4.88's too much for my transfer case?

[LongrangeLauber]

Well ever since I installed the new differentials geared to 4.88 and got my new lift installed and truck aligned, I keep hearing this roaring type of sound coming from somewhere underneath. I took it to the shop I got my diffs. installed at and they took it for part of the day and said it was my transfer case. It never made that noise before from my stock 3.73 gears, but I figured it had 345k miles on it so it could have been. I replaced the case with one I had sitting in my garage and took it for a test drive. Well the noise is still there. Now Im pissed because I just spent $100 on a new rear output shaft seal, gasket, and 2 quarts of fluid.

 

Took it back again to the shop and I stayed and watched them diagnose it this time. With the truck up on the lift, I would hit about 40mph and the noise would be really noticeable. He started listening and said it was still coming from the tcase and my dad even confirmed it. Unless this tcase is bad to, I have my doubts.

 

So, finally my question. Has anyone with 4.88's and an np246 transfer case ever had this problem? The guy who diagnosed it was saying that maybe cause the 4.88's are spinning a lot faster than the 3.73's that the chain inside the tcase could be stretched and be slapping the housing, but I ran my truck in 3rd gear all the time (with 3.73's) which is the equivilant RPM to 4.88's in overdrive (4L60E tranny). Plus it sounds highly unlikely that two transfer cases are bad, not saying it isnt possible, but just sounds unlikely. Now Im stuck with either shelling out more money for another diagnosis for them to possibly tell me the same thing or replace the tcase and it could quite possibly still do the same thing, in which then Im stuck.

 

Any help would be much appreciated

[NitroCherokee]

In my professional opinion you need a new shop 1st, 2nd the lower gear ratio will actually in turn put less stress on the T-Case since it takes less torque to get the tires rolling. Your description of the noise doesn't sound like a chain slapping the case because it happens at 40. At 40 the chain wouldn't be slapping the case if it was stretched enought to touch it at 40 it would be more of a constant noise as it was sawing itself through the case

[LongrangeLauber]

The best luck I've had in my area is my dealer and they do a good job but you also pay for it as well. Should I start by having them take a look at it and seeing what they say? I guess it's worth the $80 or so.

 

I keep taking it to the other shop too because they installed the gears so if it is the gears they should pay for parts and labor. Wish there was a way to run the front diff. at 2k RPM's without the tcase or driveshaft hooked up to it

[NitroCherokee]

If you put it in 4WD does the noise change? How bout tossing the trans into neutral? Pop the front driveshaft out and take it for a short run and see if anything changes.

[LongrangeLauber]

The guy said the noise goes away in 4wd, sounded the same in when we took it for a test drive today.

 

Right now I am running without the front shaft and it is quite as possible. All I hear is tires and wind

[Carder09]

I thought that was gear whine from being installed incorrectly or not in spec.

[LongrangeLauber]

If that was gear wine I would take them out cause at 70 its almost unbearable. I have the music up pretty high at that point. It only gets worse the faster I go.

[kstruckcountry]

Disconnect your driveshaft and put it in gear and see what happens. If it still makes noise it can't be the diff.

[LongrangeLauber]

Driveshaft is out and no noise. But that means there's nothing in the transfer case either so I'm not sure how to eliminate one at a time.

 

I did mention this is for my front differential, correct?

[kstruckcountry]

Do you have the aftermarket style driveshaft for your lift?

[LongrangeLauber]

Nope stock. The lift kit company (McGaughy's) did not say I needed it. Besides they don't even sell it so I doubt I need it.

 

Is that the one with like 2 u joints on one side? I think its called the double cardan style driveshaft?

[kstruckcountry]

Yep most lift companies recommend them.

[Silverado4x4]

So you say with the front driveshaft going to your front diff is disconnected and the noise is gone? Try putting the front shaft in again and mark it, take it for a drive and see if the mark on the shaft has moved , if it moved then that sounds like your truck is not coming out of 4wd, the front shaft should not turn when in 2wd.

[LongrangeLauber]

I'll give it a try.

 

I thought the shaft spins because the chain in the transfer case is always hooked up and then the actuator up front engages 4wd? I haven't familiarized myself with the 4wd portion of my truck. That's the only thing I haven't had trouble with until now haha

[kstruckcountry]

Basically everything but the CV's should be still when you're out of 4x4.