Okay, the other day I got on the freeway and when I was accelerating to about 60-65mph my xj felt like someone (the night before) had put a drive shaft limiter on it. The drive train noise increased, not a grinding or clanking sound, just a louder whirring noise as if there was something binding somewhere. If I stayed below 60mph there was no sound or resistance. I shifted from 2WD to full-time 4wd and the sound and resistance went away until I reached 75mph. Around town at lower speeds everything seems normal. It's all stock, no lift or anything. Also when I shifted from Drive to Neutral (on the T shifter) the sound and resistance went away. I could coast on a decline to any speed with no issues. In neutral or park it revs up just fine. I went underneath to check the drive shaft for any play in the diff and there wasn't any. I changed the tranny and t-case fluids (no debris in old fluid). The rear diff was a little low but after topping off the same thing happened. I went underneath to check the drive shaft for any bearing play in the diff and there wasn't any. I did find a leak in the rear seal of the diff and the exhaust pipe near it has a lot of carbon like the gear oil was spraying on to it and burning off, but no oil is visible on the vehicle except for the bottom of the seal. It wasn't missing much oil since I topped it off earlier.
Any ideas?
Stock 91 XJ limited 4.0L, AW4, NP242, D35 rear diff,

 

Well if I had to take an educated guess, from you say I would start in the T-case. I would say that you have an issue with the main shaft as well as the gears inside.

(Please get other ideas cause I would hate to see you tear it apart from what I say and it be wrong.)

The reason I say that is because you say you go from 2-4 and 4 is better. The only thing you changed was were your T-Case was at.

 

Check your U-joints on your rear driveshaft for excessive play. Those things can make all manner of odd noises, especially at highway speeds.

Not making the sound while coasting, in 4wd, or in neutral would be because you're taking away torque force from the joint.

 

i agree with this, u joints can make some weird sounds, and its a "speed" thing, which indicates, an issue past the tranny, and x-fer case. ie-ujoint, wheel hub, brakes, tires.

 

When I try to move the drive shaft while it's in gear with the wheels on the pavement there's no movement whatsoever. Should I jack up the back end and then try rotating the shaft?

 

I guess I'll just start at the tires and work my way toward the t-case.

 

that's the idea, places like wheel bearings, and u-joints, as for the u-joints, you may have to completely remove the rear drive shaft, and very closely inspect the u-joint on each end, for missing bearings, cracked caps, any sort of anything odd or loose, or miss-aligned.
beyond that, check for a bent drive shaft, or missing drive shaft counter weights. and of course anything that may have become tangled into around the drive shaft.

hope this helps.

 

I have to remove the shaft to replace the pinion seal. Might as well replace the u-joints while I'm at it. They look like the original u-joints from the factory.
Both my repair manual and AllData don't have information on the rear wheel bearing. Every "wheel bearing" reference has info on the front not the rear. They just have the rear axle bearing. Is there a difference?
The auto parts stores sell a rear wheel bearing for the Dana35.

 

Hey! When I was like 5, I lived in Walnut Creek. My parents hammered it into me "1415 Spring Brook Rd.", (Tell them you don't live there! Lol).

If something anywhere is causing enough friction to rob your power from that 4.0 while you are trying to go, it should get hot. Granted places like the tranny or transfer case might be hard to tell. The pinion/diff, U-joint or wheel bearing, something like that should be as hot as a stuck brake.

 

Chock the wheels.
Engage E Brake.
Shift to N.

Now you are ready to check. Checking while in gear will not tell you anything because there is pressure on the joints to keep the vehicle from rolling while parked.

 

X2^ if you lay a finger from one hand on the gap, and rotate it with the other hand you might feel the play.

 

yea new ujoints are cheap, and a broke one has you sitting still, so replacing them isn't a bad idea, if they're the noise source or not. what ever the sound source is, its related to over all speed, if it was engine speed, it would be before the tranny/xfer, but since its vehicle speed it must be after. all i can think of after, is 2 ujoints, and the drive shaft it self.

thats possible, but id go ujoints first

 

Thanks for the help. Also how can I tell if I have a Dana 35 or a Dana 35C?

 

According to my research it looks like all stock XJ's come with the Dana 35c not the Dana 35. Is that correct?

 

Well, the rear u-joint by the axle was the problem. Now if I could only get my rear pinion nut off, I'd be able to change the seal. Any ideas on how to get a 21 year old pinion nut off?