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Discussion Starter #1
I've had a vibration while driving between about 10-20 mph, and at speed (about 40 and over), when needing power like going uphill, in either 3rd or OD, I'll occasionally feel a momentary jerk, like just for an instant, power stopped being transmitted to the wheels. It's happening more often now, but it's not periodic (as in, like a missing tooth in a ring gear).



The engine doesn't speed up at all when this happens, and there are no engine or transmission codes. I rebuilt the transmission and installed a Transgo 4L80E-HD2 about 50k miles ago, and the u-joints & carrier bearing were replaced at the same time, and the driveshaft was balanced (it was also shortened to make room for the transfer case). In hindsight, I should have also replaced the torque converter, but it seems to be working fine. A couple months back, I replaced the transmission filter & fluid, and there was just the usual small amount of fine silt in the pan, and the fluid didn't smell burnt at all.



A brief check under the truck, I noticed I can move the driveshaft in the carrier bearing quite a bit (I can move it more than 1/4" up and sideways), so it needs replacement.


From googling, the low speed vibration can be due to the carrier bearing, but it's not clear if that jerking could also be due to it, or if the jerking could be from something else.


Idea/comments on what the problem could be?
 

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Discussion Starter #2
As an aside, what would the gm part number be for the carrier bearing (also known as the center support bearing)?


From looking at rockauto, acdelco, and wholesalegmpartsonline.com, it's not clear which one is for my truck.


'04 Sierra 3500 cab&chassis, extended cab, 161.5" wheelbase, RWD (now 4wd)
 

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Jerking on a loaded condition is usually a misfire, though your badly worn carrier bearing is also a culprit. The ECM can cut power without causing any RPM flares up or down by retarding the timing radically when it detects a misfire, making it feel like all the power went away(because it did). Personally I would get the bearing changed first, then test again. My reasoning on that is it is a known bad part that can make knocking or clicking noise and harmonics. The ECM monitors noise and harmonics from multiple sensors in the trans and engine. It could think it is knock, or something out of spec and cuts power temporarily, but not long enough or often enough to trigger a check engine light.

If it is still there after the bearing replacement I would put some higher grade fuel in from a different station to see if it cleans up. Like if you are using some Costco 87, throw in some Shell or Chevron 91 for a single tank. If it is still there after that start looking at plugs/wires, fuel pressure regulator, or fuel filter.

Most of these are easy checks or cheap easy to replace parts. Plugs take minutes to check, wires the same and are cheap to replace. OEM wires from rockauto are el cheapo. 10mm race wires can be had on ebay for cheap.

The FPR just remove the vacuum line inlet and see if there is any fuel, if there is, it is bad. If none, 99% chance it is fine.

Fuel filters are like $10.00 and 10 minutes to replace, yet everyone forgets about them. Its on the frame rail in front of the tank. Mine is right behind the ABS pump and in front of the tank, though I have an 8.1L suburban, multipl other GMs of thise chassis are in the same area. 2 open end wrenches and a 10mm wrench for the mount and it was swapped after about 6 minutes with the fuel draining.

The pumps can be on the way out, but usually they manifest in a hard start first.

If you had the 8.fun I could point you towards some sensors that are known to cause that, but am unsure if they do the same on the 6.0. The crank sensor on the 8.1 can cause the issue, as well as hard or no starts, but the 6.0 has a completely different crank sensor and location.
 

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Discussion Starter #4
Thanks for your response.


My truck is an '04, with the returnless fuel system, so the pump in the tank is the "all in one unit" (pump, fpr, and filter). I did plumb in an inline fuel filter like earlier trucks had, and it was replaced earlier this year with very little dirt in it.


Also recently (as in, 2 months ago) replaced plugs & plug wires, with no change.


Once I figure out which center support bearing to get, I'll replace it and see what happens. I'll also try hooking up a scanner and seeing if any misfires show up when viewing live data.
 
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