First post... love the website!

I have a 07 (NBS) Z71 4x4 Crew Cab LTZ with the 5.3 V8 (with active fuel mgmnt) and 3800 miles.

I've noticed when I stop at a light for a few, the transmission "bumps" a little. Almost as if someone barely tapped the rear bumper with their car. It doesn't do it all the time and it's usually after waiting at a light in Drive with my foot on the brake for at least 5 seconds. The truck did this before I towed or put a load on the drivetrain.

I've monitored the Info Center and it shows the truck is steady in the V8 mode.

Any thoughts or input is greatly appreciated.

(Also, I've done a couple trips from So. California to Lake Mead towing a 5000 boat and the truck performs excellent! I held out for a truck with 4:10's and I'm glad I did. I have the 18" off-road rims and went up one tire size with some Terra-Grapplers and couldn't be happier.)

 

probably the slip yoke on the drive line unloading if it gets worse take to dealer they will grease it so it doesn't bind any more. The old body style did this also and it is the same tranny.

 

The bump that you feel is normal and is the transmission completing a downshift into first gear.

Many other transmissions will complete this shift just as the vehicle comes to a stop and some will go to 1st as you lift off the brake or push the accelerator after being stopped, the torque management system and electronic transmission control module on the new GMT900 products is programmed to complete the 2-1 shift while stopped in certain conditions.

 

Sounds like another nice innovation if that's the case. If the truck is designed to stay in second gear when you are standing still and going to first when you hit the gas, i'd say you are gonna have to wait till they come up with a reflash to get rid of that garbage. Your trans should be in 1st gear before you come to a full stop, so when your going about 5 mph you should feel that slight engine breaking from the trans going down back to first gear. The newest trans i've looked at was a 2006 and I still operated like the 4l60e that has been around for years. Do you have one of those new 6 speed trannies? Either way i'd get in touch with the dealer and ask them if this is normal operation, and if so ask them what they are doing to fix that paticualar problem.

 

It could be the torque convertor unlocking.

 

I have the same problem with my 6 speed GM auto. It happens about 10% of the time while under 20 mph and coasting to a stop for a light or an intersection. It feels like someone has bumped you from behind. Additionally, if I am coasting down (under 20 mph) for a traffic light and then apply gas lightly when light turns green, I will sometimes hear a distinct CLANK noise and feel a shutter through the truck. I don't know if this is a transmission problem or something to do with the AWD system. I am having the dealership work on the problem. They tried to totally B.S. me telling me it is normal for the transmission to bump, clank and shake the vehicle. Yes, that's what I like about GM, they sell vehicles that bump, clank and shake but they maintain in their ads boldly, "WE EXAMINED EVERYTHING. WE OVERLOOKED NOTHING." Yea, sure. I believe everything that GM says like any good mindless gnome. World class? I think NOT.

 

ZX1100F1:
Respectfully, you are in complete error. If what you say were slightly true, the bumping would occur routinely. But it does NOT. It happensfairly occasionally but sufficiently enough to be a real defect and problem. If you drove this vehicle, you would quickly observe the problem. That clanking noise that sometimes accompanies the bump is a real stunner to hear!~