In a truck magazine I noted a new product from Gear Vendors for Duramax with Allison that will provide up to +20% better fuel mileage.
It bolts up in place of the 8 bolt tailstock and requires the drive shaft to be shortened. At the cost of diesel fuel and slightly over $3K for the unit, the math begins to look like a reasonable investment.
What year truck do you have? If its a 5 speed model, you can just do the Suncoast 6 speed conversion, and be into it for about half the cost.
See, its $3k for the GV, then you have to have it installed, and have the driveline shortened. More money. . . . .
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I have a GMC 2005 Duramax w/Allison 5 speed that is being driven fewer and fewer miles all the time - so a more cost effective Suncoast conversion is an ideal alternative considering I can also wrench it myself.
Also the Suncoast literature at least shows the applicable gear ratio changes (.71 final becomes .61, and at same RPM the effects on road speed changes from 62mph to 72mph with 3.73 gears).
I put a gear venders in a 2000 powerstroke dually that had 4:10's. Lowered the rpms by 3-400 but saw no real mileage gains, but it was a lot nicer on the ears at the lower rpm. The best mpg was around 17 and I had a mild chip, 4" exhaust and K&N filter. Also had to have the driveline done twice since the first guy did a terrible job of shortening and balancing it. Save your money, I would not do it again.
__________________ 2005 GMC Sierra 2500hd SLE, 4X4, Allison 5 speed, Extra Cab-short bed. 6.6 Duramax, Stan's Headers 4" Turbo back w/cat opened to 4", PPE Economy, BFG's, MB Alloys.
jskylar - thanks for sharing your own experience with the Gear Vendors OD. That seems almost a triple disappointment to me - cost, no significant mpg improvement, and complications with cutting the driveshaft. Clearly the 6 speed conversion by changing valve bodies at half the cost seems a better route, although by my calculations it is still a 5 year payback at $5 per gal.
check out last issue of diesel power then did a gear vendors and it hurt mileage dramaticaly
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