What size rearend? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

four-eyed stang · 03-20-2006, 12:46 AM

I have an 1/2 ton 81 LWB with a 305cid and TH350C. What size rearend do I have? I am looking to buy some 3:73's for pulling and need to now the housing size.

cliffsta · 03-20-2006, 01:38 AM

My 80 C10 305 + TH350C has 2.56 but who knows.

There's another post referencing gear sizes, might wanna check it out, too.

79BIG10 · 03-20-2006, 02:15 AM

Easiest way to tell is to count the bolts at the rear cover. This will tell you what bolt size you have. It's probably a 10 bolt but it may be a 12 bolt. You also need to pop the cover off the differential to find out what carrier size you have unless you're wanting to install a new one. Count the teeth on the ring gear and the pinion. Divide smaller number into larger number and this will give you a gear ratio on what you have in there now. You will need this to find out what carrier you have. "Usually" the lower numerical numbers like 2.56, 3.08, 3.42 have a Series 3 carrier and a larger number gear ratio have a series 4 carrier. You can resue the carrier as long as you know what size it is and get the correct gear ratio for the carrier. If you want a 3.73 and you have a series 3 carrier you may have to get a thicker set from the manufacturer but need to contact them to be safe.

Nolowrider · 03-20-2006, 09:28 AM

79Big10 hit the nail on the head. I would say to probably have a 3.08. Not really sure what year they switched to the 10 bolt. But an 81 is around that time. Take a look on the rear end housing for a stamped number or a tag if you don't want to yank the cover off.

**swervin ervin** · 03-20-2006, 06:24 PM

Brandon is correct. I think a 3 series carrier will go up to 3.73 on a 10 bolt, at least it did on my 85.

four-eyed stang · 03-21-2006, 01:53 AM

I am looking for gears on Summit. It is a ten bolt. Would it be an 8.5?

**swervin ervin** · 03-21-2006, 02:03 AM

Yes, it's a 8.5.

piecesparts · 03-21-2006, 08:39 PM

Look at Rand'ys Ring and Pinion website for more info.

four-eyed stang · 03-22-2006, 12:24 AM

Thanks everyone

03-20-2006, 12:46 AM	#1
four-eyed stang Registered User Join Date: Dec 2005 Location: Dallas Posts: 29	What size rearend? I have an 1/2 ton 81 LWB with a 305cid and TH350C. What size rearend do I have? I am looking to buy some 3:73's for pulling and need to now the housing size.

03-20-2006, 01:38 AM	#2
cliffsta Stepsides RULE Join Date: Jul 2004 Location: Pineville, LA Posts: 1,921	Re: What size rearend? My 80 C10 305 + TH350C has 2.56 but who knows. There's another post referencing gear sizes, might wanna check it out, too. __________________ 1981 Chevy C10 Custom Deluxe Stepside 350 V8, headers, side exhausts, 3-speed auto SOLD 1980 Chevy C10 Custum Deluxe Stepside 305 V8, Edelbrock Performer Intake, Edelbrock 1406 600CFM 4-barrel, TH350C. Bent rod. SOLD 1984 GMC Sierra Classic Longbed 6.2L Diesel SOLD 2009 Kawasaki KLX-250S too many mods for this signature 1999 Honda Accord EX 4-cylinder, 17" Motegi Wheels 215/45/17 Sumitomo tires, Tein S-Tech lowering springs, KYB GR2 shocks, Acura TL 20mm rear swaybar, debadged, blackhoused headlights, Short-Ram Intake Cardomain of the Accord

03-20-2006, 02:15 AM	#3
79BIG10 I'm back with 2nd truck! Join Date: Feb 2002 Location: Texas Posts: 3,775	Re: What size rearend? Easiest way to tell is to count the bolts at the rear cover. This will tell you what bolt size you have. It's probably a 10 bolt but it may be a 12 bolt. You also need to pop the cover off the differential to find out what carrier size you have unless you're wanting to install a new one. Count the teeth on the ring gear and the pinion. Divide smaller number into larger number and this will give you a gear ratio on what you have in there now. You will need this to find out what carrier you have. "Usually" the lower numerical numbers like 2.56, 3.08, 3.42 have a Series 3 carrier and a larger number gear ratio have a series 4 carrier. You can resue the carrier as long as you know what size it is and get the correct gear ratio for the carrier. If you want a 3.73 and you have a series 3 carrier you may have to get a thicker set from the manufacturer but need to contact them to be safe. __________________ 1979 Chevrolet Bonanza Big10 "Tootsie Roll" 1985 Chevrolet Silverado (wife's) Member of the Southern Bowties Club "Don't underestimate how sexy a fat man who drinks to excess can be." Homer Simpson

03-20-2006, 09:28 AM	#4
Nolowrider Senior Member Join Date: Jan 2005 Location: New Orleans Posts: 1,365	Re: What size rearend? 79Big10 hit the nail on the head. I would say to probably have a 3.08. Not really sure what year they switched to the 10 bolt. But an 81 is around that time. Take a look on the rear end housing for a stamped number or a tag if you don't want to yank the cover off.

03-20-2006, 06:24 PM	#5
swervin ervin You get what you pay for Join Date: Dec 1999 Location: Cherryville, NC Posts: 4,798	Re: What size rearend? Brandon is correct. I think a 3 series carrier will go up to 3.73 on a 10 bolt, at least it did on my 85. __________________ Mike 1985 Chevy C-10

03-21-2006, 01:53 AM	#6
four-eyed stang Registered User Join Date: Dec 2005 Location: Dallas Posts: 29	Re: What size rearend? I am looking for gears on Summit. It is a ten bolt. Would it be an 8.5?

03-21-2006, 02:03 AM	#7
swervin ervin You get what you pay for Join Date: Dec 1999 Location: Cherryville, NC Posts: 4,798	Re: What size rearend? Yes, it's a 8.5.

03-21-2006, 08:39 PM	#8
piecesparts Parts and more parts Join Date: Nov 2003 Location: Lebo, Kansas (middle of nowhere Posts: 6,821	Re: What size rearend? Look at Rand'ys Ring and Pinion website for more info.

03-22-2006, 12:24 AM	#9
four-eyed stang Registered User Join Date: Dec 2005 Location: Dallas Posts: 29	Re: What size rearend? Thanks everyone



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