6sp Trans Down Shift

[Stex]

Since new, my CC 6sp 5.3 will "sometimes" bump or bang the down shift from 4 to 3 when slowing down at a fair rate, light braking etc..I think it is the 4 to 3 shift as it is around 40 -35 miles per hour. Sales guy said his wifes Denali does this. He, the service mgr and parts mgr all drive 4 sps so no help there.

 

Anyone notice this issue on their 6sp? thanks for a reply.

[Dzlbudman]

Mine does the same thing. I never brought it in tho I hate dealers. I am bringing it in next week because of the body mouldings coming off again and ill let them know about this problem too.

[Stex]

Let us know what they say. I mentioned to my dealer about 6 months ago when the 5.3 6sds were still fairly new. They had no TSB or any come backs at that time.

[cerbomark]

mine didn t before the aftermarket tune and doesn t do that now either.

[Stex]

Any others out there? It is a real slam on 4-3 downshift...happens about 3 times a week etc..while braking..I tend to think it is computer generated...

[torch345]

Any others out there? It is a real slam on 4-3 downshift...happens about 3 times a week etc..while braking..I tend to think it is computer generated...

 

It's happened to me a few times when my Tahoe had less than 2000 miles. It hasn't happened for 6 months now. In my case the tranny was doing 4-2 downshift while coasting into a particular off ramp on my commute. To see if you are slamming into 2nd, put the shift lever into M right after the downshift and the dic will tell you what gear you are in.

[TorkFaze]

Pulling into M to see what gear you shifted into is a good idea (thanks Torch345) to help the dealer understand the issue. Pay attention to the AFM state, too to see if it seems to be tied to V4---> V8 transition. You can also drive in M5 for a while (eliminates V4 operation) and see if you notice a difference.

 

Since it's an '09, do you have firm light throttle 2-3 shifts, too? If you have an early '09 and are getting firm 2-3 shifts at lighter throttles, it could be a hardware thing causing both.

 

TF

[pm26]

Seems to me that it will take a while for GM to work out the bugs from these 6 speed transmissions. In the meantime I would still opt for the old proven 4 speed with the non AFM 4.8 liter engine. I test drove a new 2009 crew cab 2WD equipped this way with the 3.73 gears. Nice smooth shifts, just like my truck. I never experienced any rought upshifts or downshifts with my 4L60 and 5.3 L non AFM engine equipped crew cab Z71, also with 3.73 gearing.

[Wires]

Since new, my CC 6sp 5.3 will "sometimes" bump or bang the down shift from 4 to 3 when slowing down at a fair rate, light braking etc..I think it is the 4 to 3 shift as it is around 40 -35 miles per hour. Sales guy said his wifes Denali does this. He, the service mgr and parts mgr all drive 4 sps so no help there.

 

Anyone notice this issue on their 6sp? thanks for a reply.

 

I get that in my 08 SD even with the tune. I only get it when running in tow/haul though. You can try unhooking the battery for a minute and reconnecting it. The ECU could be learning your driving habits and is cranking up the shift pressures. Mine was a lot worse until I reset it.

[Stex]

Thanks for the good feed back. The 4-2 shift maybe it and I will try to watch for it. Will try the relearn. As for the 6sp the trans is a smooth shifter and does not lag or hard shift even on slow accel. Only the every now and then bump on down shift.

[Stex]

From MS3DALE: (could this be the 6sp problem I asked about):

 

Its normal.....

 

 

Service Information 2007 Chevrolet Silverado - 4WD | Sierra, Silverado (VIN C/K) Service Manual | Document ID: 2394678

--------------------------------------------------------------------------------

 

#01-07-30-042F: Information on 2-3 Upshift or 3-2 Downshift Clunk Noise - (Feb 5, 2010)

 

 

Subject: Information on 2-3 Upshift or 3-2 Downshift Clunk Noise

 

 

Models: 2010 and Prior GM Passenger Cars and Light Duty Trucks

 

2010 and Prior HUMMER H2, H3

 

2005-2009 Saab 9-7X

 

with 4L60-E, 4L65-E or 4L70-E Automatic Transmission (RPOs M30, M32, M70)

 

 

 

Important: For 2005 model year fullsize utilities and pickups, refer to Corporate Bulletin 05-07-30-012.

 

Some vehicles may exhibit a clunk noise that can be heard on a 2-3 upshift or a 3-2 downshift.

 

During a 2-3 upshift, the 2-4 band is released and the 3-4 clutch is applied. The timing of this shift can cause a momentary torque reversal of the output shaft that results in a clunk noise. This same torque reversal can also occur on a 3-2 downshift when the 3-4 clutch is released and the 2-4 band applied. This condition may be worse on a 4-wheel drive vehicle due to the additional tolerances in the transfer case.

 

This is a normal condition. No repairs should be attempted.

 

 

 

--------------------

[daylower]

Since new, my CC 6sp 5.3 will "sometimes" bump or bang the down shift from 4 to 3 when slowing down at a fair rate, light braking etc..I think it is the 4 to 3 shift as it is around 40 -35 miles per hour. Sales guy said his wifes Denali does this. He, the service mgr and parts mgr all drive 4 sps so no help there.

 

Anyone notice this issue on their 6sp? thanks for a reply.

 

 

Mine did this as well, apparently its pretty common. My BB tune got rid of that issue though.

[TorkFaze]

From MS3DALE: (could this be the 6sp problem I asked about):

 

Its normal.....

 

 

Service Information 2007 Chevrolet Silverado - 4WD | Sierra, Silverado (VIN C/K) Service Manual | Document ID: 2394678

--------------------------------------------------------------------------------

 

#01-07-30-042F: Information on 2-3 Upshift or 3-2 Downshift Clunk Noise - (Feb 5, 2010)

 

 

Subject: Information on 2-3 Upshift or 3-2 Downshift Clunk Noise

 

 

Models: 2010 and Prior GM Passenger Cars and Light Duty Trucks

 

2010 and Prior HUMMER H2, H3

 

2005-2009 Saab 9-7X

 

with 4L60-E, 4L65-E or 4L70-E Automatic Transmission (RPOs M30, M32, M70)

 

 

 

Important: For 2005 model year fullsize utilities and pickups, refer to Corporate Bulletin 05-07-30-012.

 

Some vehicles may exhibit a clunk noise that can be heard on a 2-3 upshift or a 3-2 downshift.

 

During a 2-3 upshift, the 2-4 band is released and the 3-4 clutch is applied. The timing of this shift can cause a momentary torque reversal of the output shaft that results in a clunk noise. This same torque reversal can also occur on a 3-2 downshift when the 3-4 clutch is released and the 2-4 band applied. This condition may be worse on a 4-wheel drive vehicle due to the additional tolerances in the transfer case.

 

This is a normal condition. No repairs should be attempted.

 

 

 

--------------------

 

 

Bulletin only applies to 4-speeds. There's no band in the 6-speed and the way the trans is controlled is completely different.

 

Daylower, did your BB tune disable AFM?

[daylower]

Daylower, did your BB tune disable AFM?

 

Yeah, Justin pretty much disabled everything but stability control.

[TorkFaze]

BTW, 6-speed learns do not reset with battery disconnect.

 

Odds are the OP's issue is on a 3-2 shift and AFM going from V4 to V8 at the same time. This is why I asked about Daylower's AFM being disabled.

 

It's not likely a 4-2 shift as this trans doesn't usually do 4-2 while coasting.

 

TF