Neemox

Hey YotaTech, I need your magic.

My 87 runner has started doing some really scary stuff. This is an intermittent problem, it comes and goes, and was first noticed last year sometime, but has become much more frequent recently. When I accelerate, the vehicle jerks hard to the right, and more than "jerking" it feels like the truck is trying to "pivot" to the right. When I let off the gas, or engage the clutch, I get about an equal pivot back in the other direction. It does not give the lurch if I am coasting down the road and apply brakes (My first thought was hung up caliper, doesn't seem to be the case).

My troubleshooting wasn't getting me anywhere, so after I completely rebuilt the left knuckle (brass spindle bushings for unrelated problem, UBJ, LBJ, Tie rod, new CV axle, re-pack outer wheel bearing) I had the shop do an alignment. So it has recently been aligned, and neither the alignment or re-building the Left Knuckle made a difference.

Took it into Toyota for them to try and diagnose. They came back with Upper Control Arm bushings (play), idler arm (play), and re-pack front right wheel bearings. Long story short, I put on a new UCA and re-packed the wheel bearings on the right side, replaced the blown Upper Ball Joint that they failed to diagnose, and didn;t touch the idler arm because there was zero play in it whatsoever. (Silly dealership, I knew better).

Anyhow, after all of that, the truck is still doing this pivot lurch like crazy, and it's scary to drive. I have read online that this can be caused by issues with the driveshaft, but for the life of me I can't imagine how? There is a tiny amount of play in one of my spider joints, but that's the best I can find, and I just cannot think that is causing one side of the truck to lurch forward or backward. Is there a chance that my rear differential is sometimes only engaging one tire? I can't imagine how that could be without pieces of diff on the ground... The problem happens in 4wd or in 2wd, it happens when the lubs are in the locked position or not in the locked position. I'm not ruling out that it could be some weird locked hub issue, because I know sometimes my hubs don't "unlock" fully, but again, even if I had one hub locked and the other wasn't I can't imagine the jerk I'm getting.

Any help or ideas of where to look next are greatly appreciated!

RJR

I would suspect it's in the drive train, most likely front, because of the opposite effects of acceleration vs. deceleration, but it's going to be tricky to diagnose because of the intermittent nature.

I would jack up the front end and rotate the wheels, looking for any hesitation, clicking, etc. as they rotate. Check if the hubs are really disengaging by watching the CV axles as you turn the front wheels. Check if 4wd is really disengaging by trying to rotate the front driveshaft while in 2wd. It should rotate freely, and be locked in 4wd.

Any chance you have an automatic locker in the front?

Neemox

Thanks for the reply.

I have the truck up on jackstands right now, and I definitely found some weird stuff in the rear, rear left tire is getting stuck (when the truck idles, or when in first gear with a little gas), I pulled it out and the bearing is bad, so going to be doing bearings and seals on the back axle (along with new brakes) this week.

I have looked over the front end a bunch, but I will do as you describe again, just to double check. The transfer case is leaking a bit and making some noise, but there is also play in the U-joint there (going to the rear) so I suspect that's most of it. That's getting fixed this week as well.

Talking it over with someone offline, they thought that perhaps something in the rear suspension was letting my axle housing twist, bad leaf springs, sheared leaf spring pin, something. My no weld ZUK mod on one side (right) had bounced off the bump stop where it was and was shifted to the back by about an inch on the bottom side, so that spring was in there slightly crooked. Not sure if that is a symptom or a cause, or unrelated, but it's been corrected now. How else could my axle be off? Wheel bearing plus bad leaf bushings? Does this seem like a realistic place to look for problems?

akwheeler

My initial thoughts are:
#1 if it does this in 2wd your front end isn't being powered, so it isn't likely to be anything shifting position in the front, there is weight transfer from front to back so if you have been through the front suspension already you need to look at the rear of the vehicle.
#2 knowing what type of differential you have in the rear might help, if you have a solid rear diff or a locker you could have a broken right rear axle, so power is only going to the left rear when you get on the gas.
#3 if there is anything uneven about your rear springs (shifted ZUK mod) when the weight transfers under acceleration it could do what you are experiencing.

My best suggestions are:
check your rear spring hangers to make sure they haven't separated from the frame due to rust.
Look for signs that the rear axle has shifted position due to loose u-bolts.
Make sure your tires are all the same size and similar wear.
check your frame for cracks, not all alignment shops or technicians will catch seemingly obvious issues.

If your alignment came with a printout post it here so we can see the results. In this case the "rear thrust angle" is important.

Neemox

Your #1 makes perfect sense to me. I suppose if the t-case was getting stuck and not really letting the truck back into 2WD, it could still be in the front, but I can feel the difference between 2 and 4wd when I turn and it doesn't seem like it's in 4. As I said, I'll triple check that tonight.

I forgot to address your #2, and although I know the rear diff is not original (it has junk yard point on the carrier cover) I don't think there is anything funny or additional in there in terms of lockers. Certainly the rear tires behave as though the diff were open (My e-brake is broken and currently only reallyu applies break to one side, when it is one, the other tire spins free, when the e-brake is off, I spin one tire and the other spins opposite, just like an open diff ought to.

I'm guessing that #3 was contributing significantly to the issues, but I will check out all the leaf springs (which I have honestly ignored completely for three years since I did the ZUK mod.) tonight. I didn;t think about frame cracks, I sure hope that isn't an issue...

Thanks much for the reply, and here's a print of my alignment results: 0.12° Thrust angle in the rear