What is normal operation for the Allison?

[DIESELMAX403]

When pulling an 8000# load up a slight grade at 70 mph and the Allison downshifts into 3rd under full throttle, my rpm's hit max (3250) and then drops relatively quickly to about 2800-2900 rpm before power is felt. Is this normal? It almost feels like the tranny is slipping. I can not tell anything from my temp gage as it stayed rock solid on 190 degrees my entire trip.

Also, I do not get much power in first gear. Once it shifts at 20 mph I feel more power in 2nd gear. I would have thought that with such a short gear there would be plently of acceleration felt. Am I mistaking?

[DonG]

DIESELMAX403,

You need to give your truck some time to break in and "learn" how to shift properly. This takes many miles. Many report better power AFTER 20,000 miles.

The Allison is more likely downshifting to 4th, not third. It does not make a 2 gear jump unless you force it into 3rd, and even then it will not go if the rpms would be too high.

The Duramax engine is defueled in first gear because the torque would be too much for the system. Full power is applied in second gear.

No one can "lay rubber" from a standing start with a stock Duramax/Allison without doing something special, like spooling up the turbo.

I would recommend the search feature on this forum. Most of your concerns/questions have been talked about in the past.

Don

[DIESELMAX403]

Don,

Thanks for the info. Opps, when I said 3rd, I meant to say 4th. It is definitely not jumping 2 gears. Until now, all the transmissions I have messed with have been 4 speeds.

Thanks again

[Searay90]

The RPM drop you are seeing is when the Torque Converter clutch locks back up after the down shift.

[mdrag]

Transferred to the 2500HD/3500 HD Trucks & Drivetrain forum.