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| | | | Joined: Jun 2011 Posts: 124 Shop Shark | | Shop Shark Joined: Jun 2011 Posts: 124 | I've just drove my subject project truck to the exhaust shop for a new exhaust this morning. The truck is actually running pretty good with the exception of it being extremely low geared. I need to change the diff fluid to see what gearing it is but it has 235 75 15 tires and I can pretty much take off from a rolling stop in 3rd gear. In 4th at 45 mph it seems to be starting to rev pretty high. I'm thinking it is 4.10 or 4.56. I'm thinking 3.55 would be just right. Any thoughts? I don't want it to be under powered but I do want it to bee a bit more driveable on the highway. Thanks.... | | | | | Joined: Jan 2001 Posts: 5,337 'Bolter | | 'Bolter Joined: Jan 2001 Posts: 5,337 | A 65 C10 would most likely have a 3.7
See the USA in your vintage Chevrolet! My Blog | | | | | Joined: Jun 2011 Posts: 124 Shop Shark | | Shop Shark Joined: Jun 2011 Posts: 124 | I'm wondering if anyone has ever geared one of these applications up to say 3.55 or 3.42? I'm thinking it would be fine especially being that I would like to run some shorter wider tires. | | | | | Joined: Sep 2011 Posts: 2,951 'Bolter | | 'Bolter Joined: Sep 2011 Posts: 2,951 | A 65 C10 would most likely have a 3.7 My 65 C10 has a 3.73 rear. I used the common method of jacking both rear wheels off the ground and counting tire rotation and drive shaft rotations, (I randomly decided on 20 total rotations of the DS, but more would be even better). To do the math: Double the DS rotations and divide by the Tire rotations. Mine was 20 DS rotations for 10.75 tire rotations. So 20 X 2 = 40 and 40/10.75= 3.72 Hot Rod Lincoln once explained it well . . . You've got three moving parts, the driveshaft, and both rear axles. Whichever one has the most drag will sit still, and the other two will move. If you just jack up one wheel and turn the other one, the spider gears between the axles will alter the speed of the other parts. One turn of the driveshaft will result in the wheel turning at twice its normal speed if both axles were free to turn. Remember this if you encounter wheelspin on one side in mud or snow- - -30 MPH on the speedometer will be 60 MPH at the spinning wheel.
The most accurate way I've found to estimate the rear axle ratio is to roll the vehicle straight forward exactly one turn of the rear wheels, and count the turns of the driveshaft. With both wheels on the ground, it's impossible to get an error induced by the differential gearing.
Jerry | | | | | Joined: Jun 2011 Posts: 124 Shop Shark | | Shop Shark Joined: Jun 2011 Posts: 124 | Thanks, but I don't really want to know what ratio I have. I want to see what others have done as far as making the truck more driveable on the highway. I know with my current setup 65-70mph on the highway for extended periods puts strain on the engine. I know some guys install newer 5 spd transmissions, or regear the rear to higher gears or both. I kind of want to keep my 230/4pd stock setup and just work with higher gears. My question is, how high can you go without losing too much power on a 4spd granny gear tranny? | | | | | Joined: May 2006 Posts: 8,351 'Bolter | | 'Bolter Joined: May 2006 Posts: 8,351 | You will need to find out what the existing gear ratio is, because it can have an effect on what gearing can be installed in your existing rearend. The carriers in the 12 bolt rearend are different depending on what the oem ratio is. There is some overlap between the lowest 3.XX:1 ratio and the highest 4.XX:1 ratio. Depending on what you have, it will dictate whether you will need to change the carrier as well as the gears.
Bill Burmeister
| | | | | Joined: Jun 2011 Posts: 124 Shop Shark | | Shop Shark Joined: Jun 2011 Posts: 124 | Gotcha, what you are referring to is Carrier break. How many years do these 12 bolts interchange with? | | | | | Joined: May 2006 Posts: 8,351 'Bolter | | 'Bolter Joined: May 2006 Posts: 8,351 | '63-'76, though I have seen 12 bolts in a few '77s. After '71, the 2wd version will have 5 bolt axles. Also, the '63-'64 (I've heard of some early '65s like this, too) will have the older 17 spline axle shafts instead of the 30 spline.
Bill Burmeister
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