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

NINERS1 · 05-31-2012, 11:59 PM

been having issues with my transmission, sluggish,lots of rpm's to get moving. the problem started after i installed my new monster trans. and my 20" coys. was told by the guy that set up my 12 bolt that it had 273 gears and that my stall(1800-2200 rpm) are not matched, and that going to 373's would fix that. dont know why a 71 pickup would have 273 rearend in it, maybe to P.O. put it in for gas milage, but not what i want. anyway, really soft shifts also. so would this fix my issues? 373's and a shift kit?

clinebarger · 06-01-2012, 08:57 PM

Quote:

Originally Posted by NINERS1

been having issues with my transmission, sluggish,lots of rpm's to get moving. the problem started after i installed my new monster trans. and my 20" coys. was told by the guy that set up my 12 bolt that it had 273 gears and that my stall(1800-2200 rpm) are not matched, and that going to 373's would fix that. dont know why a 71 pickup would have 273 rearend in it, maybe to P.O. put it in for gas milage, but not what i want. anyway, really soft shifts also. so would this fix my issues? 373's and a shift kit?

Ive never seen a truck 12-bolt have 2:73's, Alot of 3:08's though.
Im guessing you have a 700R4? If so go 3:73's.....A standard 3:73.1 gear set will not fit your 3-series carrier, You will need a gear set with a thick ring gear like this http://www.summitracing.com/parts/MGR-GM12-373X/ Or buy a 4-series carrier & a gear set.

On the soft shifts...I really need to know what trans you have & what was done when it was rebuilt?

**Captainfab** · 06-02-2012, 12:44 AM

Yep, GM did put 2.76 gears in some of the truck 12 bolts. In fact I sold a set to another forum member a few months ago. He has since decided against using them.

Quote:

Originally Posted by clinebarger

Ive never seen a truck 12-bolt have 2:73's, Alot of 3:08's though.
Im guessing you have a 700R4? If so go 3:73's.....A standard 3:73.1 gear set will not fit your 3-series carrier, You will need a gear set with a thick ring gear like this http://www.summitracing.com/parts/MGR-GM12-373X/ Or buy a 4-series carrier & a gear set.

On the soft shifts...I really need to know what trans you have & what was done when it was rebuilt?

NINERS1 · 06-02-2012, 12:45 AM

hey clinebarger, it has a 400 turbo from monster transmission, they said it does not have a shift kit in it, I ordered a set of 373's, so it won't fit my carrier? please excuse my ignorance, don't know much about rear end gears, the set you posted from summit looks like what i ordered, 373's for 12 bolt gm truck. so i need to change the carrier too? thanks for helping me!

**Captainfab** · 06-02-2012, 01:02 AM

If you bought the set with the thick ring gear, as clinebarger linked to, you will be okay. If you just ordered the standard gear set, you will need a 4 series carrier to install those gears.

KQQL IT · 06-02-2012, 01:10 AM

2:73's in late 70's diesel pickups. Got one by accident... already had axle pads welded on the bottom.
Made for awesome long burnouts!
Posted via Mobile Device

NINERS1 · 06-02-2012, 02:34 AM

Quote:

Originally Posted by Captainfab

If you bought the set with the thick ring gear, as clinebarger linked to, you will be okay. If you just ordered the standard gear set, you will need a 4 series carrier to install those gears.

not sure if it is the thick ring gear or not, discription says(GM12BL 8.875R/P 3.73 MG

clinebarger · 06-03-2012, 08:14 PM

Quote:

Originally Posted by NINERS1

hey clinebarger, it has a 400 turbo from monster transmission, they said it does not have a shift kit in it, I ordered a set of 373's, so it won't fit my carrier? please excuse my ignorance, don't know much about rear end gears, the set you posted from summit looks like what i ordered, 373's for 12 bolt gm truck. so i need to change the carrier too? thanks for helping me!

Quote:

Originally Posted by NINERS1

not sure if it is the thick ring gear or not, discription says(GM12BL 8.875R/P 3.73 MG

With a 3-speed auto, You might consider 3:42.1 gears, Standard 3:42's will fit your 3-series carrier.

The thick ring gear 3:73's will have a X at the end of the part number.

A TransGo shift kit http://transgoonline.com/products.ph...dcountview=Yes will help your soft shifts.

NINERS1 · 06-04-2012, 12:15 PM

Yea I ordered the wrong one! I would not have known with out you guys!!! Got a b&m shift kit also. thanks guys for your help!!!

05-31-2012, 11:59 PM	#1
NINERS1 Registered User Join Date: Feb 2006 Location: weatherford ok. Posts: 255	Trans & rear end compatible been having issues with my transmission, sluggish,lots of rpm's to get moving. the problem started after i installed my new monster trans. and my 20" coys. was told by the guy that set up my 12 bolt that it had 273 gears and that my stall(1800-2200 rpm) are not matched, and that going to 373's would fix that. dont know why a 71 pickup would have 273 rearend in it, maybe to P.O. put it in for gas milage, but not what i want. anyway, really soft shifts also. so would this fix my issues? 373's and a shift kit? __________________ 71 chevy cheyenne lwb http://s321.photobucket.com/albums/n..._tab_my_albums Democracy is two wolves and a lamb voting on what to have for lunch. Liberty is a well-armed lamb contesting the vote!

06-02-2012, 12:45 AM	#4
NINERS1 Registered User Join Date: Feb 2006 Location: weatherford ok. Posts: 255	Re: Trans & rear end compatible hey clinebarger, it has a 400 turbo from monster transmission, they said it does not have a shift kit in it, I ordered a set of 373's, so it won't fit my carrier? please excuse my ignorance, don't know much about rear end gears, the set you posted from summit looks like what i ordered, 373's for 12 bolt gm truck. so i need to change the carrier too? thanks for helping me! __________________ 71 chevy cheyenne lwb http://s321.photobucket.com/albums/n..._tab_my_albums Democracy is two wolves and a lamb voting on what to have for lunch. Liberty is a well-armed lamb contesting the vote! Last edited by NINERS1; 06-02-2012 at 12:54 AM.

06-02-2012, 01:02 AM	#5
Captainfab 60-66 Nut Join Date: Mar 2007 Location: Coeur d'Alene, Idaho Posts: 23,254	Re: Trans & rear end compatible If you bought the set with the thick ring gear, as clinebarger linked to, you will be okay. If you just ordered the standard gear set, you will need a 4 series carrier to install those gears. __________________ Power Steering Box Adapter Plates For Sale HERE Power Brake Booster Adapter Brackets For Sale '63-'66 HERE and '67-'72 HERE and '60-'62 HERE and "60-'62 with clutch HERE Rear Disc Brake Brackets For Sale. Impala SS calipers HERE Camaro Calipers HERE D52 Calipers HERE 6 Lug HERE Hydroboost Mounting Plates HERE

06-02-2012, 01:10 AM	#6
KQQL IT At the body shop. Join Date: Aug 2009 Location: Land of fruits and nuts. Posts: 5,316	Re: Trans & rear end compatible 2:73's in late 70's diesel pickups. Got one by accident... already had axle pads welded on the bottom. Made for awesome long burnouts! Posted via Mobile Device __________________ " That didnt make it any newer " " Dont antique the equipment "

06-04-2012, 12:15 PM	#9
NINERS1 Registered User Join Date: Feb 2006 Location: weatherford ok. Posts: 255	Re: Trans & rear end compatible Yea I ordered the wrong one! I would not have known with out you guys!!! Got a b&m shift kit also. thanks guys for your help!!! __________________ 71 chevy cheyenne lwb http://s321.photobucket.com/albums/n..._tab_my_albums Democracy is two wolves and a lamb voting on what to have for lunch. Liberty is a well-armed lamb contesting the vote!



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