GMC transmission issue
I'm not sure where to post this, but we have a 2012 GMC 3500 Sierra and a Cyclone 3010 5th wheel 35 foot toyhauler. Lately we have been experiencing "clunking" when the transmission drops a gear, ...
Forum Discussion
With Tow Haul mode the transmission runs cooler, which is a key part of the function of this mode. Last week with a heavy load going through the desert with temps over 100 degrees outside and going from 3000 feet to over 7000 feet of elevation the trans temp in my 2011 Duramax/Allison never went above 172 degrees. The GM trans coolers are the best you can get.
Tow Haul changes the operation of the locking of the torque converter and you get hard shifts at times. It is part of the nature of the beast and not something to worry about. The truck has a 5 year 100,000 mile drivetrain warranty. I only get the clunk when shifting with a full load and going up a steep grade - not unexpected under those conditions.
The transmission fluid change out is at 25,000 miles. The external filter should be changed at 7500 miles and then with each fluid change. No reason and no benefit to doing it any sooner with these Allison transmissions.
Tow Haul changes the operation of the locking of the torque converter and you get hard shifts at times. It is part of the nature of the beast and not something to worry about. The truck has a 5 year 100,000 mile drivetrain warranty. I only get the clunk when shifting with a full load and going up a steep grade - not unexpected under those conditions.
The transmission fluid change out is at 25,000 miles. The external filter should be changed at 7500 miles and then with each fluid change. No reason and no benefit to doing it any sooner with these Allison transmissions.
