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what is the gear ratio that i need

BUCKEYE BOB

Florida Chapter member
on a 51 f1 with a 302 & a c4 what gear ratio in a 9 in do i need?
i am not going to hot rod it i want to have low rpm's & good gas mileage
& i would like to do some highway driving.i know that is a lot to ask
any help would be appreciated. thanks Bob what year 9 in?
 

mtflat

Flatheads Forever
2,559
147
Just my opinion for what it cost you - I'd suggest something in the 3.25 to 2.75 range with an automatic trans for mileage and low rpms. Your final drive is 1:1 so depending on tire/wheel size you use.....

2.75 will have less power on take off, but lower rpm at speed. 3.25 will have more power on launch but higher rpm at speed.

9" rear from F100 - 1957 to '72. (68 - 72 the brakes are wider)

28 spline axles will be fine behind a stock 302, especially with auto.

Lots of variables I haven't mentioned.
 

BUCKEYE BOB

Florida Chapter member
Tim,thank you a guy just called me & said that he has a 9in
with 325 gears that i can have for $150 & if i want he will make the
switch for $100.I like what you said about the 275 gears.who would
be intrested in my original 373 rear that is in the truck now? Bob
 

tinman52

Tin bender
What Tim said is right.....just remember to get a pickup 9 inch, not one for a car. 3.00 rear gears would work fine as well......
Your original rear should have either 3.92's or 4.27's....not much demand for those.
 

mtflat

Flatheads Forever
2,559
147
There has been some discussion about those ratios. As near as Ross and I can determine, the shop manual is a mis-print about the universal application of the 3.92 ratio.

If I remember right how it went, some of the early (48) F1's had 3.92 gears, but after that Spicer went to 3.73. Probably where the 49-51 Shop Manual picked up the error.

How about you guys with 49-52's - what is your ratio?
 
3.25's were pretty common gears in late 60's-early 70's F-100's 9" rears. They'll work great with your combo. I had that same setup in my '50 F1 with a 289 and C4 trans. I was very happy with it.
 

mtflat

Flatheads Forever
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The tag on my 50 says 47/11 that's why I'm
looking for a later f100 bolt in with a higher ratio.

My 48 had that lovely 4.27 ratio too. I swapped it for a 9" 3.50 from a mid-60's F100. The old axle is still sitting in the shed if anybody ever wants to do a restoration.....
 

mtflat

Flatheads Forever
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U joints are the same. The driveshaft will be approx 1 1/4" too short... actually the new differential is shorter by that much.

I solved that by going to a driveline shop and purchasing a new splined yoke that was the right length. BUT, mine has the HD 3 spd which uses the sliding yoke on the driveshaft, same as the 4 spd. If you have the LD 3 spd, your options will be different and more of a challenge.

I've heard of diff yokes on similar year station wagons that were longer than the truck variety and can be used. Or have a driveline shop lengthen your driveshaft. Or.......... anybody else have ideas?
 

havi

third member
Dana 41 ('48-mid50) or early 44 (mid50-56) with the 3.73's would be something I'm looking for (they're out there). The parasitic hp needed to turn a 9" is more than the stock Dana. Your 302 need not worry about such a thing.

Most 9" rears from F100's '57-72 had 3.25 gears, some higher, some lower. There is an oddball rear end that looks like a 9" but is actually a 9.38" (housing should stick out the back a little), and would typically be found behind camper specials.

Due to the OP having a 302 and C4, a stock driveshaft is probably out of the question.
 
Last edited:

tinman52

Tin bender
My 48 had that lovely 4.27 ratio too. I swapped it for a 9" 3.50 from a mid-60's F100. The old axle is still sitting in the shed if anybody ever wants to do a restoration.....
Every F-1 I've ever had (4) was the 4.27 rear gear...
 

tinman52

Tin bender
If you have the LD 3 spd, your options will be different and more of a challenge.

I've heard of diff yokes on similar year station wagons that were longer than the truck variety and can be used. Or have a driveline shop lengthen your driveshaft. Or.......... anybody else have ideas?
I changed the yoke on mine. Actually, the yoke from a chevy powerglide trans has the same spline and is longer (requires a conversion U joint). I have the Spicer part# if anyone needs it.
I also have the old drive shaft from my F-1 freshly balanced with longer yoke and new joints for sale if any one needs one. since going 5 speed I doubt I'll ever need it......
 
Back when I had a 302 c4 in my truck I ran the stock 3.92 rear axle ratio and found it to be a good ratio.

Once I built and installed the built 393W and built c4 in the truck I found the 3.92 impossible to get traction...then I broke that rear and went to a 3.73 9"...again no traction and breakage...so I went to a 3.50 geared N-case and love it it is a great compromise gear wise. The 0-60 is still 5.5 seconds BUT I get 17mpg on highway trips.


I also have 3.50 gears in my 4x4 f-1 and they are a little too highway friendly....my little inline wants more gear ESPECIALLY WHEN LOADED...so I may re-gear it sometime in the future. but on the flats it gets around 22 MPG
 

mtflat

Flatheads Forever
2,559
147
There has been some discussion about those ratios. As near as Ross and I can determine, the shop manual is a mis-print about the universal application of the 3.92 ratio.

If I remember right how it went, some of the early (48) F1's had 3.92 gears, but after that Spicer went to 3.73. Probably where the 49-51 Shop Manual picked up the error.

How about you guys with 49-52's - what is your ratio?


Ross said I screwed that up - here's his email:
"The ‘48 - ‘50’s had 3.73’s, then they switched to 3.92’s, had to do with the switch from D-41’s to D-44’s."

That's what I get for trusting my memory
 

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