4 speed vs. 6 speed transmissions.... is there a big difference?

[WiJeff]

Just wondering if there is a big difference in a diesel rig with a 4 speed vs. the newer 6 speed transmissions? Is it more to do with mileage or just engine performance? I'm new to all of this so any info will help. Thanks, Jeff

 

[Marc L]

The more gears available, the more the engine can be in the optimum power band throughout various speeds and conditions.  Every engine has less power at very low RPM and it drops again once you get really high RPMs.  So with more gears, you don't have to stretch each gears as much, so the engine does not end up in the really low and high RPMs.  Now diesel engine are better than gas when it comes to have power in most of the range, but they can still take advantage of more gears.  That's why 18 wheelers have so many gears.

 

[Jeff]

Jeff:

Yes.

Jeff ;D


With a few exceptions on the very high end and the older low-powered diesels most units today use the Allison 3000 series 6 speed transmission. It provides a combination of Murphy-proof service and smooth shifting throughout the speed range.

 

[John From Detroit]

You know,,, One of the more interesting things about these forums is when someone says

"Which is better: This make or That make"

Or "What is the best make of _____"

Well, it's like two people walked into each other's church and shouted "MY RELIGION IS BETTER THAN YOURS"

But when someone says "What is the best transmission?"

The sound of ALLISON!!!!  drowns out even the slightest mention of another brand

And since my rig has an allison 5 speed... I agree.