Bothersome shifting behavior, 2011 Challenger R/T

[Ryan]

Hi, New subscriber here. I just read the ‘best advice’ and ‘Primer’ stickies.

I have a 2011 Challenger R/T (in the U.S.) with a 5-speed automatic transmission. This is the WA580 (aka W5A580, also known as the Mercedes NAG1) transmission. The car has 42K miles on it, of which I’ve driven all but the first 7K.

There are circumstances where, if I drive “just right”, I can make the powertrain slightly ‘clunk’ as it shifts from 3rd to 4th. I know, I know; “don’t drive like that”. The problem is, driving it ‘like that’ it is exactly how you would want to drive in a suburban area, completely with stop signs, school zones, etc… exactly what I encounter in my morning commute.

The above is easiest to reproduce before the powertrain warms up: from first gear, if I grandpa my way up to 1500 RPMs in 3rd gear, I am generally going about 29-30 MPH at that point. 30 MPH happens to be the speed limit in my neighborhood, so that’s pretty much where I ease off the gas pedal (which I believe is fly-by-wire.) About 3 seconds after I’ve eased off the gas– and the engine is no longer under much load– at 30 MPH @ 1500 RPMs, the transmission decides then to shift up to 4th. RPMs immediately drop to 1000, and I hear/feel a subtle ‘clunk’… after which, the tach eases back up into the 1400-1500 range (still in 4th.)

The ‘clunk’ kinda sounds/feels like it might physically happen at the differential, but I don’t really know that for sure. (Like, maybe for a moment the differential was not under load, and then suddenly it was again. But again, I don’t know for sure.) The AT has the sport shift feature, where I can manually choose a gear while driving, and I have successfully recreated the problem with that, so long as I time it right (RPMs a tad too high, for instance, and the shift to 4th will be smooth.)

The above is easier to reproduce before the engine and tranny have warmed up. However, it does sometimes happen at normal operating temps, as well. Also, while I call it a ‘subtle’ clunk, sometimes it is less subtle than others (more loud than jarring.)

Is this something I should be worried about? If so, what’s the suspected problem? Note that I’ve never seen the AT fluid, because the manufacturer thought it would be nice to seal off the dipstick tube, and not give me a dipstick.

Topic

[Ryan Wofford]

Check your U-joints, they might be going out and the excess play might be making a clunk, luckily they are very cheap and easy to fix

[Ryan]

Fair enough, that’s a quick and easy thing to check. But: then why only in that gear, under those very particular conditions?

[Ryan Wofford]

I cant say unless i were to see it but I remember my truck when the U-joint started going out, it would clunk between 1st and and 2nd, but it did fine everywhere else except for a small squeak at all speeds.

[Author]

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