2011 Tahoe, driveline clunk more noticeable after 87 Octane

[bcb1]

I have a 2011 Tahoe, 5.3L, 4WD, and I've been running the 87 octane tune for about 2 weeks now. I'm really liking the increased power. However, I notice a driveline clunk when I'm driving at slow speeds - usually coasting or decelerating in the 10-30 mph range. It happens when I accelerate. It's intermittant, doesnt happen every single time. The driveline clunk is a well known GM truck issue - my 2000 Yukon had it, but only after about 170,000 miles - and greasing the slip yoke with heavy duty marine grease fixed it. GM recommends not using the grease anymore, especially on 4WD trucks.

I'm not blaming the Diablo tune - I'm just thinking that the tune has changed some parameters that makes the clunk more noticeable. It seems like the rpm's are increased when at idle and when driving at slow speeds or coasting, and I'm sure torque management has been reduced or eliminated in the tune - which I'm guessing makes the driveline clunk more noticeable when it happens.

Can this be fixed with a custom tune? I'm very happy with the 87 octane canned tune overall, it's just this one little annoyance that I'd like fixed.

Maybe Lew can chime in...?

[mikel]

Not something I have heard from others, lets see if anyone else chimes in...

[Mike_Levy]

I would think this would be caused by the reduced torque management. If theres a known problem, sending more power through it is gonna make it worse.

If GM knows its a problem, why aren't they bothering to fix it? I smell class-action lawsuit.

[bcb1]

Just a cursory google of tahoe driveline clunk or silverado driveline clunk yields a ton of hits. The issue has been around for many years. In the past (say, pre-2009 era), the standard advice was to grease up the slip yoke on the driveshaft with a very heavy duty grease, put it back in, and you'd be good to go - at least for six months to a year. In the case of my Yukon, I greased the slip yoke a couple years ago and it's still clunk free. But times have changed, GM says not to grease the slip yoke anymore because the grease is not compatible with the fluid in the trans. Basically what they say is that some slop in the driveline is normal.

My '11 Tahoe has just 15,000 miles and though it probably clunked once in a while - mildly - before I did the 87 octane tune, I guess I just notice it more now with the torque management gone. And is it my imagination - or does the truck really idle at a higher rpm than stock? Because it sure seems like it to me. Not just sitting at idle, but also while coasting at low speed, the rpm's seem higher than stock.

[06MonteSS]

yeah, would need to get a custom tune done in order to set the torque management settings back to stock values...

or, take the truck to the dealer and tell 'em to fix the truck

replied to your email too BCB....

[LGSONE]

On my 08 Silverado I noticed the clunk much more with the Torque management turned off. The previous fix was to lube the slip yoke assembly, which helps for about a month, then back to normal clunking. There is an updated TSB for this issue and they have replacement parts to address it instead of a Band-Aid. Mine is scheduled to be done next week, I'll let you know how it turns out. Its loud, I had the windows down on a bridge with concrete sides and as I was coasting and then tipped into the gas it was like, WTF was that, I could hear it much more with the sound bouncing off the side walls..

LGSONE

[BlackZ71Silverado]

OP, sounds like you have the slip youe issue that a lot of us have had problems with. It is a known issue and there is a TSB from GM to address this issue. Take it to the dealer and have them perform the needed work.

TECHNICAL
Bulletin No.: 09-04-21-003D
Date: January 14, 2011
Subject: Clunk Noise at Stop or from Launch (Clean/Lubricate Rear Propshaft Slip Yoke Splines)
Models:
2007-2009 Chevrolet Silverado 1500 Series
2008-2009 Chevrolet Avalanche, Suburban, Tahoe 1500 Series
2007-2009 GMC Sierra 1500 Series
2008-2009 GMC Yukon, Yukon XL 1500 Series
Equipped with 4WD (RPO NQG, NQH)

Attention:
This bulletin contains a procedure to clean/lubricate the rear propshaft Slip yoke splines and replace, if necessary. Check the history on this vehicle. If the lubrication procedure has been performed previously, then continue on and replace the transfer case rear output shaft.

Supercede:
This bulletin is being revised to update the warranty statement. Please discard Corporate Bulletin Number 09-04-21-003C (Section 04 - Driveline/Axle).

Condition
Some customers may comment on a bump feel or clunk noise at a stop or on launch. Customers may also comment that the bump feel or clunk is noticed after the vehicle has come to a complete stop and that it feels as if the vehicle was bumped from behind.
Cause
This condition may be caused by a slip/stick condition between the rear propshaft Slip yoke and the transfer case rear output shaft splines. Braking to a complete stop can force the propshaft Slip Yoke forward into the transfer case while the vehicle rebounds slightly backward after stopping its momentum.
Correction
Note
Do not use grease for lubrication of the Slip yoke splines on 4WD vehicles. The output shaft in a 4WD transfer case does not have a grease retainer to keep the grease from migrating into the transfer case and mixing with the fluid inside. Grease is not compatible with the automatic transmission fluid (ATF) used in the transfer case and can cause damage if mixed.

Note
The clunk noise may also be due to fuel movement in the fuel tank when not completely full. If the condition is eliminated after filling the fuel tank, the noise is isolated to the fuel movement in the tank. Please make no repair attempts, as this noise is considered an operating characteristic.

Verify the customer's concern.
Clean/Lubricate Rear PropShaft Slip Yoke Splines 1. Remove the rear drive shaft. Refer to One-Piece Propeller Shaft Replacement in SI. 2. Inspect the rear propshaft Slip yoke splines.
Note
Protect the transfer case rear seal from Brake Clean.
3. Clean the rear propshaft Slip yoke splines with Brake Clean or equivalent and a shop towel. 4. Assure that the splines are free of rust or other foreign material. 5. Lubricate the spline with Automatic Transmission Fluid, P/N 88861003 (in Canada, 19264717). 6. Reinstall the rear drive shaft. Refer to One-Piece Propeller Shaft Replacement in SI. 7. Road test the vehicle and verify that the noise is gone. 8. If the vehicle has a repeat concern after lubricating the Slip yoke splines, replace the rear output shaft.

Replace Transfer Case Rear Output Shaft
Note
Do Not replace the output shaft unless the cleaning and lubrication procedure is ineffective.
1. Remove the transfer case assembly. Refer to Transfer Case Assembly Replacement in SI. 2. Disassemble the transfer case. Refer to Transfer Case Disassemble in SI. 3. Replace the transfer case rear output shaft. Refer to the Parts Information below. 4. Assemble the transfer case. 5. Reinstall the transfer case assembly.

[bcb1]

Thanks for posting the TSB, much appreciated.

Also appreciate the reply MonteSS. I might be contacting you for a custom tune (see below)

Mine has a relatively minor clunk - it's just as LGSONE describes above. I notice it when I'm slowing down (coasting) and then hitting the gas. It only happens at low speeds, like in the 5mph to 30mph range. I just never really noticed it before I did the tune though.

I guess I'll flash the stock tune back on the truck and test it for a day or two and see if it goes away. If so, then I'll just have to get a custom tune with most (maybe not all?) of the torque management put back to factory settings.

[bcb1]

Ok, I restored the factory tune last night. The only thing changed now is that I've disabled DOD on the factory tune. Driving to work this morning it seemed like the driveline clunk at low speeds was no longer noticeable. I'm going to leave the factory tune on there for another day or two to be sure.

If that's the case, can my 87 octane tune be modified to restore most or all of the factory torque management values? I.E., would there be any benefit of running the 87 octane tune with torque management enabled or would it be virtually like running the original factory tune?

***UPDATE*** Yes, it's definitely better after restoring the factory tune. The driveline "bump" is basically gone now.