Stock rear gear ratio info

[Kiwi]

1. Does anyone know what the available (stock) rear gear ratios were for a 1971 Chevrolet C10 truck?

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2. I know there were optional gear ratios, but does anyone know what the standard gear ratio would likely have been for:

1971 Chevrolet C10 (non Cheyenne)
350 V-8, 4V carb
TH350 automatic transmission
1/2 ton, long bed
2WD (non 4WD)
5-lug wheels
leaf spring rearend
factory A/C

[68Stepbed]

3.07

If had a 3 or 4-speed manual, it would've had 3.73, 4.11, or in some rare cases, 4.56.

[dag19]

I have a '70 and the SPID (which I looked at last night) said 4:11.

[Blazer1970]

With the 350 engine, 3.08 (3.07) was the standard ratio.

[Kiwi]

Anyone happen to have an original type chart that shows the available rear gear ratios?

[68350]

I don't have a chart, but 3.07/3.08 is standard for automatic trucks. 3.54 if it was a 3/4 ton. 3.73 was standard for manuals or I believe 4.10 for 3/4 tons.

[Kiwi]

For what it's worth, I pulled the rearend cover and looked at the ring/pinion gears. The math indicates that my truck has a 3.07:1 ratio with an open differential ... just like 68350 stated.

[Longhorn Man]

Base 1/2 ton trucks got a 3.73. Most 3 speeds were also 3.73. 3.07 was the norm for 4 speeds, although if memory serves, a 307 with a 4 speed still got the 3.73
As for the original question... 350 with an auto got 3.07 gears unless optioned in a 1/2 ton.

Most of whats been said here is acurate, although, 4.56 I don't think was ever in a 1/2 ton, 3/4 tons didn't get a 3.54 with a small block, that was a big block gear. Small blocks and inlines would get a 4.57, 4.10, or a 5.13.

[292farmer]

this is a thread for a 72, but at least it still all matchs whats been said and its cool to see original style brochure
http://67-72chevytrucks.com/vboard/s...d.php?t=424698

oh yeah be glad u don't have 5.13s they suck fuel, like a rusty fuel tank with no bottom

[CollinH]

I think it most likely has 3.73 or 4.11

[Longhorn Man]

Originally Posted by CollinH

I think it most likely has 3.73 or 4.11

Looking at the info given;

does anyone know what the standard gear ratio would likely have been for:

1971 Chevrolet C10 (non Cheyenne)
350 V-8, 4V carb
TH350 automatic transmission

3.07 is the base ratio for this description of truck. By stock gear ratio, I am assuming he means base ratio... any other stock ratio would be listed on the SPID, and the question as a whole would be moot.

[LONGHAIR]

Originally Posted by dag19

I have a '70 and the SPID (which I looked at last night) said 4:11.

That fact that is says anything on the SPID indicates that it is an optional gear. Nothing is listed when the standard ratio is installed, which is the reason that this question comes up so often.

[AndyInOC]

Hello all, new guy here. I am considering buying a '67 C20 for a daily driver and curious as to the gearing. As stated its a 67 with a 327 and 3 speed auto.
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[aintmisbehavinn]

Originally Posted by CollinH

I think it most likely has 3.73 or 4.11

I think you are right, my auto 72 GMC tachs like hell at 55, it came with leafs and trailor towing package. I think it is at least a 3.73.

[Longhorn Man]

what exactly is this "trailor towing package", what's the RPO on that?

[capev86]

1/2 ton

12 bolt: 3.07, 3.73, 4.11, 4.56

3/4 ton

corp/eaton 10 bolt: 4.10, 4.57, 5:13, 6:13

Dana 60: 3.54

the 3.54 was standard for the big block 400 as it didn't need as much gearing. the 3.07 was pretty standard on the 1/2 ton with an auto unless you ordered otherwise. my 72 burb c20 automatically came with a 4.57 because it is 2wd and has a manual 3 on the tree. the 4x4 burb got the 4.10 normally as did most c/k 3/4 ton pickups as they are lighter. i put a 4.10 third member in my burb because it was an easy swap and the 4.57 is a little too low once you get rolling. with a q-jet in place of the 2bbl the 307 is much spunkier now because of the quick response small primaries and the extra air flow potential. i picked up a 66-69 saginaw-borg warner overdrive trans (my rig is a 3 on the tree) and that will give me a far better highway ratio than a straight 3.07.....so i get the best of both worlds.

[Longhorn Man]

somewhat acurate

[aintmisbehavinn]

Originally Posted by Longhorn Man

what exactly is this "trailor towing package", what's the RPO on that?

YE9 Cheyenne Super; G70 Rear Leaf Springs; Z84 Custom Sport Pack w/ sway and a 3 tank rad? I was told by the man who originally order the truck a combination of options was considered "towing". I still don't know the ratio of the rear, it isn't printed anywhere, it's not a 307, it tachs and is the orig equipment. Ok so it's only a super. Forgive anything to do with trailors.

[DANTIP]

Originally Posted by capev86

1/2 ton

12 bolt: 3.07, 3.73, 4.11, 4.56

3/4 ton

corp/eaton 10 bolt: 4.10, 4.57, 5:13, 6:13

Dana 60: 3.54

the 3.54 was standard for the big block 400 as it didn't need as much gearing. the 3.07 was pretty standard on the 1/2 ton with an auto unless you ordered otherwise. my 72 burb c20 automatically came with a 4.57 because it is 2wd and has a manual 3 on the tree. the 4x4 burb got the 4.10 normally as did most c/k 3/4 ton pickups as they are lighter. i put a 4.10 third member in my burb because it was an easy swap and the 4.57 is a little too low once you get rolling. with a q-jet in place of the 2bbl the 307 is much spunkier now because of the quick response small primaries and the extra air flow potential. i picked up a 66-69 saginaw-borg warner overdrive trans (my rig is a 3 on the tree) and that will give me a far better highway ratio than a straight 3.07.....so i get the best of both worlds.

FYI, at least in 72, the only gear available for 1/2 Ton Big Blocks was 3.07.

[capev86]

yeah....i forgot that you could get a big block in the 1/2 ton trucks.....like a bare bones precursor to a chevy SS of the early 90's. even with the 400bb, a 3.07 is still kinda soft if you do any serious towing because it only has 30 more ft-lbs than the 350 according to my 72 burb brochure. however it would be perfect for a modern diesel swap (you'd still want a mild overdrive gear with a diesel). perhaps you could special order a 3.73 or a 4.11 if you needed it for towing. there was also a 4.56 available on 3/4 ton trucks and that was for the the dana 60 without the big block as the 4.57 is the corp/eaton. 3.73 was standard on all 1/2 ton burbs and the 4.10 was an option available for the K20 burbs.

i like a 3.42 to 3.73 on a 1/2 ton and a 3.73 to 4.11 range on a 3/4 ton (unless i had huge diameter tires). an overdrive is the other piece of the puzzle and there are several bolt-in routes you can go with depending on what model/type of trans you have to begin with!

[Longhorn Man]

you are still off. 3.73 was not standard on all burbs.
The gear ratio depended on the engine, trans, and the size of truck (10/20/30) and also it depended on what rear axle it was equipped with.
in 2 wheel drive 1/2 tons, on the base model, either CE or CS trucks, the standard gear was 3.73. However, throw in an optional engine, or optional tranny, and that may not be the case.
Same for a C/20. The 4.57 was standard, but a 4.10 was included in certian engine/tranny combos.
You could opt for any of the avalible gear ratios, but sometimes you couldn't get that gear with certian engine or trans or even rear axle options.

[capev86]

i was talking standard equipment (base engine, trans, etc). other gears options are obviously dependent on configuration/package. GM doesn't always play by its own rules and who is to know if a previous owner didn't do some customizing?

look at the gas tank size on the burb. according to the brochure all C/K 10/20 came with a 21 gallon tank, and i believe that because it took about that to fill it up after i ran out of gas once. but according to the glove box handbook the C20 and K20 burb should have a 23 gallon tank. just 2 extra gallons (and an extra part number) doesn't make much sense from a marketing and money making standpoint. they had the 45 gal tavel tank for those needing more capacity!

[raycow]

Originally Posted by aintmisbehavinn

I still don't know the ratio of the rear, it isn't printed anywhere, it's not a 307, it tachs and is the orig equipment.

If it is a C-10 you probably have a 3.73, but there is no need to guess about it.

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

[R.L.]

Originally Posted by raycow

If it is a C-10 you probably have a 3.73, but there is no need to guess about it.

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

Thanks Ray

[Olive1970]

Wanted to bring up this subject again...my truck SPID is a factory TH350 trans with a 307 engine. Likely rear gear ratio? It seems that most of the 350 engines were 3.08 gear ratio with automatic, didn't know if it would be different on a 307 engine?

Thanks!