Someone straghten me out on posi diffs - The 1947 - Present Chevrolet & GMC Truck Message Board Network

ckhd · 09-03-2002, 04:57 PM

OK, I have a 12-bolt posi in the '72 (I am not sure if it's Eaton or GM), and it has 3.73 gears.

Here's my q's:

1) What 'series' is it?
2) What gear ratios will fit on it?
3) What are the other series and what gears will fit on them?
4) Are the Eaton posi and GM posi series different as far as gear ranges go?

Mike C · 09-03-2002, 10:25 PM

The GM posi was built/designed by Eaton. It is an Eaton posi, but different than the new ones from Eaton (slightly) 3.73 in truck is a 4 series carrier. 3.73-3.90-4.10-4.56-4.88-5.13(with crossshaft) will fit. THere are "thin" and "thick" gears available from the aftermarket that make a wider range of ratios that fit a given carrier.

BobbyK · 09-04-2002, 01:21 AM

My 71 Blazer has a 12 bolt,3:73 gears and an Eaton Gov Loc.Not the strongest posi for off-roading but just fine for street use.I had no idea what the heck it was when I first opened up the rear-end.

frg41 · 09-04-2002, 02:26 AM

i have a 72 cheyenne c-20,
was told it's a dana 60 what are the gear rations.

dmnall · 09-04-2002, 02:50 AM

Didn't Auburn also make a posi for Gm as well ??

**'68OrangeSunshine** · 09-04-2002, 04:51 AM

I don't know if Auburn made original production Posi's for the GM trucks. I'm pretty sure it was mostly Eaton, but Auburn does make a good aftermarket posi unit for the '67/'72 GM 12 bolt differentials. I had one in my '67 K/10 Sub. Worked real good. I put an Eaton posi on my '68 C/10 Stepside, years ago [cannibalized off a j-yard '69 GMC step] and my '71 Jimmy came with an Eaton from the factory. All are 3.73s.
I'd be hard pressed to say which is the better unit. It's all good. Maybe the Auburn was a little grabbier, but then it was also behind a 454.

Rod · 09-04-2002, 05:36 AM

Dana 60 gears came with 3:54, 4:10 or 4:57.

BigGreenMachine · 09-04-2002, 07:22 AM

frg41,

If you have a factory 402 with that rear-end, then it's 3.54, unless someone has changed it.

Scott

frg41 · 09-04-2002, 09:24 AM

it came fact, w/ 350 if that helps any

thanks guys for the info...

Stout72 · 09-04-2002, 11:36 AM

My Dana 60 has 4:10 gears with a 350 driving it. The only way for you to tell what you have is to drain the oil out of it, remove the cover plate and look on the periphery of the ring gear. The ratio should be stamped on it there.

Mike C · 09-04-2002, 11:40 AM

All Dana axles originally came with a tag on the cover specifying ratio and a part #. Many times people leave it off after servicing the rear axle, but start by cleaning the grease off the tag. Otherwise you will have to pull the cover. My Longhorn parts truck had 3.73 gears, not sure if original since it was supposed to be a Max Trac rear axle as well according to the glove box, but it was open. Maybe gears and diff replaced, maybe just the diff, maybe the housing from another truck, who knows? But there are 3.73 as well.

frg41 · 09-04-2002, 05:35 PM

i'll remove the cover and chk it out.

thanks ya'll for everything

*Fast68Chevy* · 09-05-2002, 10:21 PM

4.57= standard ratio in 3/4 and 1 ton eaton axle, with 4.10 optional
4.56 = standard dana 60 3/4 ton ratio, with 3.54 and 4.10 optional
not all BB got dana 60 3.54 only did with certain trannies. in 70 there was a 1/2 ton BB truck that could have dana 3.54 axle, is rare as hell though.
90% of dana axle trucks got leaf type rear G70 suspension

4.55= front dana axle on 3/4 4x4 67-72

BigGreenMachine · 09-06-2002, 06:39 AM

Fast,

What is the leaf type G70 suspension? Is that just the designation for leaf springs?

Were 3.54 Danas only rare in the 1/2 tons, or with the 3/4 tons too?

What transmission besides the TH400 was the 3.54 Dana available with?

Thanks!

Scott

frg41 · 09-06-2002, 10:15 AM

build sheet says it has both g50 and g70 springs with the fact. 350/350

09-03-2002, 04:57 PM	#1
ckhd Registered User Join Date: Oct 2000 Location: St. Johns, Arizona Posts: 2,660	Someone straghten me out on posi diffs OK, I have a 12-bolt posi in the '72 (I am not sure if it's Eaton or GM), and it has 3.73 gears. Here's my q's: 1) What 'series' is it? 2) What gear ratios will fit on it? 3) What are the other series and what gears will fit on them? 4) Are the Eaton posi and GM posi series different as far as gear ranges go? __________________ my 2¢ - t.i.o.l.i. Bowen 1968 K20 fleet 1969 K10 swb fleet 1972 K10 Suburban 1972 C10 lwb step 1992 K1500 'burb 1995 K2500 'burb 1997 C1500 'burb 1999 K1500 2000 K1500 'burb Why do I own so many Suburbans?

09-03-2002, 10:25 PM	#2
Mike C Registered User Join Date: Dec 1999 Location: Austin, TX, USA Posts: 7,715	The GM posi was built/designed by Eaton. It is an Eaton posi, but different than the new ones from Eaton (slightly) 3.73 in truck is a 4 series carrier. 3.73-3.90-4.10-4.56-4.88-5.13(with crossshaft) will fit. THere are "thin" and "thick" gears available from the aftermarket that make a wider range of ratios that fit a given carrier. __________________ 44 Willys MB 52 M38A1 64 Corvette Coupe 68 Camaro 'vert LT1 & TH700 69 Z/28 355 12.6's @110 69 Chevy Short Step 4 1/2"/7" drop 72 Jimmy 4WD 4spd 4" & 35's 02 GMC 2500HD 4x4 Duramax

09-04-2002, 01:21 AM	#3
BobbyK Registered User Join Date: May 2000 Location: Petrolia,Ontario,Canada but working in Port Huron,Mi. Posts: 1,771	My 71 Blazer has a 12 bolt,3:73 gears and an Eaton Gov Loc.Not the strongest posi for off-roading but just fine for street use.I had no idea what the heck it was when I first opened up the rear-end. __________________ 71 blazer,350SBC,approx.375HP,700R4,factory GM TPI.Dual electric fans,33x12.5x15 ATR on stock suspension. Petrolia,Ontario,Canada but working in Port Huron,MI. See ALL my Blazer pic's HERE

09-04-2002, 02:26 AM	#4
frg41 love these trucks Join Date: Sep 2002 Location: ventura, calif. Posts: 59	need help i have a 72 cheyenne c-20, was told it's a dana 60 what are the gear rations. Attached Images

09-04-2002, 02:50 AM	#5
dmnall Registered User Join Date: Apr 2001 Location: Goleta, CA Posts: 505	Didn't Auburn also make a posi for Gm as well ?? __________________ 1968 C10 Truck LWB Fleetside 1968 C10 Truck SWB Stepside 1994 K2500 Ext Cab Fleetside 2008 Honda Civic Si lease

09-04-2002, 04:51 AM	#6
'68OrangeSunshine Senior Member Join Date: Feb 2002 Location: Tucson, AZ USA Posts: 7,210	I don't know if Auburn made original production Posi's for the GM trucks. I'm pretty sure it was mostly Eaton, but Auburn does make a good aftermarket posi unit for the '67/'72 GM 12 bolt differentials. I had one in my '67 K/10 Sub. Worked real good. I put an Eaton posi on my '68 C/10 Stepside, years ago [cannibalized off a j-yard '69 GMC step] and my '71 Jimmy came with an Eaton from the factory. All are 3.73s. I'd be hard pressed to say which is the better unit. It's all good. Maybe the Auburn was a little grabbier, but then it was also behind a 454. __________________ Every 25 years I like to rebuild that 292, whether it needs it or not.

09-04-2002, 05:36 AM	#7
Rod Join Date: Dec 1999 Location: Eastern - Manitoba Canada, Winnipeg Posts: 4,369	frg41 Dana 60 gears came with 3:54, 4:10 or 4:57. __________________ Senior active founding member. 70 3/4 ton GMC Suburban 4x4 250/4 spd. 71 1/2 ton Suburban Chevy 4x4, 350/350 72 Chev 1 ton tow truck 402BB w/Holmes 440 wrecker on propane 2005 FLSTSCI Harley Springer 85 FXSB Harley Lowrider 72 Triumph 650 Bonneville 5spd "Poor people don't have hobbies" Quote from wife.

09-04-2002, 07:22 AM	#8
BigGreenMachine Registered User Join Date: Mar 2001 Location: Lynchburg, VA Posts: 144	frg41, If you have a factory 402 with that rear-end, then it's 3.54, unless someone has changed it. Scott __________________ 1970 C/20 400(402)BB/TH-400 Factory A/C Factory Dual Exaust

09-04-2002, 09:24 AM	#9
frg41 love these trucks Join Date: Sep 2002 Location: ventura, calif. Posts: 59	dana 60 it came fact, w/ 350 if that helps any thanks guys for the info...

09-04-2002, 11:36 AM	#10
Stout72 Not my good side. Join Date: Mar 2002 Location: Fairfield, California Posts: 222	My Dana 60 has 4:10 gears with a 350 driving it. The only way for you to tell what you have is to drain the oil out of it, remove the cover plate and look on the periphery of the ring gear. The ratio should be stamped on it there. __________________ 72 Chevy K20 Custom Camper, 350/350, 4" lift, dual shock suspension front & rear. Daily driver and a work in progress. 00 Suburban LT 90 Camaro RS 79 Yamaha XS1100 Special (Ol' Reliable)

09-04-2002, 11:40 AM	#11
Mike C Registered User Join Date: Dec 1999 Location: Austin, TX, USA Posts: 7,715	All Dana axles originally came with a tag on the cover specifying ratio and a part #. Many times people leave it off after servicing the rear axle, but start by cleaning the grease off the tag. Otherwise you will have to pull the cover. My Longhorn parts truck had 3.73 gears, not sure if original since it was supposed to be a Max Trac rear axle as well according to the glove box, but it was open. Maybe gears and diff replaced, maybe just the diff, maybe the housing from another truck, who knows? But there are 3.73 as well. __________________ 44 Willys MB 52 M38A1 64 Corvette Coupe 68 Camaro 'vert LT1 & TH700 69 Z/28 355 12.6's @110 69 Chevy Short Step 4 1/2"/7" drop 72 Jimmy 4WD 4spd 4" & 35's 02 GMC 2500HD 4x4 Duramax

09-04-2002, 05:35 PM	#12
frg41 love these trucks Join Date: Sep 2002 Location: ventura, calif. Posts: 59	dana 60 i'll remove the cover and chk it out. thanks ya'll for everything

09-05-2002, 10:21 PM	#13
Fast68Chevy Account Suspended Join Date: May 2000 Location: IL Posts: 0	4.57= standard ratio in 3/4 and 1 ton eaton axle, with 4.10 optional 4.56 = standard dana 60 3/4 ton ratio, with 3.54 and 4.10 optional not all BB got dana 60 3.54 only did with certain trannies. in 70 there was a 1/2 ton BB truck that could have dana 3.54 axle, is rare as hell though. 90% of dana axle trucks got leaf type rear G70 suspension 4.55= front dana axle on 3/4 4x4 67-72

09-06-2002, 06:39 AM	#14
BigGreenMachine Registered User Join Date: Mar 2001 Location: Lynchburg, VA Posts: 144	Fast, What is the leaf type G70 suspension? Is that just the designation for leaf springs? Were 3.54 Danas only rare in the 1/2 tons, or with the 3/4 tons too? What transmission besides the TH400 was the 3.54 Dana available with? Thanks! Scott __________________ 1970 C/20 400(402)BB/TH-400 Factory A/C Factory Dual Exaust

09-06-2002, 10:15 AM	#15
frg41 love these trucks Join Date: Sep 2002 Location: ventura, calif. Posts: 59	my rear build sheet says it has both g50 and g70 springs with the fact. 350/350



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