6 speed Allison question

froggman180 · 03-28-2007, 03:32 PM

I am planning a transmission swap in my 1998 H1. The donor transmission is going to be an Allison.
I was wondering from anyone who has experience towing how is the 6 speed compared to the 5 speed?

Right now I am having a hard time finding a 6 speed, but I have found some 5 speeds for $900 to $1000. I know if I can find a used 6 speed it would be at least double.

Would that extra overdrive on the 6 speed benifit my truck?
Would the extra money that I would pay be worth it?

My hummer is over 10,000 lbs and has very poor aerodynamics. But I guess anyone towing a large 5th wheel is also heavy with limited aerodynamics.
Thanks for any help,
Duane.

**aggar** · 03-28-2007, 07:19 PM

The 6 spd would give you 1 more gear and bring your rpms down a little and help keep the strain off your motor and it might help it stay cooler by not overworking it. I've got a 6spd and dad has a 5 spd. I like mine better b/c it idles back more and its got the manual shift option on it also and I don't know if that'd work in your H1.

froggman180 · 03-28-2007, 10:13 PM

Thanks for the info.
How is it when your towing? Does it go into overdrive in both 5th and 6th?
The reason I ask is that my Hummer is about 4,000 lbs heavier and has awfull aerodynamics, so I dont drive much faster than 60 mph. I usually keep it between 55 and 60.
I am trying to estimate if I will get any use out of the 6th speed at all, considering the weight and shape of my truck.
I think the best way to make a comparison is a standard truck (no modifications engine or transmission) towing a standard small to medium sized 5th wheel. How does the Allison perform? On a flat road does it get into the overdrive 5th and 6th?

**TYREBOYZ_DEMAXIN** · 03-29-2007, 05:46 AM

at 54mph it slips into the 6th gear and stays there even if you coast down to 46mph if you don't give it to much fuel you can hold 6th gear and regain your speed with out down shifting,i have a 05 LLY with the 5speed and a 06 LBZ with the 6speed and the 6th speed handles the loads alot better and runs down the interstate at 1750rpm's doing 70mph..sun coast transmission builds a conversion kit that will take the 01 thru 05 stock 5peed ally and make it into a 6speed and still have the same tranny as befor only with the 6th speed http://www.suncoastconverters.com/gmc/gm_products.html good luck there,keep us posted on what happens

06LBZ · 03-29-2007, 08:16 PM

you ought to look into the H1 alpha, i believe it already has an allison and a duramax!!!!! nice