Trans 'double' downshift

[turbo78vair]

Good evening! We have an '05 Z71 Tahoe with 53k miles on it. Just got back home from a 1600+ mile trip from central Indiana to the NC coast and back. In the hills of VA, WV and NC had one time in which during a typical one gear downshift that the trans dropped down a second gear with significant RPM increase.

Load was normal with two people and luggage. Speed was 65 to 70 depending on traffic. We've put about 15k on our Z71 since we bought it last fall. It has maybe done a similar shift three times total.

Any ideas?

Thanks - Gary - Franklin, IN

 

[oomindwarpoo]

Assuming your going 60-75 you are in 4th gear, punching it will down shift into 2nd.. makes sense to me?

 

[turbo78vair]

Trans 'double' shift

Thanks for your reply. I'm not 'punching' it! Just normal road cruising through the hills on the interstate. Typical hills would cause one gear downshift, but on very rare times, got this quick shift down to 3rd and then another right away to a roaring 2nd. Doesn't feel right as Tahoe isn't pulling that hard - just cruising.

Gary - Franklin, IN
2005 Z71 - 5.3 - 4x4

 

[jey_]

I think that's normal behaviour. It will even shift to 2nd when I have it on cruise control on the Interstates and I approach a hill. And these are not steep hills (think Midwest). We have the 3.73 rear axle - maybe it does this less on the 4.10.

Not sure if GM put this logic in to try to reduce wear on the transmission? (straining in high gears is not good for it I think, even if there is enough engine torque to pull it)

Also I noticed that the points on the throttle where the transmission decides to do the double-downshift are MUCH lower (less throttle input) than on previous GM cars I have driven (like from the 90s). Or maybe I'm just not used to the drive by wire throttle. Maybe it's a marketing gimmick to try to show how powerful the Tahoe is? Or maybe I'm not used to the mad power that the Vortec 5300 has versus the older small block V8s :lol:

Either way, it's not bad for the car by any means to let it do the downshifts.

 

[1CLNTHO]

Im gonna second what everyone else is sayin. My first trans had a hard shift that would kick to 2nd from 4th if i jumped on it, and it was definitely noticable. In my new trans im running a different torque converter and a shift kit and when it drops down now everyone in the truck feels it. I wouldnt worry too much about it? if its doin it for no reason there might be a problem with your passing solenoid (electronic trannys=blah)