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Allison 3000 Speeds and Indicators

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When driving my RV, with an Allison 3000 transmission, I can see it shift through the following "7" speeds, even thought it is a 6 speed transmission (see below).








Does anyone know what the "C" and "L" mean. I'm thinking the "L" might mean "Lock", but even if I am correct (not sure I am correct), what does the "C" stand for and why do I have "7" vice "6" speeds on a "6" speed transmission?




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found this on a transmission info sites:


Description Allison 5th Generation Electronic Controls with closed loop adaptive shifts
Shift Sequences [C = Converter mode (lockup clutch disengaged); l = lockup mode (lockup clutch engaged)]


  • Option 1: 1C–[1l]–2C–2l–3l–4l–5l
  • Option 2: 1C–[1l]–2C–2l–3l–4l–5l–6l
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ASK and the Google Genie, if properly phrased and fondled, will provide satisfaction….

It is pretty hard to find a Class A Diesel motorhome without an Allison 3000 or 4000 transmission. There are a few, but not many. One exception is the Newell with a ZF-ASTronic 12-speed. I don't know what the Prevost conversions use. The Allison 3000 and 4000 work the same but the 4000 is for about 400 horsepower and up. 

It is a standard feature of the Allison to provide "lock up". My rig has a computer screen that shows the gear and mode. From a dead stop it starts in "1C". The "C" is for clutch. At about 5 mph it "shifts" to "1L". The "L" stands for lock. It will continue shifting through "2L", "3L', "4L", "5L" and finally at about 59 mph it will end up in "6L". 

The standard Allison provided shift pad only shows the numbers. 

In REALITY….you ONLY have 6 forward gears….but, first gear is “clutch engaged”….the Locked….as in the Torque Converter is locked….

NOW….continuing to ask….gets this….

All Allison 3000 and 4000 transmissions lock up in "high" second gear (at higher RPM) and ARE locked up in 3,4,5 and 6th gear. If you listen/feel very carefully, you will feel the "mini-shift" in second as the converter locks up and see the engine RPM drop on the tach.

Having the converter locked in all higher gears materially lowers transmission temperatures, increases efficiency and allows for an efficient engine/exhaust brake.

I called Allison for confirmation. Yes they do have applications where the torque converter is locked in 1st gear, but more oil field equipment, etc.

Bill,  yours could be programmed to lock up in 1st but the tech I talked with said it would be very unusual in an RV application. You might give Allison a call with your transmission serial number to verify just for curiosity sake: 800 252 5283

BTW….if our Monacos were using the Option 1, we would never….I REASON….ever see “6”.  There is a performance and economy/standard mode.  It changes the “speed (related to RPM) shift points”.  In the performance you shift at a higher RPM/speed…so you get max Torque….but the final 5 - 6 shift point is the same.  But….if you use the Standard/economy mode….then the “downshift” out of 6 to 5 will be at a LOWER RPM…so you can lug up a grade….and not shift into 5….thus you get better economy.  Mine has a “economy rear end” or a higher ratio….as in i need a higher shift point (62 MPH) than a Dynasty with same engine/tranny.  The Dynasty has a lower ratio….so it shifts around 56 MPH.

I can get down to maybe 53 MPH on a straightaway with Economy….and then it will downshift…. In performance….it will shift around 58 MPH.

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