace the frame side track bar mount with one that positions the track bar parallel with the drag link and pushes the mount outward to get closer on the lengths? Matching up the drag link and track bar angles and lengths certainly won't hurt anything, but it may not solve the drivability issue described.

I like this idea on getting length by moving the drivers side of track bar out board of the frame but not sure I can get 6.5 inches to match lengths. I do like this approach more than tying into tie rod mid span since it keeps angles lower for both (if I can match lengths and angles)

Gonna crawl under truck after work and poke around, will report back.

Maybe not a huge pot hole, but not small ones. And when driving with a concrete barrier on one side (with no shoulder) and 18 wheeler on other side, got me puckered up a bit. And honestly, I *think it should drive better and I enjoy tinkering and love the dialogue from the experts on ways I can make it better.

Based on @ntsqd CAD and eye watering movement at knuckle with much more at wheel diameter, it’s becoming apparent it’s much more than “are they parallel”!

 

[ntsqd]

With a plumb-bob, some string, maybe a wall-board square, and a measuring tape you can plot this out full scale on the floor, don't need CAD to do it.

 

[lars]

The discussion about drag link and panhard rod geometry is interesting, but I wonder how relevant it is to your perceived "darting" behavior. Did you answer @toddz69's question about type of front suspension? Clearly you don't have OEM radius arms.

I've had link geometry on my Bronco that looked a lot like yours in the past. I experienced bump steer on big dips, especially in corners, but it didn't feel unstable otherwise on smooth ground. With the geometry I have now I have to go over some serious woopdedoos to get the steering wheel to saw around, and it's not really a bother.

Random thought out of left field: you have a hydraulic ram on your steering. Is it essential for driving around on the street? If not, could you disconnect it and try driving without it? If nothing else it would rule out the possibility that stiction in the ram was contributing to the problem.

 

[ksagis]

Crawled under truck a bit after work and summarizing my general thinking - matching the length of the track bar and the drag link seems at least as important as matching angles. This comment is based on the math from @ntsqd, along with qualitative comments from @toddz69 and @Yeller.

Answering various posts:

I'd love to see side pics of your front suspension too.

Todd Z.

Front suspension pictures, please let me know if more would be helpful.

In the pic it hard to see the front to back spacial orientation of the components. A lot of builders insist on putting the coilover on the center line of the axle, which is completely unnecessary and complicates track bar and steering terribly

Pic of passenger side showing track bar gussets pretty much butted up to C, not too much room here to get the 6.5 inches I need to match lengths. Might be able to pick up a few inches on this side and get some more on driver's side per suggestion from @Apogee

Is the coilover in the way, or could you just replace the frame side track bar mount with one that positions the track bar parallel with the drag link and pushes the mount outward to get closer on the lengths? Matching up the drag link and track bar angles and lengths certainly won't hurt anything, but it may not solve the drivability issue described.

I love this idea but worried about clearance to tire at full right lock. Only 3" or so remaining with wheels straight if I got the full 6.5" only on this side.

The discussion about drag link and panhard rod geometry is interesting, but I wonder how relevant it is to your perceived "darting" behavior. Did you answer @toddz69's question about type of front suspension? Clearly you don't have OEM radius arms.

I've had link geometry on my Bronco that looked a lot like yours in the past. I experienced bump steer on big dips, especially in corners, but it didn't feel unstable otherwise on smooth ground. With the geometry I have now I have to go over some serious woopdedoos to get the steering wheel to saw around, and it's not really a bother.

Random thought out of left field: you have a hydraulic ram on your steering. Is it essential for driving around on the street? If not, could you disconnect it and try driving without it? If nothing else it would rule out the possibility that stiction in the ram was contributing to the problem.

The best way I can describe the behavior is one wheel going into a pot hole and then the vehicle wanting to dart from the straight line it was on. I think I answered Todd questions, please let me know if more data is helpful. I have thought of disconnecting ram but haven't done it yet. I need to think about your stiction comment, I had not considered that, thanks.

What is the horizontal distance, and the vertical distance between the frame end of the trac-bar and the pitman arm end of the drag-link? Easy enough to plot the two arcs of travel with those numbers added to the numbers posted at the top.

Looks to me like parallelism could be greatly improved by simply moving the drag-link to the top of the dropped pitman arm. It may not work well in real life there, but it would be closer to parallel. However, that doesn't solve the length difference problem.

It was roughly 2.5" outboard and 2.5" of vertical offset between pitman and track bar centerlines. Your approximations were plenty accurate for this round.



I am currently thinking that matching lengths might be the best first step since the track bar work on either side is pretty messy and would take work on both sides to get the 6.5" I need to match length.

Thinking it might be better if I move the drag link attach point from the knuckle to the tie rod, and then I can very nearly match the angle and the length. Thinking of some kind of similar setup as the ram (on the backside of tie rod) with adding gussets, a bracket, and a ball and heim to attach the drag link to. Need to look at clearance and possible binding on the heim and ball, may need one of the high clearance do-hickeys.

Couple pics of the area and my thoughts below - tho not super thrilled about trying into tie rod. Let know what folks think.

By the way, I need to modify the tie rod anyway since it doesn't allow infinite adjustment of toe due to the ram which then permits me to adjust toe by turning the drivers heim in 180 degree turns, versus rotating the entire tie rod and locking in in place)

Appreciate all the critical thinking and feedback from folks.

 

[ntsqd]

Sketch adjusted for the new dims:

Maybe use something like this to attach the ram to the tie-rod?
https://www.ruffstuffspecialties.com/R1697.html

Do you happen to have a stock drop pitman arm? I'd be curious to see what it does to the angle of the drag-link.

It works and is done a lot, but not a fan of connecting the drag-link to the tie-rod. You end up with a little slop in the linkage as the drag-link 'rolls' the tie-rod when reversing direction. RuffStuff does make a hard polymer "washer" to counteract this when the system uses TRE's. I'm sure something similar can be done for SRE's.

 

[1969]

I am not an expert as some others here by any means but I think you are missing your passenger side upper radius arm. You have a 3 link style set up that is not triangulated correctly as is. The single upper arm needs to be corrected or add that passenger upper arm I believe. I have a 4 arm radius set up on my Bronco, and if I was to pull one upper arm, it would flex and wheel a lot better, but also ruin the road manners of it.


Here is my set up

 

[Yeller]

The wristed front suspension is a bit of an adder to the issue if your on the brakes, it will lift the driver’s side, not a deal breaker just something to keep in mind.

There’s room to gain on the axle side of the track bar, remember 1” there and 3” on the other side is a 73% improvement. It is not too difficult to remove the springs and use an engine hoist to cycle the suspension to prove concepts on clearances if your worried about them.

I’ll share my opinion on a 3 link not being stable. If link geometry is sound and the center of gravity is not too high they drive very well. I have played with both on my bronco and felt the 4th link was completely not needed, it actually made it ride rough on the street. It also induced under steer on the street like having too stiff of a front sway bar. I did both on it because I felt the need to quantify that all of the three links that I had built (It’s a LOT) up to that point were the correct decision, I feel it is. I will say though that if the CG is too high and/or shocks improperly valved they can become wallowy.

That being said, I need to clarify, that is with 3 individual control arms, not one of them being a radius arm where 2 of those control arms are joint together. In that configuration both sides being the same is more stable and predictable.

With coil overs I’m a huge proponent of very light “Anti Rock” type sway bars. They help cover up a multitude of coil over sins regarding spring rates, shock valving, center of gravity, and suspension geometry.

No suspension design is perfect in all conditions, they are all a compromise, it is a matter of getting those compromises to play nice together to get a result that works and is safe.

 

[ksagis]

Sketch adjusted for the new dims:

Maybe use something like this to attach the ram to the tie-rod?
https://www.ruffstuffspecialties.com/R1697.html

Do you happen to have a stock drop pitman arm? I'd be curious to see what it does to the angle of the drag-link.

It works and is done a lot, but not a fan of connecting the drag-link to the tie-rod. You end up with a little slop in the linkage as the drag-link 'rolls' the tie-rod when reversing direction. RuffStuff does make a hard polymer "washer" to counteract this when the system uses TRE's. I'm sure something similar can be done for SRE's.

Thanks for updated CAD, surprised that fairly small change took it from about 1/4” to almost 0.300”. Shows how sensitive this is.

i actually bought one of those clamp fittings and never installed it as I wasn’t too excited about relying on clamping pressure on the shaft of the ram assist even though only maybe 2500 lbs of ram force at full pump pressure and likely the clamping would hold.

Thanks for reminding me about the concern on rolling, is the worry that the constant reversing loosens the jam nuts, general wear on heims, or something else?

Any opinions on putting the ball and socket on top of tie rod, or rotate it 90 degrees towards the front of tie rod being better?

 

[ksagis]

The wristed front suspension is a bit of an adder to the issue if your on the brakes, it will lift the driver’s side, not a deal breaker just something to keep in mind.

There’s room to gain on the axle side of the track bar, remember 1” there and 3” on the other side is a 73% improvement. It is not too difficult to remove the springs and use an engine hoist to cycle the suspension to prove concepts on clearances if your worried about them.

I’ll share my opinion on a 3 link not being stable. If link geometry is sound and the center of gravity is not too high they drive very well. I have played with both on my bronco and felt the 4th link was completely not needed, it actually made it ride rough on the street. It also induced under steer on the street like having too stiff of a front sway bar. I did both on it because I felt the need to quantify that all of the three links that I had built (It’s a LOT) up to that point were the correct decision, I feel it is. I will say though that if the CG is too high and/or shocks improperly valved they can become wallowy.

That being said, I need to clarify, that is with 3 individual control arms, not one of them being a radius arm where 2 of those control arms are joint together. In that configuration both sides being the same is more stable and predictable.

With coil overs I’m a huge proponent of very light “Anti Rock” type sway bars. They help cover up a multitude of coil over sins regarding spring rates, shock valving, center of gravity, and suspension geometry.

No suspension design is perfect in all conditions, they are all a compromise, it is a matter of getting those compromises to play nice together to get a result that works and is safe.

Thanks Yeller, you’re totally right that knocking out 4 of the 6.5 inches would likely make things a lot better. Weighing the amount of fab work required and whether I can find a decent shop in NorCal.

I have a buddy in Denver that I could fly the drag link and tie rod to and we modify. (and a handy excuse to visit)

If anybody knows of a fab shop in NorCal for something like this, please let me know.