Rear swap help - The 1947 - Present Chevrolet & GMC Truck Message Board Network

brad20653 · 07-25-2003, 10:06 PM

Can someone give me step by step maybe pictures on swapping my rear gears for 3:73's its a 72 chevy longbed 1/2 ton

brad20653 · 07-26-2003, 08:15 AM

t

brad20653 · 07-26-2003, 02:30 PM

1

70c10 · 07-26-2003, 03:06 PM

Brad , what are your current gears?. Are they 3:07's. If so, you will need a 4 series carrier to accomodate 3:73's.

brad20653 · 07-26-2003, 03:48 PM

i dont know what they are

68_c10_on20s · 07-26-2003, 05:55 PM

my best advise is do what i did take it to a shop it will cost about 800 for a new posi and gear and seals and carriers but its worth it its a pain in the azz to do....

lukecp · 07-26-2003, 06:07 PM

You need to find out what gear ratio you have right now....do you have a tach? If so, what RPM is your engine turning at various speeds?

If you do have 3.07's, and want to swap to 3.73's the cheapest way to do it would be to go pick up a used rear axle that already has 3.73 gears from a salvage yard. The rear axle will proably cost less then just a new set of 3.73 gears alone. You can bolt it in yourself, or take it somewhere to get it done.

brad20653 · 07-26-2003, 08:06 PM

no tach

jewels. · 07-26-2003, 09:12 PM

i measured my rearend by lifting the rear end and turning the tire. then count the number of rotations of the driveshaft for one full turn of the rear tire.

my gears are 3.73, and here is how i found that out:

1 turn of rear tire = 1-7/8 turn of driveshaft (or 1.875 turns)

2 wheels x 1-7/8 = 3.75 (which is approx 3.73)

this estimate is enough to give you a good idea of your current ratio.

if you cannot get it this way, or you prefer a more exact approach, you can open up the rear end and read the exact ratio off of the main gear (i believe it is marked on the face of the ring gear).
it cant hurt to open up the rear and replace the old diff fluid (which probably could stand to be replaced if it hasnt been replaced in its 30-year lifetime)

good luck!
jewels.

Low69CST · 07-27-2003, 09:07 AM

I've got some open carriers with 3.73's. If you'd be interested in one let me know, they would need to be gone through though.

07-25-2003, 10:06 PM	#1
brad20653 Senior Member Join Date: Jul 2003 Location: So. MD Posts: 218	Rear swap help Can someone give me step by step maybe pictures on swapping my rear gears for 3:73's its a 72 chevy longbed 1/2 ton

07-26-2003, 03:06 PM	#4
70c10 67-72 Addict! Join Date: Feb 2002 Location: The TAX State! Posts: 7,857	Brad , what are your current gears?. Are they 3:07's. If so, you will need a 4 series carrier to accomodate 3:73's. __________________ Jim 1970 C/10 Fleetside w/Ghost Flames Lowered 4.5" front and 4" rear (Raked) 355/350 Turbo w/shift kit 10" Redneck Performance Verter w/2500 stall Hooker Super Comps part#2808-1 Performer RPM Air-Gap 12 Bolt w/3:73 gears- Eaton Posi Comp Cams XE262 with 1.6 Crane Energizers, Road Demon 625 and Brodix IK 180 heads

07-26-2003, 05:55 PM	#6
68_c10_on20s Registered User Join Date: Aug 2002 Location: Waxahachie TX Posts: 773	gears my best advise is do what i did take it to a shop it will cost about 800 for a new posi and gear and seals and carriers but its worth it its a pain in the azz to do.... __________________ 93 Fleet Budget Build http://s150.photobucket.com/albums/s...zted71/hoopty/

07-26-2003, 06:07 PM	#7
lukecp Formerly yellow72custom Join Date: May 2001 Location: Austin, TX Posts: 7,531	You need to find out what gear ratio you have right now....do you have a tach? If so, what RPM is your engine turning at various speeds? If you do have 3.07's, and want to swap to 3.73's the cheapest way to do it would be to go pick up a used rear axle that already has 3.73 gears from a salvage yard. The rear axle will proably cost less then just a new set of 3.73 gears alone. You can bolt it in yourself, or take it somewhere to get it done. __________________ '72 Chevy C10 Mild 350/TH350/3.07. Ochre/White. Old high school ride. '70 GMC C2500 '62 327 4bbl/SM465/4.56-geared Dana 60. White/White. Project or parts truck. '97 Saturn SL DD. 1.9/5-speed. 40+ highway mpg

07-26-2003, 09:12 PM	#9
jewels. Registered User Join Date: Jul 2001 Location: Munster, IN Posts: 1,100	i measured my rearend by lifting the rear end and turning the tire. then count the number of rotations of the driveshaft for one full turn of the rear tire. my gears are 3.73, and here is how i found that out: 1 turn of rear tire = 1-7/8 turn of driveshaft (or 1.875 turns) 2 wheels x 1-7/8 = 3.75 (which is approx 3.73) this estimate is enough to give you a good idea of your current ratio. if you cannot get it this way, or you prefer a more exact approach, you can open up the rear end and read the exact ratio off of the main gear (i believe it is marked on the face of the ring gear). it cant hurt to open up the rear and replace the old diff fluid (which probably could stand to be replaced if it hasnt been replaced in its 30-year lifetime) good luck! jewels. __________________ 68 C10 Red Step 350 my first child & main focus 58 3200 Apache LWB Step the upcoming project

07-26-2003, 08:15 AM	#2
brad20653 Senior Member Join Date: Jul 2003 Location: So. MD Posts: 218	t

07-26-2003, 02:30 PM	#3
brad20653 Senior Member Join Date: Jul 2003 Location: So. MD Posts: 218	1

07-26-2003, 03:48 PM	#5
brad20653 Senior Member Join Date: Jul 2003 Location: So. MD Posts: 218	i dont know what they are

07-26-2003, 08:06 PM	#8
brad20653 Senior Member Join Date: Jul 2003 Location: So. MD Posts: 218	no tach

07-27-2003, 09:07 AM	#10
Low69CST Registered User Join Date: May 2000 Location: Frankfort, Kentucky, USA Posts: 2,163	I've got some open carriers with 3.73's. If you'd be interested in one let me know, they would need to be gone through though. __________________ '69 CST Short fleetside Lowered, 400 small block, 700R4, 4 wheel disc brakes, front sway bar & rear camaro sway bar (in progress) '87 V10 4x4 Short Fleetside Quad Suspension and Dual Tanks



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