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Old 01-13-2019, 09:16 AM   #1
04ls1gto
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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.
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Old 01-13-2019, 10:28 AM   #2
Ziegelsteinfaust
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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.
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Old 01-13-2019, 11:20 AM   #3
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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.
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Old 01-13-2019, 01:32 PM   #4
04ls1gto
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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
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Old 01-13-2019, 06:40 PM   #5
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Re: Posi recommendations

I know it sounds counterintuitive but a higher numeric ratio will help reduce wheel spin
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1967 Burban the WMB,1991 S(stink)-10 Blazer,1969 GTO, 1970 Javelin, 1952 F3 Ford 4X4, 29 Model A, 72 Firebird. 85 Alfa Romeo
If it breaks I didn't want it in the first place
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Old 01-14-2019, 03:40 AM   #6
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Re: Posi recommendations

Quote:
Originally Posted by 04ls1gto View Post
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.
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Old 02-06-2019, 06:06 PM   #7
04ls1gto
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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
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Old 02-07-2019, 01:56 PM   #8
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Re: Posi recommendations

3 series
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Old 02-12-2019, 02:45 PM   #9
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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.
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Old 02-12-2019, 06:08 PM   #10
04ls1gto
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Re: Posi recommendations

So Eaton doesn't make a trutrac in a 3 series. Gonna have to go with a spring type
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Old 02-12-2019, 09:48 PM   #11
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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.
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Old 02-13-2019, 02:34 PM   #12
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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.
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Old 03-02-2019, 04:25 PM   #13
04ls1gto
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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
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Old 03-02-2019, 05:02 PM   #14
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Re: Posi recommendations

What axle do you have?...
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1981 C30 LQ9 NV4500..http://67-72chevytrucks.com/vboard/s...d.php?t=753598
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Old 03-02-2019, 05:20 PM   #15
04ls1gto
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Re: Posi recommendations

Quote:
Originally Posted by mongocanfly View Post
What axle do you have?...
Truck 12 bolt with factory 3:73 gears, want to install posi but not sure which series I have
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Old 03-02-2019, 05:22 PM   #16
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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
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1981 C30 LQ9 NV4500..http://67-72chevytrucks.com/vboard/s...d.php?t=753598
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Columbus..the 1957 IH 4x4...http://67-72chevytrucks.com/vboard/s...63#post8082563
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Old 03-02-2019, 05:33 PM   #17
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Re: Posi recommendations

http://www.drivetrainshop.com/Detroi...at-913a555.htm
Shows it'll work with 3.73s
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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
2013 GMC Z71..daily driver
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Old 03-02-2019, 05:36 PM   #18
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Re: Posi recommendations

And I found this also....
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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
2013 GMC Z71..daily driver
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Old 03-02-2019, 05:38 PM   #19
04ls1gto
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Re: Posi recommendations

Quote:
Originally Posted by mongocanfly View Post
That's a car 12 bolt diff
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Old 03-02-2019, 05:43 PM   #20
HO455
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Re: Posi recommendations

Mongo's information matches what I learned when I had my rear end rebuilt.
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Thanks to Bob and Jeanie and everyone else at Superior Performance for all their great help.
1967 Burban the WMB,1991 S(stink)-10 Blazer,1969 GTO, 1970 Javelin, 1952 F3 Ford 4X4, 29 Model A, 72 Firebird. 85 Alfa Romeo
If it breaks I didn't want it in the first place
The WMB http://67-72chevytrucks.com/vboard/s...d.php?t=698377
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Old 03-02-2019, 05:52 PM   #21
04ls1gto
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Re: Posi recommendations

Quote:
Originally Posted by HO455 View Post
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
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Old 03-02-2019, 08:23 PM   #22
mongocanfly
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Re: Posi recommendations

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

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

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
2013 GMC Z71..daily driver
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Old 03-03-2019, 03:49 PM   #23
HO455
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Re: Posi recommendations

Quote:
Originally Posted by 04ls1gto View Post
So it's a 4 series, what posi did you use when you rebuilt
I have the factory clutch style.
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Thanks to Bob and Jeanie and everyone else at Superior Performance for all their great help.
1967 Burban the WMB,1991 S(stink)-10 Blazer,1969 GTO, 1970 Javelin, 1952 F3 Ford 4X4, 29 Model A, 72 Firebird. 85 Alfa Romeo
If it breaks I didn't want it in the first place
The WMB http://67-72chevytrucks.com/vboard/s...d.php?t=698377
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