gearing??

[Dirtkid93]

okay guys so i just picked up my 64' c20.
it's a 230 3.8 liter inline 6 engine. 4 speed on the floor, with granny gear. the thing takes forever to get to speed and barely maintains 65 mph, steady 55-60 realistically. I want more out of it, is there a different tranny I could buy to do so? or would it be easier and more cost efficient to regear the differential?

[BADAZ chevy guy]

Unless you go with a transmission with an over drive, a transmission swap wont gain you anything. All transmissions have a 1:1 ratio in high gear. You need to get closer to 3.08 or at leased further away from 4.56
Here's a graph of the gears available from 1958 to 1970>>> http://www.348-409.com/differential.html

[66Submarine]

x2 the above. 4.10 gears are available (used) for your original axle for $100-200 and can be changed without gear setup (third member type axle), otherwise you'll need an OD trans or axle swap. My truck with a 250/SM420 and 4.10 gears with a 32" drive tire will run 70MPH fine, but it's spinning close to 3,100RPM there.

Now, if you are finding the truck just doesn't actually have the power to maintain 65MPH (IE, throttle wide open and unable to maintain speed), then the gears won't help that. A 230 is a real small engine to begin with, but it should be able to maintain 65MPH with an empty truck (under most conditions) IMO.

I don't really have a problem with my 250, and I towed a 4000LB car the other day with it without much trouble at all, but the truck certainly isn't a rocketship with the 250, and it won't be with the 230. One thing is how fast you're shifting, too--shifting too soon with the SM420's widely spaced gears will just make that little six bog. I shift at something like 2,500-3,000RPM most of the time.

Hope this helps

[Captainfab]

A C20 is going to be low geared to start with. Your truck will likely have 4.57gears or possibly the 4.10's. In reading your post, it sounds to me like the engine is struggling. If that is the case, and if the engine is in basically good condition, I would start with a thorough tune up and oil and filter change.

[kieth]

Originally Posted by Dirtkid93

okay guys so i just picked up my 64' c20.
it's a 230 3.8 liter inline 6 engine. 4 speed on the floor, with granny gear. the thing takes forever to get to speed and barely maintains 65 mph, steady 55-60 realistically. I want more out of it, is there a different tranny I could buy to do so? or would it be easier and more cost efficient to regear the differential?

Measure the rear tire from the ground to the top of the tire.......find out your rear axle ratio, then refer to these charts, sounds like someone may already have changed the rear gearing in your truck, or the motor is really weak.....after you figure out what gearing you have then we can figure out what to do to solve the problem. Kieth


TORQUETOGROUND_Master_r.pdf