Posi recommendations - The 1947 - Present Chevrolet & GMC Truck Message Board Network

04ls1gto · 01-13-2019, 09:16 AM

Just starting to drive my LS swapped suburban And the open diff isn't cutting it. What are you guys running for posi units? I am guessing that it has either 3.08 or 3.42 gears which work pretty well with the 6l80 not sure if I should swapped to 3.73 while it's out.

Ziegelsteinfaust · 01-13-2019, 10:28 AM

3.42's will work great with a 27" tire, but alot depends on tires size.

I am a fan of the Detroit wave Trax for the street.

**HO455** · 01-13-2019, 11:20 AM

What rear end do you have in the truck? Some rear end styles have fewer limited slip carriers styles available.
If you get a 12 bolt 3.07 or 3.42 carrier to run the 3.73 ratio you would need to get a thick gear set. The thick gear set has some limitations. With a 6l80 transmission I wouldn't think twice about running 4.11's for a daily driver Burban. Much quicker when shooting around town.

I am running 3.73's on the 3.07 factory posi carrier (thick gear set) with 28" tires. With a T400 and limited highway driving it works well, but I don't run much above 60 mph for any length of time.

04ls1gto · 01-13-2019, 01:32 PM

I think that I will stay with current gears as traction is a problem already. Tires are 245/45/20 which are 28.7 tall. I have a Detriot Trutrac in my GTO and like it so I was thinking about doing one of those

**HO455** · 01-13-2019, 06:40 PM

I know it sounds counterintuitive but a higher numeric ratio will help reduce wheel spin

Ryan Hubbard · 01-14-2019, 03:40 AM

Quote:

Originally Posted by 04ls1gto

I think that I will stay with current gears as traction is a problem already. Tires are 245/45/20 which are 28.7 tall. I have a Detriot Trutrac in my GTO and like it so I was thinking about doing one of those

I am running a Trutrac in my 90 3/4 Ton Suburban and really like it. I am running 4.10 gears but have a 33" tire. I am putting an LS3 E-Rod in but already am running a 4L80 and with the tires I am only turning 2500 rpms at 75 mph.

04ls1gto · 02-06-2019, 06:06 PM

So I checked the gear ratio and its a 3.73 which was a nice surprise. What series carrier do I have a 3 or 4? Eaton has a trutrac in 4 series but not sure if that will work for me

**mongocanfly** · 02-07-2019, 01:56 PM

3 series

AnotherWs6 · 02-12-2019, 02:45 PM

I vote for a trutrak as well, but only in a 2wd vehicle. Put one in my lifted 2000 silverado and it's terrible in the snow. It needs some resistance to actually work, so the slipperier the conditions are the worse it performs/locks. I would happily run one in my burb but really havent had a need.

04ls1gto · 02-12-2019, 06:08 PM

So Eaton doesn't make a trutrac in a 3 series. Gonna have to go with a spring type

61_FL_Apache · 02-12-2019, 09:48 PM

A 3.73 is a fun street gear, but may be too short for the highway depending on tire size. I had a 3.08 Eaton in a 94 Caprice cop car and it was pretty decent, but which I had the 3.73 in it.

AnotherWs6 · 02-13-2019, 02:34 PM

It's not gonna be too short. I'd actually go 4.10. With your .67 sixth gear that puts your final ratio at 2.75. So it's basically the equivalent of running a th350/400 and 2.73's.

04ls1gto · 03-02-2019, 04:25 PM

I'm getting some mixed information, is a 3.73 gear a 3 series or 4 series carrier? Some say 3 series goes to 3.42 some 3.73. is there a was to tell what diff I have if I pull the cover

**mongocanfly** · 03-02-2019, 05:02 PM

What axle do you have?...

04ls1gto · 03-02-2019, 05:20 PM

Quote:

Originally Posted by mongocanfly

What axle do you have?...

Truck 12 bolt with factory 3:73 gears, want to install posi but not sure which series I have

**mongocanfly** · 03-02-2019, 05:22 PM

Looks like when I said earlier that you had a 3 series that the chart I was looking at was for passenger cars...not trucks...(my bad)
Assuming you have a 12 bolt truck axle..
I got this from just differentials site...

GM 8.875" (8-78") 12 Bolt - Truck Carrier Breaks:
2 Series: 2.73 & Down
3 Series: 2.76-3.42
4 Series: 3.73 & Up

So I'm gonna say you got a 4 series carrier if you have 3.73s
A pass car 3.73 carrier is a series 3

**mongocanfly** · 03-02-2019, 05:33 PM

http://www.drivetrainshop.com/Detroi...at-913a555.htm
Shows it'll work with 3.73s

**mongocanfly** · 03-02-2019, 05:36 PM

And I found this also....

04ls1gto · 03-02-2019, 05:38 PM

Quote:

Originally Posted by mongocanfly

http://www.drivetrainshop.com/Detroi...at-913a555.htm
Shows it'll work with 3.73s

That's a car 12 bolt diff

**HO455** · 03-02-2019, 05:43 PM

Mongo's information matches what I learned when I had my rear end rebuilt.

04ls1gto · 03-02-2019, 05:52 PM

Quote:

Originally Posted by HO455

Mongo's information matches what I learned when I had my rear end rebuilt.

So it's a 4 series, what posi did you use when you rebuilt

**mongocanfly** · 03-02-2019, 08:23 PM

dang it!!!!...im getting myself confused....sorry

lets try this one.....https://www.summitracing.com/parts/d...a315/overview/

**HO455** · 03-03-2019, 03:49 PM

Quote:

Originally Posted by 04ls1gto

So it's a 4 series, what posi did you use when you rebuilt

I have the factory clutch style.

01-13-2019, 09:16 AM	#1
04ls1gto Registered User Join Date: Aug 2014 Location: Portsmouth ri Posts: 363	Posi recommendations Just starting to drive my LS swapped suburban And the open diff isn't cutting it. What are you guys running for posi units? I am guessing that it has either 3.08 or 3.42 gears which work pretty well with the 6l80 not sure if I should swapped to 3.73 while it's out.

01-13-2019, 10:28 AM	#2
Ziegelsteinfaust Registered User Join Date: Dec 2012 Location: Temple City Posts: 3,623	Re: Posi recommendations 3.42's will work great with a 27" tire, but alot depends on tires size. I am a fan of the Detroit wave Trax for the street.

01-13-2019, 11:20 AM	#3
HO455 Post Whore Join Date: Feb 2016 Location: Portland Oregon Posts: 11,275	Re: Posi recommendations What rear end do you have in the truck? Some rear end styles have fewer limited slip carriers styles available. If you get a 12 bolt 3.07 or 3.42 carrier to run the 3.73 ratio you would need to get a thick gear set. The thick gear set has some limitations. With a 6l80 transmission I wouldn't think twice about running 4.11's for a daily driver Burban. Much quicker when shooting around town. I am running 3.73's on the 3.07 factory posi carrier (thick gear set) with 28" tires. With a T400 and limited highway driving it works well, but I don't run much above 60 mph for any length of time. __________________ Thanks to Bob and Jeanie and everyone else at Superior Performance for all their great help. RIP Bob Parks. 1967 Burban (the WMB),1988 S10 Blazer (the Stink10 II),1969 GTO (the Goat), 1970 Javelin, 1952 F2 Ford OHC six 4X4, 29 Model A, 72 Firebird (the DBP Bird). 85 Alfa Romeo If it breaks I didn't want it in the first place The WMB repair thread http://67-72chevytrucks.com/vboard/s...d.php?t=698377

01-13-2019, 01:32 PM	#4
04ls1gto Registered User Join Date: Aug 2014 Location: Portsmouth ri Posts: 363	Re: Posi recommendations I think that I will stay with current gears as traction is a problem already. Tires are 245/45/20 which are 28.7 tall. I have a Detriot Trutrac in my GTO and like it so I was thinking about doing one of those

01-13-2019, 06:40 PM	#5
HO455 Post Whore Join Date: Feb 2016 Location: Portland Oregon Posts: 11,275	Re: Posi recommendations I know it sounds counterintuitive but a higher numeric ratio will help reduce wheel spin __________________ Thanks to Bob and Jeanie and everyone else at Superior Performance for all their great help. RIP Bob Parks. 1967 Burban (the WMB),1988 S10 Blazer (the Stink10 II),1969 GTO (the Goat), 1970 Javelin, 1952 F2 Ford OHC six 4X4, 29 Model A, 72 Firebird (the DBP Bird). 85 Alfa Romeo If it breaks I didn't want it in the first place The WMB repair thread http://67-72chevytrucks.com/vboard/s...d.php?t=698377

02-06-2019, 06:06 PM	#7
04ls1gto Registered User Join Date: Aug 2014 Location: Portsmouth ri Posts: 363	Re: Posi recommendations So I checked the gear ratio and its a 3.73 which was a nice surprise. What series carrier do I have a 3 or 4? Eaton has a trutrac in 4 series but not sure if that will work for me

02-07-2019, 01:56 PM	#8
mongocanfly Post Whore Join Date: May 2015 Location: Alabama Posts: 14,662	Re: Posi recommendations 3 series __________________ 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

02-12-2019, 02:45 PM	#9
AnotherWs6 Registered User Join Date: Feb 2016 Location: Westchester, NY Posts: 602	Re: Posi recommendations I vote for a trutrak as well, but only in a 2wd vehicle. Put one in my lifted 2000 silverado and it's terrible in the snow. It needs some resistance to actually work, so the slipperier the conditions are the worse it performs/locks. I would happily run one in my burb but really havent had a need. __________________ 1968 C-10 Suburban - Original 396/TH400 2002 Transam WS6 - M6 - Black/Black - Evil Garage Queen 2000 Silverado - DD - Small lift+Body lift+35" Duratracs+4.88's + Eaton TruTrac - Monster Truck 2010 Cadillac CTS Wagon Sport - Wife's DD and the only classy car we have.

02-12-2019, 06:08 PM	#10
04ls1gto Registered User Join Date: Aug 2014 Location: Portsmouth ri Posts: 363	Re: Posi recommendations So Eaton doesn't make a trutrac in a 3 series. Gonna have to go with a spring type

02-12-2019, 09:48 PM	#11
61_FL_Apache Who Me? Join Date: Sep 2010 Location: Royal Palm Beach, FL Posts: 4,067	Re: Posi recommendations A 3.73 is a fun street gear, but may be too short for the highway depending on tire size. I had a 3.08 Eaton in a 94 Caprice cop car and it was pretty decent, but which I had the 3.73 in it. __________________ Steve 1997 Tahoe LT 4D 2WD (DD) 2001 Blazer 4D 2WD 1961 Apache 10 (sold) 1965 C10 Stepper (sold)

02-13-2019, 02:34 PM	#12
AnotherWs6 Registered User Join Date: Feb 2016 Location: Westchester, NY Posts: 602	Re: Posi recommendations It's not gonna be too short. I'd actually go 4.10. With your .67 sixth gear that puts your final ratio at 2.75. So it's basically the equivalent of running a th350/400 and 2.73's. __________________ 1968 C-10 Suburban - Original 396/TH400 2002 Transam WS6 - M6 - Black/Black - Evil Garage Queen 2000 Silverado - DD - Small lift+Body lift+35" Duratracs+4.88's + Eaton TruTrac - Monster Truck 2010 Cadillac CTS Wagon Sport - Wife's DD and the only classy car we have.

03-02-2019, 04:25 PM	#13
04ls1gto Registered User Join Date: Aug 2014 Location: Portsmouth ri Posts: 363	Re: Posi recommendations I'm getting some mixed information, is a 3.73 gear a 3 series or 4 series carrier? Some say 3 series goes to 3.42 some 3.73. is there a was to tell what diff I have if I pull the cover

03-02-2019, 05:02 PM	#14
mongocanfly Post Whore Join Date: May 2015 Location: Alabama Posts: 14,662	Re: Posi recommendations What axle do you have?... __________________ 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

03-02-2019, 05:22 PM	#16
mongocanfly Post Whore Join Date: May 2015 Location: Alabama Posts: 14,662	Re: Posi recommendations Looks like when I said earlier that you had a 3 series that the chart I was looking at was for passenger cars...not trucks...(my bad) Assuming you have a 12 bolt truck axle.. I got this from just differentials site... GM 8.875" (8-78") 12 Bolt - Truck Carrier Breaks: 2 Series: 2.73 & Down 3 Series: 2.76-3.42 4 Series: 3.73 & Up So I'm gonna say you got a 4 series carrier if you have 3.73s A pass car 3.73 carrier is a series 3 __________________ 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

03-02-2019, 05:33 PM	#17
mongocanfly Post Whore Join Date: May 2015 Location: Alabama Posts: 14,662	Re: Posi recommendations http://www.drivetrainshop.com/Detroi...at-913a555.htm Shows it'll work with 3.73s __________________ 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



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03-02-2019, 05:36 PM	#18
mongocanfly Post Whore Join Date: May 2015 Location: Alabama Posts: 14,662	Re: Posi recommendations And I found this also.... Attached Images __________________ 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

03-02-2019, 05:43 PM	#20
HO455 Post Whore Join Date: Feb 2016 Location: Portland Oregon Posts: 11,275	Re: Posi recommendations Mongo's information matches what I learned when I had my rear end rebuilt. __________________ Thanks to Bob and Jeanie and everyone else at Superior Performance for all their great help. RIP Bob Parks. 1967 Burban (the WMB),1988 S10 Blazer (the Stink10 II),1969 GTO (the Goat), 1970 Javelin, 1952 F2 Ford OHC six 4X4, 29 Model A, 72 Firebird (the DBP Bird). 85 Alfa Romeo If it breaks I didn't want it in the first place The WMB repair thread http://67-72chevytrucks.com/vboard/s...d.php?t=698377

03-02-2019, 08:23 PM	#22
mongocanfly Post Whore Join Date: May 2015 Location: Alabama Posts: 14,662	Re: Posi recommendations dang it!!!!...im getting myself confused....sorry lets try this one.....https://www.summitracing.com/parts/d...a315/overview/ __________________ 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

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