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

flashed · 11-19-2010, 11:52 PM

My truck is a 72 short fleet ,former owner removed original 6 cylinder engine and put in a mild 350 . It still has its original auto trans and rear end .I dont know what rear gear it has now but its original. What gear ratio would have been in it if it was originally equipped with the 350 engine rather than the 6 cylinder. The reason I ask is a friend of mine has a reae end with (308?)rear gears that I could get cheap if that is what I need.

63chevyll · 11-19-2010, 11:59 PM

3.07 or 3.73 or 4.11 were all options, but not for sure with the auto

gonzo6869 · 11-20-2010, 03:14 AM

My truck came with 3.73's and it was a 6 clyinder from factory.

raycow · 11-20-2010, 05:50 AM

There is no need to guess about the ratio when you can find out for certain easily enough.

Jack one rear wheel off the ground, put the transmission in neutral, and the parking brake off. Put matching marks on the pinion yoke and differential housing. Turn the wheel exactly TWO revolutions and count how many times the driveshaft turns, estimating any fractional turn as closely as possible. That number is your axle ratio.

If the wheel is difficult or impossible to turn, you may have posi. In that case, jack both rear wheels off the ground and turn either of them only ONE revolution. Count the driveshaft turns the same way as for an open rear.

Ray

flashed · 11-20-2010, 09:27 PM

Let me re ask the question .What would be the best all around gear for a 350/350 combo for better gas mileage than the original 6 cylinder /auto,and current gear whatever it may be. ?

gonzo6869 · 11-21-2010, 12:13 AM

I think it’s the 3.48 or something like that; I would not go with the 3.08. If you’re looking better MPG you might want to save up for a new OD Tranny like a 2004R or a 700R4. I prefer the 200, and it’s a direct bolt on with minimal changes to make it work.

68Stepbed · 11-22-2010, 10:52 AM

The 3.07 or 3.08 gear would be the best for overall fuel mileage with that combo. You probably have a 3.73 gear now. I have a 350/TH350 combo as well with a 3.73 gear. I currently get about 14mpg if I can keep my foot from getting heavy and keep it under 60mph. Once I get up to 65-70mph, mpg's start to drop. The 3.08 gears would help alot at highway speeds, but it wouldn't be as much fun at the redlights.

As mentioned above, an OD trans. would give the best of both worlds.

flashed · 11-22-2010, 01:09 PM

Thanks Matt ,that is what I was looking for .An overdrive is not in my near future plans uless I find a buyer for my 55 Bel Air or my 68 Malibu or both .Right now I have entirely too many toys to keep up with ,but I love my old beater truck.

gonzo6869 · 11-22-2010, 01:50 PM

The 3.08 would be a good highway gear, if that’s all the driving you do. If you’re on the city streets a lot, I really don't see you liking it. I don't know how you plan on doing the swap, but having your rear end worked on can cost you big$$$. A mildly built 2004R will start around $1000.

With all that said, it’s your truck, enjoy driving and working on it.

Critter · 11-22-2010, 03:30 PM

Quote:

Originally Posted by gonzo6869

The 3.08 would be a good highway gear, if that’s all the driving you do. If you’re on the city streets a lot, I really don't see you liking it. I don't know how you plan on doing the swap, but having your rear end worked on can cost you big$$$. A mildly built 2004R will start around $1000.

I agree! 3.08s if its a lot of highway/commuting but 3.42s are a great all around combo in my opinion. The 200r4 seems to be the way to go as well if you can find one.

tdp67 · 11-22-2010, 04:15 PM

I have the 3.08 and it's great on the highway. I would prefer something in the 3.43 range however.

**Clyde65** · 11-22-2010, 05:16 PM

I would 2nd that! I have 3.08's and wish I had 3.73 or 3.42's, just for the acceleration from stop. I had my RE built before the LSx swap, so no reason to through out good $ at the time.

I get around 15 MPG city and 20+ on the HWY, but with the OD the 3.7.'s would be real nice and not much of a MPG eater.

I vote for the OD tranny, if someone was asking that is.

**WIDESIDE72** · 11-24-2010, 12:49 AM

IMO, if on a budget, if the current axle does in fact have 3.73 gears, I would swap the current rear axle for the 3.07, but hang on to the stock axle and swap it and a 2004r in at a later date. You would then have the best of both worlds.

63chevyll · 11-25-2010, 01:40 PM

my vote is for 3.07's

raycow · 11-25-2010, 02:40 PM

I agree. Assuming normal size tires, 3.07 is about the only commonly found gear that is comfortable at highway speeds without OD.

Ray

peglegs · 11-25-2010, 03:32 PM

i have the same delema i have a 327/4sp 74 camaro trans/411rr. and hardly drive it on the 65 mph xpressway. i have a 400 trans i will be changing 2 and also was thinking of 3:08's. i will be towing a small travel trailer occasionally perhaps on a long haul @ times and now reading this thread im concerned bout what ratio 2 go 2. also living in a mountain region/occasional snow im thinking bout keeping the posi.
im told by Summit Racing that all 3 series posi carrier units (these will house the 3:08's and 3:42's......4 series hold the 3:73 & 4:11's) from 64 - 82 blazers, c & k series and the k20 series posi carriers will interchange with my HOUSING all are 30 splines w/8.875 ring gear dia. ,according to Richmond as quoted by Summit, also it was suggested ,from a rear end shop in reno or vegas i forget which 1 said also that the 75-6 chevy auto truck will bolt in but check splines, i realize that i can purchase all new but $ as usual will be limited as i require 4 wheel disc. tires, fr. end rebuilt, windshield ....on & on if im keeping the truck as my only driver i have 2 sell my dodge dakota 4 x 4to fund all this......whew what a mouth full
so
im asking for options
#1 to go from 4:11 to 3:08's .....cheapest option if possible and what 2 use
#2 3:08's ok for towing a small (12') camper

lol

thank u so much for all opinions now and in the past this site rocks
From a vietnam vet to all
HAPPY THANKSGIVING TO YOU & ALL OUR TROOPS AND FOR
HEAVENS SAKE PRAY FOR PEACE.

**WIDESIDE72** · 11-25-2010, 05:23 PM

#1 IMO, find an axle out of a big block truck. Most of those had 3.07's.
#2 With a 327, I am not sure you will have enough torque to get away with 3.07's if doing any towing. 4.11's and a 700r4 or 2004r would be the best bet. $1,000 MINIMUM for the swap, though.

68Stepbed · 11-26-2010, 05:43 PM

peglegs, your best bet may be switching to 3.42 gears. You'll still get some highway friendliness, and still be able to apply some of the 327's torque. I think the 3.08's would not be good for towing anything heavy with the 327.

As for the OP, flashed, if you can get another whole rearend with the 3.07 gear, that would be the easiest and least expensive route to go. You will still be able to haul decent loads and use the truck for a "beater".

LostMy65 · 01-05-2011, 02:36 AM

So, if I turned my wheel one turn, and the driveline turned roughly 2-1/4 turns, I have 4.50 gears?

**WIDESIDE72** · 01-05-2011, 12:57 PM

Quote:

Originally Posted by LostMy65

So, if I turned my wheel I turn, and the driveline turned roughly 2-1/4 turns, I have 4.50 gears?

Probably more like 4.10, as 1/4 turn = .25

Ryan Hubbard · 01-05-2011, 03:45 PM

I am running a 3.55 gear in my truck and I really like it. I drove my truck from Detroit to Los Angeles towing a car trailer the whole time and I had no problems on the grades and was only turning 3000 rpms while maintaining 75 mph. I have a spercharged 350 with a turbo 400 transmission.

11-20-2010, 03:14 AM	#3
gonzo6869 Cops, ha, catch me if you can! Join Date: Jun 2009 Location: Santa Barbara, CA. Posts: 271	Re: Rear Gears My truck came with 3.73's and it was a 6 clyinder from factory. __________________ 72 C-10 Stepper 350/TH350 3.73 in the back Edelbrock intake and Carb Hooker Comp Headers 275/60R15 on Rallies

11-20-2010, 05:50 AM	#4
raycow Registered User Join Date: Mar 2003 Location: San Francisco, CA USA Posts: 2,454	Re: Rear Gears There is no need to guess about the ratio when you can find out for certain easily enough. Jack one rear wheel off the ground, put the transmission in neutral, and the parking brake off. Put matching marks on the pinion yoke and differential housing. Turn the wheel exactly TWO revolutions and count how many times the driveshaft turns, estimating any fractional turn as closely as possible. That number is your axle ratio. If the wheel is difficult or impossible to turn, you may have posi. In that case, jack both rear wheels off the ground and turn either of them only ONE revolution. Count the driveshaft turns the same way as for an open rear. Ray __________________ Live more responsibly. Eat lower on the food chain. Eat vegetarians.

11-20-2010, 09:27 PM	#5
flashed Registered User Join Date: Oct 2009 Location: canton ga Posts: 12,724	Re: Rear Gears Let me re ask the question .What would be the best all around gear for a 350/350 combo for better gas mileage than the original 6 cylinder /auto,and current gear whatever it may be. ?

11-21-2010, 12:13 AM	#6
gonzo6869 Cops, ha, catch me if you can! Join Date: Jun 2009 Location: Santa Barbara, CA. Posts: 271	Re: Rear Gears I think it’s the 3.48 or something like that; I would not go with the 3.08. If you’re looking better MPG you might want to save up for a new OD Tranny like a 2004R or a 700R4. I prefer the 200, and it’s a direct bolt on with minimal changes to make it work. __________________ 72 C-10 Stepper 350/TH350 3.73 in the back Edelbrock intake and Carb Hooker Comp Headers 275/60R15 on Rallies

11-22-2010, 10:52 AM	#7
68Stepbed Registered User Join Date: Mar 2005 Location: 10-Uh-See Posts: 5,609	Re: Rear Gears The 3.07 or 3.08 gear would be the best for overall fuel mileage with that combo. You probably have a 3.73 gear now. I have a 350/TH350 combo as well with a 3.73 gear. I currently get about 14mpg if I can keep my foot from getting heavy and keep it under 60mph. Once I get up to 65-70mph, mpg's start to drop. The 3.08 gears would help alot at highway speeds, but it wouldn't be as much fun at the redlights. As mentioned above, an OD trans. would give the best of both worlds. __________________ Matt 68 C10 stepside, LS1/700R4, TCI Engineering suspension system

11-19-2010, 11:52 PM	#1
flashed Registered User Join Date: Oct 2009 Location: canton ga Posts: 12,724	Rear Gears My truck is a 72 short fleet ,former owner removed original 6 cylinder engine and put in a mild 350 . It still has its original auto trans and rear end .I dont know what rear gear it has now but its original. What gear ratio would have been in it if it was originally equipped with the 350 engine rather than the 6 cylinder. The reason I ask is a friend of mine has a reae end with (308?)rear gears that I could get cheap if that is what I need.

11-19-2010, 11:59 PM	#2
63chevyll gets board easy....... Join Date: Mar 2009 Location: Colorado Springs Posts: 717	Re: Rear Gears 3.07 or 3.73 or 4.11 were all options, but not for sure with the auto

11-22-2010, 01:09 PM	#8
flashed Registered User Join Date: Oct 2009 Location: canton ga Posts: 12,724	Re: Rear Gears Thanks Matt ,that is what I was looking for .An overdrive is not in my near future plans uless I find a buyer for my 55 Bel Air or my 68 Malibu or both .Right now I have entirely too many toys to keep up with ,but I love my old beater truck.

11-22-2010, 01:50 PM	#9
gonzo6869 Cops, ha, catch me if you can! Join Date: Jun 2009 Location: Santa Barbara, CA. Posts: 271	Re: Rear Gears The 3.08 would be a good highway gear, if that’s all the driving you do. If you’re on the city streets a lot, I really don't see you liking it. I don't know how you plan on doing the swap, but having your rear end worked on can cost you big$$$. A mildly built 2004R will start around $1000. With all that said, it’s your truck, enjoy driving and working on it. __________________ 72 C-10 Stepper 350/TH350 3.73 in the back Edelbrock intake and Carb Hooker Comp Headers 275/60R15 on Rallies

11-22-2010, 04:15 PM	#11
tdp67 Registered User Join Date: Apr 2010 Location: Rowlett, TX Posts: 325	Re: Rear Gears I have the 3.08 and it's great on the highway. I would prefer something in the 3.43 range however.

11-22-2010, 05:16 PM	#12
Clyde65 1965 Chevy C10, 2005 4.8L/4l60 Join Date: Aug 2004 Location: DFW Texas Posts: 8,546	Re: Rear Gears I would 2nd that! I have 3.08's and wish I had 3.73 or 3.42's, just for the acceleration from stop. I had my RE built before the LSx swap, so no reason to through out good $ at the time. I get around 15 MPG city and 20+ on the HWY, but with the OD the 3.7.'s would be real nice and not much of a MPG eater. I vote for the OD tranny, if someone was asking that is. __________________ Clyde65 Rebuild of Clyde http://67-72chevytrucks.com/vboard/s...84#post8338184 69 Aristocrat Lo Liner build http://67-72chevytrucks.com/vboard/s...84#post7561684 *support our troops!* Last edited by Clyde65; 11-22-2010 at 05:17 PM.

11-24-2010, 12:49 AM	#13
WIDESIDE72 Senior Member Join Date: Aug 2008 Location: Cedar Park, Texas Posts: 7,500	Re: Rear Gears IMO, if on a budget, if the current axle does in fact have 3.73 gears, I would swap the current rear axle for the 3.07, but hang on to the stock axle and swap it and a 2004r in at a later date. You would then have the best of both worlds.

11-25-2010, 01:40 PM	#14
63chevyll gets board easy....... Join Date: Mar 2009 Location: Colorado Springs Posts: 717	Re: Rear Gears my vote is for 3.07's

11-25-2010, 02:40 PM	#15
raycow Registered User Join Date: Mar 2003 Location: San Francisco, CA USA Posts: 2,454	Re: Rear Gears I agree. Assuming normal size tires, 3.07 is about the only commonly found gear that is comfortable at highway speeds without OD. Ray __________________ Live more responsibly. Eat lower on the food chain. Eat vegetarians.

11-25-2010, 03:32 PM	#16
peglegs Registered User Join Date: Jul 2009 Location: grants pass, oregon Posts: 390	Re: Rear Gears i have the same delema i have a 327/4sp 74 camaro trans/411rr. and hardly drive it on the 65 mph xpressway. i have a 400 trans i will be changing 2 and also was thinking of 3:08's. i will be towing a small travel trailer occasionally perhaps on a long haul @ times and now reading this thread im concerned bout what ratio 2 go 2. also living in a mountain region/occasional snow im thinking bout keeping the posi. im told by Summit Racing that all 3 series posi carrier units (these will house the 3:08's and 3:42's......4 series hold the 3:73 & 4:11's) from 64 - 82 blazers, c & k series and the k20 series posi carriers will interchange with my HOUSING all are 30 splines w/8.875 ring gear dia. ,according to Richmond as quoted by Summit, also it was suggested ,from a rear end shop in reno or vegas i forget which 1 said also that the 75-6 chevy auto truck will bolt in but check splines, i realize that i can purchase all new but $ as usual will be limited as i require 4 wheel disc. tires, fr. end rebuilt, windshield ....on & on if im keeping the truck as my only driver i have 2 sell my dodge dakota 4 x 4to fund all this......whew what a mouth full so im asking for options #1 to go from 4:11 to 3:08's .....cheapest option if possible and what 2 use #2 3:08's ok for towing a small (12') camper lol thank u so much for all opinions now and in the past this site rocks From a vietnam vet to all HAPPY THANKSGIVING TO YOU & ALL OUR TROOPS AND FOR HEAVENS SAKE PRAY FOR PEACE.



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11-25-2010, 05:23 PM	#17
WIDESIDE72 Senior Member Join Date: Aug 2008 Location: Cedar Park, Texas Posts: 7,500	Re: Rear Gears #1 IMO, find an axle out of a big block truck. Most of those had 3.07's. #2 With a 327, I am not sure you will have enough torque to get away with 3.07's if doing any towing. 4.11's and a 700r4 or 2004r would be the best bet. $1,000 MINIMUM for the swap, though.

11-26-2010, 05:43 PM	#18
68Stepbed Registered User Join Date: Mar 2005 Location: 10-Uh-See Posts: 5,609	Re: Rear Gears peglegs, your best bet may be switching to 3.42 gears. You'll still get some highway friendliness, and still be able to apply some of the 327's torque. I think the 3.08's would not be good for towing anything heavy with the 327. As for the OP, flashed, if you can get another whole rearend with the 3.07 gear, that would be the easiest and least expensive route to go. You will still be able to haul decent loads and use the truck for a "beater". __________________ Matt 68 C10 stepside, LS1/700R4, TCI Engineering suspension system

01-05-2011, 02:36 AM	#19
LostMy65 But Found Her 25yrs Later! Join Date: Oct 2010 Location: Oregon City, Oregon Posts: 10,530	Re: Rear Gears So, if I turned my wheel one turn, and the driveline turned roughly 2-1/4 turns, I have 4.50 gears? __________________ I lost my 65 - Found it 25 years later: http://67-72chevytrucks.com/vboard/s...d.php?t=426650 66 C20 Service Truck: http://67-72chevytrucks.com/vboard/s...d.php?t=428035 Last edited by LostMy65; 01-05-2011 at 04:39 PM.

01-05-2011, 03:45 PM	#21
Ryan Hubbard Registered User Join Date: Aug 2007 Location: Mission Viejo, CA Posts: 288	Re: Rear Gears I am running a 3.55 gear in my truck and I really like it. I drove my truck from Detroit to Los Angeles towing a car trailer the whole time and I had no problems on the grades and was only turning 3000 rpms while maintaining 75 mph. I have a spercharged 350 with a turbo 400 transmission.

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