Suburban shifting/rear end issue

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I’m trying to diagnose something I’ve noticed the last few months in my 2008 Suburban 1500. It may be one issue or a couple.

The 4L60E shifts perfectly from 1 to 2. 2 to 3, though, is almost always soft. It’s not a slip or hesitation as much as it is what I’d describe a nosedive of momentum. 3 to 4 seems perfectly fine, FWIW. Both shift solenoids were replaced with OEM about 12,000 miles ago. If I accelerate a little more aggressively, the problem seems to subside. Some 2-3 shifts are just fine. I didn’t really notice this when I bought it a year ago, but it may have been there.

I’ve also started to notice a small clunk or thunk that seems to coincide with shifts. It seems to be downstream of the transmission - maybe driveshaft or the rear end. (It’s not quite the same, but it reminds me of issues I had with a 2001 Jeep Cherokee. They were caused by an ungreased slip yoke.) There’s also a little play in the driveline, a slight hesitation between acceleration and engagement in the differential. I call it slack. The same Jeep had this issue, albeit considerably more advanced, and it was solved by new spider gears.

The truck has 121,00 miles on it. Transmission fluid is good and at the correct level. The gear oil in the diff. is a synthetic with 12,000 miles on it.
FWIW, none of this is to the point that the average driver would notice any of this. Just being a car OCD BITOGer, it’s bugging me.

Any ideas? I'd appreciate your thoughts.
 
My 2005 1500 Avalanche had similar issues a year or so ago. Replaced the drive shaft U joints and all is good.
 
SuperTech Dexron VI. I dropped the pan last year when I first got it. Did the pan filter and the solenoids and then added a cooler and inline filter a few months later. Also a pan plug to make drains/refills 100X easier.
 
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Originally Posted By: HawkeyeScott
SuperTech Dexron VI. I dropped the pan last year when I first got it. Did the pan filter and the solenoids and then added a cooler and inline filter a few months later. Also a pan plug to make drains/refills 100X easier.


Just a stab in the dark , temporarily take the inline filter out & test drive for a few days . When / if you put it back , make sure the filter is not directional . If it is , be sure to install it in the right orientation .

And , yes , while you are att it , check the u-joints .
 
Thanks, everyone. U joints had crossed my mind when this first started. I'd love it if that's the issue.
 
There was a lot of talk about re-greasing a driveshaft yoke or slip joint in the early years of the new body style. I don't know how long that continued.

I bought a 2001 Silverado new, and would say the 2-3 shift has always been softer than 1-2. The 700R4 in my '87 Caprice acted the same way, even with a shift kit.
 
Just to close the loop on this in case others find this thread. I finally figured out what was going on. After "greasing" the slip yoke (with ATF) and putting in new (greasable!) Spicer U-joints, nothing changed. I decided to replace the transmission mount. This actually helped, but didn't solve the problem. So I kept thinking and thinking and finally popped the hood and checked the motor mounts.

In the end, it was a broken driver's side motor mount. What I was feeling was the movement of the engine/tranny when it shifted. It wasn't completely torn, but it had failed enough that the driver's side of the engine was lifting an inch or so under heavier load.

I spent the money on new OEM, had it installed this morning and finally, she's fixed. Now, back to life.
 
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