Rear gear ratio

[legendman]

Pulled my rear cover off and counted the teeth on ring and pinion
16 on the pinion and 41 on the ring gear, which means its got 2:56 gear ratio.

Originally it had a 305 with a th350 trans.
And I swapped in a 700r4 but I need to figure out which speedo gears to get.

Seems odd that it would have a 2:56 ratio.

Anybody else have a th350 and know what their rear gear ration is?

[cory d]

i dont recall trucks having 2.56? i thought 2.73 was the highest the trcks went. i have 2.73's useless on anything but the freeway

[legendman]

Yea 2:56 seems kinda odd to me

Got all the numbers off the ring gear:

GM 1235401 16 41 11 83

Last batch "11 83" I think means built 11/83 which would be right in a 84 truck.

[C-10 simplex]

Yes, i have 2.56 with a TH-350C.

Stiff as hell. This kind of setup of good for if you use the truck for light hauling---lumber, appliances, weekend projects etc.

It is not so good for other things such as towing.

P.S. my GVWR is only 4900 and i guess yours is too.

[legendman]

^^^ Good to hear, so I guess I am identifying it correctly then.

I am fine with the ratio, I am dropping a 6.2 diesel in it and see what I can get for mileage with it. Not gonna be in a big hurry to get anywhere and more of a show truck than a work truck.

[maxxxy]

I was just now taking apart y rear end to clean up and paint and decided to check what ratio I have. It's 16 41 2 81. So I have a 2.56 as well.
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[Firebirdjones]

2.56 is actually a very common gear found in the 8.5's in both cars and trucks.

[shawno72]

Originally Posted by legendman

Yea 2:56 seems kinda odd to me

Got all the numbers off the ring gear:

GM 1235401 16 41 11 83

Last batch "11 83" I think means built 11/83 which would be right in a 84 truck.

Are there two dots between the 41 and the 11. On my rear end there was which meant the ratio was 3.73, 41 divided by 11.

[maxxxy]

Is a 2.56 rear end useless? I've never heard of people wanting that high of a ratio...
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[clinebarger]

Originally Posted by maxxxy

Is a 2.56 rear end useless? I've never heard of people wanting that high of a ratio...
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Yeah, And only 2:41's & 2:56's fit that carrier, So if you want lower gears.....You need a carrier also.

[maxxxy]

Is the 2.56 at least good for gas mileage? I don't plan to do any towing or anything? Will keeping it affect my acceleration or anything?
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[C-10 simplex]

Originally Posted by maxxxy

Is a 2.56 rear end useless? I've never heard of people wanting that high of a ratio...
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Originally Posted by maxxxy

Is the 2.56 at least good for gas mileage? I don't plan to do any towing or anything? Will keeping it affect my acceleration or anything?
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i guess if you don't live in hilly/mountainous areas it might be ok. In my opinion a fullsize truck with such a high gear is good for moving large but not necessarily heavy things----washing machines etc. The thing that baffles me is my truck has the heavy duty springs, yet has the 2.56 rear---it can support the weight, but has problems moving it------doesn't make sense to me?

As far mileage, probably good with a th-350 or other 3 sp trans. i think i tach around 1800 at 55 mph.

P.S. It affects acceleration big time. Switching to say 4.56 will make a world of difference.

[clinebarger]

Originally Posted by maxxxy

Is the 2.56 at least good for gas mileage? I don't plan to do any towing or anything? Will keeping it affect my acceleration or anything?
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If you had 26" tall tire's maybe. & will still be a dog off the line.

With 28" to 30" diameter tires & 3 spd auto......A 3:08 gear will return the best mileage in my opinion. 3:42's will give better acceleration with a small increase in fuel consumpsion at highway speeds.

[legendman]

I am swapping in a 6.2, so these gears with an ole slug 6.2 and a 700r4 it will take a week to get up to speed but I will be able to pass a few gas pumps though

[Rich84]

My truck had the 2:56 rear.. When I went with the 700 tranny, it was practically asleep on the highway with a 30" tire...found a nice posi carrier and 3:73 gears at the boneyard really woke up my TPI..
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