Downshift kick when approaching a stop

[jjvd21]

I'm experiencing a bump or kick when approaching a stop, usually below 5 mph. I don't fully understand the workings of a transmission, so I'm looking for suggestions on the cause. When approaching a stop, or a hard slow down my rig lurches forward almost like I'm being pushed or bumped from behind. I imagine the transmission is shifting to a lower gear with the rpm's remaining high so that when it engages it pulls the rig forward for a moment. Or, the other thought I had was that there is a delay in the transmission shifting into neutral - so it lags then when it gets into neutral it coasts forward quickly. This is something totally different than the lurch leaving a stop that other posts have covered, which is solved by a software update. I am not giving the rig any gas when I'm experiencing this and it's happening when I'm slowing down or coming to a stop. I appreciate any feedback, thanks!

 

[Houm_WA]

...although it is different than that posted, the same fix may apply.

 

[jjvd21]

Houm I wish you were correct, but my dealer has tried to correct the problem twice. It seems to be getting worse which makes me think it is a mechanical problem rather than a software shifting pattern issue.

 

[mustbeaudi]

For what this is worth, automatic trannys don't shift into neutral at stops. The torque converter essentially permits some slop and the drivetrain stays in (usually first) gear, hence the creep at idle in D with foot off both pedals. Engine speed should not be too high, in fact the throttle should not be a factor if you are not on it. In other words, a downshift too early would not add momentum but usually is felt as a sudden added drag due to the forces of engine compression braking. That you feel a push at what seems like the the 2 to 1 downshift suggests that the engine is racing?

The key is to take any dealer employee with you for a ride (even the lot boy) to verify the condition. Otherwise, you waste time and get the dreaded "could not verify" and more aggravation. This is more true if your warranty expired, in fact!

 

[Houm_WA]

My transmission does something a bit crazy too. Once in a while (maybe once every 12 downshifts) when I downshift to 1st gear as I approach a stop, the tranny will pop back into 2nd in defiance. When the vehicle comes to a stop, it goes into 1st just fine. This never happened until after the s/w fix for the lurch. I could not replicate for the dealer...

 

[racehorse]

Houm I wish you were correct, but my dealer has tried to correct the problem twice. It seems to be getting worse which makes me think it is a mechanical problem rather than a software shifting pattern issue.

I'm not sure if it's the same principal, but I when I drive my lr3 in sport mode it seems to have a more aggressive stop/shift from slow to stop, the lurch you're describing. It almost seems like it's similar to a big rig where the motor is helping the brakes to stop. In normal drive, it disappears for me but it does do the power shift in sport mode.

 

[jjvd21]

Thanks for the suggestions. Today it happened about five (5) times. It feels like a car is bumping me from behind just before I come to a stop. Its actually such a jolt that I get a knock in the front wheels because I have the brakes applied. RPM's are below 1000. The comment above regarding the torque converter - could this be the cause? Thanks again and even with this nusaince that I'll get fixed I still love the rig.

 

[jjvd21]

After driving the past few days I'd like to clarify the symptoms. Just before I stop (under 5 mph) there seems to be a delay in the transmission shifting into neutral (or first gear). Its almost as if the transmission is using the engine to help slow down, when it finally shifts out of gear to neutral (or 1st gear) it surges forward because of the lack of resistance from being in gear. I wish I could explain it better. Any recommendations are appreciated before I visit my dealer on this.

 

[roverman]

I really wish I could help, sounds extremely unusual, and dangerous. Like mustbeaudi said, the trans will not (and should not) shift into neutral. As it shifts down to first, you should get more engine braking -- not less. I'd get it into the shop and have them take a look at it, hopefully you can reproduce it for them. Let us know...

 

[mustbeaudi]

When you visit the store, don't use this neutral language. It could confuse them. Use the "final or last downshift, presumably to first" description as the point below 5 mph when the vehicle surges forward against your expectations. Should not surge at that point.
BE SURE TO REPRODUCE it for them when you drop it off. I sometimes practice nearby the store, then pick up a service employee for a ride and drive around the block. Works each time.