'77 12 Bolt w/ 3:55 gears - The 1947 - Present Chevrolet & GMC Truck Message Board Network

littlebubba · 03-14-2003, 11:11 PM

Can anybody tell me for sure if the 77 12 Bolt truck rearends came with stock 3:55 gears? Guy near me says he has an original matched set out of 77 (pinion has 11 teeth, ring gear has 39), I can buy cheap to put in my '81 12 bolt.

AirMale · 03-15-2003, 09:39 AM

Most stock truck 12 bolts came with 3.08's. I've only seen 3.42 or 3.73 gears for a 3 series carrier.

low 84 · 03-15-2003, 09:13 PM

i don't think any fo the truck rears came with 3.55's. if you look in a catalouge for gears, like richmond, the don't list any 3.55 gears available for 12 bolt truck rears. but if you look at the car 12 bolt listing they sell 3.55's for them. so i think only car 12 bolts came with 3.55's from the factory. not 100% sure though

**crossy** · 03-15-2003, 11:47 PM

the 3.55's COULD be aftermarket ?? but Chevrolet offered them with 2.73. 3.07( most common), 3.40 and 3.73 in the 1/2 ton 12 bolts during their whole run from 73-80 , the 10 bolt actually became available as early as 78 . the 10 bolt had 2.56,2.73 (most common), 3.08, 3.42 and 3.73 ratios available. DAVE

**swervin ervin** · 03-16-2003, 03:36 PM

I may be wrong, have been before, but I don't think any truck ever came with 2.56 ratio gears. The highest ratio in a 10 bolt was 2.73. 2.56 was options is cars.

**crossy** · 03-16-2003, 04:38 PM

MIKE, you were right in being wrong :-) , 81-82 they were not that uncommon. i had an 82 SWB with em and when i dropped in the 3.73's it felt like I added 200 HP to that 305. DAVE

gchemist · 03-17-2003, 03:01 AM

The neighbor that sold me the aluminum wheels on BAD BOW had the 2.5? gears. His was a 305 with 350TH tranny. That thing was a real dawg. Best gas milage I ever saw on these trucks though.

Tom · 03-17-2003, 07:23 PM

Both my trucks have 12bolts with 3.42's from the factory.

**swervin ervin** · 03-17-2003, 08:15 PM

Well damn, I thought they were stupid for using 2.73's. What good would a truck be with 2.56 gears. I swear, GM does some weird stuff sometimes. Although, if you think about it. 2.56 gears and a TH350 would be better than 2.73's and a 700R4, right? Maybe not. At least the 700R4 does have a very low first gear to help get it moving.

I guess when they thought of 2.56 ratio, they were saying "well, let's build a truck that can run on Bonneville Salt Flats". Yeah that's it. We need to get it up to 200 mph. Too bad they didn't put a better engine over a sucky 305.

Ah, the 80's. Beginning of the great fuel crunch.

03-14-2003, 11:11 PM	#1
littlebubba Registered User Join Date: Jun 2002 Location: Clinton Twp., Michigan Posts: 321	'77 12 Bolt w/ 3:55 gears Can anybody tell me for sure if the 77 12 Bolt truck rearends came with stock 3:55 gears? Guy near me says he has an original matched set out of 77 (pinion has 11 teeth, ring gear has 39), I can buy cheap to put in my '81 12 bolt.

03-15-2003, 09:39 AM	#2
AirMale Senior Member Join Date: Jan 2003 Location: Atlantic City, NJ Posts: 1,073	Most stock truck 12 bolts came with 3.08's. I've only seen 3.42 or 3.73 gears for a 3 series carrier. __________________ 86 SWB 9.0 LITER T-400-OD 4.11 eaton-4/5 drop Best 1/4 12.51 @112mph no traction

03-15-2003, 09:13 PM	#3
low 84 Registered User Join Date: Jan 2002 Location: Houston, TX Posts: 2,144	i don't think any fo the truck rears came with 3.55's. if you look in a catalouge for gears, like richmond, the don't list any 3.55 gears available for 12 bolt truck rears. but if you look at the car 12 bolt listing they sell 3.55's for them. so i think only car 12 bolts came with 3.55's from the factory. not 100% sure though __________________ '51 F100, backhalf with a narrowed 9 and coil overs, 18.5" mickeys, monte front clip, +400" sbc in the works '05 1500 Crew Cab RIP '84 swb 5/7 drop, solid cammed 408 w/ fully ported dart heads, th350 w/ 10 inch hughes, 12 bolt w/ 3.73 richmonds and a locker '80 swb 4x4 in progress: 7" lift, 350 th350/np205, d44 and 1.5" ORD tie rod, 14BFF w/discs , armored diff covers, 40" MTR's

03-15-2003, 11:47 PM	#4
crossy Oh,you can't buy that new Join Date: Apr 2000 Location: Pennsville,N.J. 08070, USA Posts: 2,039	gears the 3.55's COULD be aftermarket ?? but Chevrolet offered them with 2.73. 3.07( most common), 3.40 and 3.73 in the 1/2 ton 12 bolts during their whole run from 73-80 , the 10 bolt actually became available as early as 78 . the 10 bolt had 2.56,2.73 (most common), 3.08, 3.42 and 3.73 ratios available. DAVE __________________ "been there, done that, ruined the T-shirt". 2007 LBZ GMC Sierra, ECSB 2006 LM7 RCSB Silverado 98 Vortec project. 94,3500,6.5L 4L80 81 SWB GMC POS finally gone 73 Pinto, stock, w/CragarSS's-eww LOTS of Cummins trucks.

03-16-2003, 03:36 PM	#5
swervin ervin You get what you pay for Join Date: Dec 1999 Location: Cherryville, NC Posts: 4,798	I may be wrong, have been before, but I don't think any truck ever came with 2.56 ratio gears. The highest ratio in a 10 bolt was 2.73. 2.56 was options is cars. __________________ Mike 1985 Chevy C-10

03-16-2003, 04:38 PM	#6
crossy Oh,you can't buy that new Join Date: Apr 2000 Location: Pennsville,N.J. 08070, USA Posts: 2,039	MIKE, you were right in being wrong :-) , 81-82 they were not that uncommon. i had an 82 SWB with em and when i dropped in the 3.73's it felt like I added 200 HP to that 305. DAVE __________________ "been there, done that, ruined the T-shirt". 2007 LBZ GMC Sierra, ECSB 2006 LM7 RCSB Silverado 98 Vortec project. 94,3500,6.5L 4L80 81 SWB GMC POS finally gone 73 Pinto, stock, w/CragarSS's-eww LOTS of Cummins trucks.

03-17-2003, 03:01 AM	#7
gchemist BAD BOW-Silverado XST Join Date: May 2000 Location: Senior Member from Austin, TX Posts: 6,431	The neighbor that sold me the aluminum wheels on BAD BOW had the 2.5? gears. His was a 305 with 350TH tranny. That thing was a real dawg. Best gas milage I ever saw on these trucks though. __________________ Gerardo a.k.a. Mad Chemist Silverado XST videos

03-17-2003, 07:23 PM	#8
Tom driving is in my blood Join Date: Dec 1999 Location: Mesa AZ Posts: 5,748	Both my trucks have 12bolts with 3.42's from the factory. __________________ -78 c10 short/step: 388cid, M20, 5/5 drop, lots more. Playtoy and first vehicle. -98 c1500 x-cab: 5.7L, 17" rims, 5/6 drop, flowmaster, helper bags,NBS rear disk brakes. -02 Suburban 4x4: leveled front -CBR600F4i, CBR600RR, CBR1000RR, and standup skis DISCLAIMER: I cant spell for the life of me.

03-17-2003, 08:15 PM	#9
swervin ervin You get what you pay for Join Date: Dec 1999 Location: Cherryville, NC Posts: 4,798	Well damn, I thought they were stupid for using 2.73's. What good would a truck be with 2.56 gears. I swear, GM does some weird stuff sometimes. Although, if you think about it. 2.56 gears and a TH350 would be better than 2.73's and a 700R4, right? Maybe not. At least the 700R4 does have a very low first gear to help get it moving. I guess when they thought of 2.56 ratio, they were saying "well, let's build a truck that can run on Bonneville Salt Flats". Yeah that's it. We need to get it up to 200 mph. Too bad they didn't put a better engine over a sucky 305. Ah, the 80's. Beginning of the great fuel crunch. __________________ Mike 1985 Chevy C-10



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