[theturbominivan]

i have 2000 2500 4x4 with about 250,000 miles on it. the 4x4 has always worked great with no issues when needed (rarely) and i dont abuse the 4x4.
yesterday it was about -13*F (cold) and i used 4hi to the store, put it in 2hi on the highway, then put it back into 4hi when leaving the store, and it began making a humming/grinding noise so i promptly put it back in 2hi.
it was defiantly locked in to 4x4 and not slipping. it is not acting like it is a transfer case issue, or an engagement issue. the 4x4 is working like it should, it just makes a low hum of something grinding now, that speeds up with the throttle. otherwise, everything seems fine. i thought it was just something to do with the extreme cold but is still doing it today when i tested it in much warmer weather.
it only makes the noise in BOTH 4hi and 4lo, which leads me to weed out things like front wheel bearings. it dosnt sound to be coming from the left or right side specifically, making me think its not a CV joint (they also both look fine).

doing a quick search online leads me to believe it is most likely my front drive shaft. i read a few places of others with a similar issue and it happened to be a bad joint on the front drive shaft.

has anyone else had this issue who could confirm my diagnosis? are there any other ways to more specifically diagnose this to be sure? would a drive shaft (or something else) just fail like this so suddenly with no warning?

thanks for you help.

 

[theturbominivan]

alright, i just pulled the front drive shaft and its totally fine. i changed the oil in the transfer case just for good measure, and i topped up both front and rear diffs. the front diff was lower than it should have been but not empty.

im still getting the same noise. when i had the front drive shaft out, i tryed turning the front diff knuckle by hand. it would turn but had some definite stiffer spots. it didnt turn as freely and easily as i suspect it should have in places. im not really sure what i should have expected, but assumed it would be a bit more of a smooth fluent rotation.
either way, i dont think with even the bit of resistance i felt in its rotation that it would be causing the kind of noise and vibration im feeling in 4x4. or could it?
so now im out of ideas......
anyone?

 

[irish power mad]

Isn't there a chain to transfer the power when 4x4 is engaged? would it cause the noise and vibration your having?. TBH reading your last post I wouldn't be surprised if the front diff is your problem, there shouldn't be any stiff spots on it.

 

[theturbominivan]

i was going to look at the 4x4 CAD unit thinking perhaps its something in there?????
im hoping its not the front diff! what could have possibly happened in there if thats what it is? like i say, things still work, just not smoothly or quietly.

 

[theturbominivan]

its not an issue with the CAD unit. checked that out today and everything looks fine inside.
my next assumption would be a bad carrier bearing at my front Diffs yoke. thats gona suck to check unless i can drop the front drive shaft again and tell a bad bearing by wiggling the yoke. i never thought to do that yesterday when the drive shaft was already out, but it didnt seem to have any kind of play to it that i remember.
im assuming its a bearing rather than actual teeth or gears inside because it does go into 4x4 still and seems fine other than the noise and rumblings its making.

anyone with advise? ive never opened or taken apart a diff before. will i need to drop my steering arms to get the front cover off? to take the gears out to get at bearings, is this a huge job?

 

[irish power mad]

I've never worked on a diff either so I can't comment on what you will have to do so free bump.

 

[Ramitt]

I have a slight hum while in 4wd. Just thought it was the nature of the beast.

 

[badmpr1]

Okay I had the same issue in my 97. It was a CAD issue. The fork was wearing and not connecting the axles all the time. I replaced the fork and installed a 4x4posilock kit and it never happened again. It was more than likely a vacuum issue though that's why I took it out of the equation. hope this helps.

 

[moparguy55]

Are all 4 tires the exact same size ? ie matching set worn the same all around ?

My 97 I found out that 1/2 inch in tire height is a big NO. All 4 are the same size but two different brands, enough to throw things out of whack. I said noway can 1/2 inch be the difference (wrong). I bought a matching set of 4 winter tires and back to normal 4x4 operation.

 

[bwallace530]

Have you changed fluid? I know it seems so simple that it couldn't work but it has worked for me before when I thought I had a t case problem.

Change it with some good high end fluid.


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[dozer12216]

different size tires can screw things up. could it be a worn TC chain? With drain plug out, you can rotate drive shaft and hear it hit/rub the housing.

 

[theturbominivan]

my tires are all the same with the same wear, its defiantly more of a rumble than a 'change the fluid' kinda thing. i did top everything up with about 8-10oz into the front diff. probably lower than it should have been by a decent amount.

when i opened my CAD i looked at everything and it all seemed to move smooth and fine. fork seemed ok but ill admit i didnt look at it too hard as i wasnt sure what i would have been looking for anyways.


like i say, when i turn the front drive shaft by hand it turns, but has some stiffer spots... like what one would assume to feel when a bearing race gets so worn that it begins to develop groves from the roller bearing. this is why i think it may be the yoke bearing. but i cant even fathom why that would have gone bad seeing as i use 4x4 so rarely and the rumbling just began the other day all of a sudden with no warning. one second 4x4 was quiet and normal, and when i put it n 4x4 20 minutes later, its noisy and hates me.

 

[theturbominivan]

ok, googled the TC chain.
im doubting thats what it is as it 'sounds' like its a noise coming from the front of the truck.
also when i had the drive shaft down from the front yoke and turned the shaft by hand, i felt no resistance, roughness or noise from the transfer case side of things.

 

[theturbominivan]

Okay I had the same issue in my 97. It was a CAD issue. The fork was wearing and not connecting the axles all the time. I replaced the fork and installed a 4x4posilock kit and it never happened again. It was more than likely a vacuum issue though that's why I took it out of the equation. hope this helps.

can describe the "wear" your fork had? was it chewed up? slowly worn looking like being polished, or was it bent or something?
im gona take a look at my CAD again. when i looked at it, i never looked to closely at the stuff in the CAD unit itself (like the fork), i mostly looked at the gears inside and slid the ring gear back and forth and it seemed perfectly fine.
can you describe your issues you had? and the CAD forks wear?

 

[theturbominivan]

bump. i haven't had much time to look at things since i last posted here but looking for some more ideas.
basically ive come up with it having to be one of these...
-a worn CAD fork
-a bad 'ball' in the front drive shaft (although the shaft dosnt seem to have play when i grab it like people describe when they go bad)
-a bad front pinion bearing (seems less likely to me??)
-broken or worn teeth in the front diff (also seems less likely to me)

if the 'ball' in the front drive shaft goes, how much play will i be able to fel with my hands if i tug on it and try moving it side to side?

the thing that has me confused is that this rumbling 4x4 issue just suddenly appeared one day out of nowhere. it didn't slowly present itself like something slowly wearing out.

that being the case, what are my most likely culprits?