Gear Ratio and Carrier - The 1947 - Present Chevrolet & GMC Truck Message Board Network

smoky02 · 04-22-2009, 03:03 PM

I am about to start upgrading a few things on my truck. I thought maybe a few people on here would be able to give me some advice as to whether I should go with a 4:10 or 3:73 gears. I am running 700R4 and don't usually do a lot of top end driving, most of the time she stays around 40 or 50, but on occasion I do drive to bama or take the truck on road trips. At 80 MPH I'm doing 2,000 RPM's. Also my rear end came out of a 71 or 72 (or so I was told) how do I find out if it's a series 3 or series 4 housing?

smoky02 · 04-22-2009, 04:25 PM

Really no one?

So.Cal.Super · 04-22-2009, 04:43 PM

see if this helps

http://www.coloradok5.com/axleguide.shtml

hope it does

**john** · 04-22-2009, 04:47 PM

Most of the trucks are running 3:73.1 with a 700r4. I think your converter might be fouling up your readings.A 700r4 with a .70 overdrive would need a 2:73.1 ratio for 80 mph at 2000 rpm.

So.Cal.Super · 04-22-2009, 04:47 PM

this might help you figure out what rpm you would see

http://www.ringpinion.com/Calc_RPM.aspx

MrC1 · 04-22-2009, 04:53 PM

Would need to know more info.

Tire diameter?
What type rear do you have (fat is not a good answer)?
What ratio do you have now? This will also tell you what carrier you have!

You don't need quite as much rear gear with a 700R4 as with other transmssions since 1st gear is pretty steep. It really depends what you use the truck for. If you do truck duty (hauling, towing, etc.) I would suggest going with as much gear as you canhandle while keeping your cruising RPM in an acceptable range.

smoky02 · 04-22-2009, 05:21 PM

My speedo is more than likely off, but I know it reads slow. Right now I have 3:08 gears. My tires are 285/55R18. I will check out that site ya'll mentioned, thank you

Mike C · 04-22-2009, 09:05 PM

Your tires are approximately 30" tall. (285/25.4=11.2" 11.2*.55=6.17" sidewall height *2+18=30.344) Stock tires were approximately 28 tall. That is why your speedo is off. 2*pi*r for your new tire is 94" while the OEM tire would be 88". The new tire rolls 6" further for every rev or 7% which will be approximately what your speedo is off. Assuming the 3.08 is your original gear.

The 3.08 is a 3 series carrier which would be good up to 3.55 gears. 3.73 and up would be 4 series, in a truck. Different break point on gears in cars.

smoky02 · 04-23-2009, 06:52 AM

Quote:

Originally Posted by Mike C

Your tires are approximately 30" tall. (285/25.4=11.2" 11.2*.55=6.17" sidewall height *2+18=30.344) Stock tires were approximately 28 tall. That is why your speedo is off. 2*pi*r for your new tire is 94" while the OEM tire would be 88". The new tire rolls 6" further for every rev or 7% which will be approximately what your speedo is off. Assuming the 3.08 is your original gear.

The 3.08 is a 3 series carrier which would be good up to 3.55 gears. 3.73 and up would be 4 series, in a truck. Different break point on gears in cars.

So that means that if I want to run a gear higher than 3.55 I would have to change out my entire rear end? Or can you buy 4.10s for a series 3 rear end?

texnician01 · 04-23-2009, 08:10 AM

Smokey, you will need to either find a series 4 carrier if you want to use 4.10 gears or buy a set of thick gears (very common) for use on your series 3 carrier. I think I may have an open series 4 but I would have to look, if you are interested. I've never used a thick set of gears but I have to wonder about strengh, does putting that thicker gear in, moving the force away from the flange add extra stress? Anyone ever used a set of these gears. You can get thick gears about anywhere you can get normal gears, a quick search led me to several places to get them but they are about $50 higher because of the extra metal.

Good luck

texnician01 · 04-23-2009, 08:28 AM

Just noticed you have a posi, the best thing then will most likely be the thick gears. When I was looking for a posi it proved to be quite a daunting task, people either didn't want to part with them or they didn't have any.

Also, you will not have to change the whole rearend, just the carrier. The housings and axles are all the same except for length. Your truck would have originally had a narrow axle, the 70 and up trucks had an axle 1 1/2 inches wider, 3/4 on each side. The carriers are interchangeable for any truck 12 bolt and they used them up into the 80's. When changing a carrier and gears, it's not a bad time to rebuild the whole rearend with minimal extra cost.

smoky02 · 04-23-2009, 08:28 AM

Alright, thank you, I am going to do some checking around about the thicker gears. She isn't going to be a track truck, just my toy to drive when I feel like playing. And also it seems a waste and have to take out a posi, just to buy another posi.

smoky02 · 04-23-2009, 08:30 AM

Also the rear end that I have came from a 71, so it wouldn't be the narrower one correct?

texnician01 · 04-23-2009, 08:34 AM

Correct, yours should be a wide rear, that won't ever matter unless you have to replace a housing or axle.

smoky02 · 04-23-2009, 08:40 AM

cool, thanks for ur help

faribran · 04-23-2009, 08:50 AM

Morning bud
pap

smoky02 · 04-23-2009, 08:57 AM

LOL...hey pap, the week is almost over...any luck on finding your shift linkage?

smoky02 · 04-23-2009, 11:54 AM

Called summit, jegs, and also called motive gear, and they set me up with the best deal on ring and pinion and a bearing set. The shop that is supposed to install the gears for me told me that motive is a good name, and just wanted to check with you guys and see if anyone is running gears from them? Also I'm going with the 4.10s

04-22-2009, 03:03 PM	#1
smoky02 Registered User Join Date: Oct 2003 Location: Sunny, Florida, some might call it South Alabama Posts: 834	Gear Ratio and Carrier I am about to start upgrading a few things on my truck. I thought maybe a few people on here would be able to give me some advice as to whether I should go with a 4:10 or 3:73 gears. I am running 700R4 and don't usually do a lot of top end driving, most of the time she stays around 40 or 50, but on occasion I do drive to bama or take the truck on road trips. At 80 MPH I'm doing 2,000 RPM's. Also my rear end came out of a 71 or 72 (or so I was told) how do I find out if it's a series 3 or series 4 housing? __________________ Just sold my C10...sad day... Looking for a 1972 Blazer to hopefully fill the hole in my heart.

04-22-2009, 04:25 PM	#2
smoky02 Registered User Join Date: Oct 2003 Location: Sunny, Florida, some might call it South Alabama Posts: 834	Re: Gear Ratio and Carrier Really no one? __________________ Just sold my C10...sad day... Looking for a 1972 Blazer to hopefully fill the hole in my heart.

04-22-2009, 04:43 PM	#3
So.Cal.Super It'll Buff Out! Join Date: Apr 2007 Location: San Diego Posts: 603	Re: Gear Ratio and Carrier see if this helps http://www.coloradok5.com/axleguide.shtml hope it does __________________ "Instructions are just another mans opinion" Become a Supporting Member http://67-72chevytrucks.com/vboard/payments.php Man Card Rules http://67-72chevytrucks.com/vboard/s...d.php?t=634550 72 Chevy Cheyenne Super 400 LWB

04-22-2009, 04:47 PM	#4
john member #16 Join Date: Dec 1999 Location: Yuba City Ca. Posts: 3,618	Re: Gear Ratio and Carrier Most of the trucks are running 3:73.1 with a 700r4. I think your converter might be fouling up your readings.A 700r4 with a .70 overdrive would need a 2:73.1 ratio for 80 mph at 2000 rpm. __________________ john http://67-72chevytrucks.com/vboard/showgroups.php board vendors http://www.flickr.com/photos/1745471...7602865984234/ Last edited by john; 04-22-2009 at 04:48 PM.

04-22-2009, 04:47 PM	#5
So.Cal.Super It'll Buff Out! Join Date: Apr 2007 Location: San Diego Posts: 603	Re: Gear Ratio and Carrier this might help you figure out what rpm you would see http://www.ringpinion.com/Calc_RPM.aspx __________________ "Instructions are just another mans opinion" Become a Supporting Member http://67-72chevytrucks.com/vboard/payments.php Man Card Rules http://67-72chevytrucks.com/vboard/s...d.php?t=634550 72 Chevy Cheyenne Super 400 LWB

04-22-2009, 04:53 PM	#6
MrC1 Dork For Days Join Date: Aug 2005 Location: Dallas Posts: 407	Re: Gear Ratio and Carrier Would need to know more info. Tire diameter? What type rear do you have (fat is not a good answer)? What ratio do you have now? This will also tell you what carrier you have! You don't need quite as much rear gear with a 700R4 as with other transmssions since 1st gear is pretty steep. It really depends what you use the truck for. If you do truck duty (hauling, towing, etc.) I would suggest going with as much gear as you canhandle while keeping your cruising RPM in an acceptable range. __________________ 1972 C20, 402/700R4 - My first classic truck, bought in September 2005. 85% transformed from "Farm" to "Cool" status! 1970 Dodge Challenger 440, 4sp (my other toy) 12.67 @ 117 MPH, with a pathetic 2.022 60' 2007 Dodge Charger SRT-8 2008 Cadillac CTS All-American garage, baby!

04-22-2009, 05:21 PM	#7
smoky02 Registered User Join Date: Oct 2003 Location: Sunny, Florida, some might call it South Alabama Posts: 834	Re: Gear Ratio and Carrier My speedo is more than likely off, but I know it reads slow. Right now I have 3:08 gears. My tires are 285/55R18. I will check out that site ya'll mentioned, thank you __________________ Just sold my C10...sad day... Looking for a 1972 Blazer to hopefully fill the hole in my heart.

04-22-2009, 09:05 PM	#8
Mike C Registered User Join Date: Dec 1999 Location: Austin, TX, USA Posts: 7,723	Re: Gear Ratio and Carrier Your tires are approximately 30" tall. (285/25.4=11.2" 11.2.55=6.17" sidewall height 2+18=30.344) Stock tires were approximately 28 tall. That is why your speedo is off. 2pir for your new tire is 94" while the OEM tire would be 88". The new tire rolls 6" further for every rev or 7% which will be approximately what your speedo is off. Assuming the 3.08 is your original gear. The 3.08 is a 3 series carrier which would be good up to 3.55 gears. 3.73 and up would be 4 series, in a truck. Different break point on gears in cars. __________________ 44 Willys MB 52 M38A1 64 Corvette Coupe 68 Camaro 'vert LT1 & TH700 69 Z/28 355 12.6's @110 69 Chevy Short Step 4 1/2"/7" drop 72 Jimmy 4WD 4spd 4" & 35's 02 GMC 2500HD 4x4 Duramax

04-23-2009, 08:10 AM	#10
texnician01 Senior Member Join Date: Mar 2002 Location: 12 Miles South of Des Moines, Iowa Posts: 359	Re: Gear Ratio and Carrier Smokey, you will need to either find a series 4 carrier if you want to use 4.10 gears or buy a set of thick gears (very common) for use on your series 3 carrier. I think I may have an open series 4 but I would have to look, if you are interested. I've never used a thick set of gears but I have to wonder about strengh, does putting that thicker gear in, moving the force away from the flange add extra stress? Anyone ever used a set of these gears. You can get thick gears about anywhere you can get normal gears, a quick search led me to several places to get them but they are about $50 higher because of the extra metal. Good luck __________________ 69 C-10, 340HP 327 55 chevy 4 door 150 47 Willys CJ-2A 05 Harley Night Train 06 1200 Sportster (Wife's bike) 70 Honda CL350 OIF2 & OIF7 Veteran Nathan & Tiffany

04-23-2009, 08:28 AM	#11
texnician01 Senior Member Join Date: Mar 2002 Location: 12 Miles South of Des Moines, Iowa Posts: 359	Re: Gear Ratio and Carrier Just noticed you have a posi, the best thing then will most likely be the thick gears. When I was looking for a posi it proved to be quite a daunting task, people either didn't want to part with them or they didn't have any. Also, you will not have to change the whole rearend, just the carrier. The housings and axles are all the same except for length. Your truck would have originally had a narrow axle, the 70 and up trucks had an axle 1 1/2 inches wider, 3/4 on each side. The carriers are interchangeable for any truck 12 bolt and they used them up into the 80's. When changing a carrier and gears, it's not a bad time to rebuild the whole rearend with minimal extra cost. __________________ 69 C-10, 340HP 327 55 chevy 4 door 150 47 Willys CJ-2A 05 Harley Night Train 06 1200 Sportster (Wife's bike) 70 Honda CL350 OIF2 & OIF7 Veteran Nathan & Tiffany

04-23-2009, 08:28 AM	#12
smoky02 Registered User Join Date: Oct 2003 Location: Sunny, Florida, some might call it South Alabama Posts: 834	Re: Gear Ratio and Carrier Alright, thank you, I am going to do some checking around about the thicker gears. She isn't going to be a track truck, just my toy to drive when I feel like playing. And also it seems a waste and have to take out a posi, just to buy another posi. __________________ Just sold my C10...sad day... Looking for a 1972 Blazer to hopefully fill the hole in my heart.

04-23-2009, 08:30 AM	#13
smoky02 Registered User Join Date: Oct 2003 Location: Sunny, Florida, some might call it South Alabama Posts: 834	Re: Gear Ratio and Carrier Also the rear end that I have came from a 71, so it wouldn't be the narrower one correct? __________________ Just sold my C10...sad day... Looking for a 1972 Blazer to hopefully fill the hole in my heart.

04-23-2009, 08:34 AM	#14
texnician01 Senior Member Join Date: Mar 2002 Location: 12 Miles South of Des Moines, Iowa Posts: 359	Re: Gear Ratio and Carrier Correct, yours should be a wide rear, that won't ever matter unless you have to replace a housing or axle. __________________ 69 C-10, 340HP 327 55 chevy 4 door 150 47 Willys CJ-2A 05 Harley Night Train 06 1200 Sportster (Wife's bike) 70 Honda CL350 OIF2 & OIF7 Veteran Nathan & Tiffany

04-23-2009, 08:40 AM	#15
smoky02 Registered User Join Date: Oct 2003 Location: Sunny, Florida, some might call it South Alabama Posts: 834	Re: Gear Ratio and Carrier cool, thanks for ur help __________________ Just sold my C10...sad day... Looking for a 1972 Blazer to hopefully fill the hole in my heart.

04-23-2009, 08:50 AM	#16
faribran Registered User Join Date: Jul 2005 Location: AL Posts: 1,828	Re: Gear Ratio and Carrier Morning bud pap __________________ "



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04-23-2009, 08:57 AM	#17
smoky02 Registered User Join Date: Oct 2003 Location: Sunny, Florida, some might call it South Alabama Posts: 834	Re: Gear Ratio and Carrier LOL...hey pap, the week is almost over...any luck on finding your shift linkage? __________________ Just sold my C10...sad day... Looking for a 1972 Blazer to hopefully fill the hole in my heart.

04-23-2009, 11:54 AM	#18
smoky02 Registered User Join Date: Oct 2003 Location: Sunny, Florida, some might call it South Alabama Posts: 834	Re: Gear Ratio and Carrier Called summit, jegs, and also called motive gear, and they set me up with the best deal on ring and pinion and a bearing set. The shop that is supposed to install the gears for me told me that motive is a good name, and just wanted to check with you guys and see if anyone is running gears from them? Also I'm going with the 4.10s __________________ Just sold my C10...sad day... Looking for a 1972 Blazer to hopefully fill the hole in my heart.

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