Allison + 6.5??

[mobilevet]

I want to get better highway mileage from my suburban (see sig). I was wondering if putting in a 6 speed Allison to replace the stock transmission would do that and if that were a doable conversion?

thanks for the opinions

[DmaxMaverick]

No. It would be an exercise in futility. Even if you fronted the cost of the transmission, needed parts and conversion time (yours or a shop), you won't live long enough to recover the expense with increased economy, if there would be any at all. The Allison MT1000 is a medium duty tranny, and has a higher parasitic loss than your current tranny (requires more energy/power to operate).

If your intent is to increase your final drive ratio, there are much better, less expensive, less conversion-intensive, and much more common solutions. A gear ratio change or Gear Vendors auxiliary transmission are infinitely more practical.

[More Power]

And.... there's the factory 6L85 and 6L90, and there's an aftermarket 6x conversion offered for the 4L80.

All would require a custom programmed stand-alone TCM. Total cost, as DmaxMav suggested makes it not too cost effective for a potential fuel economy improvement.

Parasitic loss in the transmission is a factor in fuel economy. I'm considering the difference between a 700R4 and a 4L80 for a purely fuel economy rig.

Jim

[mobilevet]

I appreciate the replies. I'm just a bit jealous of those that can run 70 at 1500 rpms instead of the 2500 mine turns! Also, - maybe a different topic, but - it seems that the Dmax's that I've ridden/driven seem a whole lot quieter than my 6.5...???

[DmaxMaverick]

A lot of the noise reduction is due to body and chassis refinements, and not necessarily engine noise. The Duramax trucks are quieter, and more quieter as the model years increased. Noise specific to only the engine is very similar, with only a slight edge to the Duramax, comparing stock to stock, RPM to RPM, and highway speed to highway speed. Once modifications enter the equation, it can go in either direction for either engine/vehicle.

If you want to lower your cruising RPM, there are several ways to do it, with an Allison conversion being the very last on the list, for several reasons. The simplest would be an auxiliary transmission, which would allow you to keep your current gearing for other conditions. A gear ratio change is the least expensive, but is a permanent change that affects gearing across the entire operating range. Tire size change can also be considered, but this usually is a trade-off of RPM/gearing for mileage (no change, at best).

Or..... Just drive slower. Less noise, and you get the advantage of increased economy.

[mobilevet]

Well, I still run 2.25k rpms even at 65 and I'd never get my calls done poking around slower than that... that aux trans is interesting... never heard of that.. i've done a gear swap before - but the other way to get a little Toyota to pull some 35" tires.... you have a link for the aux trans??

I just figure one day the current trans is going to go kaput and was wondering about the Allison as a replacement...

oh yeah - any ideas on noise reduction??

[a5150nut]

Look for GearVendor trans

And noise reduction, some extra waffle pad and thick carpet.

[DennisG01]

You must have 4.10 gears? I have 3.73's and at 70 (with 265 tires and the VSSB adjusted properly for the tire change) I run a tad bit over 2100RPM.

This is going back a ways, but I'm about 99% positive that I lost some MPG when I went to 265's. But, I didn't keep good enough fuel records back then to verify.

Do you use your 4X4? I would imagine that removing the front drive stuff could help. BUT, I can tell you from experience that ONLY removing the front driveshaft won't make any noticeable differences.

I like the idea of a GearVendor, but even that is on the costly side -- referencing the time it would take to recoup the savings in MPG, anyways.

Dropping your gears down to 3.42's might be a good idea?