Rear end gears??? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Oldironracing · 01-19-2018, 09:47 AM

What rear end gear to run with a 4L70E and LS3 500hp???

**Clyde65** · 01-19-2018, 10:55 AM

Depends on tire size and what objective you have, speed or driver.

Normally a 3.42:1 is the go to! But a 3.73:1 is what I run with my 4l60e.

**mongocanfly** · 01-19-2018, 12:02 PM

use a rpm calculator to determine what you need. ...one like this. ...http://www.csgnetwork.com/multirpmcalc.html

**GMC-YA68** · 01-19-2018, 02:27 PM

I'm going 3:73 in my C10 with 4L60E and 27-28" tires.

Steve Cole · 01-19-2018, 02:56 PM

I will also be using 3:73:1 in my stock 5.3 / 4L60E combo.

Custom 68 · 01-19-2018, 03:38 PM

In my 1968 truck I have the 12 bolt truck rear. It seems limited to either 3.08, 3.73 or 4.11:1. There might be some on the extreme ends I don't remember but I have not found the 3.42 or others in that range. You may have a different rear end so you may have those options. I am running 3.73:1 my trans is a 4l80 so it is geared a little different.
Dave

ls1nova71 · 01-19-2018, 05:11 PM

I'd go with 3:73 if you're starting from scratch. I have that in my Blazer with a 6.0 and its a nice gear. My Green truck with the 5.3 has the factory 3:08 posi and I feel like it hurts it a bit, just a little too tall of gear for the overdrive.

BR3W CITY · 01-19-2018, 09:22 PM

3:73 is the one-size-fits-all recommendation for swaps IMO, especially since the 12 bolt variation is fairly common, and if you switch rear ends staying with 3:73 is easy across the board. I run it in my 12 bolt and its quite good behind my 6.0

Oldironracing · 01-20-2018, 10:59 AM

I'm using the 12 bolt that came in it just going to rebuild it. The 3:73 gear was what I'm thinking. Tire size is up in the air don't know what will fit or look good. Want to put as much tire as I can (width) Thinking a 18 or 20 tall rim. Don't like that rubber bad look for tires.

01-19-2018, 09:47 AM	#1
Oldironracing Registered User Join Date: Oct 2007 Location: Austin Arkansas Posts: 252	Rear end gears??? What rear end gear to run with a 4L70E and LS3 500hp??? __________________ OLDIRONRACING

01-19-2018, 10:55 AM	#2
Clyde65 1965 Chevy C10, 2005 4.8L/4l60 Join Date: Aug 2004 Location: DFW Texas Posts: 8,546	Re: Rear end gears??? Depends on tire size and what objective you have, speed or driver. Normally a 3.42:1 is the go to! But a 3.73:1 is what I run with my 4l60e. __________________ Clyde65 Rebuild of Clyde http://67-72chevytrucks.com/vboard/s...84#post8338184 69 Aristocrat Lo Liner build http://67-72chevytrucks.com/vboard/s...84#post7561684 *support our troops!*

01-19-2018, 12:02 PM	#3
mongocanfly Post Whore Join Date: May 2015 Location: Alabama Posts: 14,670	Re: Rear end gears??? use a rpm calculator to determine what you need. ...one like this. ...http://www.csgnetwork.com/multirpmcalc.html __________________ Mongo...aka Greg RIP Dad RIP Jesse 1981 C30 LQ9 NV4500..http://67-72chevytrucks.com/vboard/s...d.php?t=753598 Mongos AD- LS3 TR6060...http://67-72chevytrucks.com/vboard/s...34#post8522334 Columbus..the 1957 IH 4x4...http://67-72chevytrucks.com/vboard/s...63#post8082563 2023 Chevy Z71..daily driver

01-19-2018, 02:27 PM	#4
GMC-YA68 Senior Member Join Date: Mar 2004 Location: Lee's Summit, MO (KC) Posts: 742	Re: Rear end gears??? I'm going 3:73 in my C10 with 4L60E and 27-28" tires. __________________ -Keegan- '72 Jimmy 4x4 - 5.3/4L65E/NP205 swap http://67-72chevytrucks.com/vboard/s...d.php?t=663780

01-19-2018, 02:56 PM	#5
Steve Cole Registered User Join Date: May 2012 Location: Faith,NC Posts: 1,626	Re: Rear end gears??? I will also be using 3:73:1 in my stock 5.3 / 4L60E combo.

01-19-2018, 03:38 PM	#6
Custom 68 Registered User Join Date: Nov 2001 Location: Springfield, MO Posts: 2,939	Re: Rear end gears??? In my 1968 truck I have the 12 bolt truck rear. It seems limited to either 3.08, 3.73 or 4.11:1. There might be some on the extreme ends I don't remember but I have not found the 3.42 or others in that range. You may have a different rear end so you may have those options. I am running 3.73:1 my trans is a 4l80 so it is geared a little different. Dave __________________ Dave 1968 Custom Chevy with turbo charged 5.3 gen III 4l80e swap 1967-71 GMC 3/4 ton long step 4x4 (not sure what year exactly?) "A good friend will bail you out of jail...but a true friend will be sitting next to you saying "that was frekin awesome". "If it doesn't fit force it...If it breaks then it needed to be replaced anyway!"

01-19-2018, 05:11 PM	#7
ls1nova71 Registered User Join Date: Dec 2009 Location: Independence Mo Posts: 4,119	Re: Rear end gears??? I'd go with 3:73 if you're starting from scratch. I have that in my Blazer with a 6.0 and its a nice gear. My Green truck with the 5.3 has the factory 3:08 posi and I feel like it hurts it a bit, just a little too tall of gear for the overdrive. __________________ My '72 short bed build. http://www.ls1tech.com/forums/conver...6-0-4l80e.html 5.3 swap into my RUSTY '71 C10 http://ls1tech.com/forums/conversion...71-c-10-a.html

01-19-2018, 09:22 PM	#8
BR3W CITY meowMEOWmeowMEOW Join Date: Sep 2009 Location: MKE WI Posts: 7,128	Re: Rear end gears??? 3:73 is the one-size-fits-all recommendation for swaps IMO, especially since the 12 bolt variation is fairly common, and if you switch rear ends staying with 3:73 is easy across the board. I run it in my 12 bolt and its quite good behind my 6.0 __________________ *'66 Short Step / SD Tuned / Big Cam LQ4 / Backhalfed /Built 4l80e / #REBUILDEVERYTHING* MY BUILD THE H8RDCPTR //\\ MY YOUTUBE CHANNEL REV J HD

01-20-2018, 10:59 AM	#9
Oldironracing Registered User Join Date: Oct 2007 Location: Austin Arkansas Posts: 252	Re: Rear end gears??? I'm using the 12 bolt that came in it just going to rebuild it. The 3:73 gear was what I'm thinking. Tire size is up in the air don't know what will fit or look good. Want to put as much tire as I can (width) Thinking a 18 or 20 tall rim. Don't like that rubber bad look for tires. __________________ OLDIRONRACING

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