What kind of Posi do I have here? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Gene · 08-23-2009, 08:45 PM

Pulled the covers to check ratios and I noticed the rear diff. looks to be a posi? It looks different than my 71 (no clutches) is this factory or aftermarket? Oh and i'm planning on running 35's with either the set that came with the truck(3.07) or these (3.42). Yeah I know that's pretty tall gearing for such large tires, but I don't plan on any rock crawling in this truck. Will I notice a huge difference between the two ratios?

67chevtruck · 08-23-2009, 10:36 PM

it looks like an auburn posi to me and i would get rid of it as soon as possible if you want to spin both tires because i had one in my truck after about 2 months it was just like an open it would not ever spin both tires

OLDCHEV4X4 · 08-24-2009, 07:58 AM

It looks after market. But looks simular to a Eaton. Was the fluid clean? Was there any chunks of stuff in the fluid?
Hold one axle and get a buddy to try and turn the other axle. If its tight, run it. But not hard, cause 35" tires will be hard on it.

Gene · 08-24-2009, 05:04 PM

Both sides turn, yes the fluid was very clean and looks like it was assembled not long ago. So I have a choice between factory posi(3.07), or one-legged(3.07), or this one(3.42) which one is best? BTW this rear came out of a 91 Burb if that helps?

**special-K** · 08-25-2009, 07:40 AM

I`d go with the 3.42 and Auburn,if that`s what it is.I ran one in my`90 Blazer with 33s,3.08s,and 4spd.It performed flawlessly.I think you`ll be about the same with 35s and 3.42s.I`m not sure if Auburns are recommended for over 33" tires,though.

Gene · 08-25-2009, 09:09 PM

Quote:

Originally Posted by special-K

I`d go with the 3.42 and Auburn,if that`s what it is.I ran one in my`90 Blazer with 33s,3.08s,and 4spd.It performed flawlessly.I think you`ll be about the same with 35s and 3.42s.I`m not sure if Auburns are recommended for over 33" tires,though.

This truck will probably never see rocks or mud, and will just be a driver. So I doubt that I will have any problems with breakage.

Now my next question, what kind of RPM can I expect with 35's TH350 and 3.42 gears at 65mph?

**71blksuper4x4** · 08-25-2009, 10:19 PM

Gene, I run 3.73 with my 35''s for a couple of years. The factory tach read right around 2700-3000 at 65mph. Trevor

martindc1 · 08-26-2009, 12:19 PM

Quote:

Originally Posted by Gene

This truck will probably never see rocks or mud, and will just be a driver. So I doubt that I will have any problems with breakage.

Now my next question, what kind of RPM can I expect with 35's TH350 and 3.42 gears at 65mph?

I came up with 2134 RPM. I always thought 3.42s would be about right.

Gene · 08-26-2009, 05:28 PM

Quote:

Originally Posted by martindc1

I came up with 2134 RPM. I always thought 3.42s would be about right.

That's just about what my 99 runs at 65 in overdrive, and it's a3.73 rear, thanks Martin.

08-23-2009, 08:45 PM	#1
Gene Registered User Join Date: Aug 2002 Location: Muskogee, Oklahoma Posts: 2,914	What kind of Posi do I have here? Pulled the covers to check ratios and I noticed the rear diff. looks to be a posi? It looks different than my 71 (no clutches) is this factory or aftermarket? Oh and i'm planning on running 35's with either the set that came with the truck(3.07) or these (3.42). Yeah I know that's pretty tall gearing for such large tires, but I don't plan on any rock crawling in this truck. Will I notice a huge difference between the two ratios? Attached Images

08-23-2009, 10:36 PM	#2
67chevtruck Registered User Join Date: Jan 2008 Location: west richland WA Posts: 61	Re: What kind of Posi do I have here? it looks like an auburn posi to me and i would get rid of it as soon as possible if you want to spin both tires because i had one in my truck after about 2 months it was just like an open it would not ever spin both tires __________________ 67' chevy k10 350 sm420 Last edited by 67chevtruck; 08-23-2009 at 10:41 PM.

08-24-2009, 07:58 AM	#3
OLDCHEV4X4 Registered User Join Date: Apr 2000 Location: Chester County PA, USA Posts: 1,228	Re: What kind of Posi do I have here? It looks after market. But looks simular to a Eaton. Was the fluid clean? Was there any chunks of stuff in the fluid? Hold one axle and get a buddy to try and turn the other axle. If its tight, run it. But not hard, cause 35" tires will be hard on it. __________________ 72 k/10 short wideside 72 k/5 Blazer 72 K/5 Blazer - obstacle course racer 72 custom/10 8' bed 70 K/5 Blazer 67 C-30 GMC Flat bed 86 GMC K2500 Plow Truck 85 GMC K3500 84 M1008 85 M1008 77 G30 Motor Home 72 Sears 12hp Tractor Glenmoore, Pennsylvania

08-24-2009, 05:04 PM	#4
Gene Registered User Join Date: Aug 2002 Location: Muskogee, Oklahoma Posts: 2,914	Re: What kind of Posi do I have here? Both sides turn, yes the fluid was very clean and looks like it was assembled not long ago. So I have a choice between factory posi(3.07), or one-legged(3.07), or this one(3.42) which one is best? BTW this rear came out of a 91 Burb if that helps? Last edited by Gene; 08-24-2009 at 05:05 PM. Reason: forgot info

08-25-2009, 07:40 AM	#5
special-K Special Order Join Date: Nov 2004 Location: Mt Airy, MD Posts: 85,862	Re: What kind of Posi do I have here? I`d go with the 3.42 and Auburn,if that`s what it is.I ran one in my`90 Blazer with 33s,3.08s,and 4spd.It performed flawlessly.I think you`ll be about the same with 35s and 3.42s.I`m not sure if Auburns are recommended for over 33" tires,though. __________________ "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 ~

08-25-2009, 10:19 PM	#7
71blksuper4x4 SWB 4x4 Collector Join Date: Jun 2001 Location: Osage City, KS Posts: 5,151	Re: What kind of Posi do I have here? Gene, I run 3.73 with my 35''s for a couple of years. The factory tach read right around 2700-3000 at 65mph. Trevor __________________ TREVOR 1970 CST swb 4x4 (speedwarning,cruise,tilt,tach,8track, original red shoulder belts,tow hooks) 1972 Jimmy (soon to be Hickey cloned) 1971 Cheyenne Super 4x4 swb (tilt,tach,buckets, original blue shoulder belts,am/fm,cruise,tow hooks, dealer 8 track) 1972 Cheyenne Super K20 4x4 Custom Camper (tilt, tach, am/fm, tow hooks, bed toolbox, aux gas tank 1972 Cheyenne Super Crew Cab K30 4x4 Duramax, Allison, np205, buckets, tow hooks (CURRENT PROJECT) http://67-72chevytrucks.com/vboard/s...d.php?t=624819 1989 V3500 Crew Cab (454tbi, NV4500, np205) 1970 Chevelle SS (LS5 454,th400,8track,buckets,tach) :2004 Jeep Wrangler Rubicon (daily driver) WTB: 1968-70 Cruise Control Lever



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