Gear change and Allison Transmission

by Schleprock on 5/2/2011, 5:20 am

Has anyone changed their gear ratio on their TV that also has an Allison Transmission?
I need to upgrade mine from the 3.73's to something that can handle the Rockies. Then I am worried about it messing with my Allison tranny?
Think I could have the tranny "reprogrammed" or just let it "relearn" itself without having any issues?

by Portagie1968 on 5/2/2011, 5:39 am

by MountainMan on 5/2/2011, 11:12 am

I doubt it would affect your tranny much unless you went with a crazy low gear.

I will offer a little experience with gear changes though. I've had it done several times in my Jeeps. Don't just go to the next gear lower 4:10 and expect a world changing effect. Matter of fact, I would not consider the expense of a gear change for one jump in gears. 3:73 and 4:10 are very close and I doubt you'll notice much difference when towing.

If I'm spending the money for it, I want to feel the difference. I would go to 4:54 and be sure I got what I was after.

by mattebury on 5/2/2011, 1:18 pm

You've got 4x4, so you'll have to change your front differential too. Personally, I'd go no lower than 4.10 unless you are towing real heavy and all the time. The MPG hit from driving around town will be less with 4.10 than 4.54. I've got 4.10's on my Ford and can pull the grades with no problem with the Cat. It's fun to wave at my brother and his 3.73 in his Chevy as we hit the local mountains on the way home from the desert. He always manages to give me the one finger salute. Huh, go figure. Very Happy

by schrowang on 5/2/2011, 5:21 pm

Reprogramming depends on your truck's computer. Some can learn and some have to be manually programmed (usually by the dealer).

If it were me, I'd just use a lower gear going uphill and down and use the exhaust brake going down too. I don't think the change from 3.73 to 4.10 will make much of a difference, except in your pocketbook (fuel and the cost of the changeover).

by Mopar_Earl on 5/2/2011, 6:28 pm

3.73's are perfectly fine for any public mountain roads. Big rigs normally run 3.55's and have no probs pulling 80K up a mountain. The trans will downshift as needed. If your hitting steep mountain trails, just pop her in 4-low.

Earl

by mattebury on 5/3/2011, 1:31 pm

Mopar_Earl wrote:3.73's are perfectly fine for any public mountain roads. Big rigs normally run 3.55's and have no probs pulling 80K up a mountain. The trans will downshift as needed. If your hitting steep mountain trails, just pop her in 4-low.

Earl

But big rigs can have up to an 18-speed transmission . . . You can't compare a big rig to a pickup Very Happy

by Mopar_Earl on 5/3/2011, 5:34 pm

mattebury wrote:
Mopar_Earl wrote:3.73's are perfectly fine for any public mountain roads. Big rigs normally run 3.55's and have no probs pulling 80K up a mountain. The trans will downshift as needed. If your hitting steep mountain trails, just pop her in 4-low.

Earl

But big rigs can have up to an 18-speed transmission . . . You can't compare a big rig to a pickup

Most only have a 10 speed trans, better know as the super ten. Fleet company's are too cheap to buy more than a 10 speed. Plus it's really not needed unless you're hauling overweight loads often or doing off road work. Axle ratio is axle ratio and doesn't matter if you have 2 speeds or 21. The only time you'll find 18 or 21 speed trans are in logging, off road, oversize haulers and some owner operators that like the extra gearing for bragging rights.
Other than their air brakes, weight ratings and size, class 8 trucks aren't much different than light duty trucks. They even share the same size king pins.

Earl

by joelabq on 5/4/2011, 3:06 pm

I'm surprised someone with a 5 speed Auto and an 8.1L engine wants more than 3.73s. The 8.1 already drinks gas pretty good, I don't think the gear ratio change will make it any better, and empty will make it worse.

I live in New Mexico and my uncle used to have an 8.1L. It worked over the rockies just fine, including some of them outside of Durango. He went the wrong way out of Yellowstone once at got to a 10% pass. Said it was still moving forward but conditions were foggy and had to turn around anyway.

Joel

by Schleprock on 5/6/2011, 4:17 am

Last year we drove over the Rockies (I70) to camp in Rifle, Co. and the truck was struggling pretty bad. I couldn't get her above 35 on some of the inclines and the 8.1 was screaming just to get up and over the pass. (RPM's were hovering around 3800).

Leaving it in 2nd or 3rd winds the RPM's up WAY too much for my liking so I was thinking maybe a gear change......

The Cat was packed with food only, no water, so I wasn't even close to the max trailer weight. Not sure what else I can do? scratch

by Glen Schumann on 5/6/2011, 4:58 am

You need a diesel. Your 8.1 is losing power with every foot gained in elevation. That may very well be a larger issue than the rear end ratio. Diesels do not lose power at elevation.

by MountainMan on 5/6/2011, 5:59 am

Schleprock wrote:Last year we drove over the Rockies (I70) to camp in Rifle, Co. and the truck was struggling pretty bad. I couldn't get her above 35 on some of the inclines and the 8.1 was screaming just to get up and over the pass. (RPM's were hovering around 3800).

Leaving it in 2nd or 3rd winds the RPM's up WAY too much for my liking so I was thinking maybe a gear change......

The Cat was packed with food only, no water, so I wasn't even close to the max trailer weight. Not sure what else I can do?

Thats exactly why I recommended jumping two ratio's. Even that big ol' 8.1 will turn some serious rpm's over those long, steep mountains. One small step lower in gear ratio simply would not make enough difference to justify the cost for me.

A gear change would help but it will cost MPG's unloaded as others stated. ( I think you may actually gain a little towing if you keep your speed down on the flat land.)

Is your truck a daily driver or just a tow vehicle? If its primarily a tow vehicle and the mountains are your thing... Its either simply slow down to a crawl (Use 4 Low if needed) or an expensive gear change.

The ultimate option is Diesel. There is no describing the difference in towing ability. Its something you must experience yourself to believe.

by onetonford on 5/6/2011, 8:54 am

Over Under two speed splitter by gear vendors is another way only it is very expensive!

by Mopar_Earl on 5/6/2011, 12:21 pm

Glen Schumann wrote:You need a diesel. Your 8.1 is losing power with every foot gained in elevation. That may very well be a larger issue than the rear end ratio. Diesels do not lose power at elevation.

Very wise advice!

Earl

by Mopar_Earl on 5/6/2011, 12:29 pm

Schleprock wrote:Last year we drove over the Rockies (I70) to camp in Rifle, Co. and the truck was struggling pretty bad. I couldn't get her above 35 on some of the inclines and the 8.1 was screaming just to get up and over the pass. (RPM's were hovering around 3800).

Leaving it in 2nd or 3rd winds the RPM's up WAY too much for my liking so I was thinking maybe a gear change......

The Cat was packed with food only, no water, so I wasn't even close to the max trailer weight. Not sure what else I can do?

Sounds normal for a gasser. That's why you don't see gasoline engines in anything but light trucks and cars. Only two ways you're going to pick up speed. One is install a turbo system if they exist to help with the elevation as NA engines lose power as the elevation goes up OR upgrade to a diesel truck. As long as your below redline, you're fine. If the truck isn't hot, it's handling it well. I'd be more worried about trans temp and coolant temp myself. If you go 4.10's or greater, your RPM's will be higher yet for the same road speed.

Earl

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Gear change and Allison Transmission

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