Gear ratio???
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Freshman User
Joined: Oct 2004
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Gear ratio???
I want to install a speedometer cable on my '55 F100. Although it has a 390 and a top loader 4 speed, it has the original rear end. The guy at the parts store told me these trucks came with either a 3.91 or 4.30 ratio. Is there a code on the truck that will tell me the axle ratio? With my aging eyes I don't trust the 4.3 turns to 1 versus 3.9 turns to one.
Lead Driver
Joined: Apr 2002
Posts: 8,813
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From: Littleton, New Hampshire
Originally Posted by twofast4u
I want to install a speedometer cable on my '55 F100. Although it has a 390 and a top loader 4 speed, it has the original rear end. The guy at the parts store told me these trucks came with either a 3.91 or 4.30 ratio. Is there a code on the truck that will tell me the axle ratio? With my aging eyes I don't trust the 4.3 turns to 1 versus 3.9 turns to one.
Vern
Cross-Country
Joined: Oct 2004
Posts: 95
Likes: 21
From: Cape Cod
Data plate in glovebox?
On the earlier trucks, the rear ratio was stamped on the data plate inside the glovebox.
Some rears have a metal tag under one of the bolts which has the info.
If you try the rotate the tire method, use 10 rotations rather than one - 39 to 10 or 43-10, less margin of error. But without a posi, one wheel will turn twice as many times as if both were turning. So does that make it 39 driveshaft to 20 wheel rotations? I think so. Have fun counting with your trusted friends!
Jonas
Some rears have a metal tag under one of the bolts which has the info.
If you try the rotate the tire method, use 10 rotations rather than one - 39 to 10 or 43-10, less margin of error. But without a posi, one wheel will turn twice as many times as if both were turning. So does that make it 39 driveshaft to 20 wheel rotations? I think so. Have fun counting with your trusted friends!
Jonas
Senior User
Joined: Oct 2003
Posts: 317
Likes: 1
From: Lancaster SC ,
For what it's worth most of the trucks came with a 3.92 rear end gear in 55. Vern is correct in saying the correction will be made in the tranny. The thing to do is if it works now, Have someone with a correct speedo check the accuracy of yours, then you will know which way to adjust your speedo gear at the tranny.
Hope this helps
Bubba
Hope this helps
Bubba
