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What gear to run?

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Discussion Starter · #1 ·
A new rear end is the next mod for my truck. Trying to decide between 3.73 and 4.10. Specs are:

weight - 4200lbs
engine - L29 Vortec with Performer intake, 3310 carb, headers, 225/225 @ .050 cam
trans - 4l80e with stand-alone TCI controller
275/60x15 tires (28" tall)

99.9% street driven with frequent freeway jaunts. Occasional highway trips, but with a 16 gallon tank the range is not that great. I do haul stuff, and sometimes tow a trailer.

Currently the truck has a 2.73 peg leg. Surprisingly it pulls pretty good, but the overdrive is almost useless unless you are doing about 95mph. I have an Eaton posi and some 3.73 gears in the garage that I bought years ago for an ImpallaSS but never installed. I realize I would need new axles if I used this posi because the spline count is different. But the question is should I use these 3.73 gears or maybe go with 4.10's? The engine is about out of breath by 5000rpm, so I don't want to go too steep. Which would you use?
 

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I'd use the 3.73's. Going to be night and day compared to the 2.73 and the price is right.
 

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I vote for the 3.73's since this is a 99% street deal. You'll notice the difference more at cruise than WOT. There won't be much performance gain between the two but the couple hundred RPM difference on the freeway will be appreciated with the smaller gears.
 

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I did a quick calculation, I think the overdrive on a 4l80e is .75:1.

So at 65mph, with a 3.73, your motor would be spinning around 2183rpm. With 4.10, you will be at 2400rpm.

Like the other recommendations above, I would stick with the 3.73 for the street use.
 

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With an overdrive trans, 4.10 gears are a piece of cake to drive on the street even on the highway. I installed 4.56 gears in a daily driver that i had with an overdrive trans, and it was great like that for the next 2 years driving it to work on the highway daily. Go with the 4.10 gears.
 

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4.10's and OD behind a 6.0 Silverado... I don't know anyone who drives 65 on I-95 :noway:
I would go something in the mid 3 series like .42's or .55's for the best MPG. I say this because... how much towing/hauling do you really do ?
 

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I think there are differences between the truck gears and the car gears, the car pinion gear may not fit and line up in your truck housing.
 

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4.10's and OD behind a 6.0 Silverado... I don't know anyone who drives 65 on I-95 :noway:
I would go something in the mid 3 series like .42's or .55's for the best MPG. I say this because... how much towing/hauling do you really do ?
Checkout the link below. With the 4.10 gears and a 28" tire height, you'll only be reving at about 2,500 RPM at 70 MPH, and even at 80 MPH, you'll only be reving at about 2,800 RPM. That isn't that bad at all. but yes, it depends on what you want out of this vehicle, and how you drive it. If you want acceleration, and/or you'll be towing a lot, then go with the 4.10's. But if you want the best gas mileage....well then, I don't think that you would even be asking about a rear gear swap if you wanted that.



http://www.richmondgear.com/101032.html
 

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I'd go 373 but 410 would not be a bad choice either with your od trans with lockup.

But comming off the 273s your currnetly running & going to 373 or 410 your vehicle will feel like it got some new found HP/TRQ out of nowhere,thats for sure,the old BUTTOMETER will really like it./LOL!!!!!!

But keep this in mind,when going for such a large change in gear that will spin the driveshaft a lot faster esp at highway speeds of 70mps etc i would at the very least install new joints and then have the d-shaft reballanced.

Most times i have been involved with a sig gear swaps that resulted in the the d-shaft turning a lot faster then it used to more times then not there were vibes isseus comming from slightly worn u-joints (post gearswap) that didnt seem all that bad along with the d-shaft being out of ballance enough to vibrate at the higher d-shaft rpm too but didn't vibrate at lower d-shafts speeds prior to the gearswap.

Scott
 

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Discussion Starter · #11 · (Edited)
The 12-bolt truck has a smaller diameter pinion shaft compared to a car 12-bolt. But I'm pretty sure truck and car 10-bolts, which is what I will be using, use the same gears.

Now one difference for sure is the Impala gears have a provision for a reluctor ring that the anti-lock brakes need. Of course the truck does not need this, but I don't think that would prevent me from using the gears. I should confirm this I guess.

And no worries on the drivshaft. I've already got a 3-1/2" Denny's Nitrous Ready shaft with 3150 U-joints. :D
 

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Greg, the 3.73's will be great on a street deal. I've got 3.73's in my 12 bolt w/ a th400 in front ( same ratios as the 4L80E w/o the OD ) and it pulls hard. I'm switching to 4.11's but only because i need more revs for 1/4 mile racing. 3.73's + the 700R4 I had previously w/ the 454 combo and 27" tires would knock down 16-17 mpg ( imp gal ) and still run 13.7 at the track.
 

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3.73. Still, from 2.73: what a difference! Honestly, I'd go 3.55's--:cool:
 

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I run 4.10's in my '74 chevelle with a 406 sbc, TH350 3500 stall, and 28" tall tires. It is great for around town and for short freeway drives, though I limit my highway speed to around 65 mph. It is not for everyone and buzzes pretty high but I spend most of my time around town so its great for me.
 

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I own a 98 silverado 2500 with the vortec l-29 454 and 3:73 gears and can tell you as far as all around versatility the 3:73 is pretty good. I tow a wide range of things on a regular basis from a loaded double axle landscape trailer, car trailers and a fifth wheel camper and it does just fine. My engine is bone stock except for a K&N cold air intake, mass airflow sensor and accel super coil. Yours combo will be much better in the h.p. and torque dept. so in my opinion the 3:73 should be just fine. I also have the 4l-80e tranny. Now if I got a chip and got rid of the torque management system.......he he!
 

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Discussion Starter · #20 ·
Thanks for the input guys. I've got a line on a complete 10-bolt truck rear with 3.42 gears in it for $75. If if pans out I will buy it just to try for a while.

I still have not made a decision on which gear to go with for the long term though. And to complicate things further, after I posted this I remembered I've got a Mopar 8-3/4" rear housing and a 489 carrier already set up with a Detroit Locker and 4.10 gears. All I would need to get to build this rear end up is a set of axles with 5x5 bolt pattern and some new drums. hmmmmm.
 
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