Pulling left - Still losing my mind.

[blistovmhz]

98XJ, 5.3/4l65e, 6.5", long arm (radius), 63" rear leaf, 1 ton x-over, WJ knuckles, 1.5" ram, 35x10.5 KM2 .

Been chasing this left pull for goddamn years now. It's survived several complete rebuilds, but I think I may be honing in on it now.
I used to think it was just a little bit of torque steer, as it'd pull left on acceleration and right on deceleration.

This started long before the 5.3 swap, 63" leafs, 1 ton steering, WJ knuckles, and the ram assist so I'm confident none of those are the cause.

I recently stuck a ram in front and got it all dialed in, and now the pull is worse, which sorta doesn't surprise me because the pre-existing pull would be forcing the pitman toward driver, which is now sending feedback to the ram, so the pull is even stronger.

With Jeep up in the air, engine running, the wheel does not start moving by itself, so it's not a steering box or ram issue (besides which, this problem survived 3 steering boxes now, including my durango box).

As I have nothing really left to "upgrade" at this point, I've started looking back into the pull. Last night I checked all alignment numbers again. I found that the caster was 4* out on the driver side (which didn't surprise me) so I adjusted the uppers to force it within a degree. Caster is now bang on where it should be on both sides. No change. Set toe to 1/8. No change.
I've noticed that my rear tires are wearing unevenly. The driver tire always wears faster than passenger. A few months ago I first noticed this, and swapped the fronts to the rear and the pull decreased or maybe even went away, so last night I swapped the rears side to side, but no change.
I measured wheel base both parallel and diagonally and numbers were within' 1/16 in every direction, but then I had a thought. I was measuring from the tire, and some tires are worn. It's entirely possible my measurements were only correct because one tire was worn more than the other side. Then it occurred to me that when I disconnect my sway bar and pull the arms down when pulling the pitman, the arm on the driver side hits the coil, but not on the passenger side. Just looking at the coil vs the bump stop, the driver definitely looks like the axle is farther forward than the passenger side. This would make perfect sense to me if it was the other way around. I figured the driver being further forward, would cause a RIGHT pull, not a left, but I figure this is the only thing that looks to be out of spec.

Before I go pull the front end apart again and push the passenger side forward or bring the driver side back to match, who here thinks that the driver being FORWARD of the passenger, would cause a LEFT pull on accel and while cruising, and a SLIGHT RIGHT pull on decel? (intuitively that seems backwards to me due to thrust angle).

 

[dan1977p]

I would assume the axles were out of alignment front to rear if your toein, caster and camber are all correct and verified by an alignment shop. Is your front axle centered? I had the same issue with things binding on the driver's side until I pulled the axle over that way. it was off by almost 2 inches when I followed the directions on the lift kit vs doing the measurements myself. Is it possible your left rear brake is dragging or that axle isn't squared to the front? Bad wheel bearing? Diff locked or too tight causing it to not slip when it's supposed to?

 

[blistovmhz]

Brakes and bearings are definitely all good. Front axle is definitely centered (it wasn't, but I set it properly yesterday and no change).
The only thing I can think is that the front axle being pushed forward (on driver side) is causing this. It just seems like it should push me the other direction.

 

[dan1977p]

Does it get worse if you pull the rear drive shaft and run it in 4hi?

 

[blistovmhz]

No idea. Can't run in 4x on the street. Front/rear lunchboxes.

 

[dan1977p]

That's why you pull the rear driveshaft. Then they aren't competing against each other. Plus, I'm talking a short 100m test of letting the front do all the work when you jam on the gas.

 

[VAhasnoWAVES]

thrust angles will make the jeep "crab" down the road, but shouldnt cause a pull or odd tire wear.

its interesting that the ram made the issue worse. its also interesting that the rear tires are wearing funny. ive only ever seen that on bent axles or toasted bearings.

 

[blistovmhz]

It's entirely possible I've got bent axles, but I can't figure out a reliable way to check. None of the shops in my area are even remotely competent, so I'm on my own for this sorta stuff (all stuff really).
I did have both my axle retainer plates bow out a bit, which may account for the uneven wear on the rear, but both plates have been rebuild with 1/4" thick steel and no change on handling.

I agree. Thrust angle should only make me crab walk at cruise, but under load, it SHOULD cause a pull. This isn't noticeable with open diffs, but front/rear locked plus crab walk will definitely cause a pull. But, as I said, the axles are now both center side to side and no change. The only number I can find that is not matching up... isn't really a number.... Measurement from wheel to wheel front to rear is the same on both sides, but the sway bar is definitely hitting the coil on the driver side, and not on the passenger, but I'm still using the stock sway bar mount locations (on the frame side), and my sway bar arms are definitely the same length, so the driver front has to be pushed forward. This is a bit annoying because the distance from front to rear is equal left and right, which makes me wonder if I welded on my rear leaf perches based on the location of the front axle (in which case both my axles are probably spun pointing a bit passenger). I can't think of any reliable location to measure the rear axle from though, as there's nothing stock left on the bottom of my jeep. I think the most likely is that I swapped the slightly burned rear driver tire over to the passenger side, and THEN measured the wheel base, and got the same measurement purely by coincidence, because of the tire size discrepancy. The sway bar to coil clearance I think is probably the most reliable indicator of front axle thrust vector (as it's really the only thing on my Jeep using stock mounts), and based on that, the driver front has to come back at least 3/4" (or passenger forward 3/4").

What I'm really looking for though, is someone who can confirm (or refute) that the front axle thrust vector being pointed towards passenger, would somehow cause a left pull on accel and cruise. It's just not making sense to the section of my brain dedicated to "pull some numbers out of my ass physics".


I think the ram compounding the problem makes perfect sense. Anything that's trying to pull the steering to the left, will cause the pitman to move left, which then cracks the valve in the box, which then drives the ram left as well. That's how it SHOULD work, or you'd have no steering feedback. I actually fully expected the ram to multiply the left pull slightly, and felt sorta vindicated when it did

 

[blistovmhz]

That's why you pull the rear driveshaft. Then they aren't competing against each other. Plus, I'm talking a short 100m test of letting the front do all the work when you jam on the gas.

This is actually something I haven't tested (cause too lazy), but now that I've got nothing left to do to the heep, maybe it's time. But DAMN is it goona be sketchy driving a locked FWD XJ on 35's .

 

[dan1977p]

If you do what I suggested, it will amplify the problem if it really is coming from the front end and help you decide whether or not to continue spending time up front or at the rear. I actually think your axles are tweaked, especially if you are saying you had to rebuild the backing plates to straighten them. If it's the rear axle like I suspect, running the 4hi test will show now change in the symptoms and you can look at the rear in more detail until you rule absolutely everything out back there.

 

[dan1977p]

This is actually something I haven't tested (cause too lazy), but now that I've got nothing left to do to the heep, maybe it's time. But DAMN is it goona be sketchy driving a locked FWD XJ on 35's .

Why? You're just driving in a straight line and if you let off the gas before you turn the wheel, the lunchbox will disengage.

 

[blistovmhz]

But WOULD symptoms change if it was the front axle out? In RWD I'd be pushing into the problem, but in FWD I'd be dragging the rear axle, which should still try to kick out sideways if the angle is out.

It's not the backing plates that were bent. Just the axle shaft retainer plate. Stock plates are paper thin (D44). That said, the backing plates COULD be bent and I just don't know it, which wouldn't surprise me either as I put them on a long time ago (they're from a KJ disc setup). But, if the backing plates were bent, I should see that as a toe in/out problem, which I'm not seeing. Rear toe looks to be 0.

 

[blistovmhz]

Why? You're just driving in a straight line and if you let off the gas before you turn the wheel, the lunchbox will disengage.

Yes, but if there's a constant pull, then I'm ALWAYS steering . I had to try to drive it home in 1wd (front driver) once. I've also tried to drive it in FWD once after blowing up the rear DS. There is no steering it under torque, and with an automatic trans mated to 300hp of V8, driving a 5000lbs truck, there's always enough torque to lock up the axles.

 

[old_man]

I've seen this with my Detroit in the rear. One way on accel, the other with compression braking. With mine, you can put it first and be going along at almost idle. When you bump the gas, I can watch the body twitch to one side.

 

[blistovmhz]

Yup. And that makes sense if something isn't quite straight. I've seen that on lots of other trucks (more pronounced with a shorter wheelbase), but I've also been able to correct it in every case, by getting the thrust vectors corrected.

Just took some pictures to show the front axle location, relative to the coil towers and sway bar arms (the only places I can think of that are stock location).

As you can see, the driver side definitely looks like it's pushed forward. Less space between sway bar arm and coil and coil looks swept forward on the rear, compared to the bump stop).
And every time I have to pull the arms down, the driver side hits the coil and I've gotta push the coil back to get the arm down.

 

[TRCM]

Why? You're just driving in a straight line and if you let off the gas before you turn the wheel, the lunchbox will disengage.

true, but the loud pedal will blow away the fronts if you get crazy with it.....

 

[blistovmhz]

Eyup. I've already managed to twist one of the new chromoly shafts a little. I NEVER hammer on it when the front is doing all the work.

 

[ftwelder]

If you have established that the hard parts are square and parallel, It would be my thought that there is some potential that your rear wheels don't have the same circumference. may be add a few PSI to one side and see what happens.

 

[Transpoquick]

Yeah it looks like your drivers is farther forward than your passenger from the pics., fix that first.
But if you got "lunchbox" lockers front and rear, 35's and you don't drive it on the street, ?.
That type of locker is prone to, failure.
Why is there a sway bar on it?

 

[blistovmhz]

Yeah it looks like your drivers is farther forward than your passenger from the pics., fix that first.
But if you got "lunchbox" lockers front and rear, 35's and you don't drive it on the street, ?.
That type of locker is prone to, failure.
Why is there a sway bar on it?

? It's daily driven. Just built primarily for offroad use, but still street legal. I definitely don't agree that lunchboxes are prone to failure. The only failures I've seen thus far either were due to incorrect installation (ie: forgetting thrust washers when they're required), or... torque that would've broke a case locker anyway. Mine hold up to 300hp, 4.56 gears and 35's all day.

If you have established that the hard parts are square and parallel, It would be my thought that there is some potential that your rear wheels don't have the same circumference. may be add a few PSI to one side and see what happens.

Somehow, my measurements for wheelbase were off. I think it's cause I probably welded one of the LCA mounts on in the wrong spot or something. I finally measured wheel to wheel today, which showed the passenger short 1/2". Confirmed by measuring tube to the only place on my Jeep that should be square, my CM and that also showed 1/2" short. Adjusted passenger out 1/2" and took it for a test drive. DIdn't feel fixed. Really didn't notice any change, but I also didn't get up to speed, so I'll report back tomorrow after a proper drive on the highway.

I did swap the rear wheel around and no change, but the LAST time I thought I'd fixed this, it was by swapping front to rear... I dunno. If the axle location didn't fix it, I'm goona assume it's a real tweaked frame (that I can't seem to prove) and just drive it and keep an eye out for an Eagle wagon shell to swap everything to I miss my eagle.