Allison 6 Speed Transmition

From the brochures I downloaded it appears that the 6-speed Allison has a double overdrive and a manual mode where you select "M" with the shifter then shift between gears with an up-down rocker switch on the end of the lever. From what I've been told, the only real difference is the computer programming, the guts of the tranny are the same between the 5-speed and the

6-speed, and that after the 6 becomes available you should be able to have your 5-speed tranny's computer reprogrammed to give you the double overdrive. The only thing is if you make the 5- to 6-speed conversion you won't have the manual mode - no problem in my opinion. If/When the 5 to 6 conversion comes out I'd do it in a heartbeat.

Cheers - Jonathan

linking

Upper midrange gears likely becaue 1st, 2nd and 3rd are well spaced but 3rd to 4th and 4th to 5th as not compared to the first 3 gears. A taller OD would serve no purpose.

Upper midrange gears likely becaue 1st, 2nd and 3rd are well spaced but 3rd to 4th and 4th to 5th as not compared to the first 3 gears. A taller OD would serve no purpose.[/quote:feb35cd8fc]

I stand corrected here are the specs for it

GEAR RATIOS First 3.10 Second 1.81 Third 1.41 Fourth 1.00 Fifth 0.71 Sixth 0.61 Reverse -4.49

Big mistake because I have drive them and there is a big RPM drop from

3rd to 4th and even more going to 5th and this new tranny will not fix this at all somthing like below would have been nicer

GEAR RATIOS (wishfull thinking) First 3.10 Second 2.12 Third 1.72 Fourth 1.32 Fifth 1.0 Sixth 0.73 Reverse -4.49

I this would help a lot with a load on a hill accelerating.

With a .61 OD the impressive 600FTlbs of a Dmax is down to 366ftlbs and even a 6.0 has more torque than that in drive pulling and can rev to use it too. Somehow when people think about that torque, they loss site of the fact that as you gear it taller, the torque advantage disappears. GM would have been better servered with another gear in the middle and not on top.

Hey SnoMan,

I think the point of the extra gear on top is not anything at all about pulling or hauling but strictly to reduce RPM's on an unloaded truck at top end to try to get a few extra MPG. I haven't been able to confirm this, but I've heard folks talking about the Tow/Haul mode on the 6-speed not only changes the shift points but also locks out 6th gear. Overdrive lock-out will lock out 6th and 5th as well. Drop it out of OD with the shifter and you only get 1st - 3rd. And of course 6th will drop your torque down to

366ft-lbs, you don't need 600+ pushing an empty truck down the highway!

Cheers - J>>[quote:feb35cd8fc="Charlie"]I was in The GM Dealer this week and he

shifter

I agree that that is what it is meant for but I have read lots of posts were guys boost engines a lot to tow big loads in OD and blame tranny when it fails and this will open door for more failures and send wrong message I fear.