GMC transmission issue

I'll check with DH and take a look at the fuild. We had it in and would hope that the dealership looked into the fuilds. I don't think we have changed the transmission fuild since we just got the GMC March/May 2012. We have done two oil changes on it since we got it (from what I can remember).

I forgot to mention that sometimes I feel like I 'smell' burning after hauling the RV for a while. I told DH this and his answer was, "It's a diesel, they smell." which I don't agree with. And at the last two (5 hour drive) - when we parked I heard a 'clicking' noise when the truck was in idle. DH doesn't think it's anything but I do.

It was happening before we turned it to tow only and it almost ALWAYS clunks when we down shift. It's more noticable when we have something in tow but happens even when we are driving (on a highway).

Thanks for the suggestions and keep them coming.

larry barnhart wrote:
Doesn't seem likely a 2012 would have dirty trannie fluid.
chevman

'Dirty' as in ash from over heating the ATF

The temps reported in most all gauges are 'mixed' with the rest of the
fill charge.

True ATF temp is at the tips of the vanes where the fluid is sheared

A lot depends on the drivers style (throttle positions, rate of change, etc),
terrain and what is being towed. Guess that then goes along with sizing
vs the TV's ratings

A faulty tranny computer and/or solenoids sticking can have it not
lock up properly. That would then leave it in slip mode, which would
have higher levels of shear on the ATF

May not be the transmission. I've had these symptoms from a universal joint or a pilot bearing.

Doesn't seem likely a 2012 would have dirty trannie fluid.
chevman

I assume you probably have the Allison? If so, in Tow haul mode the shifts can be a bit harsher. That is on purpose. T/H is designed to firm up the shift points and also hold them longer for better power when towing. When letting up on the throttle, and the transmission senses a downshift, like you tapped the brakes it will downshift kind of hard assuming your going down a hill and it needs to change gears to help maintain speed. I think your concern is normal transmission function and you just need to get used to it. If your dealer is good he scanned for any set codes on the TCM. Without any he is pretty much stuck. No one is going to pay for any non issue repairs.

X2 on changing the fluid. Sounds like your torque converter clutch isn't unlocking all the way during shifts. Dirty fluid and varnish can cause the solenoids to become sluggish, which can affect shift quality since things aren't synched up the way they should be.

How many miles and has the fluid been changed ? I have a 2011 and it did that for a few thousand miles after having the fluid changed. It eventually went away.