Best 12-bolt Posi Unit? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

TIMSPEED · 04-02-2003, 02:17 AM

I'd like to turn my factory 12-bolt one-legger into a posi. What's the best overall unit to get for it? (price wise and performance wise) Eaton? Detroit? Also, do I need to get new gears? (I've got factory 3.75's, and I'd like to go down to about a 3.5x) Thanks!

low 84 · 04-02-2003, 02:47 AM

i here good stuff about eatons. its gonna be hard to find 3.5x aftermarket gears for a truck 12 bolt. most manufacturers go from 3.42 to 3.73 with nothing in between

BaggedC10 · 04-02-2003, 02:57 AM

My 12-bolt rear-end is equipped with a 33-spline Eaton posi., Moser drive axles, and 3.73 gears.

79BIG10 · 04-02-2003, 03:38 AM

Eaton are better than Auburn due to they can be rebuilt. What about a power trax locker? Tough stuff there.

**Captkaos** · 04-02-2003, 12:53 PM

Eaton Clutch is whatl I would reccomend, but it depends on you use.
Mostly Street = Eaton
Offraod = Locker

TIMSPEED · 04-02-2003, 12:55 PM

It's going to be 100% street. Well, I guess I'll have to go with a 3.73 gear then...gotta change my speedo gears when I do that though

Can I just reuse my factory gears?

AirMale · 04-02-2003, 03:51 PM

Auburn-->good
Eaton--->best
3spd auto---->3.42 street
4spd auto---->3.73 street

I reccommend a series 3 Eaton posi. You can get a 3.73 gear to fit a 3 but a series 4 can only run 3.73 and up. So if you go with a #3 and 3.42's and you want more you can go up to 3.73's. A #4 will not accept anything lower than a 3.73. Check Ebay...type in 12 bolt you'll see a total Eaton posi, choice of gears and everything you need to fully rebuid your 12 for $559. NO randy's can't beat this, I called.

Mike76251 · 04-02-2003, 05:30 PM

Auburn has felt the heat from Eaton and recently announced that it will swap a broken Auburn out.
I don't know what the fine print is but it should not cost much.

04-02-2003, 02:17 AM	#1
TIMSPEED Join Date: Jan 2003 Location: Modesto, CA Posts: 1,321	Best 12-bolt Posi Unit? I'd like to turn my factory 12-bolt one-legger into a posi. What's the best overall unit to get for it? (price wise and performance wise) Eaton? Detroit? Also, do I need to get new gears? (I've got factory 3.75's, and I'd like to go down to about a 3.5x) Thanks! __________________ I have a few cars... See Them Here

04-02-2003, 02:47 AM	#2
low 84 Registered User Join Date: Jan 2002 Location: Houston, TX Posts: 2,144	i here good stuff about eatons. its gonna be hard to find 3.5x aftermarket gears for a truck 12 bolt. most manufacturers go from 3.42 to 3.73 with nothing in between __________________ '51 F100, backhalf with a narrowed 9 and coil overs, 18.5" mickeys, monte front clip, +400" sbc in the works '05 1500 Crew Cab RIP '84 swb 5/7 drop, solid cammed 408 w/ fully ported dart heads, th350 w/ 10 inch hughes, 12 bolt w/ 3.73 richmonds and a locker '80 swb 4x4 in progress: 7" lift, 350 th350/np205, d44 and 1.5" ORD tie rod, 14BFF w/discs , armored diff covers, 40" MTR's

04-02-2003, 12:53 PM	#5
Captkaos www.73-87chevytrucks.com Join Date: Dec 1999 Location: Birmingham, AL Posts: 6,935	Eaton Clutch is whatl I would reccomend, but it depends on you use. Mostly Street = Eaton Offraod = Locker __________________ Chris Lucas 1973 Chevy C-10 1978 GMC Jimmy (2WD) - SOLD 1987 R10 twin turbo LS 1991 R3500 SRW CrewCab 1985 K5 diesel swapped project 1989 K5 2WD conversion w/ Vette susp Project Captkaos Customs 73-87chevytrucks.com

04-02-2003, 12:55 PM	#6
TIMSPEED Join Date: Jan 2003 Location: Modesto, CA Posts: 1,321	It's going to be 100% street. Well, I guess I'll have to go with a 3.73 gear then...gotta change my speedo gears when I do that though Can I just reuse my factory gears? __________________ I have a few cars... See Them Here

04-02-2003, 03:51 PM	#7
AirMale Senior Member Join Date: Jan 2003 Location: Atlantic City, NJ Posts: 1,073	Auburn-->good Eaton--->best 3spd auto---->3.42 street 4spd auto---->3.73 street I reccommend a series 3 Eaton posi. You can get a 3.73 gear to fit a 3 but a series 4 can only run 3.73 and up. So if you go with a #3 and 3.42's and you want more you can go up to 3.73's. A #4 will not accept anything lower than a 3.73. Check Ebay...type in 12 bolt you'll see a total Eaton posi, choice of gears and everything you need to fully rebuid your 12 for $559. NO randy's can't beat this, I called. __________________ 86 SWB 9.0 LITER T-400-OD 4.11 eaton-4/5 drop Best 1/4 12.51 @112mph no traction

04-02-2003, 02:57 AM	#3
BaggedC10 Under construction! Join Date: Aug 2002 Location: NorCal Posts: 1,065	My 12-bolt rear-end is equipped with a 33-spline Eaton posi., Moser drive axles, and 3.73 gears. __________________ 2001 Silverado bagged on 22's. Sold

04-02-2003, 03:38 AM	#4
79BIG10 I'm back with 2nd truck! Join Date: Feb 2002 Location: Texas Posts: 3,774	Eaton are better than Auburn due to they can be rebuilt. What about a power trax locker? Tough stuff there. __________________ 1979 Chevrolet Bonanza Big10 "Tootsie Roll" 1985 Chevrolet Silverado (wife's) Member of the Southern Bowties Club "Don't underestimate how sexy a fat man who drinks to excess can be." Homer Simpson

04-02-2003, 05:30 PM	#8
Mike76251 Senior Member Join Date: Mar 2003 Posts: 2,499	Auburn has felt the heat from Eaton and recently announced that it will swap a broken Auburn out. I don't know what the fine print is but it should not cost much.



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