1.98 Rear End?

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BlindSquirrel

BlindSquirrel

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Hello, Guys and Gals,

Although I have been visiting your wonderful site for several months, I just recently purchased a 1967 Barracuda, so I figured that I should join up. I am trying to repair several items that are not working on the car, and need some help with a speedometer. My original speedo was broken, and I replaced it with a nice used unit, but the new speedo doesn't work. I thought I should check out the rear end gears so that I can check for the proper pinion gear while I am troubleshooting. It appears that the car has 1.98 gears in the rear, and the speedo pinion chart in the shop manual doesn't go that low. Any suggestions? Any comments on the gear ratio?

Thanks.

BlindSquirrel
 
Never heard of a 1.98 before. Should get great gas mileage on the highway!
 
Welcome, and nope, no 1.98 gears. 2.73ish is as low as you could go until sometime in the 80's there was a 2.54. How exactly did you figure the 1.98?
 
I put a paper tape on the drive shaft and spun the rear wheel for 1 revolution. The drive shaft spun 1.98 times in the 1 revolution of the wheel. Is this the correct way to determine the gear ratio?
 
that is a logical way to determine gear sets, but only in a sure-grip (posi) style diff or a spool. The open diff likes to trick ya. The simplest way is to look at the edge of the ring gear. Most ring gears have the gear set ratio stamped into them. (ie 2.76, 2.96, 3.23)
 
that should work but doesnt sound right. sure you didnt miss one revolution?
 
If it's not a sure grip, it doesn't work like that. When you turn one tire, if the other tire is motionless or turning the opposite direction or turning the same direction at a different speed, then counting the revolutions at the yoke will not give you an accurate gear ratio.
 
Thank you, all of you, for the help. It is not a sure grip rear end, so I guess I have to do some more work and get at the ring gear.

Thanks again for the help.
 
To check the ratio of non sure grip. Jack up one wheel, mark the wheel and drive shaft. Rotate the wheel TWO revolutions, and count driveshaft turns.
How did you determine 1.98, I have never been able to get that acurate? If that is really correct, it looks like you have a 3.91 gear. That ratio was available but they are relativly rare in a factory installed situation.
 
Charrlie_S said:
To check the ratio of non sure grip. Jack up one wheel, mark the wheel and drive shaft. Rotate the wheel TWO revolutions, and count driveshaft turns.
How did you determine 1.98, I have never been able to get that acurate? If that is really correct, it looks like you have a 3.91 gear. That ratio was available but they are relativly rare in a factory installed situation.
Click to expand...

or jack up both sides and have a friend spin the other wheel at the same speed as u for 1 turn...
 
Charrlie_S said:
To check the ratio of non sure grip. Jack up one wheel, mark the wheel and drive shaft. Rotate the wheel TWO revolutions, and count driveshaft turns.
How did you determine 1.98, I have never been able to get that acurate? If that is really correct, it looks like you have a 3.91 gear. That ratio was available but they are relativly rare in a factory installed situation.
Click to expand...

Charlie's right. That's the way to do it and is easier than jacking up and getting a friend to spin the other wheel and another friend to count the driveshaft rotations. I agree it sounds like you have some good hot rodding 3.91 gears.
 
The speedo should work with any speedo gear installed properly and a good cable. It might be X mph wrong but it would work.
 
fishy68 said:
Charlie's right. That's the way to do it and is easier than jacking up and getting a friend to spin the other wheel and another friend to count the driveshaft rotations. I agree it sounds like you have some good hot rodding 3.91 gears.
Click to expand...

very true lol then u don't have to swear at ur friend for turning the wheel too fast/slow lol
 
Charlie, and everyone else, thanks for your help. I'll have to try your method to see what gears I have. As to my method for determining the 1.98, I taped a paper tape to the driveshaft (the circumference of the shaft was 10.25") and aligned the "0" up with a rafter square so that I could determine exactly where the shaft stopped. I then put a strip of tape on the wheel, and aligned it with another square so that I could determine when the wheel had made exactly 1 turn. When I made 1 turn of the wheel, the driveshaft had rotated exactly 1 full turn plus 10" out of 10.25". 10 divided by 10.25 is 0.975, so I assumed that I had 1.975 or 1.98 gears. I checked the measurement twice, and got the same answer. I'll have to check it with the 1 wheel method, and see what I get.

Thanks again to all who replied.
 
No need to get that detailed, about it. There are only certain ratios available. When turning the wheel 2 turns, if the driveshaft turns about 3 3/4 turns, it is a 3.73. If it turns almost 4 turns, it is a 3.91, if a little more then 4 turns, a 4.11, you get the idea.
 
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