When I downshift and I am in 2nd just before car stops and goes into 1st the car bucks forward. Dealer has reprogrammed TCM and ECM per TSB. This made no change in problem. Does anyone else have this problem in convertible or coupe?

I have another problem when I am driving at 50 or faster in DS mode and I press medium pressure on brake car downshifts and rpm rises. This is okay if I want to slow down but if this is a momentary slow down and I hit the gas the car really takes off at a high rpm. Any one else have this problem?

 

There is no need to downshift to 1st to start with

As for DS, it's how it's been designed, it's assuming you're driving aggressively.

To avoid confusing my car, I either drive on D or M

 

I do not downshift to 1st, that happens automatically. Before it goes into 1st on its own (while it is still in 2nd) the car bucks forward when it is going about 5 mph. Any suggestions?

 

Are you on the brake as it's down shifting/engine braking? A lot of people have posted similar "issues" with the transmission while it's down shift rev matching. Who knows. I think if there is still enough momemtum after it downshifts the car will move forward if you are not on the brake at that point.
Just a thought.

Anyway, check out these threads and see if it helps. Seems normal to me.

https://www.myg37.com/forums/g37-sed...raking-11.html

https://www.myg37.com/forums/g37-sed...n-braking.html

 

yup, i do get the exact same thing as the OP. on 4 occasions my car leapt forward more than 10 feet, twice i was very close to hit the car in front. it's bad to the point that i really consider it a safety issue. i repeatedly (read - 5 times) took the car to the dealer and brought up the issue with them. unfortunately, the attitude is that if you cannot reproduce a defect in front of them, then that thing doesnt happen. i got a few lectures about how their great, intelligent and adaptive gearbox is supposed to work, but no attempt to fix the issue whatsoever.

not only this, but the reaction times that i get when i cruise at 35mph and i need to accelerate are downright horrible. at that speed, when in D, my car is in 6th; if i need to accelerate, it regularly takes more than 2s to downshift, and by that time my foot is deep into the gas pedal, trying to get a reaction from this damn car. when i finally get it, the gearbox downshifted all the way into the 2nd, and the engine vrooms at 7000rpm, making me look like a you know what. so much for having an "S" badge.

 

wow.
Hypertech solves that 7AT log for the most part. But to accellerate quickly you would need to downshift one gear or two depending on what you are cruising in. It's a known behavior.

https://www.myg37.com/forums/engine-...st-got-it.html

 

its a valve body / hydraulic issue in the tranny.

you can re-flash the tcm/ecm all you want- but when that faulty system opens the valve and the high hydraulic pressure rushes through and jams in the gear and the clutches grip = your car lurches forward.

 

ImStricken: you sure about that? not that i doubt what youre saying, but all the explanations i had were of the software / electronic nature, and youre the first one bringing in another perspective. i must say, i did have pertinent explanations, and most them made sense - like when in D, with a deceleration of this many g's, if the downshift is this many gears, then the revs are boosted by that many rpm's - or similar thing, other numbers, for DS. which is great in theory, i can see where they're coming from, i can feel that system at work a lot of times, doesnt make me happier or anything, but thats the way it is. what they (dealer, mechanic, regional rep, manufacturer's specialist) failed to understand, was that i'm talking about a totally different (and hairy) experience. could be either their elaborate tcm algorithm gone wrong in edge situations, or some other system, of the nature you suggest. the only thing they did was to try to convince me that i'm overreacting to such a marvel of technology that's been offered to me. well, in one situation, with plenty of time and room to stop, i ended up in parallel with the car in front, both feet on the brake pedal, wtf did just happen. since that day, my son doesnt ride on the blue car anymore. overreaction or not.

cereal2k: i sometimes do hit, or hit-hit, the downshift paddle. there's no significant difference - the reaction is just as slow. i get slightly better reaction if i pull into DS and then try to accelerate. i'm going to read that post entirely and try to figure out how can i do that mod - thank you.

 

Why would you down shift like that? I think that hard on the Transmission to do that. 2nd maybe but to 1st? If your having problems, you should go back to the dealers to get that fix.

 

My problem occurs only when I am manually downshifting and the tranny is in 2nd - when the car is between 5 to 10 mph it bucks forward instead of continuing to slow down. Any one else have this problem? The car does this about 75% of the time.

 

I've examined my driving habits recently and although I have the hypertech programming done on the city driving I do I'm always in D unless downshifting for a stop, BUT, I never go into second. I've never had to that I can remember for city driving. The downshift rev matching takes care of 2 to 1 while also slowing with the brake.

Mountain runs are a different story. It's M mode and going down to 2 on hard stops and shifting up from 1 to get going again. I did not have the hypertech then either. No lurchng forward.

 

I agree with you, your totally correct imstricken. I could not have said it better myself.