Front Diff or Transfer case of tranny.....

[Mr T]

Folks:
2008 Denali with 191,000 miles. I’ve changed all fluids as I should (usually around 30k) with proper types; engine when the I reach 20 to 10% of the monitoring tool.

When driving and under power, you can hear engine noise but it’s often not quite as loud as a general humm. If you let off the gass everything is quiet.

Ive replaced both wheel bearings as they went out last year.

My question is how do I know if my front Diff is going or if my transfer case is going?

I know the mounts for the transmission or transfer case are gone or going as when the transmission downshifts you hear/feel a thud but it shifts between all gears just fine.

many diagnosis thoughts?

TKH

 

[donjetman]

Exhaust manifold bolts breaking is a common problem that causes noise like you describe. Check yours out. It is usually the bolts at the ends of ea manifold.

I installed 3 Dorman clamps to patch the broken bolts. Here's a thread I did about broken exhaust bolts: https://www.tahoeyukonforum.com/threads/exhaust-manifold-bolts-no-bueno.108605/page-3

 

[swathdiver]

My question is how do I know if my front Diff is going or if my transfer case is going?

They stop working! Usually they just start getting louder as a bearing somewhere inside begins to wear out. That's what the volume knob on the radio is for. Replace the mounts so things stay where they are meant to be.

 

[Mr T]

Donjetman:

So I tried something that may be steering me away from it being the exhaust manifold. I drove down a flat street @ 45 MPH. In drive, and under light power, I keep it at that speed. I can hear humming noise. Not loud, not the sound of a bad hub as I know that sound....its slower in rotation....but I hear it.

I then disengage the transmission by going into neutral. The noise goes away. While in neutral and car slowing a bit, I then gas the motor to 2 and 3,000 RPM and only slightly hear the motor...not the noise. So the engine sound is quite, normal and as expected.

I re-engage the transmission, no gas just put it in drive, sound comes back quieter....then i give it a little gas and you hear it more as normal.

So somewhere in the drive line I'm getting feedback in sound.

I HATE to replace the differential with HOPE that fixes it. Do I need to put it up on stands, put it in drive and then put a pipe to each the transfer case and the differential and see which transmits that sound through the pipe to my ear?

 

[swathdiver]

I then disengage the transmission by going into neutral. The noise goes away. While in neutral and car slowing a bit, I then gas the motor to 2 and 3,000 RPM and only slightly hear the motor...not the noise. So the engine sound is quite, normal and as expected.

Transmission Pump?

Time to get all four wheels off the ground, put it in drive slow with helper, and crawl under and have a listen.