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3:73 gears?

C

Cheapazz

Full Member
Joined
Jul 16, 2015
Messages
82
Location
Reno, NV
Just changed the rear diff fluid and noticed the gears have a scoring on them, not polished at all. I was thinking of installing 3:73 gears since I am running 285's and will be going to true 33's next. On an 09 z71 6 speed trans with 3:42 gears now. What is the stock rpm's at 70? Right now mine is just under 1700 at 70. The only trucks I have to compare it to are work trucks, one is a 3500 and runs just about 2100 and a 2500 that is about the same, both are completely stock. I'm hoping that's where I'll end up. Any input is helpful. Thanks!
 
That 3/4ton and 1ton diesels or gas?
 
Dang, a 1ton with a 6.0, I can understand that seeing high RPMs. I was going to say earlier both of my F350s see 1500 at 70, they don't even hit 2k until 85. Both have 3.55 gears and run 275 65 30

From what I know, I'd say you could get away with the 3.42, but you will lose mpg, and your truck will move a but slower
 
james21 said:
Dang, a 1ton with a 6.0, I can understand that seeing high RPMs. I was going to say earlier both of my F350s see 1500 at 70, they don't even hit 2k until 85. Both have 3.55 gears and run 275 65 30

From what I know, I'd say you could get away with the 3.42, but you will lose mpg, and your truck will move a but slower
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I have the 3:42's and was wondering about the 3:73's. Probably will go that route.
 
Going to 3.73 gears from the 3.42 your rpms will increase by 9% in same gear and locked torque converter.  (3.73/3.42 = 1.09)

Use similar math with the tires diameter, although larger tires decrease instead increase rpm.  If going from say 32 to 33 diameter tires rpm will decrease by 3%.  (32/33 = 0.97)
 
Cheapazz said:
Guess I'm not smart enough to figure it out, couldn't even get it to match what I have now. Too many variables not included in that calculator,  I'm thinkin.
Click to expand...

There are.  You probably have the 6-spd transmission which has two overdrive gears and no direct drive gear.  The 4-spd has one overdrive and one direct drive.  The calculator probably assumes specific transmission ratios that are different than what we have.

FWIW, I'm running 3.73 with 35" tires and the 6-spd and my performance is basically like stock 3.08 with factory tires.  That means that 3.73 with 33's would probably run just like it did with factory tires.  Might even correct the speedometer for the most part without needing a programmer.
 
That's what I'm looking for, close to stock rpm's. Not building a hot rod, just want a tick better umph.
Thanks for the input y'all!
 
Got em installed. Good improvement, just what I was wanting. Would have loved some 3:90's but the front gears were more than I wanted to spend.
Just some info, apparently the 2009 is a bastards year for rear ends. Everything I bought for it for the ring and pinion install was wrong. Too small. Apparently the best guess for it is buy for a 2010 and it'll work. Only place that had that info was a local rear end shop and they sold me the bearing kit, none of the parts houses had a clue and we have em all here (almost all). Time for the mileage tests...
Thanks for the info!
 
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