Noticeable forward lurch/early downshifting during deceleration (2011LC) (1 Viewer)

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Providence, RI
I recently bought an '11 Lc at 166,000 miles with great service history. The last transmission service/flush was at 140k at a dealership.

At lower speeds, I am noticing a significant forward momentum shift a second or so after letting off the gas, with a correlating spike and then drop in the tach of around 500-700 rpm (it typically spikes from 1400 to 2000 or so, then immediately back down to 1000ish.) The momentum shift is quite noticeable (to me, at least) and lurches the truck nearly as much as a physical tap on the brakes would. In S drive mode, the momentum shift doesn't seem to happen, so I've more or less honed in on the AT as the cause of the lurching.

There's part of me that thinks this might just be the nature of the 6-speed transmission that I'm still unfamiliar with (I've only driven around 2,000 miles so far.) However, the timing and significance of the shift feels stronger and more sudden than I would imagine any type of automatic engine braking/brake assist system would feel.

Any insight will be hugely appreciated!
 

Taco2Cruiser

Rob @ BudBuilt Off Road
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That is not the case with my 2011 with 130k on the clock.

It’s... smooth and pretty normal. Push it hard and it shifts fast and a bit harder to get in gear quicker, but to slow the truck down during shifts, that doesn’t sound like any 200 I’ve driven.

A recent service could mean a lot of things. If it was just a dump and fill, that’s only about 4 qt and not going to change anything. If it was a full exchange (I hope no one actually flushed your trans) then you could have everything from a failing solenoid to a damaged torque converter.

First things first, find out what the service actually was.
 
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The Invoice for the 140k service (and for a similar service record at 66k) shows that the following was performed:

"PERFORM TRANS SERVICE ON SEALED TRANSMISSION AND LEVEL CK TO CORRECT TEMP OF FLUID"

The parts for that services were listed as follows:
4x 00289-ATFWS WORLD STANDARD AUTOM
1x 90430-A0003 GASKET
1x 35178-30010 GASKET, TRANSMISSION

So it looks like drain and fill with just 4 qts. replaced and some crush washers.
 
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After a few more days of driving, it seems like the issue is much more noticeable after the engine/trans has come up to temperature.

In reading through various transmission-related threads, I've seen mentioned several times that the 6-speed is particularly sensitive to overfilled fluid. Does anyone have any thoughts on the possibility that the trans was overfilled after the last fluid swap and it could be causing this shifting issue to occur more when the fluid heats up and expands?

I also take back what I said in the original post about the issue occurring only in D mode, and not S. I've learned more about that mode, and it doesn't make much sense that it would affect the shift sensitivity at lower speeds. It was probably just a fluke the first few times I tried to feel a difference.
 

bentonrover

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You sure its the transmission? I know there was a TSB on the rear end thunk/clunk. Usually on take off from a stop or low speeds then acceleration rapidly. Easy to check if over filled. You can check temp on a tech stream. Some even say to let truck idle for 10 min then pull the overfill plug. Not sure if that works but maybe.
 
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You sure its the transmission? I know there was a TSB on the rear end thunk/clunk. Usually on take off from a stop or low speeds then acceleration rapidly. Easy to check if over filled. You can check temp on a tech stream. Some even say to let truck idle for 10 min then pull the overfill plug. Not sure if that works but maybe.

I'm not 100% sure it's the trans. In fact, I'd obviously love to find out it's something unrelated that is more or less inconsequential. I'll do some reading on the Clunking TSB and see if it lines up with what I'm experiencing - do you happen to have any specific references to it that might be helpful reading? My main reason for assuming it's a transmission-related issue is the RPM spike and drop that is timed almost precisely with the forward-momentum shift every time I feel it.
 
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I know this thread didn't get too much traction, but I figured a quick update couldn't hurt in case someone's searching with a similar issue in the future. Today when I got a dealership oil change, I requested a transmission fluid level check. I realize that I could do it myself using the manual process folks have discussed on the forum, but I didn't want to second guess myself after the fact if nothing was resolved (e.g. "maybe my driveway is too unlevel," "was the fluid drip the same as a fluid dribble," etc.)

It was absolutely worthwhile, because it turns out my trans was overfilled by a little more than a quart of fluid at the previous owner's dealership after the most recent drain and fill around 30,000 miles ago. The tech at my dealership said he was able to drain it to the correct level using the scan tool procedure, and I can immediately tell the difference. No more lurching or RPM spikes after 20 or so miles of driving after picking it up.

A quart is a significant amount to be overfilled, but fortunately I don't believe it's enough to cause any long-term damage to the trans. I suppose time will tell, but for not I'm just glad that I wasn't completely crazy in thinking that the lurching was abnormal.
 

bentonrover

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Feb 19, 2012
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Im sure the transmission level is fine. My issue was the rear drive shaft ujoints. Swapped the whole shaft with new oem all good now. I too had that lurching feeling at stop lights then acceleration.
 

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