speedometer And gearing question
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speedometer And gearing question
I searched for and found much info on the subject here. I have been able to narrow my questions to these!
A little history NP 435 trans in 66 F100 2wd. Plastic speedo gear in trans is hourglassed and toast. It makes no contact with the gear on the end of the cable. The axle code in the door jam looks like 09. The numbers do not line up well with the labels on the tag , but I think this is correct. The tag on the diff reads as follows DM-K on the top line. The bottom line reads 3 70 6FA 302. Unknown PO mods or swaps may have rendered any/all of this info useless. I did mark the Dline and the tire and count rotations. For the sake of more acuraracy I spun the Dline 4 times and ONE tire spun 2.25 times. If ONE tire spins should I double the the number of tire revolutioons? If so this still makes little sense to me. That would make my R&P ratio 1.12 to 1. That cannot be right!
Any idea what the axle codes on the door and diff tag mean?
Am I going about finding the axle gear ratio the wrong way?
TIA Todd
A little history NP 435 trans in 66 F100 2wd. Plastic speedo gear in trans is hourglassed and toast. It makes no contact with the gear on the end of the cable. The axle code in the door jam looks like 09. The numbers do not line up well with the labels on the tag , but I think this is correct. The tag on the diff reads as follows DM-K on the top line. The bottom line reads 3 70 6FA 302. Unknown PO mods or swaps may have rendered any/all of this info useless. I did mark the Dline and the tire and count rotations. For the sake of more acuraracy I spun the Dline 4 times and ONE tire spun 2.25 times. If ONE tire spins should I double the the number of tire revolutioons? If so this still makes little sense to me. That would make my R&P ratio 1.12 to 1. That cannot be right!
Any idea what the axle codes on the door and diff tag mean?
Am I going about finding the axle gear ratio the wrong way?
TIA Todd
Ford Parts Specialist
Joined: Nov 2006
Posts: 88,826
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From: Simi Valley, CA
09 = 3.70-1 / Ford WDM 9 Inch / 3300 lb Axle Capacity
---------------------------------------------------------
New Process Transmission / Axle ratio 3.70-1 / 15" wheels
C3OZ-17285-C .. Speedo Drive Gear 7 Tooth~on output shaft
C0DD-19271-C .. Speedo Driven Gear 19 tooth
---------------------------------------------------------
New Process Transmission / Axle ratio 3.70-1 / 15" wheels
C3OZ-17285-C .. Speedo Drive Gear 7 Tooth~on output shaft
C0DD-19271-C .. Speedo Driven Gear 19 tooth
Cargo Master
Joined: Feb 2004
Posts: 2,056
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From: Central Texas
Originally Posted by NumberDummy
09 = 3.70-1 / Ford WDM 9 Inch / 3300 lb Axle Capacity
---------------------------------------------------------
New Process Transmission / Axle ratio 3.70-1 / 15" wheels
C3OZ-17285-C .. Speedo Drive Gear 7 Tooth~on output shaft
C0DD-19271-C .. Speedo Driven Gear 19 tooth
---------------------------------------------------------
New Process Transmission / Axle ratio 3.70-1 / 15" wheels
C3OZ-17285-C .. Speedo Drive Gear 7 Tooth~on output shaft
C0DD-19271-C .. Speedo Driven Gear 19 tooth
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FWIW, BOTH wheels were in the air! That is why I thought maybe I should double the wheel rotations. I did some convoluted equation where(using the same numbers) I came up with 3.7something to 1. Then I saw the 302 on the dif tag and could not even figure out how I got the 3.7something number in the first place? Maybe I will check it again.
I did make a stop at Ford and got the 7 tooth trans gear for the 435(that was the gear I took out as it happened), and a new seal. Seal was $1.89 and the gear was $14 and change. I dont have reason to think that the diff has been changed especially since the tag also indicates 3.07:1 Rand P ratio. I will count the gear on the spedo cable and see where it comes out.
NumberDummy, you sir rock!!
Todd
I did make a stop at Ford and got the 7 tooth trans gear for the 435(that was the gear I took out as it happened), and a new seal. Seal was $1.89 and the gear was $14 and change. I dont have reason to think that the diff has been changed especially since the tag also indicates 3.07:1 Rand P ratio. I will count the gear on the spedo cable and see where it comes out.
NumberDummy, you sir rock!!
Todd
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As luck would have it I did have the 19 tooth speedo gear on the end of the cable. Got it all buttoned up and now the thing even works! I think I am now ready for my first official road test.
Todd
Todd
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Joined: Apr 2003
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From: Too close to Houston
Based on the revolutions you reported you have a 3.55:1 ratio, open differential. One wheel turned 2.25 times, so both wheels would have turned 1.125 times. 4 driveshaft revolutions divided by 1.125 ring gear revolutions equals 3.55. Is there a bolted cover plate on the back of the differential or does it separate in front of the axle?
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