what's the easiest way to find my diff gear ratio? I have an 03 C5500 with allison, and I'm cruising at about 70 mph and turning around 2550-2600 rpm. I believe this truck is in tow/haul all the time, as I don't have the on-off switch for it. Any help would be appreciated...is there a code on the diff itself?

Code in the glove box I believe. Not sure what code is what though.

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4.44:1
1 - (Requires diesel engine)
2 - , (Requires diesel engine and GL8 or H08 rear axles)
3 - , (Requires diesel engine and GL8 or H08 rear axles)
4 - , (Requires diesel engine and GL8 or H08 rear axles)
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004
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thanks Max..no glove box tho...hehe


this code will be on the sticker with all the alpha-numeric codes on it? It was on my visor when I bought the truck and I moved it to the centre console..I'll check tomorrow for one of those codes.

Just bought a new 4500 RV hauler, Duramax automatic and my rear-end code is 004 4.78 ratio, at 65 mph my tach was running 2300 rpm in 5th gear. Hopes this helps, Also, you can check the tow-haul button on dashboard.





the animalEdited by: animal

yep mine's code 004 as well..no tow/haul on the dash..I do have an overdrive defeat button tho...