Best Rear End Gears?

[HotRod73]

I was wanting to know if anyone could tell me what my stock 1973 chevrolet 3/4 ton cheyenne 20 2wd has for stock gears.... also what would be best gears for fuel mileage or for quick speed?

[piecesparts]

You will have to tell us some more about the truck: type of tranny, tire size, motor size, and type of driving. Gears for fuel mileage and quick speed do not mesh well. The lower the gears the quicker the acceleration, but the lower the top end speed is. The higher the gear ratio, the better the top end speed and hopefully the better the mileage. I have found that most GM motors like to be around the 2100 RPM range or the economy founders. If you drop much lower than that then the motor has to work hard to get the vehicle up and down hills. You might try working out your rear axle ratio using a formula like this:


Rear axle ratio = RPM X Tire Diameter
MPH X Transmission Output ratio X 336

[swervin ervin]

If you look on the axle tube, about 6" out from the center on the passenger side front, there is a die punched code. The letters/numbers are not big (around 1/8") so you will have to clean the axle real good and look hard to find them. Let me know what the code is and I can tell you what gears came in the axle.

[HotRod73]

okay i can do that tomorrow.... bye the way... its a 1973 or 1974 chevy 3/4 ton cheyenne 2wd.... has a 350... i dont know what transmission, i guess turbo 350?....has 16" wheels not 16.5 but regular 16" its just going to be used for driving to and from work and crusing mainly...will also do some work in it here and there... want to try and get some better fuel mileage but just dont know how i figured gears... kinda want some more acceleration speed its not too quick but then again its a 3/4 ton... buddys 92 camaro 305.. gets 20mpg and gets up decent lol wish i had the same results but there is a big difference plus he has a 700r4 with od...

[68Stepbed]

How long have you owned the truck? What kind of carb and ignition setup do you have(points or HEI)? Have you given it a tune up? Where will you be doing most of your driving(city, highway, or Interstate)?

A 3/4 ton should be geared somewhat low, but decent for street use.
Something to remember, your buddy's Camaro has fuel-injection and was somewhat designed to go fast. I would look more at fuel and spark upgrades first.

Let us know what you got, and we'll try to help.

[Ironclad454]

You can also find out by checking the RPO list located in the engine bay on the driverside. Standard gears for your set up were 3.73's. If there is a code that read ZL8 then you have 4.10 and ZL9 means you have 4.56's. Or at least thats what my books say. If it turns out to be a 74 it may be different but i don't know as I only have info on 73's. Hope that helps you.

[HotRod73]

sorry didnt see an rpo list??
i know there is a deal in glove box with options but that glovebox isnt stock one so not accurate
also grandpa had since 80s its got 91k miles original... he barely drove it since had a huge camper... we took it off... all ive done is changed plugs... i havent touched the wires or ignition or anything ... it has points btw... stock carb (q-jet) most driving in city.... also while looking for rpo numbers i saw my breather said motor size 350 and.... FAMILY number 113 what is that?

[HotRod73]

accord to this http://www.chuckschevytruckpages.com/73-87specs.html i have 4.10 or 4.56 gears? scroll down and take a look... i have a c20

[68Stepbed]

OK. The Q-jet and points ignition is what is holding you back. The Q-jet is a great carb if you can find someone to tune it for you. Unless you're an expert, I wouldn't recommend messing with it yourself. An aluminum intake, HEI distributor, and new wires should be your first agenda. Regap your plugs to .045. I recommend an Edelbrock Performer intake. It will work well with the Q-jet. Depending on your budget, an Edelbrock 500cfm carb would be an excellent upgrade as well. The carb, intake, and dist. will really wake it up and probably leave your buddy's Camaro sittin in your exhaust fumes.
Also, don't run a direct drive or flex fan. Use a clutch fan with a shroud. It should have a clutch fan on it originally. If not, get one from a junk yard.

As far as your original question about the gears, 3.73 or 3.42 gears will work best in a street vehicle. If you don't plan on much freeway driving, I suggest 3.73's. I would go 3.42's if you were doing alot of freeway driving. 4.11 and 4.56 gears will give you awesome take-offs, but will suffer in gas mileage. The best way to know what you have is count the teeth. Take your diff. cover off and count the number of teeth on the ring gear and the pinion. Divide them to get your ratio. Sometimes GM stamped the numbers on the ring gear. For example, if you see 41:11, you have 3.73. If it says 41:10, you have 4.10 or 4.11. I think 4.56's will say 41:9

Good Luck. Let us know what happens.

[HotRod73]

so an aluminum intake (edelbrock or holley etc.) and a 500cfm carburator? is 500cfm bigger than my stock 4bbl qjet? is 500 a good size to go with? also i was going to convert it to HEI as soon as i got the money for a kit... also im going to get plug wires soon... and ill regap my plugs to .045 .... so i should look for a 3.73 gears?.... if i regap my plugs, put some new plug wires on, get the aluminum intake and a nice carb it will have some more NOTICEABLE power? then the 3.73 gears will help me with my city driving fuel mileage?
thanks for helping me out by the way i kinda wanna beef this thing up just dont know how to go about doing it.... also... i bought a chrome breather... but my stock one has alot of crap hooked up to it... hoses etc... can i not add a chrome breather?

[79BIG10]

Hotrod73 where in OK you located? I'm in Texas and maybe we can meet up one day and help out on your truck. I don't think OK has emissions yet so you should be able to reduce if not eliminate your hoses on the air cleaner with some minor parts.

I would suggest a Edelbrock 600cfm rather than a 500. I have a 600 and have rejetted and rodded it to help out to fine tune it. The carb is a great carb for someone that isn't a carb guru. I like since I can set it and forget it where a Holley requires more tuning. A Q-jet I never have learned to tune. I'm no carb guru by any means but I can at least tune my Edelbrock with minor work.

The gears you have like you mentioned a 4.56 or 4.10 are pretty steep gears. I had 3.07 and swapped to a 3.73 driving a TH350. It made a big difference. It may be easier for you to swap a whole rear instead of just the gears. Depending on the axle you have and your need you might find a 4x4 guy that might want to swap your low gear axle for his higher ratio gear.

[piecesparts]

I agree with the upgrades for the intake and the HEI. I am wondering if you wouldn't be better off with an Edelbrock #1406 carb, which is actually a 625 CFM carb, and an Edelbrock Performer RPM manifold. The truck motor that you are working on would do well with the carb size and it has a lot of needles and jets available to allow for the adjustment (if needed). The 3.73 gears will definitely give you a good strong pull on acceleration and a fair to moderate driving mileage. I have a bored and stroked Chevy motor that I am running an 700R4 overdrive tranny and 3.73 gears, pushing 400hp. I get around 14.5 MPG with this setup and it will pull over a Mustang in a moments notice. I am running an aftermarket air cleaner with only the air source for the PCV connected to it. Most of the tubes connected to the original air cleaner are for the different air sources and sensors for the original smog equipment. Those can be connected elsewhere or removed depending on what they actually feed. Be sure to look into a good quality set of spark plug wires for your system.

[HotRod73]

im in norman... having help would be great, seeing how im only 17 lol... i know bout motors and stuff just not alot...
i want to tune this up to do a little better than she is now.. oklahoma has no emissions or inspections anymore... i just dont know how to eliminate and or what to take off... got any parts for sale?

[HotRod73]

i really appreciate all of you helping me... ill check into a edelbrock intake/carb and some plug wires as well as hei dist.... i wish someone on the board has somethin in this area cheap lol... the rear end may wait a little bit till i tune up motor and see what she does (with the mods you mentioned) then maybe swap rear end or just gears...

[piecesparts]

So what truck do you really have 1/2 ton or 3/4 ton? I have a complete 1/2 ton, 10 bolt, 3.08 geared rear end setting beside my garage. I realize that we have been talking 3.73 gears, but if you decide that this is more to your liking, it has the drums, brakes and rear end lube all intact. I live in Lebo, Kansas.

[79BIG10]

Originally Posted by piecesparts

So what truck do you really have 1/2 ton or 3/4 ton? I have a complete 1/2 ton, 10 bolt, 3.08 geared rear end setting beside my garage. I realize that we have been talking 3.73 gears, but if you decide that this is more to your liking, it has the drums, brakes and rear end lube all intact. I live in Lebo, Kansas.

He's got a C20 which is a 3/4 ton.

[HotRod73]

its a 3/4 ton (wish it was 1/2 ton i wont be using much hauling)

[68Stepbed]

I have always had better experience with the 500 Edelbrock over the 600 on stock 350 engines. The 600 will work well, but as stated before, rods and jets need to be changed. The 500 truly is a set it and forget it deal. The air/fuel mixture is pretty much dead on for stock 350's. The 500 Holley 2-barrel also works great, but needs some fine tuning.
Over the years, people have stuck to the idea that bigger is better. People say this formula isn't correct, but I swear by it, and it works great for my engines. CID x max rpm/ 3456 = cfm In HotRod 73's case, 350 x 5000 rpm / 3456 =506.3657. With his engine being a smog-era engine, this formula is even more true. The larger plenum intake won't help much on a truck engine more than a car engine. The truck engines had smaller valves and intake runners for more torque and less hp.

If you plan to add stuff like a cam and heads, the 600 would still be a good investment.