Auburn posi - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Omaha68C10 · 11-20-2014, 09:52 PM

I have a buddy of mine who has a 12 bolt truck rear with a 4.88 auburn posi unit. The grear ratio is too steep for my use. Does anyone know if the posi unit will swap into my 68 c10? My truck is a 307 with a SM465 4 speed from the factory which has a 3:73 gear ratio. Thanks,Jon

Willys47 · 11-20-2014, 11:47 PM

I belive it will fit but check the Auburn web site to confirm the carrier change over ratio

Mike C · 11-21-2014, 07:54 PM

It should. The carrier break for truck 12 bolts is 3.73 and up. On cars it's 3.90 and up. I have a set of aftermarket thick gears on my truck 3 series carrier that I ran in my Jimmy. That would be the one concern that they are aftermarket gears or something, but most likely not a problem.

**special-K** · 11-22-2014, 08:40 AM

x2 ^^

the break off is 3.73-down. Auburns are awesome units. my project has a factory posi and one of the refinements once running will be changing to Auburn for a stronger set-up. My rear was a 3.08 and I changed it to 3.42 for more 4spd (car) grunt while remaining hiway friendly w/o overdrive, and still do well with if I get to that

Mike C · 11-22-2014, 08:23 PM

The only real drawback to the Auburn unit is the cone type units are non-rebuildable.

Here is West Coast Differentials Carrier Break Chart. This is a good source for just about any rear diff. If you ever look at a 3.73 truck gear set, the ring gear is really thin because of the pinion gear diameter and the fact that the 4 series carrier is 3.73 and up.
http://www.differentials.com/technic...carrier-breaks

**special-K** · 11-22-2014, 08:47 PM

Gear ratios can confuse people. Mike and I are saying the same thing, but he's saying "up", meaning higher number and I'm saying "down", meaning lower gearing. The higher the numbers the lower the gearing. Just wanted to clear that up. I always ask,"Do you mean higher gears or higher numbers?", to be sure when getting info. I'm starting to use tall & short to be more clear...but not consistently

Mike C · 11-23-2014, 01:32 PM

Agreed. Most people don't have a clue what tall and short mean so it adds an additional degree of confusion!

**special-K** · 11-23-2014, 10:04 PM

I don't understand what you mean.

11-20-2014, 09:52 PM	#1
Omaha68C10 Registered User Join Date: Jan 2014 Location: Omaha, Nebraska Posts: 56	Auburn posi I have a buddy of mine who has a 12 bolt truck rear with a 4.88 auburn posi unit. The grear ratio is too steep for my use. Does anyone know if the posi unit will swap into my 68 c10? My truck is a 307 with a SM465 4 speed from the factory which has a 3:73 gear ratio. Thanks,Jon

11-20-2014, 11:47 PM	#2
Willys47 Registered User Join Date: Dec 2007 Location: Nanaimo B.C. Posts: 604	Re: Auburn posi I belive it will fit but check the Auburn web site to confirm the carrier change over ratio __________________ I was hooked on these trucks since 1982 when I drove my budys fathers 1968 Custum GMC 396 automatic dana 60 rear with a power lock diff what a ride more fun then we will we can ever tell!!

11-21-2014, 07:54 PM	#3
Mike C Registered User Join Date: Dec 1999 Location: Austin, TX, USA Posts: 7,728	Re: Auburn posi It should. The carrier break for truck 12 bolts is 3.73 and up. On cars it's 3.90 and up. I have a set of aftermarket thick gears on my truck 3 series carrier that I ran in my Jimmy. That would be the one concern that they are aftermarket gears or something, but most likely not a problem. __________________ 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

11-22-2014, 08:40 AM	#4
special-K Special Order Join Date: Nov 2004 Location: Mt Airy, MD Posts: 85,851	Re: Auburn posi x2 ^^ the break off is 3.73-down. Auburns are awesome units. my project has a factory posi and one of the refinements once running will be changing to Auburn for a stronger set-up. My rear was a 3.08 and I changed it to 3.42 for more 4spd (car) grunt while remaining hiway friendly w/o overdrive, and still do well with if I get to that __________________ "BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed" GMC '67 C1500 Wideside Super Custom SWB: 327/M22/3.42 posi.........."The '67" (project) GMC '72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 Power-Lok..."The '72" (rolling) Tim "Don't call me a redneck. I'm a rough cut country gentleman" R.I.P. ~ East Side Low Life ~ El Jay ~ 72BLUZ ~ Fasteddie69 ~ Ron586 ~ 67ChevyRedneck ~ Grumpy Old Man ~

11-22-2014, 08:23 PM	#5
Mike C Registered User Join Date: Dec 1999 Location: Austin, TX, USA Posts: 7,728	Re: Auburn posi The only real drawback to the Auburn unit is the cone type units are non-rebuildable. Here is West Coast Differentials Carrier Break Chart. This is a good source for just about any rear diff. If you ever look at a 3.73 truck gear set, the ring gear is really thin because of the pinion gear diameter and the fact that the 4 series carrier is 3.73 and up. http://www.differentials.com/technic...carrier-breaks __________________ 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

11-22-2014, 08:47 PM	#6
special-K Special Order Join Date: Nov 2004 Location: Mt Airy, MD Posts: 85,851	Re: Auburn posi Gear ratios can confuse people. Mike and I are saying the same thing, but he's saying "up", meaning higher number and I'm saying "down", meaning lower gearing. The higher the numbers the lower the gearing. Just wanted to clear that up. I always ask,"Do you mean higher gears or higher numbers?", to be sure when getting info. I'm starting to use tall & short to be more clear...but not consistently __________________ "BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed" GMC '67 C1500 Wideside Super Custom SWB: 327/M22/3.42 posi.........."The '67" (project) GMC '72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 Power-Lok..."The '72" (rolling) Tim "Don't call me a redneck. I'm a rough cut country gentleman" R.I.P. ~ East Side Low Life ~ El Jay ~ 72BLUZ ~ Fasteddie69 ~ Ron586 ~ 67ChevyRedneck ~ Grumpy Old Man ~

11-23-2014, 01:32 PM	#7
Mike C Registered User Join Date: Dec 1999 Location: Austin, TX, USA Posts: 7,728	Re: Auburn posi Agreed. Most people don't have a clue what tall and short mean so it adds an additional degree of confusion! __________________ 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

11-23-2014, 10:04 PM	#8
special-K Special Order Join Date: Nov 2004 Location: Mt Airy, MD Posts: 85,851	Re: Auburn posi I don't understand what you mean. __________________ "BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed" GMC '67 C1500 Wideside Super Custom SWB: 327/M22/3.42 posi.........."The '67" (project) GMC '72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 Power-Lok..."The '72" (rolling) Tim "Don't call me a redneck. I'm a rough cut country gentleman" R.I.P. ~ East Side Low Life ~ El Jay ~ 72BLUZ ~ Fasteddie69 ~ Ron586 ~ 67ChevyRedneck ~ Grumpy Old Man ~



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