Is my 12bolt a posi?? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Ed ke6bnl · 04-23-2003, 07:21 PM

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I can use some advice on the 12 bolt 6 lug posi 3.73 I have. I opened it up and what I see are like three spider gears in a U shape. I saw in the book some type of posi that had a flat sring like device in the center and a clutch disks. I would like to know how to tell if this is positraction and if so how can I tell if it is in working order. Both axles turn the same direction when I rotate the pinion when both wheels are off the ground. My boy needs this for his 12 bolt 5 lug that is making some serious noises. Can we put his 5 lug axles in the 6 lug rear end that appears to be the same width. Sorry about all the question I am not up on this stuff. We did pull the axles to see how it all worked from what we have read. Thanks Ed ke6bnl So.Calif

Rod · 04-23-2003, 08:47 PM

Look inside and if you see a spring pack like the picture then you have to correct type posi for these trucks.

Axles changed lenght in 1970... some 1970.. and I mean some are the same lenght as the 5 bolt pattern axles from 71 and 72. They(the 72 axles) will be able to be swapped into the 70 axle housing if it happens you have the correct 70 posi diff sitting there. http://www.americanclassic.com/paint.htm?p1=axles
Diffs can be identified as to which year they are from by a stamped number on the right tube of the axle .

There is kinda back yard mod that can work also... I have run the longer 1972 5 bolt pattern axles in say a 69 diff using 73 and up larger brake drums. Larger in that they are deeper. The larger drums takes up the 3/4 inch lenght difference between the two axles years differences... I cant recommend it but it has worked on a truck I drove and I didnt notice any worse for wear difference in braking.

Ed ke6bnl · 04-24-2003, 02:33 AM

Quote:

Originally posted by Rod
Look inside and if you see a spring pack like the picture then you have to correct type posi for these trucks.

Axles changed lenght in 1970... some 1970.. and I mean some are the same lenght as the 5 bolt pattern axles from 71 and 72. They(the 72 axles) will be able to be swapped into the 70 axle housing if it happens you have the correct 70 posi diff sitting there. http://www.americanclassic.com/paint.htm?p1=axles
Diffs can be identified as to which year they are from by a stamped number on the right tube of the axle .

There is kinda back yard mod that can work also... I have run the longer 1972 5 bolt pattern axles in say a 69 diff using 73 and up larger brake drums. Larger in that they are deeper. The larger drums takes up the 3/4 inch lenght difference between the two axles years differences... I cant recommend it but it has worked on a truck I drove and I didnt notice any worse for wear difference in braking.

Rod tha looks like what we have but there is no spring pack in there, would there be a unit without the spring pack. Does your picture one have a large pin that goes all the way through?? There are some really abeat up wahers on the end of the axle between the spicer gear and the throughpin that do nothing, could we be missing that part, and if so can the rear be used as it is?? Thanks Ed

Ed ke6bnl · 04-24-2003, 02:35 AM

Quote:

Originally posted by Rod
Look inside and if you see a spring pack like the picture then you have to correct type posi for these trucks.

Axles changed lenght in 1970... some 1970.. and I mean some are the same lenght as the 5 bolt pattern axles from 71 and 72. They(the 72 axles) will be able to be swapped into the 70 axle housing if it happens you have the correct 70 posi diff sitting there. http://www.americanclassic.com/paint.htm?p1=axles
Diffs can be identified as to which year they are from by a stamped number on the right tube of the axle .

There is kinda back yard mod that can work also... I have run the longer 1972 5 bolt pattern axles in say a 69 diff using 73 and up larger brake drums. Larger in that they are deeper. The larger drums takes up the 3/4 inch lenght difference between the two axles years differences... I cant recommend it but it has worked on a truck I drove and I didnt notice any worse for wear difference in braking.

Rod that looks like what we have but there is no spring pack in there, would there be a unit without the spring pack. Does your pictured one have a large pin that goes all the way through?? There are some really beat up wahers on the end of the axle between the spider gear and the through pin that do nothing, could we be missing that part, and if so can the rear be used as it is?? Thanks Ed

mikep · 04-24-2003, 07:12 AM

Those beat up washers are c clips and they retain the axles as in keep them from falling out. If you dont have the spring pack you dont have a positraction unit. If both axles are turning the same way when you turn the driveshaft you may have a problem with the spider gears.

Ed ke6bnl · 04-24-2003, 07:28 AM

Quote:

Originally posted by Ed ke6bnl

Rod that looks like what we have but there is no spring pack in there, would there be a unit without the spring pack. Does your pictured one have a large pin that goes all the way through?? There are some really beat up wahers on the end of the axle between the spider gear and the through pin that do nothing, could we be missing that part, and if so can the rear be used as it is?? Thanks Ed

There are C washers there that hold the axle but these washer are about .015 and are sitting loose between the C washer and the pin that keeps the C wasners in place. ED ke6bnl

Rod · 04-24-2003, 08:33 AM

If there is no spring pack...probably someone took the posi out and you have a regular carrier in there. The pin I think your talkin about is on both type carriers...posi and non-posi.

mikep · 04-24-2003, 09:47 AM

I dont think you have a posi carrier. I think someone at one point did the old poor mans posi trick in your differential and added shims between the differential cross pin and the spider gears. Theres different ways to do it but in your case it added a bit of preload between the axles. Its not very effective and it causes a lot of wear to the differential cross pin and to the spiders. I'd take the washers out and remove the cross pin to check for damage and the spiders as well. I'll bet you'll find a lot of scoring of the differential cross pin . For the cost of new parts you could probably find yourself a good used 12 bolt limited slip carrier.

04-23-2003, 07:21 PM	#1
Ed ke6bnl Registered User Join Date: Mar 2002 Location: Agua Dulce, Ca. usa Posts: 179	Is my 12bolt a posi?? -------------------------------------------------------------------------------- I can use some advice on the 12 bolt 6 lug posi 3.73 I have. I opened it up and what I see are like three spider gears in a U shape. I saw in the book some type of posi that had a flat sring like device in the center and a clutch disks. I would like to know how to tell if this is positraction and if so how can I tell if it is in working order. Both axles turn the same direction when I rotate the pinion when both wheels are off the ground. My boy needs this for his 12 bolt 5 lug that is making some serious noises. Can we put his 5 lug axles in the 6 lug rear end that appears to be the same width. Sorry about all the question I am not up on this stuff. We did pull the axles to see how it all worked from what we have read. Thanks Ed ke6bnl So.Calif __________________ Ed ke6bnl Agua Dulce 70 S.E. Los Angeles 70 Chevy short bed 1948 F3 ford pu 1949 F1 stock V8 flathead 3 on floor 1950 F1 pu street rod 1948 F6 Ford Dually/350sbc no bed stock trans&rear 1972 El Camino 4" chop 1953 Chevy 3100 2b daily driver 1970 SB 4X4 400ci 6in lift

04-23-2003, 08:47 PM	#2
Rod Join Date: Dec 1999 Location: Eastern - Manitoba Canada, Winnipeg Posts: 4,369	Look inside and if you see a spring pack like the picture then you have to correct type posi for these trucks. Axles changed lenght in 1970... some 1970.. and I mean some are the same lenght as the 5 bolt pattern axles from 71 and 72. They(the 72 axles) will be able to be swapped into the 70 axle housing if it happens you have the correct 70 posi diff sitting there. http://www.americanclassic.com/paint.htm?p1=axles Diffs can be identified as to which year they are from by a stamped number on the right tube of the axle . There is kinda back yard mod that can work also... I have run the longer 1972 5 bolt pattern axles in say a 69 diff using 73 and up larger brake drums. Larger in that they are deeper. The larger drums takes up the 3/4 inch lenght difference between the two axles years differences... I cant recommend it but it has worked on a truck I drove and I didnt notice any worse for wear difference in braking. Attached Images __________________ 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.

04-24-2003, 07:12 AM	#5
mikep Used to have a truck Join Date: May 2002 Location: port orchard WA Posts: 1,552	Those beat up washers are c clips and they retain the axles as in keep them from falling out. If you dont have the spring pack you dont have a positraction unit. If both axles are turning the same way when you turn the driveshaft you may have a problem with the spider gears. __________________ No truck :-(

04-24-2003, 08:33 AM	#7
Rod Join Date: Dec 1999 Location: Eastern - Manitoba Canada, Winnipeg Posts: 4,369	If there is no spring pack...probably someone took the posi out and you have a regular carrier in there. The pin I think your talkin about is on both type carriers...posi and non-posi. __________________ 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.

04-24-2003, 09:47 AM	#8
mikep Used to have a truck Join Date: May 2002 Location: port orchard WA Posts: 1,552	I dont think you have a posi carrier. I think someone at one point did the old poor mans posi trick in your differential and added shims between the differential cross pin and the spider gears. Theres different ways to do it but in your case it added a bit of preload between the axles. Its not very effective and it causes a lot of wear to the differential cross pin and to the spiders. I'd take the washers out and remove the cross pin to check for damage and the spiders as well. I'll bet you'll find a lot of scoring of the differential cross pin . For the cost of new parts you could probably find yourself a good used 12 bolt limited slip carrier. __________________ No truck :-(



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