Allison Transmission Question

[MartyH]

Good day,
New to me a 2008 Tiffin Allegro Bay 35TSB, Cummings I6 6.7, 6 Speed transmission with overdrive.

Couple questions?

When driving, the transmission smoothy shifts through the gears till 5th, at 62 mph, it is revving just below 2000 RPM, does not seem to shift into 6th or overdrive automatically, if i press the mode switch, a light appears above the mode switch and into 6th it goes bringing the RPM's down to about 1600, as i slow down the transmission normally drops down.
Would this be considered normal operation?

The manual speaks of using the up down buttons to manually shift, is it just that simple to gear down as i am climbing a hill or as I am cresting the hill to use the engine and transmission to descend in control.

The chassis and engine info does not explain that mode button very well

New to a diesel and lots of questions

[d23haynes57]

Originally Posted by MartyH

Good day,
New to me a 2008 Tiffin Allegro Bay 35TSB, Cummings I6 6.7, 6 Speed transmission with overdrive.

Couple questions?

When driving, the transmission smoothy shifts through the gears till 5th, at 62 mph, it is revving just below 2000 RPM, does not seem to shift into 6th or overdrive automatically, if i press the mode switch, a light appears above the mode switch and into 6th it goes bringing the RPM's down to about 1600, as i slow down the transmission normally drops down.
Would this be considered normal operation?

The manual speaks of using the up down buttons to manually shift, is it just that simple to gear down as i am climbing a hill or as I am cresting the hill to use the engine and transmission to descend in control.

The chassis and engine info does not explain that mode button very well

New to a diesel and lots of questions

The "Mode" switch sets an "Economy Mode" changing the shift point to improve fuel economy. That is a low torque engine, so it is allowed to spin a bit to make power. In normal mode it may need more than 62 mph to go to sixth if it is still trying to accelerate. Try lifting your foot. Gear selection is controlled by speed and throttle position. When cruise control is active the economy mode does not function.

[Skip426]

All Allison transmissions are not created equal, nor are all Cummins 6.7L ISBs.

Is your ISB a 340 HP version or 360 HP.

Do you have an Allison transmission series number for your coach ? 2500 or 3000 ?

Does the shift pad say Allison ? Freightliner or Arens ? on it ?

[SafariBen]

I can only speak about my MD3060, it is simple to shift, but what you're shifting is the desired gear, it won't do any shift that's outside the parameters. So if you get going down a hill 75mhp, and shift down to 2nd, it will only shift to the lowest gear that won't overspeed the engine. If you shift to 4th going slow at the top of a very steep hill, then don't use the brakes so that the engine reaches it's max speed, the trans will shift to 5th despite the "desired" gear being 4.



Also, the mode button can be programmed to any of a number of options, if the owner was so inclined and knew the right people. I drive one that the mode button is overdrive (sixth unlock), I haven't figured out what mine does yet.

[Elictrix]

I will assume that you have a MD3000 series transmission with an Allison push button selector.
This is a 6-speed transmission. 4th gear is direct drive (1:1) and 5th (0.75:1) and 6th (0.65:1) are both overdrive gears.

The Mode button can be programmed to many different functions depending on the application/vocation, eg PTO, 2nd gear start, etc.
The default is Power/Economy if not programmed for a special function.
It looks like your one is set to have Power as the primary mode and Economy as the secondary mode when you press the mode button.

In Power mode the engine will rev a bit higher before upshifting to the next gear. This is to get the engine speed up into its maximum power band and to ensure that the engine speed after the shift is sufficient to hold the new gear. You don't want shift cycling or hunting between two gears. You may have to let the engine rev up to 2100rpm to shift into 6th? You can also try lifting your foot slightly to see if it will upshift.

In Economy mode the engine won't rev as high before shifting into the next gear. This can save fuel but can be an issue if the engine hasn't got enough power to hold the new gear.

Possibly push the mode button to engage Economy every time you drive it and see how it goes. You can go back to Power mode if you have to.

Pushing the down arrow to a lower gear just determines the highest gear that the transmission will shift into.
If you arrow down to 4, the transmission will shift normally between 1st to 4th gears, eg 1-2-3-4-3-2-1. It will not go into 5th.

When going up hills, arrow down to a gear that will keep the engine speed up in the power band.

When going down hills arrow down to a gear that will keep the engine speed up so that the exhaust brake will work effectively. The exhaust brake needs high engine speed to give the most braking effect. It won't work much if the transmission upshifts to a high gear with a resulting low engine speed.

[SafariBen]

Originally Posted by Elictrix

...Pushing the down arrow to a lower gear just determines the highest gear that the transmission will shift into.
If you arrow down to 4, the transmission will shift normally between 1st to 4th gears, eg 1-2-3-4-3-2-1. It will not go into 5th...

The arrow will set the DESIRED gear, the trans won't shift to 5th even if you floor it, but it will shift to 5th going down hill if you exceed the engine speed in 4th.

[MartyH]

I will verify the exact info that you have asked or in the next few days