Bent rear LCA - how much is too much?

[kcjaz]

So I have a slight bow in my passenger RLCA. How much it too much "bow" to run with. I do not notice anything driving down the highway. I think the only thing potentially affected would be the alignment of the rear axle and I think misalignment there would only cause a "tracking issue" where the centerline of the truck becomes skewed relative to the direction of travel. Steering would compensate and there would be no impact to tire wear. If rear axle alignment was super critical, I would think there would be an adjustment on the stock RLCAs but there isn't. So I don't think a little bend is a big deal. Am I right?

I have, and always carry a spare RLCA because I know its a matter of time before I really bend one. I could swap it and try to straighten the bowed one. Here is where I think I did this:

Side note, crawl was pretty amazing but it didn't get me over this. Just not enough clearance. I would end up with only the front driver tire with any traction and that wasn't enough to pull the back up and over.

 

[gaijin]

IMHO, if you can see the "bow," it's too much.

Go ahead and replace with your spare.

HTH

 

[kcjaz]

IMHO, if you can see the "bow," it's too much.

Go ahead and replace with your spare.

HTH

Here’s a pic.

So how urgent is fixing it? I have a 400 mile road trip this weekend and no time this week to work on it.

 

[bloc]

You can do the geometry to figure out how much it has shortened based on a given bend.

IMO that shortening is going to be.. almost none.

At some point yes the changed length is an alignment issue but arguably more of a problem is the ability to resist bending further when subjected to the tensile or compressive forces from driving. But that takes more bend than you have.

If this continues to be an issue you can consider reinforcing them with angle iron welded to the top or bottom.

Personally? If I had family with me for that trip I’d replace it and keep the bent one as a spare. Swapping one lower at a time shouldn’t be very difficult with the other four links still in place.

 

[bronc076]

You can do the geometry to figure out how much it has shortened based on a given bend.

Or measure it and compare it to a measurement of the spare If you don’t feel like math.

It’s a long shot but you may have some hidden damage you can’t see like a cracked weld, but I doubt it. Might also be binding and causing premature wear on other arm bushings. It’s probably fine but I’d swap it since you have one and are going on a trip.

Are there some trick aftermarket ones you now have a great excuse to buy?

 

[kcjaz]

So doing the math yields the difference in length of 0.005”. This can’t possibly make any real difference. I doubt that the location of the mounts is that accurate.

The Complete Circular Arc Calculator

www.handymath.com

Now making sure there isn’t anything really broken certainly makes sense so I’ll for sure do that. Maybe I can find an hour to do the swap since I do have the part. It’s just that everything I’ve ever done on the truck mechanically takes 2x+1 so it will be 3 hours…

 

[bloc]

I swapped a lower link on my 80 without even jacking it up. Just drove the back onto ramps for more clearance under it. Used ratchet straps to manipulate the axle enough to get the bolts loose and swapped just that arm. The other three front-to-back links not even loosened kept the axle mostly in place.

Just one idea.

 

[2fpower]

We see this all the time in the 80 world. Don't worry about it, or turn it upside down and go up the hill again....

 

[kcjaz]

We see this all the time in the 80 world. Don't worry about it, or turn it upside down and go up the hill again....

Actually, I think flipping it around isn't a bad idea.

 

[Taco2Cruiser]

You can absolutely see the steering wheel go from center (if you wheel was centered prior) to either left or right depending on how bent the RLCA is. If you can’t see even the slightest difference in you wheel, well, then it’s not as critical as it could be.

If had a few 200 come in that said they needed an alignment, looked at the RLCA. Replaced it, and magically (it’s not magic, it’s just geometry) and everything is back in spec.

To replace, no need to loosen KDSS screws like the FSM states. Just have a large ratchet strap ready, and remove the two bolts that secure the control arm. Use ratchet strap secured to the transfer case crossmember and then to the axle housing to pull axle housing in place to make the swap much smoother.

Factory torque spec is 111 ft lbf.

 

[kcjaz]

You can absolutely see the steering wheel go from center (if you wheel was centered prior) to either left or right depending on how bent the RLCA is. If you can’t see even the slightest difference in you wheel, well, then it’s not as critical as it could be.

If had a few 200 come in that said they needed an alignment, looked at the RLCA. Replaced it, and magically (it’s not magic, it’s just geometry) and everything is back in spec.

To replace, no need to loosen KDSS screws like the FSM states. Just have a large ratchet strap ready, and remove the two bolts that secure the control arm. Use ratchet strap secured to the transfer case crossmember and then to the axle housing to pull axle housing in place to make the swap much smoother.

Factory torque spec is 111 ft lbf.

Thanks. Can I do this with the suspension dropped (i.e. in the air on a lift) or do I need to keep the weight on the axle?

 

[turbo8]

I've done it on the ground. Make sure the ground is level and put some jack stands under the frame for safety.

 

[Taco2Cruiser]

Thanks. Can I do this with the suspension dropped (i.e. in the air on a lift) or do I need to keep the weight on the axle?

It will be much easier to have the truck in the ground. If the axle housing is dropped, you’ll have to fight the springs when pulling the housing forward.

I’ve never used jack stands under the frame and have seen plenty of broken in half RLCAs on FJCs still drive. With four out of five links still attached, the axle housing is far from rotating out under the truck.

It really is a simple, slide under the truck, take one side out at a time (never both at the same time) swap. Besides, with factory deflection bushes, you have to tighten and torque those at ride height anyway. According to the FSM.