Gear ratio help needed
Thread Starter
Melting Slicks
Joined: Sep 2003
Posts: 2,114
Likes: 33
From: ct
Gear ratio help needed
I know this is not the best way to do this but just to see if the rear I have is in the ball park. What dose one turn of the rotor and 4 turns of the drive shaft come out to. I think I already know but lets see what you guy's say. The rear is out of a 77 and should be 308s by reading the codes.
Race Director
Joined: Nov 2000
Posts: 10,347
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From: Beverly Hills (Pine Ridge) Florida
Posi or open rear, and is the opposite wheel stationary or moving also?
Best method with an open gear is to have one wheel stationary (on the ground or held by a helper), while turning the opposite wheel (and counting driveshaft turns for one full turn of the wheel). However, with an open rear, you are turning the spider gears so any reading must be divided by 2. Example: 1 turn of the wheel for 4 turns of the driveshaft divided by 2 equals 2:1.
For a posi, where both wheels are turning, no spider gear action is encountered, so 4 turns of the wheel for 1 turn of the driveshaft equals 4:1 rear end ratio.
Edit: Corrected above formula for open gear per corrections from Pete and JohnZ. Geez guys, I got it 1/2 right.
Plasticman
Best method with an open gear is to have one wheel stationary (on the ground or held by a helper), while turning the opposite wheel (and counting driveshaft turns for one full turn of the wheel). However, with an open rear, you are turning the spider gears so any reading must be divided by 2. Example: 1 turn of the wheel for 4 turns of the driveshaft divided by 2 equals 2:1.
For a posi, where both wheels are turning, no spider gear action is encountered, so 4 turns of the wheel for 1 turn of the driveshaft equals 4:1 rear end ratio.
Edit: Corrected above formula for open gear per corrections from Pete and JohnZ. Geez guys, I got it 1/2 right.
Plasticman
Last edited by Plasticman; Feb 10, 2008 at 12:32 PM.
Thread Starter
Melting Slicks
Joined: Sep 2003
Posts: 2,114
Likes: 33
From: ct
Yea it's a posi. And thats just what I thought it was. Of course I do not want 411's I need 308's. I'll pull the cover this week but I came up the same as you. Thats my luck. If I needed 411's it would be a 308. It may be easyer to find a 308 rear just because now I also have a 4 series carrier. And to make it worse, guess what I just sold that came out of my 69 last year. You got it a 308 rear. Do I need to tell you what I put in the 69 ? 
Safety Car
Joined: Aug 2007
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From: Chicago IL
For a posi, where both wheels are turning, no spider gear action is encountered, so 4 turns of the wheel for 1 turn of the driveshaft equals 4:1 rear end ratio.
I think this is backwards, 1 turn of the tire = 4 turns of the driveshaft?
I think this is backwards, 1 turn of the tire = 4 turns of the driveshaft?
Team Owner
Joined: Oct 2000
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From: Washington Michigan
Safety Car
Joined: Aug 2007
Posts: 3,510
Likes: 0
From: Chicago IL
Yea it's a posi. And thats just what I thought it was. Of course I do not want 411's I need 308's. I'll pull the cover this week but I came up the same as you. Thats my luck. If I needed 411's it would be a 308. It may be easyer to find a 308 rear just because now I also have a 4 series carrier. And to make it worse, guess what I just sold that came out of my 69 last year. You got it a 308 rear. Do I need to tell you what I put in the 69 ?
