98X AWD front Diff

[24theroad]

Hello everyone,

Great forum, this is my first post after intro, thanks for having me.

My '98X 5.0L AWD was making a loud hum that varied with speed and a strong vibration in the floor starting around 10 mph and became unbearable at 25 mph. I crawled underneath and found the short stub axle had disengaged from the inner splines on the far inside end of the tube extension on the right side of the front differential.

The CV axle was still attached to the stub axle, probably a good thing since my daughter drove it like that for probably about 70 miles, but I never would have let her take it after recently having the drive train apart. Turns out, that most of the gear oil had leaked out of the front differential.

I must have somehow disturbed the inner stub axle c-lock ring when I replaced the right CV axleshaft a couple of weeks ago. I was able to push the stub axle back into the tube until the c-lock ring engaged but it didn't hold, so I tried again and the second time held when I tried to yank it back out again.

So I tried to stay hopeful, pumped in about a quart of gear oil and took it for a test drive.

It doesn't vibrate now, but the loud hum sound is still there, only slightly quieter after I removed the front d/s. There is also a bit of a whine with the hum and both vary with speed. It sounds the same coasting in neutral with the engine turned-off. So I think my t/c is probably ok.

I'm thinking it could be the front differential internal rotating cage pinion(s). Now I wish I would have measured exactly how far the stub axle slid out from the tube on the inside. But I'm almost certain the stub axle disengaged from the splines inside the differential. That would cause a huge speed difference between the right and left wheels as far as the front differential is concerned. And if I understand http://auto.howstuffworks.com/differential2.htm those pinions look like they could get toasted in a situation like this.

I'm thinking the stub axle bearing is going to be bad if not already, but there's no clunking sound yet.

I'm going to drop the diff tonight and open 'er up. I'm really glad I found this thread http://www.explorerforum.com/forums/showthread.php?threadid=53863 .

Should I just go to the j/y and get one, or should I try to rebuild mine?

Thanks again.

 

[24theroad]

tough diffy frame bolts

I need a better breaker bar and tighter 15mm socket (it's kinda old 12-point). Hasn't slipped off [yet] but I couldn't get the leverage laying on my back with what I have. I'm going tool shopping!

It was a longer day than I expected. But when I did get home, with the shortcuts it was only about 25 minutes from raising the truck to ready to break loose the front diff frame bolts. Oh yeah, I already removed the front d/s a couple of days ago, which helped on time. I also left the CV axle shafts bolted in the hubs on both sides and removed the right inboard CV and popped the left side loose. I'm sure when the diff is ready to come down, the CV axles won't be a problem.

 

[IZwack]

loud hum that varied with speed and a strong vibration in the floor starting around 10 mph and became unbearable at 25 mph.

If it feels like a jackhammer coming through the floor, it might be one of the front wheel bearings - check for play after getting the front tires off of the ground with a jack.

 

[24theroad]

If it feels like a jackhammer coming through the floor, it might be one of the front wheel bearings - check for play after getting the front tires off of the ground with a jack.

I know what you mean by the jackhammer, I've had a front wheel bearing go out on me before, not this truck though. The wheels are rock solid at 12 and 6.

It's not making any popping, banging, or clicking noises or such vibrations. The vibration was only bad when the stub axle inside the right side extension tube disengaged. Now it's loud hum and whine that varies with front wheel spin. The whine is kinda sounds like a dump truck backing up, except I'm driving forward and there's a low pitch hum. My kid ignored "it was acting weird" which went on for about 70 miles at 70 mph. When I got to it, it was out of gear oil, took about 1.5 quarts and that mostly leaked out into the pan over a week sitting in the garage.

 

[24theroad]

I tipped the the front driveshaft CV end down so I could inspect the boot, which was perfectly fine, but was surprised by a little bit of fluid leaking from a tiny hole at the rounded tip of the metal cup that mates in the corresponding cupped flange at the end of the shaft coming out of the front of the transfer case. The hole is dead center at the end of the driveshaft. Nothing came out until I held the driveshaft vertical with the CV end down.

Is this normal?

 

[24theroad]

Ok, even I can figure out any leaks from a CV=bad, that's not normal.

I extracted the pumpkin and opened it up. It looks like excessive wear on the pinion gears in the rotating cage, like I thought. There are metal shavings in the gear oil. The mating surfaces are a lot shinier and more visibly worn than the surfaces on the ring gear. If you read earlier in the thread how this happened, please let me know if you also think I'm on the right track.

All the seals are leaking, and the bearings for the right internal stub axle in the tube are probably going bad too given the unusual stress. I'm looking for a good used front diff or see if I can get someone to rebuild mine, rather than do it myself.

Any thoughts from the experts here?