rear axle ratio

B

bonanza7369

Member
how can i determine which ratio axle my 56 ford fairlane has?
it is a 292 V8 with manual transmission (no overdrive) I dont know if its ever been changed or worked on.
 
Easy. Jack both rear wheels off the ground and put the transmission in nuetral. Mark the driveshaft so that you can see how many times it rotates. Rotate a tire one full revolution. If the driveshaft rotates 3 times your ratio is 3 to 1.
 
bonanza7369 said:
how can i determine which ratio axle my 56 ford fairlane has?
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GLAmes said:
Easy. Jack both rear wheels off the ground and put the transmission in nuetral. Mark the driveshaft so that you can see how many times it rotates. Rotate a tire one full revolution. If the driveshaft rotates 3 times your ratio is 3 to 1.
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I don't really remember trying this but with a regular / non limited-slip differential does one of the rear wheels have to be kept from turning? Depending on the forces involved, the other rear wheel will often turn in the opposite direction, instead of turning the driveshaft.
55blacktie said:
Is there a tag attached to the differential cover?
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This example is 43 divided by 13 = 3.307 commonly referred to as 3.31 : 1
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dmsfrr said:
I don't really remember trying this but with a regular / non limited-slip differential does one of the rear wheels have to be kept from turning? Depending on the forces involved, the other rear wheel will often turn in the opposite direction, instead of turning the driveshaft.
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Both wheels have to be off the ground with a locker style. They will both turn in the same direction.

FORD began using a clutch style diff in 1959 (optional).
 
If there is tag on your rear-end ( ... :confused: ...), please take a photo of it installed on the carrier (if it is a FORD style).

I think (... :confused: ...) the one shown is off a DANA 44.

TAG INFO (pre-1957) is not shown in either the PARTS or SERVICE MANUALS.
 
dmsfrr said:
I don't really remember trying this but with a regular / non limited-slip differential does one of the rear wheels have to be kept from turning? Depending on the forces involved, the other rear wheel will often turn in the opposite direction, instead of turning the driveshaft.
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Good catch. With a non LSD you only jack one tire off the ground.
 
With one wheel on the ground the pinion gears come into play. I think you will need 2 rotations of the tire.
 
When the drive train is in neutral and rear wheels off the ground, both should rotate the same direction. If the transmission is shifted into a gear that that will stop motion of the drive train and the rear axle will change to differential mode where one wheel will rotate opposite the other. If there is a lot of friction in the drive train when in neutral then it will go into differential mode. This is where it would have to have the left side wheel on the ground for most rear axles.

If a rear axle has a filler plug to allow for a tooth count then that is a quick way to find the exact ratio. Ford used taller ratios for automatic transmission cars than for manual transmission cars. The higher numerical ratios were used in mountainous terrain. The unfortunate thing about the predecessor to the 9-inch is that new or unused ring and pinions are in the NOS category. No new ones are available that I'm aware of.
 
... :confused: ...​

READ THIS - https://shiftsst.com/blog/post/how-to-determine-the-rear-axle-ratio.html

If you are unsure whether you have a Posi Rear or not

Jack both wheels off the ground and turn one wheel.

If the opposite wheel turns the same direction or doesn't turn at all, then the rear axle is posi or limited slip.

If the opposite wheel turns the opposite direction, then it's probably an open rear axle (non-posi).
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When performing something as this, both wheels should be off the ground as if it has a locker or clutch style, the car may roll causing numerous embarrassing results.

You don't know who has been in there before.
 
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5851a said:
With one wheel on the ground the pinion gears come into play. I think you will need 2 rotations of the tire.
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This is correct. If it is a non-posi differential, then you will rotate ONE
tire/wheel for TWO rotations, and keep the other tire stationary.
Have someone counting the rotations the driveshaft has made.
Three and a half rotations would be a 3:50 ratio'


Block the front wheels good and trans in neutral

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You mean to tell me that even with a locker, you are gonna roll that heavy carr off a jackstand by hand? Maybe if your arnold schwarteneger...
 
Gene F said:
You mean to tell me that even with a locker, you are gonna roll that heavy carr off a jackstand by hand? Maybe if your arnold schwarteneger...
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And you think it has never happened with one wheel on the ground? Why would one think a PROFESSIONAL SHOP would give a warning?

Some of what you read here and on other forums is scary. And THE OLDE WIVES TALES just keep going.

I give up ...
 
Gene F, for safety's sake, why would you want to put it to the test?

Years ago, my friend's father was help him with his car. While under the car, it fell on him, crushing his head. Although his father survived, he was never the same.
 
I agree totally. The old saying "I'd rather be safe than sorry" applies here.

I've known 2 younger guys, both teenagers, who didn't take the time
to think things out before getting under their cars to work on them.

Both died before even graduating high school. What a damn shame.

One was under his car, to remove his driveshaft, his parents driveway
had a slight incline... I'll let you figure out what the rest of the story is :eek:

Another was under his car to remove the old automatic. Had it all
unbolted and told his buddy to let the jack down a little bit, then
the blocks toppled over, he never even had a chance to scream,
was the story told. :eek:

I'll bet most all of us ol' gear-heads have had some close calls. :o

" An ounce of Prevention is worth a pound of Cure " fit's here.

Good Luck and Be Safe, Everyone...:)




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