1970 C10 rear end questions

[69Tom]

OK, I've been running searches and not getting exactly what I want, so I'll just ask so I get it right:

(1) 1970 C-10 with a 250: what would have been original to the truck 12 bolt or 10 bolt?

(2) Original with the above, with a 3 OTT, 3.73 gears, correct?

(3) I'll be putting in a 402 with TH400. Best gear ratio? I'll be doing some mild hauling from time to time, but will also be driving long distances on highways. Was thinking 3.08, but wanted to make sure.

(4) Are there any good gear makers out there now, or am I best to go with a good used GM set?

Thanks for the help.

[GASoline71]

Came with a 12 bolt.

Some of the inlines came with 4.10 gears too. But those might have been auto tranny rigs.

I've always used Richmond gears sets and have never had a problem in 30 years. I've used one gearset made by Motive Gear and had good luck with them too. They are cheaper than Richmond gears and I have read and heard good things about them.

Gary

[ElKotze]

Pretty sure the sixes came with 4.11's. I always use YUKON gears and Master Overhaul Kit, most of their stuff is made in the USA, the quality is impressive.

['68OrangeSunshine]

My '68 C/10 Stepside came from Fremont with a 292 L6 , SM465 and Corp 12-Bolt 3.73 rear.
I added Eaton posi in the Mid-Eighties.

[70STOVEBOLT]

Straight six trucks with 250 and 3OTT came standard with 3.73 gears. They work well for hauling with the big block, but you will definitely need an overdrive trans for highway cruising. I converted from a 250 to a 402 and mine runs about 2800 rpm at 60 with the 402 and TH400 and the original 3.73 gears, with 29.5” tires. If I drive it with a light right foot I can get about 12.5-13 mpg

[69Tom]

Thanks guys. I ended up going with a used set of GM 3.08 gears. Now I just need to buy an overhaul kit.

[70STOVEBOLT]

Originally Posted by 69Tom

Thanks guys. I ended up going with a used set of GM 3.08 gears. Now I just need to buy an overhaul kit.

Tom, if you don't mind, let us know the results as far as fuel mileage, power, etc when you get the truck on the road. I had thought about switching to 3.08s or 3.42s when I put the big block in but I love the low to mid range torque the 3.73s provide. After all, I didn't put the 402 in there for fuel mileage...