Rpm change and vibration 2013 GMC 2500HD 6.0l Vortec

[Nsjenner]

Hopefully I can get some help here on an issue.  Truck is a 2013 gmc 2500HD Denali with the 6.0l Vortec, I started getting a small vibration when maintaining speed at anywhere from 60km/h to 100km/h.  The vibration will start and stop at random and at the same time I can watch the rpm go up by roughly 100 while the vibration is happening, after the vibration stops the rpm will drop back to its normal position.  The vibration will immediately stop if I let off the throttle or if I press the throttle further getting it to drop a gear accelerating, it seems to only happen under a very specific engine load.  Also the vibration is stronger if the truck is in 4wd.

 

While the vibration is happening if I open the rear sliding window it sounds like the vibration is coming from the exhaust but this could be the sound just bouncing off the inner front panel in the truck bed and being redirected up to the window. 

 

I have had the truck at a mechanic and initially he found on the scanner a completely random misfire happening across all cylinders so to start with I had the plugs and wires changed and also had both diffs, t-case, and transmission all serviced.  At the same time they inspected all u-joints, cv's, and wheel bearings.

 

The mechanic could find nothing that would seem to cause the issues and he is currently stumped.  I have the truck back for now and the problem does not seem to be getting any worse but obviously want to find the cause and get it fixed.  The truck currently has 216k km's and other than a water pump replacement this is the first major issue.

 

I have read about similar problems on the forum but nothing that matches my exact issue.

 

 

 

 

 

 

 

 

[CamGTP]

8 hours ago, Nsjenner said:

Hopefully I can get some help here on an issue.  Truck is a 2013 gmc 2500HD Denali with the 6.0l Vortec, I started getting a small vibration when maintaining speed at anywhere from 60km/h to 100km/h.  The vibration will start and stop at random and at the same time I can watch the rpm go up by roughly 100 while the vibration is happening, after the vibration stops the rpm will drop back to its normal position.  The vibration will immediately stop if I let off the throttle or if I press the throttle further getting it to drop a gear accelerating, it seems to only happen under a very specific engine load.  Also the vibration is stronger if the truck is in 4wd.

 

This is a classic torque converter that is starting to fail. The 100rpm jump up and down and when you left off the throttle is a torque converter locking and unlocking. When you release the throttle the converter unlocks and the vibration goes away and it also unlocks when you give it enough throttle to kick down a gear.

 

The 6L90e is known to go through torque converters, it's a common failure and I would replace it as soon as possible before it damages the rest of the transmission.

Edited December 9, 2021 by CamGTP

[Nsjenner]

Thanks for the reply, been so busy with work that I missed the notification.  My original thought was the torque converter but the transmission fluid was still clear and the temperature never went above normal levels so I put this out of my mind at the start.  This definitely makes sense though since the vibration sound almost sounds like bearing howl, probably the needle bearings in the converter.  I'll be booking the truck in tomorrow to get this confirmed and then changed out.

 

Thanks again!!