The Ford Barn

rhphotord · 02-19-2023, 01:27 PM

Ok bought this rear axle assembly for my car. It's in great condition externally appearing as the owner suggested as a low mileage take out with virtually no rust and light peeling original paint. I was told it was a 3:78 ratio and the numbers stamped are 9/34 which should be correct. Sounds simple enough. However out of curiosity I locked up one axle to prevent it turning and spun the pinion, counting the revolutions compared to the unretained axle rotation. I cannot count more than 2 full pinion revolutions for every axle rotation! Really baffled by this and frankly think I must be getting stupid in my old age or I have got a 2:10 axle What am I not seeing?

cadillac512 · 02-19-2023, 01:35 PM

Quote:

Originally Posted by rhphotord

Ok bought this rear axle assembly for my car. It's in great condition externally appearing as the owner suggested as a low mileage take out with virtually no rust and light peeling original paint. I was told it was a 3:78 ratio and the numbers stamped are 9/34 which should be correct. Sounds simple enough. However out of curiosity I locked up one axle to prevent it turning and spun the pinion, counting the revolutions compared to the unretained axle rotation. I cannot count more than 2 full pinion revolutions for every axle rotation! Really baffled by this and frankly think I must be getting stupid in my old age or I have got a 2:10 axle What am I not seeing?

If you're holding one axle from turning, you have to double your pinion revs to get the reading. The spider gears cause the free axle to run at twice speed.

Terry

Mart · 02-19-2023, 01:39 PM

Turn the free wheel TWICE and count the pinion rotations.

Check out this old video of mine:

https://youtu.be/bkvp3Fq21ZM

Mart.

HDowse · 02-19-2023, 06:47 PM

Easy way to figure out the ratio, Mart. And 11 years ago. Time to put up more of your golden oldies!

JM 35 Sedan · 02-20-2023, 09:02 AM

Remove the oil filler plug on the banjo housing and count the number of teeth on the ring gear.

rhphotord · 02-20-2023, 10:46 AM

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Thought this was a simple problem with a simple answer. Thank you and yes it is a 3:78

02-19-2023, 01:27 PM	#1
rhphotord Senior Member Join Date: May 2010 Location: West Salem, Wi. Posts: 281	Verify rear axle ratio Ok bought this rear axle assembly for my car. It's in great condition externally appearing as the owner suggested as a low mileage take out with virtually no rust and light peeling original paint. I was told it was a 3:78 ratio and the numbers stamped are 9/34 which should be correct. Sounds simple enough. However out of curiosity I locked up one axle to prevent it turning and spun the pinion, counting the revolutions compared to the unretained axle rotation. I cannot count more than 2 full pinion revolutions for every axle rotation! Really baffled by this and frankly think I must be getting stupid in my old age or I have got a 2:10 axle What am I not seeing?

02-19-2023, 01:39 PM	#3
Mart Senior Member Join Date: May 2010 Location: Solihull, England. Posts: 8,755	Re: Verify rear axle ratio Turn the free wheel TWICE and count the pinion rotations. Check out this old video of mine: https://youtu.be/bkvp3Fq21ZM Mart.

02-19-2023, 06:47 PM	#4
HDowse Senior Member Join Date: May 2010 Location: Hancock, New Hampshire Posts: 375	Re: Verify rear axle ratio Easy way to figure out the ratio, Mart. And 11 years ago. Time to put up more of your golden oldies!

02-20-2023, 09:02 AM	#5
JM 35 Sedan Senior Member Join Date: May 2010 Location: Near Rising Sun, Maryland Posts: 10,858	Re: Verify rear axle ratio Remove the oil filler plug on the banjo housing and count the number of teeth on the ring gear. __________________ *John* *"Never give up on what you really want to do. The person with big dreams is more powerful than one with all the facts". Albert Einstein*

02-20-2023, 10:46 AM	#6
rhphotord Senior Member Join Date: May 2010 Location: West Salem, Wi. Posts: 281	Re: Verify rear axle ratio Sponsored Links (Register now to hide all advertisements) Thought this was a simple problem with a simple answer. Thank you and yes it is a 3:78