Drivetrain jerk

[evldave]

Honestly, I don't have a reasonable idea (and so I don't spout off in the forums). Since I'm in a wordy mood today, I'll continue...

If I were to conjecture (only because you lived up here and you asked) - I'd follow the same thing I always do when diagnosing - start with the cheapest stuff first.

You wheel hard, put a lot of stress on the driveline. Check the u-joint. Reach down, try and move it perpendicular to the joints. Does it move left right (not rotationally)? If so, spend the $30 and have the u-joint R&R'd - or take it in for warranty service. Get a Spicer (sp?).

Does the driveline rotate and have some play in and out? There should be some movement in the parallel direction and rotated (not much, but a little). If none, there's binding somewhere. It could a number of things, but it's under warranty and tell the service tech.

Do you have an older rear end? If so, there was a gear lube issue with the supplier and that may have caused an issue w/the gears in the rearend, but not enough to blow it up. Since this seems to have happened when you had the service done, putting new fluids may have made it easier to feel. Might want to look up mfr date and see if it was back w/that lot of parts.

In my completely uneducated guess, I'd say the torque converter isn't unlocking quickly and so the drivetrain is under locked load when you are stepping on the gas. I don't know all this fancy computerized stuff, but a torque converter is supposed to let the engine 'throttle up' without having the drivetrain acccelerate at the same rate (it's essentially slipping to let the motor spool up without spinning the tires at the same time - it builds power faster so you can put more oomph to the wheels when it finally does engage).

There is lost efficiency in this design because of the slipping, but it's required in automatic transmissions (otherwise the engine would stall when the rear wheels stop). Most modern transmissions have a 'lockup' converter that locks in either 3 or D to maximize the power transmission between the motor and...well...the transmission. When decelerating, the converter usually locks to help with slowing (you can feel this on a lot of vehicles) - when you accelerate, it should immediately unlock and slip a little.

On the H3, the converter locks when driving normally in D. When you step on the gas on the highway, it actually unlocks (check your RPM, they will increase quite a bit but it won't actually downshift - that's the converter unlocking and hitting it's stall speed). IF (big if) it doesn't unlock and you put too much gas on, it can bog down - the equivalent of being in 5th gear in a stick driving at slow speeds. This can cause all kinds of wierd clunking and bogging.

On my H3, I noticed when I first got it that it had a significant amount of slip at lower speed - to the point of annoyance that I couldn't use engine compression to keep the rig slow on downhills. As I've now got 8k miles on it, I've noticed the converter locks up much sooner and better at low speed - it may be a design or trait of the H3 - the older the tranny, the more it locks up? I don't know, but it's noticeable to me because I've been paying attention to it.

Is this an issue? I have no idea, but I wouldn't worry about it. I'd go beat the hell out of it right now to see if it breaks - if it does, going to MOAB is a bad idea, if it doesn't, don't worry about it.

I'm sure other more edumicated people will fix any of my factually inaccurate statements - a lot of that going on lately...

And a note on axle wrap - it happens on all rigs and is expected to a small degree, however EXCESS axle wrap (that would cause this sort of problem) should only be present on older springs.