3.73 posi rear question. - The 1947 - Present Chevrolet & GMC Truck Message Board Network

cheyenne402 · 02-10-2007, 04:56 PM

I have a question about switching rear ends in my 1971 Cheyenne. I have an oppurtunity to get a 3.73 posi out of a 71-72 GMC. The only problem is I have a coil rear in my truck and the posi is a leaf spring. Can I switch gears between the two? My truck is an original 402 big block with 3 speed on the tree. Glovebox does not say what rear ratio I have.

Any help?

leftcoast66 · 02-10-2007, 04:58 PM

ya, you can switch gears, but you're gonna need to shim it so that it's setup correctly.

70GMCer · 02-11-2007, 06:58 AM

I also believe it depends on what size gears and what size posi carrier you have. Someone else can be more clear this.....

powell72 · 02-11-2007, 01:58 PM

I'm assuming you're switching gears and carrier, if that's the case, you'll be fine. If you're switching one or the other you need to find your current ratio, there is a carrier split at 3.73 and up (numerical). Use the pinion shim that is currently on the setup you're getting to get you in the ballpark for install.

cdowns · 02-11-2007, 03:15 PM

i'd think i'd be easier and cheaper to weld on the proper brackets than to take apart and reassemble 2rearends

msgross · 02-11-2007, 04:02 PM

either way you have a little work ahead of you. I'm doing a carrier swap for my front axle Dana 44. Find a buddy that has done one or the other and go that way. As long as the bearings are good in the donor axle.... Might not hurt to find a shop that has the tools and experience since it would suck to ruin your axle and gears @ 70+ MPH.

cheyenne402 · 02-16-2007, 08:35 AM

ttt

BowTieOgre · 02-16-2007, 09:49 AM

If your current rear ratio is 3.73 or above then you have a 4 series carrier, if your current ratio is below 3.73 then you have a 3 series carrier. Either way you should just have to swap the carriers with ring gear attached and shim it right. (easier said than done) If you decide to weld on some axle saddles let me know, ive got a pair im not using anymore. (a good friend talked me out of using a 10 bolt)

70GMCer · 02-17-2007, 07:50 AM

Again, I may be wrong , but if you have a 3.73 gear, you can use either the 3 or 4 series carrier.....Don't mean to hijack here.....

crazy longhorn · 02-17-2007, 10:44 AM

Quote:

Originally Posted by 70GMCer

Again, I may be wrong , but if you have a 3.73 gear, you can use either the 3 or 4 series carrier.....Don't mean to hijack here.....

AFTERMARKET, you can get 3.73/4.10/4.56 gears that fit a 3 series carrier. FACTORY, however run 2.76-3.42 on a 3 series carrier, & 3.73/4.10/4.56 are on a 4 series carrier. with the factory gears, the gears & carriers need to be swapped together (accordingly).

L

02-10-2007, 04:56 PM	#1
cheyenne402 Registered User Join Date: Jul 2005 Location: Owosso, Michigan Posts: 783	3.73 posi rear question. I have a question about switching rear ends in my 1971 Cheyenne. I have an oppurtunity to get a 3.73 posi out of a 71-72 GMC. The only problem is I have a coil rear in my truck and the posi is a leaf spring. Can I switch gears between the two? My truck is an original 402 big block with 3 speed on the tree. Glovebox does not say what rear ratio I have. Any help?

02-10-2007, 04:58 PM	#2
leftcoast66 Registered User Join Date: Sep 2006 Location: Covington, WA Posts: 770	Re: 3.73 posi rear question. ya, you can switch gears, but you're gonna need to shim it so that it's setup correctly.

02-11-2007, 06:58 AM	#3
70GMCer Senior Member Join Date: Apr 2005 Location: Joppa, Maryland Posts: 4,408	Re: 3.73 posi rear question. I also believe it depends on what size gears and what size posi carrier you have. Someone else can be more clear this..... __________________ 1997 GMC Sierra Ext 1965 Mustang

02-11-2007, 01:58 PM	#4
powell72 Senior Member Join Date: Jan 2005 Location: Loveland Co. Posts: 3,098	Re: 3.73 posi rear question. I'm assuming you're switching gears and carrier, if that's the case, you'll be fine. If you're switching one or the other you need to find your current ratio, there is a carrier split at 3.73 and up (numerical). Use the pinion shim that is currently on the setup you're getting to get you in the ballpark for install. __________________ Chris 74 Custom Deluxe SWB 350/350/3.73’s 99 2wd Silverado RCSB 5.3/4L60/3.90’s http://www.classictrucks.com/feature...short_bed.html

02-11-2007, 03:15 PM	#5
cdowns Senior Member Join Date: Jan 2003 Location: daytonabeach Posts: 22,956	Re: 3.73 posi rear question. i'd think i'd be easier and cheaper to weld on the proper brackets than to take apart and reassemble 2rearends __________________ 71c-10 350/2004r/4:11 lowered3/4 longbed/dead by hurricane MEANING OF DEATH::::: SOMEBODY ELSE GETS YOUR STUFF DONT BELIEVE EVERYTHING YOU THINK TAKE MY ADVISE;I DON'T USE IT ANYWAY

02-11-2007, 04:02 PM	#6
msgross Registered User Join Date: Jul 2006 Location: Central PA Posts: 12,201	Re: 3.73 posi rear question. either way you have a little work ahead of you. I'm doing a carrier swap for my front axle Dana 44. Find a buddy that has done one or the other and go that way. As long as the bearings are good in the donor axle.... Might not hurt to find a shop that has the tools and experience since it would suck to ruin your axle and gears @ 70+ MPH. __________________ The Garage: 1968 K-10 SWB - "Project Money Pit" 1996 Z-71 - "huntin rig" 1969 C-10 LWB (SOLD) "Project flip that truck or else" 1993 Passport, F@rd 1-ton (SOLD)"Project Cousin Eddie" My Garage Build "The 1,000 footer"

02-16-2007, 08:35 AM	#7
cheyenne402 Registered User Join Date: Jul 2005 Location: Owosso, Michigan Posts: 783	Re: 3.73 posi rear question. ttt

02-16-2007, 09:49 AM	#8
BowTieOgre Registered User Join Date: Mar 2006 Location: Pensacola, FL Posts: 1,461	Re: 3.73 posi rear question. If your current rear ratio is 3.73 or above then you have a 4 series carrier, if your current ratio is below 3.73 then you have a 3 series carrier. Either way you should just have to swap the carriers with ring gear attached and shim it right. (easier said than done) If you decide to weld on some axle saddles let me know, ive got a pair im not using anymore. (a good friend talked me out of using a 10 bolt) __________________ 1986 C10 - LWB, 305/700r4, posi, vortec heads

02-17-2007, 07:50 AM	#9
70GMCer Senior Member Join Date: Apr 2005 Location: Joppa, Maryland Posts: 4,408	Re: 3.73 posi rear question. Again, I may be wrong , but if you have a 3.73 gear, you can use either the 3 or 4 series carrier.....Don't mean to hijack here..... __________________ 1997 GMC Sierra Ext 1965 Mustang



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