GMC transmission issue

JustLabs wrote:
As far as the clicking noise,does it sound like a typewriter? If so,that's a common sound from a duramax. Most of them do it under the right conditions. Mine does it more for the first few hundred miles after an oil change.

There is a TSB from GM that says its completely normal.

A well known "characteristic" of the Dmax which is well documented on many forums. Mine does it to for the first few hundred miles after oil change. Most noticeable when pulling up to a drivethru. Just Google "Duramax typewriter"

Bob Vaughn wrote:
I had a simular problem with my 2500 chevy when I first bought it.....no dealer could figure out what was making it do it.......after a couple of years of dealing with it I took it to a private transmission shop. Within 2 minutes of driving the vehicle the owner of the shop showed me on the computer what was wrong. He promised to fix it and if he didn't I did not have to pay him....the best 1700 dollars I ever spent. That was 5-6 years ago and it has never done it again.......

And exactly how does your story here help anyone if you don't describe what the actual problem was that the guy fixed...

wintersun wrote:
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.

I have a 2012 Dmax/Ally and found out from some very knowledgeable people over on the DMax forum recently that the new 2011+ Allisons run so cool is because they run lower line pressure than previous Allisons and not due to the factory tranny cooler which was described as "average" at best. There are better aftermarket ones out there but really not needed due to the lower line pressure and resulting lower temps these things see in stock form even pulling heavy loads up steep grades.

I had a simular problem with my 2500 chevy when I first bought it.....no dealer could figure out what was making it do it.......after a couple of years of dealing with it I took it to a private transmission shop. Within 2 minutes of driving the vehicle the owner of the shop showed me on the computer what was wrong. He promised to fix it and if he didn't I did not have to pay him....the best 1700 dollars I ever spent. That was 5-6 years ago and it has never done it again.......

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.

No issues with ours - about 23,000 miles - at least 1/2 towing. I changed over to TranSynd fluid in the tranny after my first tow - drain and fill twice - changed the external filter after the second drain.

If you have not changed the rear end fluid - that needs it too - you would be surprised what the fluid looks like on the first drain.

As far as the clicking noise,does it sound like a typewriter? If so,that's a common sound from a duramax. Most of them do it under the right conditions. Mine does it more for the first few hundred miles after an oil change.

There is a TSB from GM that says its completely normal.

Have you talked with the service manager yet? Make him aware of the situation. He might take the situation more serious than that service writeup guy.

Transmissions nowadays adapt to how they are used and the shifts could get harder when loaded.

Brand new GMC HD truck and my allison does the same thing. I came from a half ton and was a bit surprised, to the point I took it to the dealer. They checked the fluid and codes, all good. The tech said its normal and a lot of drivers moving up to HD trucks experience this.