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1951 ford F1 rear axle

Jerodsford

32
0
Is there any part numbers on the rear axle that would tell me the gear ratio? otherwise what is "easiest" way to determine?

The truck I have was pieced together in 1980 from two 51's. The internet is wonderful but so far to much conflicting info. Some say the only gears available for that truck was 3.83. The info in another post says 3.92 with 4.27 option.

Thanks
 
DNFXDLI

DNFXDLI

The Token Canadian
Staff member
49,083
1,089
The Great White North
The easiest way to determine the ratio is to make a mark on the driveshaft and record where it is...like at the bottom...then make a mark on the wheel at the same place...then turn the driveshaft and count the amount of revolutions it takes for the wheel to do one complete revolution.
 

mtflat

Flatheads Forever
2,559
147
Unless it was removed (frequently happens) there should be a flat metal tag with the ratio punched in. It is attached under one of the bolts holding the rear cover on.

The two ratios available were 47/11 for the 4.27 : 1
and 41/11 for the 3.73 : 1 rear

There is some confusion about the 3.92 because it was listed in the specs page in the shop manual, but on pg 166 of the same book it lists the two ratios I printed above. Which is right? Nobody knows for sure but it looks like 3.73 is probably correct. This ratio was used by Ford in the earlier trucks and cars.
 

Jerodsford

32
0
Jerodsford said:
Thanks to both. Next question? what other years axle would fit?
Click to expand...

OK after some degreasing and some wire brushing I got
some numbers of the back of the differential. the is a tag screwed into the back of the housing that has 5A13. what does this mean? then there is another number closer to the front that appears to be split by the rib of the casting. Thant number is 05AW 4668a.

Thanks again
 
52 Merc

52 Merc

89
4
Kennewick, WA
The easiest way to determine for sure is to remove the rear cover and count the teeth on the ring and pinion gears. That way you know exactly what you have, in the event they have been changed over the years. That said, you could look for a series of numbers stamped on the right side axle tube. While this chart is for newer models and much of the info doesn't apply, our earlier trucks many times have the ratio stamped where shown.

EB_AxleID.jpg
 
52 Merc

52 Merc

89
4
Kennewick, WA
Jerodsford said:
OK after some degreasing and some wire brushing I got
some numbers of the back of the differential. the is a tag screwed into the back of the housing that has 5A13. what does this mean? then there is another number closer to the front that appears to be split by the rib of the casting. Thant number is 05AW 4668a.

Thanks again
Click to expand...

None of this sounds like anything you'd find on an original axle. It may have been changed with something newer. Can you post a pic of what you have, and what you're looking at?
 
DNFXDLI

DNFXDLI

The Token Canadian
Staff member
49,083
1,089
The Great White North
That's a 9''...is that O possibly a C?...like C5AW?
 

Jerodsford

32
0
Also pulled out the pinion gear, decide to try to count. What exactly am I counting. There are 10 teeth not 11. I have not gotten the ring gear out yet
 

mtflat

Flatheads Forever
2,559
147
C5 prefix means it was made in '65 - or at least the housing was part of a casting series that started in '65

The tooth count on the pinion is only half your job. Count the teeth on the ring gear and divide by the pinion count: X/10

ps, my example only happened to have 11 teeth on the pinion. You'll find 9, 10, 11, 12, 13 etc.
 
DNFXDLI

DNFXDLI

The Token Canadian
Staff member
49,083
1,089
The Great White North
What Tim said...also it is a very stout axle.
 

Jerodsford

32
0
well it is certainly getting interesting. I appreciate all the advice. I was under the assumption the rear end was from a '51 thus expecting 11 teeth as I beleive that is all they made back then. I ma certainly in the home stretch now. Expect to count the ring gear tonight.
 

mtflat

Flatheads Forever
2,559
147
I changed my 4.27 original axle to 3.50 by swapping in a 9" from a 63-65 F100.

I think it's about optimum - my 48 was my daily driver for 10 years and logged trips from Washing state to Ohio, and Canada to Colorado. Mountains or plains, the 3.50 handled it all with ease.

I'd say you got lucky and have the tough part already in place!

Like Ray said, the only improvement I'd make is to add an OD trans (T5) or swap gear sets to get 3.25, but you can certainly live with 3.5 - my road speed is comfortable at 62-65 with 16" tires/wheels
 
52 Merc

52 Merc

89
4
Kennewick, WA
Since you pulled the pinion assembly out of the third member, you've lost the set up and adjustment for the mesh between the ring and pinion gears. The correct set up is important for wear and noise. You might get lucky if you put it back together with all the shims exactly like you found it, but you may want to obtain the services of a professional gear guy to make sure it's right before using.
 

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