Posi rear end - The 1947 - Present Chevrolet & GMC Truck Message Board Network

super72bb · 02-10-2004, 01:54 AM

Hey there,

I had a long talk with a old mechanic the other day about installing a posi in my 1972 chev truck. He jumped up and down triing to tell me that "if I wanted to install a posi I would have to find a posi housing".

My argument was that they are all the same housing's and that installing a posi in my original limited slip housing was no problem. Even though I am still 90% sure I figured I would contact the experts for a third opinion. Am I right or wrong here.

**SS55** · 02-10-2004, 02:32 AM

You are correct. The differential housing is the same. The differential carrier determines whether it is a posi or non-posi.
The carrier also determines which range of ratios you can use.
Typically referred to as a 3-series or a 4-series. A 3-series is good for about 2.70 to 3.42, then the 4-series is good for 3.73 on up. Remember to add a limited slip additive to the gear oil when you convert to a posi carrier.

Darrell

74bowtie · 02-10-2004, 08:22 AM

Thats stange I had a guy around me say the same thing, He said that I have to check to see if the ribs are on the inside of the housing if so it can't take a posi. The ribs, I have only ever seen them on the outside to give the rearend stength. I thought to myself, this guy is nuts.

**JIMs70GMC** · 02-10-2004, 08:59 AM

Don't forget to top off the headlight fluid after installing the posi unit, the increased traction will cause it to slosh around and therefore evaporate faster.

Sounds like he was confusing carrier with housing. Just keep nodding your head.

FRENCHBLUE72 · 02-10-2004, 04:21 PM

While your under there changing the posi you may want to replace the old muffler bearing's too... Throw the posi in and show the old guy how to boil the hide's ..

Bowtie67 · 02-10-2004, 10:20 PM

67 C10 I switched mine over two years ago, no issues..

Alexis · 02-10-2004, 11:12 PM

i thought series 3 could hold a 3.73 at max and series 4 can hold 3.73 and up.

Canada20 · 02-10-2004, 11:38 PM

is it possible he meant that for a shadetree mechanic you'd need to find a complete setup, housing and all?

Greg

**SS55** · 02-11-2004, 01:42 AM

Alexis, you may right. I "refreshed"my memory by looking at Auburn Gear's posi carrier. Their 3 series is the 3.42 max. I thought that's what GM did as well, but that was many beers ago, so I could wrong.

Darrell

1969 GMC · 02-11-2004, 03:27 AM

Quote:

Originally posted by super72bb
My argument was that they are all the same housing's and that installing a posi in my original limited slip housing was no problem. Even though I am still 90% sure I figured I would contact the experts for a third opinion. Am I right or wrong here.

posi and limited slip are one in the same.

02-10-2004, 01:54 AM	#1
super72bb Senior Member Join Date: Jan 2002 Location: calgary,Alberta,Canada Posts: 387	Posi rear end Hey there, I had a long talk with a old mechanic the other day about installing a posi in my 1972 chev truck. He jumped up and down triing to tell me that "if I wanted to install a posi I would have to find a posi housing". My argument was that they are all the same housing's and that installing a posi in my original limited slip housing was no problem. Even though I am still 90% sure I figured I would contact the experts for a third opinion. Am I right or wrong here. __________________ 1972 CHEYENNE SUPER SWB BLACK. 402 BB, TH400, AIR, TILT, TACH, BUCKETS, CRUISE, AM/FM, 8 TRACK. My build thread: http://67-72chevytrucks.com/vboard/s...=1#post7120181

02-10-2004, 02:32 AM	#2
SS55 Registered User Join Date: Nov 2003 Location: San Diego, CA Posts: 62	Posi rear end You are correct. The differential housing is the same. The differential carrier determines whether it is a posi or non-posi. The carrier also determines which range of ratios you can use. Typically referred to as a 3-series or a 4-series. A 3-series is good for about 2.70 to 3.42, then the 4-series is good for 3.73 on up. Remember to add a limited slip additive to the gear oil when you convert to a posi carrier. Darrell __________________ Be wary of the light at the end of the tunnel....It might be a gorilla holding a flashlight! 71 Blazer, ex-4WD...Bought it that way 55 GMC 55 Belair 2dr HT 67 El Camino

02-10-2004, 08:22 AM	#3
74bowtie Registered User Join Date: Nov 2003 Location: Central NY Posts: 93	Thats stange I had a guy around me say the same thing, He said that I have to check to see if the ribs are on the inside of the housing if so it can't take a posi. The ribs, I have only ever seen them on the outside to give the rearend stength. I thought to myself, this guy is nuts. __________________ 69 Chevelle (Summer only ride, love to drive this) 72 Chevy Shortbox 4x2 (newest addition) 83 Chevy Shortbox 4x2 (project but its clean) 2001 S10 Ext. Cab 4x4 (daily driver)

02-10-2004, 08:59 AM	#4
JIMs70GMC user # 2756 Join Date: Jun 2001 Location: Chesapeake, Virginia Posts: 4,612	Don't forget to top off the headlight fluid after installing the posi unit, the increased traction will cause it to slosh around and therefore evaporate faster. Sounds like he was confusing carrier with housing. Just keep nodding your head. __________________ 1970 K25, 8' stepside bed 350/465/205 44 up front, 60 in the rear 4.10s rolling on 33" Dunlop MTs 1986 K5, 350/465/208 Dana 60/14 bolt from a cucv 36" Super Swampers TSL/SX 1983 K20 w/ CUCV axles, 350/700R4/208 sitting on 37" Goodyears 1986 M1031 6.2 diesel, TH400/NP205 locker in the rear and a LS in the front, all stock for now..... 1986 K30, 350/400/205 dana 60 and 14 bolt. I kept the drivetrain. Body/bad and chassis are gone. 1981 K30, 350/465/205 dana 60 and dually 14 bolt. Has a G80, and a flat bed. Going to replace the flat bed. 1985 K20, 350/400/208 10 bolt and SF 14 bolt. I wonder where I can find some 1 tons. Hmmmmm

02-10-2004, 04:21 PM	#5
FRENCHBLUE72 PROJECT 7DEUCE Join Date: Dec 2002 Location: GRANTS PASS OR Posts: 21,606	While your under there changing the posi you may want to replace the old muffler bearing's too... Throw the posi in and show the old guy how to boil the hide's .. __________________ GO BIG GREEN GO DUCKS MEMBER #6377 72 k-5 daily driver 6'' lift 35'' 350-350-205 slowly getting rust free. Project "7DEUCE" check out my build http://67-72chevytrucks.com/vboard/s...d.php?t=267665 Tim Powell..R.I.P EastSideLowlife..... R.I.P..

02-10-2004, 10:20 PM	#6
Bowtie67 Registered User Join Date: Jan 2004 Location: NH Posts: 2,266	67 C10 I switched mine over two years ago, no issues..

02-10-2004, 11:12 PM	#7
Alexis Member since 2000 Join Date: Dec 2000 Location: Mountain View Ca / Mexico Posts: 7,874	i thought series 3 could hold a 3.73 at max and series 4 can hold 3.73 and up.

02-10-2004, 11:38 PM	#8
Canada20 Registered User Join Date: Jun 2001 Location: Calgary, Alberta, Canada Posts: 802	is it possible he meant that for a shadetree mechanic you'd need to find a complete setup, housing and all? Greg __________________ No such thing as a stupid question, right?

02-11-2004, 01:42 AM	#9
SS55 Registered User Join Date: Nov 2003 Location: San Diego, CA Posts: 62	Alexis, you may right. I "refreshed"my memory by looking at Auburn Gear's posi carrier. Their 3 series is the 3.42 max. I thought that's what GM did as well, but that was many beers ago, so I could wrong. Darrell __________________ Be wary of the light at the end of the tunnel....It might be a gorilla holding a flashlight! 71 Blazer, ex-4WD...Bought it that way 55 GMC 55 Belair 2dr HT 67 El Camino



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