Wristed Control Arm Pics (1 Viewer)

I started a thread a couple of weeks ago asking about using wristed control arms to gain front-end articulation. Just as a little science experiment, I unbolted the forward bolt on the driver's side control arm and took the truck up a ramp. I compared w/ results obtained w/ the control arm bolted. The difference was pretty amazing, as I was able to get full shock extension on the low side w/ simultaneous full stuff to the bump stop on the other. The leading edge of the driver's side control arm -- i.e. the part that was unbolted -- moved surprisingly little, maybe +/- 3/4".

I was concerned about added stress on the passenger-side control arm, which would now carry all the axle torsional loads. Actually, it looks like the weak link would be the mounting bracket vice the arm itself. After reading about Land Rover and Bronco guys doing this (including a ~500-hp Bronco), I decided to test the ghetto wristed control arm on the trail.

The following weekend, my club had a run on a fairly challenging, VERY articulation-intensive trail characterized by a few rock obstacles but mostly deeply rutted climbs and descents. I was originally planning to unbolt the control arm at the trailhead. However, I found that a receiver hitch pin fits perfectly in the bolt hole and was able to simply unpin the control arm while we aired down.

The difference on the trail was amazing. We had a couple of sections where the TJ on 35s behind me almost rolled, and my LX was able to stay fairly level w/ the axles doing all the work. One downside was additional body roll on off-camber sections, but that was to be expected. It seemed as though the front and rear of my truck were fairly balanced articulation-wise. I didn't notice any binding, strange noises, or damage to the control arms or brackets. I'll caveat that with the fact that I tried to be as gentle as possible w/ the truck, especially the skinny pedal, since I didn't know what to expect.

Before you start flaming, keep in mind that this was simply an initial investigation of wristed control arm effects. I realize that the control arms, bushings, and brackets are rated for the loads they experience w/ both control arms carrying the axle torsional loads. However, with a little additional bracing on the passenger-side control arm bracket (on the axle), this may be a viable technique.

Jason

Most excellent! This is very good info.... do you have a before picture on the ramp? How about shock measurements before and after?

So you just only unbolt the drivers side one? or the pass one as well?

I don't have any quantitative data on shock measurements. However, a while back I marked the max compression/extension points on all my shock bodies w/ a Sharpie. With control arms bolted and no front sway bar, the front shocks are nowhere near their limits (even w/ a rear wheel on the ramp, putting more weight on the front). With one control arm wristed, the extended front shock was at max extension. The compressed front shock was still about 2" - 2.5" from max compression with the bumpstop just touching.

Before and after pics of the stuffed wheel attached.

After pic of the extended wheel. I'm out of space on attachments (150kB max), so I don't have room for the before pic.

Jason

jmaddocks said:

I was concerned about added stress on the passenger-side control arm, which would now carry all the axle torsional loads. Actually, it looks like the weak link would be the mounting bracket vice the arm itself. After reading about Land Rover and Bronco guys doing this (including a ~500-hp Bronco), I decided to test the ghetto wristed control arm on the trail.


Jason

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sounds like it was only drivers side. interesting idea.... i like the idea but seems like something would give given you are really putting a ton of pressure on it in those situations.

i like the way you tested it though..... keep working on it.

Jared

Wrench said:

So you just only unbolt the drivers side one? or the pass one as well?

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You only unbolt one side, as you need one radius arm to carry the axle torsional loads. I chose to unbolt the driver's side. Ideally, you would probably want to try each side to figure out which is best.

An additional downside of this technique is that caster will change based on which way the front axle is articulating. Another reason why you probably don't want to drive on the road like this. This wasn't noticeable off road.

Jason

NW-sickboy said:

sounds like it was only drivers side. interesting idea.... i like the idea but seems like something would give given you are really putting a ton of pressure on it in those situations.

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In the static case on the ramp, I think a lot of the loads are actually lower, since the dominant control arm bind is almost nonexistant (the bind that forces the control arm bushings to compress eccentrically). The torsional loads on the control arms (and bushings/brackets) are undoubtedly higher, since the control arms have to twist more. Both control arms are still available to control the axle fore and aft. Finally, the axle torsional loads are neglible in this static case -- these are the ones I'd worry about most on the trail, as they would be carried solely by the passenger arm.

Jason

I believe I asked about this when I first came on the board last year and everybody looked at me a bit funny. I've been meaning to do this experiment myself and was expecting similar results. I ran a radius arm setup on my old Jeep and experimented with wristed and unwristed and found noticeable improvements off-road with the wristed setup. I don't recall the size of the bolts on the radius arms where they bolt to the axle, but IIRC they seemed sufficient to remove one for off-road purposes. I would probably brace the bracket if I were to run this setup indefinately. I like the way you used a hitch pin, but I'm skeptical about it's long term sufficiency as I expect it will loosen up as time goes on(I realize you said it was a temporary situation, just thinking about it for long term use).

Anyway, I'm glad someone did this so that there is now proof that it makes a difference. Thanks

Ary

Because im just getting to know FJ80's... is there a manuf that makes skid plates that weld on or bolt on to the bottom lower control axle side? I can see those lower arms getting bang'd up pretty well out on a trail.

Ary, sometimes folks on here are a bit too stuck in their ways... call it mob mentality. I've always thought wristing would work well...

SOCALFJ, the front radius arms are solid forged steel, they weigh a sh*tload... you won't have problems bending them, just hanging them up.

I guess once again i'm missing the boat here. I thought wristing reffered to welding in an actual screw type link so as the arm twisted, it twisted at the threaded area? Hope that makes sense.

concretejungle said:

I guess once again i'm missing the boat here. I thought wristing reffered to welding in an actual screw type link so as the arm twisted, it twisted at the threaded area?

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On all the websites I visited, wristing referred to modifying a radius arm to pivot in the x-z plane, where "x" is the longitudinal axis of the truck, and "z" is the vertical axis. Since old Broncos have y-shaped radius arms, they modify one arm w/ a hinge (unbolting one wouldn't work for them). Land Rover guys can simply remove one bolt like us. I've also read about wristed axle housings, which achieve the same effect, though with a lot more complexity.

I understand the "wristing" that you're talking about, and I'm sure that's a valid use of the term. I don't think that type of wristing would address the dominant source of our control arm bind. The bushings appear very willing to twist. Eccentric deflection (or whatever you want to call it) just intuitively seems like it would be much more difficult for them.

Jason

This is a very good thread.

Thanks for the pics. jmaddocks.

If you have more pics., I'll be happy to host them for you. I like the data we are creating here as well as what bjowett said earlier.

Best.
-onur
Akron, OH

Here're some pics.

Or, how about a wristed front axle housing? http://www.bcbroncos.com/frontsusp1.html

More:
http://www.d-90.com/prod/hinge.html

Wow. Where you find those?

I really like the idea of the hitch pin over the elaborate Rover deal. The Rover solution won't hold the axle in alignment to the frame. As that wrist rotates the axle moves backwards while with the simple hitch pin on the front the rear bushing holds the axle more accurately in place.

you will want to pin the drivers side over the passenger side as the axle's diameter is smaller and will allow more movement before contacting the leading arm.

I'm so excited about this thread Thanks Jason for the data and going out of the box and trying this on an actual trail run! You have got some guts

I've been thinking for some time about how to get more flex out of my front without doing a major 4 link mod. I do remember reading about ppl taking out one of the bolts but the real question is which one gives the most benefit? By choosing the front DS bolt is there enough vertical room for that control arm to rotate UP before coming into contact with the axle housing? Of couse when the arm lowers you are going to be fine but won't it bind somewhat when you stuff your DS tire and the other is full flex? I've thought about all these kinds of question in detail over the past 2 weeks. I've gotta go out there and take off those front shocks and do some real tests. Like everyone else I'm still in the design mode.

What I have come up with so far are some ideas for new control arm axle mounts similiar to Slee's to correct my castor and allow the front DS bolt to pivot both upwards and down using the rear bolt as the pivot point. What about that guy who put the control arms upside down?? Whoever that was please post up some more pics of that setup!! I like the idea of the control arm protecting the tie rod but the extra clearance does look inviting too.

So I guess it's a matter of testing all bolts to see which one would benefit to be removed but at the same time allowing enough strength left in the equation to hold up on the trail.

I'll post up some flex shots of my rig with the DS front bolt off as well.

actionjackson said:

What about that guy who put the control arms upside down?? Whoever that was please post up some more pics of that setup!! I like the idea of the control arm protecting the tie rod but the extra clearance does look inviting too.

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The arms on top, remove one front bolt, raised tie rod and panhard are all old Ausie tricks. The brackets are available from vendors down there.

What about OTT's FJ-80 high steer kit? www.ottindustries.com What if you did arms on top, a quick release bolt or pin and this steering?