Solved - Noise while on accelerator - no noise when coasting

[Chris E]

Hey Guys, posted on TrailVoy and all I heard were crickets so I finally jumped ship and signed up over hear. (They sure are missing some of you guys over there! =P )

Here is the skinny:

- 06 TB LS - i6 4x4 with GU6 3.42 Non-locking Rear End 189,000 miles

- Whining/whistling/groaning (not grinding) Almost sounds like blowing air over a half empty beer bottle mixed with an electric motor. Pitch is higher at higher speeds. 99% sure not coming from engine compartment, more central or rear.

- Noise becoming more pronounced. Used to only be heard at "highway speeds" (50-75 mph) now can be heard at a lower pitch around 35-40 mph. Used to be able to drown the sound out with the radio but that isn't the case anymore.

- Only present when on the accelerator while in gear. Noise disappears when coasting and braking. Reoccurs as gas is reapplied. Shift into neutral eliminates noise too & engine rev sounds normal even while coasting.

- Same going noise straight or turning while on the gas, but no noise coasting flat or down hill.

So digesting the info above I'm leaning towards a bad pinion bearing but I have ZERO slop from the shaft to the rear diff so I'm not 100%. Last fluid change did not resolve or even improve this (Both Diffs & Transfer Case fluids). It is now time to change the fluids again though. The fact that it only happens when on the accelerator really eliminates a lot of issues. I'm hoping there is someone else out there that has seen this and can point me in the right direction. Thanks for your time!

 

[Mounce]

Maintenance history on trans? Is it acting out of the ordinary at all?

 

[Chris E]

Transmission has given zero trouble to date. Flushed and filled at 150k. Trany fluid still in good shape from what I can tell upon inspecting what's on the dip stick.

 

[Texan]

Just a suggestion. Possible dry U-Joint?

 

[Realism]

U-Joint is possible, especially if there is that nice bump when going from park to drive or brake to drive.

How many miles do you have on the fuel pump? They tend to have a bit of a whine at idle when they are getting temperamental. Since the noise is only there while giving it gas, I would suggest have someone take a listen outside the vehicle in park at idle near the fuel pump, then give it some gas and see if it gets louder from that area.

 

[littleblazer]

I can second the failing u-joint. Had one go on the Sierra and it sounded (and felt like) the rear diff was whining. Little less miles though, 160k about. It started out sounding like the chirpers on the brakes and got worse from there.

 

[Chris E]

Ok fellas, it's 8am on Saturday and thanks to the current vote I'm preparing to go bang the crap out of a u-joint. Haven't had to do one on this vehicle but the last one I did ended up meeting a plasma cutter . I no longer have a plasma cutter so it's soaking in PB blaster now hoping for an easier out come. When wife returns with u-joint complements of the 'zone I'll get started and report back.

 

[therealsethallen]

Tack on a vote from me for U-Joints. It seems like a wear item on all the GMT vehicles.

 

[Chris E]

Well life is happening as we speak.. Something has come up and looks like this will have to wait until next weekend. I'll follow up then.

 

[Sparky]

When I had a rear axle shaft bearing go bad in my old car it would sing pretty good under load (acceleration) but get quieter when coasting.

 

[Mooseman]

When doing the original u-joints, when you put it in the press, put some propane heat on the yoke surrounding the cups to melt the nylon locking the cups. Been doing this since the '80's, works like a charm. Just use caution if it's an aluminum shaft/yoke. You'll see the nylon ooze out of the injection holes.

 

[Chris E]

When I had a rear axle shaft bearing go bad in my old car it would sing pretty good under load (acceleration) but get quieter when coasting.

Thanks Sparky. Good call! I may have to look into this next if the u-joints do not produce, but I'm sure they need to be replaced anyway since they are factory.

 

[Chris E]

Update: U-joint(s) not the issue. Front U was fine the rear one was a little tight but replacing didn't resolve. A friend of the family is a full time mechanic for the local electric company and he gave it a look and is certain the pinion needs to be replaced. There is some play in spots when turning the yolk by hand. He also is worried that the bearings may go soon due to the debris in the unit.

This is my 1st time delving into the diff so I'm a little lost in regards to what "parts" exactly I'm looking for. I am going to go ahead and replace all the bearings, the ring and pinion and possibly the seals. The problem I having is building a parts list of these items. I see I can get master kits online but I'd like to know exactly what I'm getting. I'm leaning towards Timken bearings but I'm finding it difficult to compile exactly what bearings I need (by part and/or model number). Is there not a list floating around the forum?

 

[AWD V8]

When the pinion bearing is going, the added thrust under acceleration will cause the noise to increase as the pinion gear tries to move away from the ring gear and presses into the bearing, coasting actually relieves the pressure, so no noise. Very difficult to diagnose without a magnetic "ear" on the pinion casting.

A fluid change may change the noise, but doesn't repair anything.

 

[Mooseman]

Differential work does require instruments and know-how to properly set it up. It's not just a "slap the parts in" affair. There is backlash and gear contact pattern to adjust.

 

[Chris E]

Still hoping for a parts list...

As for the gear pattern that's what the paint (grease) and shims are for. I have a friend that has the meter for checking the backlash so I'm good there too.

 

[coolasice]

Why not just find a complete good used rear and just swap the whole thing?

 

[Chris E]

Found a used rear end with 150k but the seller also wants to do the install in order to offer any warranty on the rear end. He was asking close to $1000 for the rear end and labor but after speaking with him and letting him know I could do this myself he is down to $750. It does save me the trouble at the end of the day, but I figure his labor is still around $400-550... Seems steep considering I could do it myself but I'm also "cheap" as the Roadie would say. Reasonable to you guys?

 

[Sparky]

Swapping a rear axle is about a half day job IMO with the right tools (mostly basic stuff, an impact helps but not necessary).

I don't think anyone has a parts list just because it isn't a bolt-n-go type of deal inside the differential. If you don't set the gears right it'll make noise and/or tear itself up. But check in Mooseman's sig on the service manuals, all that info is bound to be in there

 

[coolasice]

Check car-part.com for a local source... $1000 is too much for a high mileage unit...

 

[Mooseman]

That's $1000 for the diff AND labour to install.

Chris, How much just for the diff itself? Seller private or a business? If private, i wouldn't trust any warranty. A couple of buddies and an afternoon will git'er done. Not a complicated job.

 

[Chris E]

So I talked to him again last night and now his prices (almost) make sense. The person that referred me to him gave him the impression I was not willing to do it myself so he saw an opportunity... He doesn't have the rear end, he has the whole truck. He was going to have to tear if off the truck to do the swap which is why he wasn't willing to sell it to me outright since there was already going to be labor involved. I let him know that was too steep so he is checking around to see if he can find me one local.

 

[Chris E]

Never really figured out what was causing this whining noise from the rear while on the accelerator, but swapping non-locking rear end with a G60 was my fix. No while while on the gas and a much nicer when pulling the boat out of the water this winter! Marking this solved... too bad the engine is knocking now.