Rear end ratio?

[OL SKOOL]

Any thoughts on what a 61 c10 3/4 ton 4 speed with granny would have for a rear end gear ratio? Haven't bought the truck yet just trying to figure what trans I can replace with . Leaning toward a 700r.

[Clyde65]

Do you know the gear ratio?

Does it currently have a 4 speed or auto?

[OL SKOOL]

I don't know the rear end ratio. That's what I was asking. The truck is a 3/4ton 4 spd. standard with granny low. I want to put auto in but not change the rear end. I want to be able to drive to town and not do 3000 rpm at 50 mph. Any thoughts on what the rear end ratio would be?

[The Rocknrod]

Here is the chart on rear axle codes. The stamp is on the top of the drivers side axle:

[Steeveedee]

If it's original, per the Rod's chart it's a 4.57 ratio. A 700R4 trans has a .7 ratio OD, so that would give you a 3.2 ratio in OD. That's a respectable drop in RPM! The 700 has a really steep first gear with a big drop in RPM from 1st to 2nd. A lot of people use a 200 for this reason. I think that I recall that a 200 needs a bit of beefing up if it's going to be used hard, though.

[OL SKOOL]

Originally Posted by Steeveedee

If it's original, per the Rod's chart it's a 4.57 ratio. A 700R4 trans has a .7 ratio OD, so that would give you a 3.2 ratio in OD. That's a respectable drop in RPM! The 700 has a really steep first gear with a big drop in RPM from 1st to 2nd. A lot of people use a 200 for this reason. I think that I recall that a 200 needs a bit of beefing up if it's going to be used hard, though.

I also have a 200r but I want to kind of use this truck for hauling a car and trailer once in a while. I didn't know if the 200r would get it done without dumping a bunch of money in it. Most of the use will just be driving around. Thank you Mr.Steve.

[OL SKOOL]

Thank you Rocknrod looks like they were all 457 ratio. Probably not too good to cruise around in even with a 700r. So probably a rear end change, so it will be more user friendly. Just trying to figure out what I will all need before I go look at this truck.

[Clyde65]

You could put an nv4500 5 speed in it since it’s already a manual.

Or you can get a 14 bolt and Captn Fabs mounts and swap that out before your trans

[65 GMC]

Originally Posted by Clyde65

You could put an nv4500 5 speed in it since it’s already a manual.

Or you can get a 14 bolt and Captn Fabs mounts and swap that out before your trans

This is the route I took with my 64 C20. I swapped the original rear axle out with a 14 bolt with 4.10 gears and also put in a NV4500 from a 98 c3500. Hope to get it running and driving this summer.

[Captainfab]

Your first post says '61 C10 3/4 ton. A C10 is a 1/2 ton with 6 lug wheels. A C20 is a 3/4 ton with 8 lug wheels. Additionally a '61 will not be a C series, it is an Apache 10 or an Apache 20. The C series did not start until 1962.

[OL SKOOL]

Originally Posted by Captainfab

Your first post says '61 C10 3/4 ton. A C10 is a 1/2 ton with 6 lug wheels. A C20 is a 3/4 ton with 8 lug wheels. Additionally a '61 will not be a C series, it is an Apache 10 or an Apache 20. The C series did not start until 1962.

I didn't notice this Captain till you pointed it out. It is an Apache 20 eight lug wheels. I have been in half ton land too long. Thank you

[OL SKOOL]

Originally Posted by Clyde65

You could put an nv4500 5 speed in it since it’s already a manual.

Or you can get a 14 bolt and Captn Fabs mounts and swap that out before your trans

When you say 14 bolt rear end? Not real up on this 3/4 ton stuff yet. Would that be a bolt in? What did they come in? Maybe I could do the rear end and leave the old trans for now. Thanks for the info

[Clyde65]

Originally Posted by OL SKOOL

When you say 14 bolt rear end? Not real up on this 3/4 ton stuff yet. Would that be a bolt in? What did they come in? Maybe I could do the rear end and leave the old trans for now. Thanks for the info

It won’t be bolt in, but Captn Fab has trailing arm mounts that you can use after you remove the leaf spring mounts.

[Steeveedee]

I don't know about the interchangeability of the rear ends, but you could probably find a Dana 60 from a big block truck that has a 3.54 axle ratio. It would have leaf spring mounts, most of the time. I see that some have coils.

[Captainfab]

The 14 bolt was available in both the 10.5" full floating and the 9.5" semi floating configuration starting in 1973 in the C/K20's and 30's up into the 2000's somewhere when GM went to the AAM differential. So there are tons of them out there. Even if you do find a Dana 60 from a '67-'72 truck, the trailing arm mounts will still have to be moved to bolt up to the trailing arms in your '61.

[Wrenchbender Ret]

Some 67-72 20 series trucks with V-8 & automatic had 4:11 gears in them & the 3rd member fits your housing. They can be hard to find though.
George