Correct speedometer gear.

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Mar 30, 2011 | 09:44 PM

Jon R

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Correct speedometer gear.

Two questions that the search function did not help me with... For a 77 f-150 eqiuped with 3.50 gears what would be the correct cable gear? 2nd question, what would have been the correct tire size? -F-150 Custom/Supercab 400 and auto transmission. Thanks for any help.

Mar 30, 2011 | 10:13 PM

Bullitt390

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Are you asking because you're speedo is off?

It's pretty simple to calculate what you need if you have GPS or a car with an accurate speedo to drive next to.

Josh

Mar 30, 2011 | 10:15 PM

mikeo0o0o0

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From: Stanley, VA

C4, C6, 3.50 ratio, 2WD
w/ tire size 6.50x16, 7x15, L78x15, H78x15 p/n C8SZ-17271-B

6.70x15, G78x15, GR78x15, HR78x15 p/n D00Z-17271-A

Not sure about the tire size.

Mar 31, 2011 | 05:50 PM

jim collins

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From: South west Idaho

My 79 f-100 ,460 with c/6 transmission. It has ' P225/70 R 15' tires. The tires are 27 in tall.The speedometer gear thats on the cable has 20 teeth . I don't know what the one thats on the output shaft has on it. The rear diff. gears are 3:50 . It show's to be off 1/10 for each mile by using a stop watch from mile post to mile post at 60 mph . It will smoke those little tires real easy. I plan to change the rear gears to 2:75 next week. I am trying for better mpg ,L.O.L.

Mar 31, 2011 | 10:08 PM

Jon R

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Thanks guys that helps. Jim the 225/70 15's are whats on my truck now. Jon

Apr 1, 2011 | 04:40 AM

lonnie1952

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From: Moreno Valley

Quote:

Originally Posted by jim collins

Your poor tires...LOL

460 with those small tires. do you go through about three sets a year ?

Apr 1, 2011 | 06:33 AM

jim collins

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From: South west Idaho

Quote:

Originally Posted by lonnie1952

Your poor tires...LOL

460 with those small tires. do you go through about three sets a year ?

NO ,they were on the truck when i got them,he,he. but it will smoke them. It was a 6/cy truck original with truck 4/speed overdrive that ford made a few of. I plan to put something in there place after i get a few other things done on it. I'm changing the rear gears to 2.75,then i will decide on the tires after i see how it performs. It would be kinda nice if i can get better mpg and still smoke the tires too.

JIM

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Apr 5, 2011 | 09:14 PM

Jon R

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Quote:

Originally Posted by NumberDummy

Bill, do you know of another source for the D0OZ-17271-B (21T) gear? PartsguyEd does not show a listing. Thanks Jon

Apr 5, 2011 | 10:16 PM

#10

mikeo0o0o0

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From: Stanley, VA

D0O-17271-B
Antique Auto Arlington, Arlington, TX has 2 (817) 275-2381
Miller Obsolete Parts, Binghampton, NY has 2 (607) 722-5371

Apr 6, 2011 | 01:05 AM

#11

NumberDummy

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From: Simi Valley, CA

The long standing problem has been...whenever there is a 0 (zero) as the 2nd digit of a part numbers prefix, it can also be typed as the letter O.

While 0 is correct, it doesn't always work, because in this case, it was entered into Ford's computer system as...

DOOZ-17271-B .. Speedometer Driven Gear-21T / Available from Ford.

MSRP: $2.29 // PARTSGUYED.COM price: $1.66.

Apr 6, 2011 | 09:10 PM

#12

joerickson

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Does anyone know how to figure out what speedo gear you need when you dont know the original tooth count?

The reason I ask is because I have been doing a restoration and combining parts from a few different trucks. I have a 400/c6/3.50 gears and plan on 33-35" tires. Just need it to be relatively close, I can always check with gps and associate how fast/slow it is.