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What rear gear ratio does a1969 C/10 350 cu. In. With a 3 speed have in it stock?

Per the GM Heritage site, 1969 Series C10
Standard equipment CE10 , 307 V8 , 3 speed transmission, rear axle ratio 3.73

Optional equipment - 350 V8 , 4 BBl Carb, 3.07 rear axle ratio, 12" clutch Option LS9 .

Ratio 3.73: available only when 350 engine is ordered....... option H05

Based on this, unless it was ordered with the H05 option, it should have a 3.07 rear axle.

How many teeth would there be on the ring gear verses the pinion gear with the 3:07 ratio?

Ring gear 43 and pinion gear 14

In that same truck were talking about, was it also equipped with the 3:07's with the automatic transmission? Part(2) at what rpm with the original 3 speed should it run at driving say 60 miles and hour?

The 3.07 rear end I have was taken from a 1969 C10 which had an auto transmission. Pretty common late 60s rear end if auto transmission was there. Good rear end, especially for a late model 235 if you mate it with a T5 with the gear chain beginning with 4.03 and ending with .86. Almost can't be better. With that setup at 60 I'll be at 2000 rpm...right at the max torque for the 1959 235.

As for rpm, if you had the original 3 speed (a 1 to 1 final ratio) and the 3.07 rear at 60 your rpm should be around 22~2300 if you have 27 inch tires.
If you have the 3.73 rear and 27 inch tires, your rpms will be around 2800.

One easy way to know what rear end you have (without counting teeth) is to look for the GM code stamped on it. Usually people don't change ring and pinion without good reason and with the 12 bolt GM truck rears you have ranges you must stay within if you do want to make changes. You have 3 deck heights: 2.73 and lower, 2.76 to 3.42 and 3.73 and higher. So you couldn't convert a 3.73 into a 3.07 or 3.08 rear end.

Code will be on the top of the axle tube, passenger side. May not be stamped very deep. In 1969, you had two letter codes for gear ratios (in 1970 they went to 3 letter codes). For trucks with 12 bolt rears, here you are:

HB, LL, RA, TR, TT, TU = 3.07

HA, HJ, HQ, MF, TQ, MI, MK = 3.73

HK, HL, HR, ME, MG, TS = 4.11

HC, HN, MU = 3.73 Posi

HO, HP, JQ = 4.11 Posi

You'll have numbers stamped with these which indicate what month, day it was made.

Hey there John G. Thanks for the info, really appreciate it..these here specs. You gave ram's mph are they for the 350' as well as the 235?

The RPM won't care if you have a 350, a 235 or an electric motor. The rpms are all a matter of your transmission gearing (final ratio will either be 1:1 or something lower if you have overdrive or a transmission geared for final overdrive gearing), the diameter of your tires and the ratio of your rear end. And when you start calculating overall gear ratios, it is instructive and important to look at what GM engineers thought you needed for all your gears. In general for a 1/2 ton pickup with an inline 6, your first gear total ratio (calculated by multiplying your first gear ratio times your rear end ratio) ought to be around 12. With a 350 you can make do with an overall ratio of 10 or possibly even 9 if you don't plan on hauling a lot of heavy stuff around. Think of it this way: if you have an inline 6 and your first gear ratio is around 2.94 and your rear end ratio is 4.11, then your overall ratio will be 12.08. A ratio of 12 will let you load 1000 pounds of stuff into your bed, add a passenger or two and drive without burning up your clutch and you can even take off on a hill. If you have an overall ratio of 8 you can put an empty ice chest in your bed and that's about all you should try to haul around. A more powerful engine lets you lower the overall ratio, though. More torque, more horsepower will do that for you. Then in second gear, your standard AD truck transmission had a gear of 1.68. This times 4.11 gives an overall ratio of 6.9 but remember please you're already moving when you start using this ratio. And your final ratio is 4.11 (the ratio of your rear end since your third gear transmission ratio is 1.1). Now if you had an overdrive transmission back in the 1960s, your overdrive ratio would have been .7, so you could multiply that times your rear end to see what your final rear end ratio would be...2.87 or so. With transmissions there will be different ratios for each gear. Friends of mine have run out and bought a 5 speed transmission without ever thinking about the overall ratios they would have, nor their rear end ratio and consequently have made their vehicle run much worse as a result. Consider in the T5, your first gear could have been 3.50, 3.76 or 4.03. If you had a rear end from a Camaro, it could have been a 2.77 ratio. 2.77 times 3.50 = 9.69. Almost worthless for a pickup. Ok for a light car with a very large engine.

As for your 350, those came in varying degrees of power and torque...ranging from not very much to a whole lot. What sort of gearing will be best for you depends on what you have there (which I don't know), but I'd say an overall first gear ratio of 10 would be ok if you're not hauling a boat, trailer or bed full of firewood. Your 350 might have only about 140 horsepower (which is about the same as the 235, give/take). If you can fill in more of the variables I or several other folks here can give our thoughts and suggestions. Also depends on whether you want to end up with a street rod that 2 or 3 people can ride in or a working pickup.

Jon, That's excellent info. I nominate you to write up a tech tip on gear ratios.

Thanks Kevin,
I would be more than happy to do that...are we still adding to tech tips?

John and I have been working on adding “Tech Tips” to each Forum as a Sub Forum. It’s a work in progress so if you write it up, I’ll be sure to get it posted!

Hey there Jon G. there for a minute I thought I was talking to that dude in Tenesee, just kidding what a well explained thread you replied back to me and others, not quite sure if I understand all of it but hey. The info I did get set my theories about r.p.m.'s m.p. and the understanding about it. Like Phak1 said add that there link to the "Tech Tips". Thanks again..

This site is extremely handy for this type of figuring:

https://spicerparts.com/calculators/transmission-ratio-rpm-calculator

I use THIS website. Very handy.
https://www.crawlpedia.com/rpm_gear_calculator.htm