Denali Help Please

[Redmanf1]

I have a 01 Denali XL and I am sure you know they are AWD but for the sake of it I will still post it. Anyway to get on with the problem is it chatters like an older 4X4 with the front hubs locked in when you turn it. It gets worse after it has been driven for awhile or the warmer the transfer case gets. Is this transfer case setup kind of like the posi units and the clutches slip when you turn? I have no idea why they would be bad but this seems to be the case as this vehicle has never been abused.

Thank you for any help in advance,

 

Newbie

Nelson

[bobcat5544]

There are many reasons for your complaint.

Most common cause is Tires,

 

TIRES

 

Tire rolling rates can be a major factor in operational characteristics. Consider the following important items:

• All tires are the same size and brand. Tires of different brands may have different circumferences (or radius) even if they are the same size.

• Tires are set to factory recommended pressures. A tire with low air pressure will roll at a different rate.

• All tires have approximately equal amounts of wear. Tires with different amounts of wear will roll at different rates.

• All tires are the same tread type. Don't mix on-off road, all-season or street tires on the same truck as they may have different circumferences and roll at different rates.

• One or more of the tires may show small, short scratches around the circumference of the tire tread. The tire "scuffing" on the road surface causes these scratches.

 

Other Causes

Wheel Bearings

Wrong fluid being use in the Front/Rear Differential or Transfer Case

Viscous coupling in transfer case going bad.

Front or Rear Diff clutches going bad

Front or Rear Diff Bearings

 

There are other thing that could cause your problem, but the things listed above are most common that I have seen

[Redmanf1]

Bobcatt5544,

Thanks for the reply. The tires are all the same, size, ware and brand. I do not think it is a wheel bearing or a differential bearing. The fluids have been taken care of at the dealer. Nothing had been changed within the time this had started. It started and has progressively gotten worse to the point that when it is hot (at running temp} it does not like to turn sharp. At that point it chatters very bad and the best way I know to describe it is like the old 4X4 locked in with posi’s. I am not sure about the Viscous coupling in transfer case but I will see what I can find out. I would bet the clutches in the V.C. are bad or down to the steel.

 

Thanks again

Nelson

 

 

 

 

 

 

 

 

 

There are many reasons for your complaint.

Most common cause is Tires,

 

TIRES

 

Tire rolling rates can be a major factor in operational characteristics. Consider the following important items:

• All tires are the same size and brand. Tires of different brands may have different circumferences (or radius) even if they are the same size.

• Tires are set to factory recommended pressures. A tire with low air pressure will roll at a different rate.

• All tires have approximately equal amounts of wear. Tires with different amounts of wear will roll at different rates.

• All tires are the same tread type. Don't mix on-off road, all-season or street tires on the same truck as they may have different circumferences and roll at different rates.

• One or more of the tires may show small, short scratches around the circumference of the tire tread. The tire "scuffing" on the road surface causes these scratches.

 

Other Causes

Wheel Bearings

Wrong fluid being use in the Front/Rear Differential or Transfer Case

Viscous coupling in transfer case going bad.

Front or Rear Diff clutches going bad

Front or Rear Diff Bearings

 

There are other thing that could cause your problem, but the things listed above are most common that I have seen

[bobcat5544]

I also forgot you may want to try to clean off the wheel speed sensors.

[Redmanf1]

How would the best way be to clean them? Use a spray brake clean?

 

Thanks

 

 

 

 

 

 

 

I also forgot you may want to try to clean off the wheel speed sensors.

[bobcat5544]

You can use brake cleaner to clean them off

[Rolling]

Even with fluids changed at the dealer, the synthetic fluid they used in the rear axle may not have the correct friction modifiers to make the limited slip function properly, you may try a $10.00 bottle of Limited slip axle additive in the rear diff before you spend too much money on further diagnosis.

[Redmanf1]

Thank you for all the help. The chatter started before the fluid change and was the same after it was changed. I know they used Mobil 1 in the axel and a synthetic trans fluid in the transfer case. Do you think the additive would still help and if so wouldn’t I also need to use it in the front axle because of the AWD?

 

Thanks again

 

Nelson

 

 

 

 

 

 

 

Even with fluids changed at the dealer, the synthetic fluid they used in the rear axle may not have the correct friction modifiers to make the limited slip function properly, you may try a $10.00 bottle of Limited slip axle additive in the rear diff before you spend too much money on further diagnosis.

[Redmanf1]

Any body have anything more to help?

[Redmanf1]

Does anyone have a picture break down of this transfer case?

[KB06YUKONXL]

Even with fluids changed at the dealer, the synthetic fluid they used in the rear axle may not have the correct friction modifiers to make the limited slip function properly, you may try a $10.00 bottle of Limited slip axle additive in the rear diff before you spend too much money on further diagnosis.

 

+1 I would recommend using the GM friction modifier additive as well. The Mobil1 75w90 does not meet the GM spec for my 2006 AWD. I know because I called Mobil and they said not to use it. I am using the GM #89021677 75w90 synthetic axle lubricant in my front & read diffs. My Tcase calls for DexronIII so I am using Mobil1 Synthetic ATF. No noise at all. But I would check your owners manual for the correct Tcase lubricant as many have changed over the years. My tcase has no clutch packs.

[Krambo]

Even with fluids changed at the dealer, the synthetic fluid they used in the rear axle may not have the correct friction modifiers to make the limited slip function properly, you may try a $10.00 bottle of Limited slip axle additive in the rear diff before you spend too much money on further diagnosis.

 

+1 I would recommend using the GM friction modifier additive as well. The Mobil1 75w90 does not meet the GM spec for my 2006 AWD. I know because I called Mobil and they said not to use it. I am using the GM #89021677 75w90 synthetic axle lubricant in my front & read diffs. My Tcase calls for DexronIII so I am using Mobil1 Synthetic ATF. No noise at all. But I would check your owners manual for the correct Tcase lubricant as many have changed over the years. My tcase has no clutch packs.

 

 

 

O.K. Everyone has an opinion and here is mine and why. I have an 03 Silverado SS with I believe the same T-case and rear diff as you. (NGV149 and the G-80). The following is information gained from other tech guys on this issue.

 

I run 75w90 Mobil one synthetic with NO ADDITIVE in the rear. The Silverado SS (and I believe your Denali) is equipped with the Eaton G80 rear differential, a mechanical-locking limited-slip unit. Production tolerances in this axle are very tight, and the clutch pack and seals are specifically designed for use with synthetic gear lube. The axle is filled at the factory with a synthetic GL-5 75W-90 fluid made by Texaco (part #2276) and resold at the GM parts counter as service #12378261 for about $25-30/qt Using mineral based gear lube in this differential will cause errant 'slip-stick' operation in the clutch pack, and if not corrected (by using synthetic fluid) will lead to shuddering around corners and clutch pack failure.

 

The problem is using the additive in the G-80was found to be a cause for the clutches sticking together and staying engaged. there was a technical service bulliten for it back in the 90's and since then they've taken it out of the fluid recomendations for that specific differential. Having it in there won't hurt anything, i'd just pay attention to your diff if you notice it staying locked in. Run some figure 8's in a big parking lot as slow speed, and then do it in reverse. You will know if yours ar sticking of disengaging.

 

Here's a copy of that bulliten:

 

LOCKING DIFFERENTIAL LUBRICANT (SERVICE INFORMATION) #91-4-109 - (Aug 15, 1991)

SUBJECT: LOCKING DIFFERENTIAL (G80) LUBRICANT - (SERVICE INFORMATION)

 

VEHICLES AFFECTED: ALL LIGHT TRUCKS EQUIPPED WITH G80 REAR AXLE ALL YEARS

 

Some light duty trucks equipped with locking rear axles (G80) may exhibit rear axle chatter, especially when turning a corner from a stop.

 

This condition of alternate engagement and disengagement of clutches in differential assembly is usually caused by contaminated axle lubricant.

 

To correct this condition, drain and refill the rear axle with SAE 80W-90 GL5 (P/N 10950849). The use of any additive in locking rear axles (G80) is not recommended. Rear axle additives are designed for use in limited slip differentials which are normally installed in cars. All light duty trucks equipped with RPO G80 make use of a locking differential and the use of additives will delay the engagement of the locking mechanism and may decrease axle life.

 

VEHICLES/COMPONENTS INVOLVED: ----------------------------- Some light duty trucks equipped with locking rear axles, RPO G80

 

 

Now on to the T-case...

 

The NVG-149 transfer case contains just under 2 quarts of light-weight lubricating oil (ATF), and this fluid must be changed at regular intervals. Normal service is listed as 50,000 miles, but it is not unusual to find an SS or your denali with a noisy transfer case (even with as little as 10,000 miles) and quiet its operation dramatically by draining and replacing the fluid. Most conservative mechanics will recommend fluid inspection and or replacement at 40,000-miles, or even sooner in severe-duty or dedicated towing applications.

 

The transfer case comes from the factory filled with Dexron-III ATF, however a much better lubricant recommended for use in the NVG-149 transfer case is a pale-blue synthetic lubricant sold by General Motors under the name AutoTrack II, it is readily available at any GM parts counter for $9-11 per quart. Regardless of your choice of fluids you will need two quarts.

 

If you choose to continue using Dexron-III ATF in the transfer case: expect to change it more frequently as it will not give as long a service life as AutoTrack II. Your needs may vary depending on your torque converter (high-stall converters produce more sheer force and heat), monthly mileage, and extra towing/hauling duties.

 

I PERSONALLY noticed a difference by going to the AutoTrack II in the noise my t-case made. Granted I am throwing 700 HP through it (38% to the front wheels). Hope this helps some.

[KB06YUKONXL]

My Denali has the Borg Warner 4400 series tcase. If you use the new GM 75w90 in the diffs you don't need the friction modifier. Sorry if I confused anyone. As for contaminated fluid, I always clean out the diffs & tcase at 2-3000 miles after break in. Then at 50k and 100k. You get very little debris after the initial clean out unless you have a mechanical part failure in progress.

[Kack]

G80 differentials don't have clutch packs, they have a locking differential that is activated with centrifugal force. One of the spider gears I believe the driver's side, has a thin gear behind it inside the carrier. A small pin with teeth on it rides on this gear. When one wheel spins faster than the other, the spider gear turns inside the carrier and the locking mechanism is flung out and locks the spiders to the carrier. Therefore both wheels turn at the same speed. I've broken quite a few of these, I have always used the recommended posi additive and have never broken one from regular wear and tear, they have always engaged and disengaged just fine. My breakage always resulted from abuse. These G80 lockers are very fragile and don't stand up to large tires or violent locking. Basically all of your engine's multiplied torque is relying on a 1/4 inch pin, Enjoy