Odd Drivetrain Noise From Sierra Denali....Any Ideas?

[analyte]

I'm chasing an odd sound that I hope someone can help me with that's more familliar with these trucks. It sounds like a compressor or motor kicking on and off. It only lasts around 3-7 seconds each time it's heard, and it isn't constant going on and off when driving.

 

It only happens when under load, speeding up and at cruise on the interstate. Therefore, I can't look for it while idling in the driveway. I have tapped the brakes and it doesn't affect or end the sound/vibration. I can feel it slightly through the gas pedal while also hearing it inside at speed. If I let off the gas pedal it seems to go away, but I've yet to be able to confirm it.

 

I feel confident that it's coming for the engine side and it almost sound like a compressor refilling a tank, though muffled. It doesn't appear to be a PS problem, but I wonder if it could be my A/C compressor coming on and off since it's climate control. It is totally random and doesn't always appear when accelerating or when cruising. Is there anything else on these trucks that would make that sound? Could it be a bearing in the A/c compressor?

 

Thanks for any help.

 

Kerry

[The_aSSet]

Front diff?

[kcsilveradoss]

does it do it with a/c or defrost off?

[analyte]

Front diff?

 

Not sure since this is my second vehicle with 4wd/AWD. I don't know how they sound when they fail or start to fail. I just drove it this morning to the store, and it did it twice going and three times coming back over just a few miles. Does a bad diff make this type of on and off sound when the bearing is going out?

 

does it do it with a/c or defrost off?

 

I drove the truck without the A/C on and it still had the issue. I know the compressor is free-wheeling, but I don't know if that definitely rules it out or not.

 

Thanks,

Kerry

[analyte]

Ok, it appears my front transfer case bearing is bad. There is a lot of up and down movement that shouldn't be there. The front diff has no slack so I'm comfortable that it's ok.

 

What is the going cost to rebuild the NVG-149 with new bearings and seals? I can do alot myself, but I don't have a press or the specialized tools to rebuild it myself.

 

Thanks,

Kerry

[mcmahan]

Would probably be better to take it to a shop and have it rebuilt if you haven done it before

[analyte]

I got a quote for $989 to remove/replace and change both bearings and seals. If my rear. Is bad, it will be another $500order to replace it.

 

Is that high? Good deal??

 

Thanks,

Kerry

[analyte]

Ok, I've done some searching and I've found the following options for NVG/NP 149 hard parts from Monster among other suppliers. Any preferred resellers for these items?

 

- Master rebuild Kit

- Overhaul kit (bearings and seals mainly)

- Replacement chain

- Alum. replacement rear case (if hole is found)

- pump rub fix from Merchant Automotive

 

What should I get for the rebuild? Should I get the complete master kit or only replace the bearings and seals that are bad? I'll most likely get a chain since I'm over 100K in the truck for my own sanity...

 

Do the hard part kits come with the new style clip for the pump, or do I have to buy that separately somewhere else?

 

Thanks again,

Kerry

[analyte]

Ok, I had the T/C gone through with new bearings, chain, merchant pump rub fix, and seals. I got it back in the truck, and it issue is still there.

 

Again, it only happens under load and stops when I let off the gas. Does it at low speed and when causing, but its not constant and can't be anticipated.

 

Turning has no effect so I've ruled out wheel bearings. Does a bad front diff howl/growl/whine constantly??

 

Thanks

Kerry