Pro and cons for dropping to 3.42 gears

KevinD

KevinD

KevinD
Nov 7, 2012
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Thinking about dropping to a 3.42 gear from stock 3.73 what are the pros and cons. I was thinking about the 6 speed conversion but this route is cheaper plus I wouldn't have to take my trans go kit out of my truck. From what I have been told the trans go kit will not work with the sun coast six speed conversion.
 
KevinD

KevinD

KevinD
Nov 7, 2012
48
0
0
The other one wouldn't show up in my threads so I thought I may have placed it in the incorrect spot and got deleted.
 
KevinD

KevinD

KevinD
Nov 7, 2012
48
0
0
I tow. Some times heavy. Just depends if I'm doing a hot shot or just towing my vehicles or camper. I drive the interstate everyday to and from work. 35 miles one way. So just looking to see what I can do to gain a little. 70 miles aday if I got 2 miles better to the gallon it should pay off. Ha might be time to sell and start over from scratch
 
fast03

fast03

Active member
Jun 15, 2008
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not gonna gain 2 mpg with gears. slow down and keep rpms at 1800-1900 and that will get the best mpg. LB7 should be seeing 19-22 with 33's depending on hills, wind etc.
 
KevinD

KevinD

KevinD
Nov 7, 2012
48
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Yeah. I cruise between 65-70. I don't be break 2000 rpm unless I'm showing up a gasser. Haha. I cruise most of the time anywhere I go.
 
Chevy1925

Chevy1925

don't know sh!t about IFS
Staff member
Oct 21, 2009
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KevinD said:
I tow. Some times heavy. Just depends if I'm doing a hot shot or just towing my vehicles or camper. I drive the interstate everyday to and from work. 35 miles one way. So just looking to see what I can do to gain a little. 70 miles aday if I got 2 miles better to the gallon it should pay off. Ha might be time to sell and start over from scratch
Click to expand...


You won't like those gears at all towing
 
V

Vsouth

Member
Oct 6, 2008
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My lbz has 3.42's and I drive on a 265/75/16 tire when towing. I did not see any mileage gain from the gear change. It also leave you with lees than ideal rpm windows versus speed. Truck is happy at 78mph plus in 5th gear putting it right at 1900-2000rpm. In 4th gear I am turning 2000 rpm at 60mph. 65-75mph is no man's land as far as rpm. 4th is too high for me and 5th is to low.

If you are looking for fuel economy, you won't see it with this. A six speed conversion will get you better cruising rpm for freeway driving, but you will not see a mileage increase with it either.

Stock tire, as little weight as possible, and rpms between 1800 and 2000 will get you your best economy. A good tune doesn't hurt either.
 
THEFERMANATOR

THEFERMANATOR

LEGALLY INSANE
Feb 16, 2009
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ZEPHYRHILLS, FL
KevinD said:
Thinking about dropping to a 3.42 gear from stock 3.73 what are the pros and cons. I was thinking about the 6 speed conversion but this route is cheaper plus I wouldn't have to take my trans go kit out of my truck. From what I have been told the trans go kit will not work with the sun coast six speed conversion.
Click to expand...
Don't know where you heard about the TRANSGO problem with the 6 speed conversion, but I'm 90% certain the SUNCOAST 6 speed conversion kit's valve body HAS a TRANSGO Jr already installed. As to the swap, I wouldn't with 33" tires. I have the stock 30.5" tall tires, and love my 3.42's, but I tried it with a 32" tall tire, and was less than thrilled. Took those tires off and sold them after a week, and went back to the stock height tires.
 
KevinD

KevinD

KevinD
Nov 7, 2012
48
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Why didn't you like them? I talked to someone at sun coast that's what he told me. I also talked yo dimitri Millard he was the one who suggested dropping to 3.42's also v south isn't yoir Lbz stock a 6 speed Allison? It should be.
 
THEFERMANATOR

THEFERMANATOR

LEGALLY INSANE
Feb 16, 2009
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To me it just felt like the straw that broke the camels back. I wasn't running a very big tune when I tried the taller tires, but the BURB just didn't feel happy. Went back to the shorter tires and she was a completely different animal. I did do a highway run with the taller tires, and found milage was pretty close to the same(got right around 20.5 VS the 21-22 I was getting with the stock 245/75/16's), but it was a tad lower.
 
KevinD

KevinD

KevinD
Nov 7, 2012
48
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You get about 21-22 in the burbalac nice. Yea I thought about dropping back down to stock height tired but keeping my 20's wondering if that would help me. And keeping my 373's
 
juddski88

juddski88

Freedom Diesel
Jul 1, 2008
4,651
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I say try it. Each truck responds differently to mods, I had great mileage results with a truck I Used a 6 speed conversion with. 33" tires, 7400lbs, lifted and tuned. I've also just recently done a lifted LLY that went from an average of 16mpg with banks tuning on 36" tires to getting a hand calc 24mpg on the trip back to Texas from my shop after being tuned properly. I dont know what his speed was but i know he made the drive in 21hrs which impressed the hell out of me. Not your typical results.
 
TheBac

TheBac

Why do I keep doing this?
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Apr 19, 2008
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Guys, his tires are 33" tall. Wouldn't changing to 3.42s actually make his problems worse? IMO, it'll cause the engine to work harder to get the truck moving, and be a pig accelerating. Mileage would probably drop as a result.

If he had stock size (or maybe 265s), I could see it working, but not with those bigger tires.
 
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