Jump to content

Denali Help Please

Redmanf1

By Redmanf1
in Ask A GM Technician

Recommended Posts

Redmanf1 Enthusiast

Redmanf1

Posted
Posted

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 Enthusiast

bobcat5544

Posted
Posted

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 Enthusiast

Redmanf1

Posted
  • Author
Posted

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

Redmanf1 Enthusiast

Redmanf1

Posted
  • Author
Posted

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.
Rolling Enthusiast

Rolling

Posted
Posted

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 Enthusiast

Redmanf1

Posted
  • Author
Posted

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.
  • 4 weeks later...
KB06YUKONXL Enthusiast

KB06YUKONXL

Posted
Posted
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 Enthusiast

Krambo

Posted
Posted
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. :rolleyes:

KB06YUKONXL Enthusiast

KB06YUKONXL

Posted
Posted

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.

  • 4 weeks later...
Kack Enthusiast

Kack

Posted
Posted

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

Archived

This topic is now archived and is closed to further replies.

Go to topic listing

  • Latest Articles

  • Posts

    • Atlas
      Wow I'm in a pickle. (Broke down truck) and a story.

      By Atlas · Posted

      I will be doing that for sure, but I need to solve who has/ where I can find a bidirectional scan tool that will support OBD 1.5. I'm kicking myself because I ebay'ed a Snap On MT2500 that I didn't think I'd ever need anymore. D'oh!! I'd rather not buy another, so I'll contact a few local shops to see if they have one and how much they'd want to do the procedure. I'd rather have the ability to do it myself... I wish there was a modern tool that could do it all, but I'd have no idea what to buy.   The theory with the pulled timing is that it mimics a rich condition. The delayed spark causes incomplete burn and the O2 sensor picks up low oxygen levels. That's interpreted as a rich condition so the PCM pulls fuel and that shows up in the deeply negative fuel trims.
    • Chuck FB
      Joke Thread

      By Chuck FB · Posted

      An ultra wealthy man had the most beautiful daughter. But, there was a problem. Everything she touched would melt in her hands. No matter what, Metal, Wood, Stone. Anything she touched would melt. She could not feed herself. Because of this, men were afraid of her. Nobody would dare marry her. Her father was despaired. What could he do to help his daughter? He consulted doctors, scientists and anybody who could solve this problem. Finally one of them said, "If your daughter touches one thing that does not melt in her hands, she will be cured." He was overjoyed and came up with a plan. The next day, he held a competition. Any man who could bring his daughter an object that would not melt in her hands would be given billions of dollars to marry her. Three extremely intelligent and handsome young men took up the challenge. The first brought a very heavy steel rod, But alas, when the she touched it, it completely melted in a matter of seconds. He sadly went away. The second brought a beautiful diamond, knowing diamonds were one of the hardest substance in the world and would not melt. But alas, once she held it in her hand, it melted. He too was sent away disappointed. So now, there was one left He was very nervous & sweating. He approached the daughter & said, “put your hand in my pants pocket and feel what is in there." She did exactly what he asked. She felt something very hard. She held it in her hand, squeezing it as hard as she could. It did not melt & remained extremely hard. Her father was overjoyed. Everybody was overjoyed. She was finally cured. Nothing never, ever melted in her hand again. They married and they both lived happily ever after, raising a wonderful family. Question: What was in the the groom’s pants pocket??? Answer below ↓ M&Ms of course! They melt in your mouth, not in your hand. What on earth were you thinking?
    • asilverblazer
      Wow I'm in a pickle. (Broke down truck) and a story.

      By asilverblazer · Posted

      There's a bunch of tea leaves that you've read, but in any case the delayed timing is unusual. Not sure how that relates to the rich at idle vs. 'normal' while driving.   If you're in this deep, might be worth investigating, and re-learning the sensor. What have you got to lose? Plus, it properly fixes the timing cover leak.
    • asilverblazer
      Wow I'm in a pickle. (Broke down truck) and a story.

      By asilverblazer · Posted

      The only problem I have seen this cause is longer crank times. 
    • Atlas
      Wow I'm in a pickle. (Broke down truck) and a story.

      By Atlas · Posted

      Injector is being sent off today for rebuild and I estimate I'll have it back in 10 days or so.   It may not be the injector...of course...now that I've torn down the intake again. But, let's rule out the injector and replace those spider legs that have been almost rubbed through.   The truck has always had negative timing and I'm reading "normal" timing at warm idle should be +16 or so. I'm negative 16 to 25 or more, and it's always been like that since I bought it.   A light turned on upstairs last night in the old noggin. Rare, I know...   This will be wild, if it turns out to be the cause!   In 2001, according to the old service documentation, the muffler was replaced. Why? I have no idea, it wouldn't have been rusted through by then. But they did a crappy job.   In 2019, another shop replaced it and noted the prior install was poorly done on the work order. "Exhaust system vibrates on crossmember". Except...I guess they just left it be? I believe the husband, the couple who were original owners, had passed by then. Maybe she said it's just not worth it to have the exhaust system fixed and declined repairs. Very few miles were driven between 2019 and 2025.   The exhaust system vibrates heavily on the crossmember and you can feel it and REALLY hear it, even today. Not always, but at idle, it gets going pretty good sometimes.   What if....   ....What if that's enough to trigger one or both of the knock sensors? Could it be tricking the sensors into sensing knock, so it's pulling timing aggressively? Pulling timing heavily means it's firing after the piston reaches full height which means incomplete burn which means the O2 sensor is sensing a rich condition, which means I've been chasing my tail, and what I thought was an inconsequential problem (janky exhaust) has been THE issue for this truck for 25 solid years?   That would be wild. Maybe it IS wild.   The service documentation thereafter, for years, shows visits for rough idle, replacing O2's, replacing the cat, replacing plugs and wires, a misfire condition, like they could never solve the issue. The injector has been replaced 4 times in 80k miles, that's just crazy.   The secondary theory....   The engine has clearly had a leak at the front seal for a very long time (the greasy trench...). I think the truck changed hands quickly ~2025 because there's Napa receipts from someone I don't recognize in the ownership history. They apparently replaced the timing cover seal, and they did a terrible job. There's RTV smeared all over and the leak I had reduced to a weep by snugging the front oil pan bolts is now a leak again.   HOWEVER....I read about replacing the crankshaft position sensor. Any time the ckp sensor is disturbed or timing cover is removed, the truck requires relearning, and that can only be done through a bi-directional scan tool. Skippy with the RTV probably didn't do the relearn procedure is my guess. His scan tool is lost in a pile of RTV goo somewhere.   So, it's very possible the sensor has been disturbed and the truck is just running on the old learn data but not setting a code for anything. The distributor has since been replaced and so has the camshaft position sensor, so all bets are off for that thing.   In the theme of one step forward, two steps back, I returned the accumulator for the AC. The gal I've been working with at O'Really's has been great. She refunded it under manufacturer's defect and we compared it to the replacement I ordered, and sure enough, the replacement is machined very differently (and a gauge actually fits on it!).   Got it home, installed it, started vacuuming it down.... and I couldn't get good vacuum.   The high side service port, where I replaced the old GM ball valve suspecting that was a source of the previous leak....well, I've clearly exposed whatever pre-existing crack in the line where the service port is welded, and made it much worse. Blessing in disguise? Except there goes another $25, now I'm waiting for a replacement AC line.   In 10-ish days ALL the parts will be here. Rebuilt injector, new exhaust system, new cat, new high pressure AC line.   Oh, did I mention the squeaking ISN'T coming from the AC pump? The truck still squeaks when started, and there were words after I started it with the new AC pump installed. But, there was more to replacing the AC pump for just a squeak. A truck with good working AC is something of value, for the comfort alone.   I've ordered a new harmonic balancer because, 30 years is a good run for one of those. Rule it out. The squeak may be something more sinister, though. I'm worried about that ckp sensor and if it was shimmed correctly, or if the timing set was installed correctly. The squeak may be coming from UNDER the timing cover.   At this point, once I get it put back together, I'm thinking I'll take a 50 mile victory lap and then promptly put it up for sale. This truck is cursed. Betty, from beyond the grave, doesn't want anyone messing with her Blazer. Or maybe she's getting revenge for 30 years of shop visits with that thing.

  • GM-Trucks.com Clubs

  • Popular Contributors

×
×
  • Create New...