rear end gears?
Fleet Owner
Joined: Jan 2004
Posts: 26,007
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From: Brentwood,CA
well with that info i can't tell you. you want to turn the wheel only enough rotations to make the drive shaft spin once. if the tire takes 3.5 turns to make one full turn of the driveshaft then you have a 3.54 rear gear.
New User
Joined: Jan 2008
Posts: 0
Likes: 24
Quote: wheel 5 times and DS 7 times.
1.40:1
Quote #2:
you want to turn the wheel only enough rotations to make the drive shaft spin once. if the tire takes 3.5 turns to make one full turn of the driveshaft then you have a 3.54 rear gear.
__________________
Better try that again
If the wheels turn once and the drive shaft turns 3.5 times you have 3.50 gears.
The best way is to turn the wheels 10 times and count the revs of the DS.
What code is stamped on your data plate ?
1.40:1
Quote #2:
you want to turn the wheel only enough rotations to make the drive shaft spin once. if the tire takes 3.5 turns to make one full turn of the driveshaft then you have a 3.54 rear gear.
__________________
Better try that again
If the wheels turn once and the drive shaft turns 3.5 times you have 3.50 gears.
The best way is to turn the wheels 10 times and count the revs of the DS.
What code is stamped on your data plate ?
Last edited by Mil1ion; Apr 27, 2006 at 08:45 PM.
Cargo Master
Joined: Apr 2001
Posts: 2,364
Likes: 3
From: Eustis FL
This all sounds odd to me. My method sounds strange and doesn't sound like it should work, but it does.
Jack up one wheel, put trans in neutral. Turn wheel two full turns and count driveshaft rotations. Those rotations are your ratio. (two and three quarter turns is 2.75, three and a half turns is 3.50, etc)
Trust me, it worked everytime I tried it, on several different vehicle! You will have to jack both wheels if it is a locking diff.: Limited slip may work ok.
Also, it is nice to put a reference mark (like chalk, or a fridge magnet) on the driveshaft to keep track of turns.
Mark
Jack up one wheel, put trans in neutral. Turn wheel two full turns and count driveshaft rotations. Those rotations are your ratio. (two and three quarter turns is 2.75, three and a half turns is 3.50, etc)
Trust me, it worked everytime I tried it, on several different vehicle! You will have to jack both wheels if it is a locking diff.: Limited slip may work ok.
Also, it is nice to put a reference mark (like chalk, or a fridge magnet) on the driveshaft to keep track of turns.
Mark
Senior User
Joined: May 2003
Posts: 160
Likes: 0
From: Benbrook, Texas
Your method did sound strange until I thought about it, trino. With an open diff, one wheel stationary with the other turning would require two rotations to equal one rotation with both wheels turning, right? So your options are to jack up both wheels, have a helper turn the other wheel with you (or have a locking diff) and count driveshaft rotations to wheel rotations OR just use one wheel and double your wheel rotations to make the driveshaft do the same thing.
If you did your 5:7 test with only one wheel off the ground, that would be equivalent to 2.5 ring gear rotations to 7 pinion rotations or 2.8:1 (double Million's correctly calculated 1.4:1), which I would assume is a 2.75:1 rear end. Does your truck cruise at low RPM's on the freeway? Have a hard time getting a trailer to break the moment of inertia? If so, your '78 is like mine was originally gear-wise. As long as your ski boat doesn't drag that old Ford into the lake when you try to pull it up the boat ramp and gas is $3/gallon, leave it!
Hope this helps you, I learned a new trick from trinogt!
Bob
If you did your 5:7 test with only one wheel off the ground, that would be equivalent to 2.5 ring gear rotations to 7 pinion rotations or 2.8:1 (double Million's correctly calculated 1.4:1), which I would assume is a 2.75:1 rear end. Does your truck cruise at low RPM's on the freeway? Have a hard time getting a trailer to break the moment of inertia? If so, your '78 is like mine was originally gear-wise. As long as your ski boat doesn't drag that old Ford into the lake when you try to pull it up the boat ramp and gas is $3/gallon, leave it!
Hope this helps you, I learned a new trick from trinogt!
Bob
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Cargo Master
Joined: Apr 2001
Posts: 2,364
Likes: 3
From: Eustis FL
I will stick with my method... easy to remember, and doesn't require coming back to the computer for an FAQ when I am at the junkyard haha
Also, I NEVER rely on door codes, as ratios can be changed like underwear throughout the life of a truck, depending on what each user needs out of his/her truck. Axle tags are also gone 90% of the time, likely from junkyard scroungers snapping them off to read easier. And, who's gonna pull the driveshaft and carrier just to count teeth?
CBob, that makes sense, bud! Now, if I can remember the reasoning for the rest of my life! lol Thanks!
Mark
Also, I NEVER rely on door codes, as ratios can be changed like underwear throughout the life of a truck, depending on what each user needs out of his/her truck. Axle tags are also gone 90% of the time, likely from junkyard scroungers snapping them off to read easier. And, who's gonna pull the driveshaft and carrier just to count teeth?
CBob, that makes sense, bud! Now, if I can remember the reasoning for the rest of my life! lol Thanks!
Mark
Last edited by trinogt; May 1, 2006 at 11:10 PM.
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Cargo Master
Joined: Apr 2001
Posts: 2,364
Likes: 3
From: Eustis FL
I have never come across a 3.33:1 ratio anyway... And if I did, JACKPOT! Between a 3.25 and a 3.50? Nice. And YES, a 'two-turn method' WILL differentiate between a 3.25 and a 3.50, the 'more common' Ford truck ratios.
Mark
Mark
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