2009 Vibe 1.8 Extremely Hard Downshift with Cruise

[Spudy]

Hey All,
Was driving my wife's 2009 Vibe (1.8, Auto, 200k Miles) the other day. Was on a slightly hilly road doing about 60mph with the cruise set. When climbing a couple of the hills it downshifted so violently it was like hitting a small deer. Never slipped or anything like that just was a big BANG and whole vibe jolted like a bad pothole or something and rpm go up and up the hill we go. The transmission was serviced about a year ago. New fluid and filter. Didnt do a complete flush just what was in the pan. Fluid is good.

Wife says it has happened to her before but only with the cruise set. Any other time it seem to be fine.

Any suggestions?

[sideshowalan]

Probably a combination of bad shift logic (oh no the rpm dipped, better downshift into the lowest gear possible and floor it) and loose transmission or motor mounts. The same thing would happen if you suddenly floored the gas.

An easy test for bad motor mounts is to look under the hood for excessive movement while a friend accelerates in park. Transmission mount would have to be visually inspected or poked at.

[Spudy]

will check the mounts next time i get a chance. Would is there any reason it only seems to do it in with cruise control?

[kumquat]

It's happened to me. I think it's just bad shift logic. If you catch the transmission just right, by pressing the gas just as it's preparing to upshift, it can respond by sort of changing its mind in the middle and downshifting instead. You get a really hard downshift as a result.

The transmission control systems are pretty bad in the 09 1.8. There is a power band that you simply can't get into. I spent a lot of time at 60, 65 on the highway cruising... but when I come to a slight hill, I lose speed. Press the throttle enough to downshift, and the car downshifts and starts accelerating quickly. Try to let off to cruise at that speed... and it upshifts and you start losing speed. It was mildly infuriating.

[ctgottapee]

Probably a combination of bad shift logic (oh no the rpm dipped, better downshift into the lowest gear possible and floor it) and loose transmission or motor mounts. The same thing would happen if you suddenly floored the gas.

An easy test for bad motor mounts is to look under the hood for excessive movement while a friend accelerates in park. Transmission mount would have to be visually inspected or poked at.

While possible, the motor mounts on the 2nd gen or meant to move according to service manual, and it says movement shouldn't be used as a diagnosis, only deterioration of the mount.
I'm not an expert here or have experience with this, but did catch it in the manual.