Highway-speed vibrations and driveshaft slip yoke binding on transmission output shaft (2wd)

Hi all,

I have a 2wd 1993 with the 3.slow (A349E transmission).

I've been trying to track down a vibration that happens at highway speeds (55-70 mph), which seems to happen primarily under acceleration. I had my wheels balanced and brakes done, and I also put in a new driveshaft with new u-joints to make sure everything is balanced.

After the new driveshaft, the vibration has decreased by quite a bit, but it's still there intermittently. I'm going to investigate the wheel bearings and suspension next, just to make sure everything is copacetic, but a portion of the vibration still seems to happen when on the accelerator.

Removing the old driveshaft was difficult. As in, pulling the old driveshaft out of the rear of my transmission took a lot of effort, including using a rubber mallet to pound the yoke out of the slip joint. I figured the old yoke was messed up somehow, but then there was equal difficulty in installing the new driveshaft.

It seems to me that either the output shaft or the bushing likely need replacing. Perhaps the splines are worn, for example. I'm also curious if this binding in the slip joint may still cause some of the vibrations, since the slip joint isn't cushioning the transmission from the driveline and rear suspension. In other words, it seems to me that the slip joint would normally allow the driveshaft to move easily in and out of the rear of the transmission, which would protect the transmission from jolts on the rear suspension and also potentially help mitigate vibrations from the front to the rear.

Another experience which makes me wonder is that I'll sometimes hear/feel a faint "clunk" when stopping at a stop sign and accelerating, which makes me think that the slip joint is still slipping in and out, though it does bind at a certain point in its movement.

Does anyone else have experience with this, or particular insight? Am I correct in my thinking so far? Ultimately, I'm hoping to get the slip joint working properly (so that things don't wear out) and I'm also hoping to completely mitigate these highway-speed vibrations.

Thanks for reading!

 

That’s odd it only does vibration when your accelerating, you’d think you’d feel it decelerating too, in the pedal or steering wheel. Have you tried removing the rear u joints and rotating the driveshaft by hand in neutral to feel if there’s any slop on the output shaft ? And at the same time with the rear wheels off the ground and rotating the pinion shaft and seeing if there’s any slop to the ring gear ?

I’d say if you don’t feel anything or visibly see anything worn in the front shaft mating grooves then maybe have the whole driveshaft re balanced.

Interesting issue, keep us posted on what you find.

 

Slip yoke sounds like a victim of neglecting to grease, that's if there is a grease fitting there to grease.

 

Check the torque on your rear differential pinion nut. I had a vibration that came in around 60 mph. The nut was finger tight, torqued it to 90 ft/lbs and the vibration went away. If the seal is leaking it’s a good time to change it also.

 

I've tested for slop in the driveshaft by hand and found a little bit of play in one axis at the rear extension of the tranny, though I haven't lifted the rear wheels and messed with anything. That's a good idea, so that'll be my next step.

The driveshaft should be balanced (it's a new one I just got from a place called DriveshaftPro) and the U-joints are new.

I'm thinking that my next step will probably be to either find a transmission shop that's willing to take a look at my output shaft for me or remove the rear extension housing on the transmission and do it myself.

These kinds of issues pop up semi-frequently, so I'll surely post any progress made.

Hmm, I would've thought the slip yoke just relies on some ATF, yeah? I think the splines can wear out over time, especially if something's been torqued harshly.

Interesting idea. Thanks for the random tip; I'll check it.

 

My bust, I thought of a entirely different slip yoke, one that a splined end of driveshaft fits in another splined end and they rely on grease to prevent rust and binding. But reading the other posts, the pinion nut being loose..... ya. Saw a loose pinion nut on a dump truck, it vibrated also.

 

Update as of today:

I got new tires on my rig (Yoko Geolandar AT G015, 235/75r15) and there's a significant improvement in the ride. The old tires were feathered and cupped, not to mention a flat spot that they had, presumably due to the previous owner's planned non-op. The ride is all around very smooth and plush now, compared to the messed up Destinations that were on there before. Nothing against Destinations, by the way.

The majority of the acceleration-dependent vibration does seem to have gone away after I replaced the driveshaft and U-joints. The driveshaft I had on there was the original driveshaft, which on the 2wd is a long shaft with a slip joint on the actual driveshaft (towards the rear diff, you'll see that the driveshaft consists of an outer shaft with an inner shaft inside of it). Whether the old shaft was imbalanced or the slip joint on the old shaft was old and worn out, the new solid shaft I got from DriveshaftPro seems to have gone a long way in fixing this vibration.

Any remaining acceleration-dependent vibration is almost unnoticeable and, along with the mild "clunk" when in stop/go situations, seems to point to the slip yoke where the driveshaft mates with the transmission.

My next steps are still:

1. investigate the rear extension of the transmission to see whether the output shaft splines are worn or the bushing needs replacing
2. potentially check the pinion nut torque on the rear diff

I'm still waiting for my FSMs to come in, so it may be a bit before I update again. Or, I may get a local transmission shop to take a look for me. There's one in my area that deals reasonably with people.

 

Here's an update to this ordeal.

Leon's Transmission didn't want to open the transmission up to check the tailshaft because they primarily work on full rebuilds, not one-off fixes. So, I took the truck over to Japanese Car Specialties over in Mission Viejo, CA. John Najem (and his wife Wendy) run that shop and specialize in 4Runners.

John inspected it in July and found the following problems:

1. The tailshaft splines were, in fact, warped
2. The rear diff yoke had significant play (not the U-joint, the actual yoke)
3. DriveshaftPro in Garden Grove sold me a new driveshaft and installed it even though the rear diff yoke had significant play (FYI, in case you were thinking about giving DriveshaftPro business... maybe find another shop)

I had John machine the tailshaft splines for me, as well as tighten up the pinion nut on the rear diff to try and reduce the play (for now). He also double-checked the driveshaft for balance and made a small tweak to it. All told, the machining job (and replacing the tail shaft housing) cost a cool $700.

After that, I was expecting to either do an expensive rear diff rebuild or source a 3rd member and install it myself. However, the vibrations have been reduced to almost nothing now. Time will tell, and I'll probably need to do something to the rear diff in coming years, but I'd say I can sit tight with it for now.