hi,first off im court new to this site.but big 73-79 fan my whole life,i'm actually a apprentice mechanic in a ford dealership because i love ford so much.lol

i need help identifying the gear ratio i currently have in my truck.

it is a 1979 ford f150 shortbox 4x4 with an 351m engine.c-6 trans and np 205 t-case.

i want to know what gears i have sitting it it,as for im planning to order new ring and pinions for front and rear.the rear differential is a 31 spline 9 inch.and the tag that normally is on the diff covers are off on both front and rear.except one on the front.the numbers on the tag print " 3 50 D9TA ACA and the bill of material is 610049-7 when i look up the number i cant find any results.

on the front crown there are numbers 42 12 on the rear crown the number are 42 10.

if you cant help thatd be great.

 

What's the axle code on the warranty tag on the door? If it's the original rear end and the door hasn't been swapped somewhere in the past I can decode it for you.

 

D9TA-ACA= Dana 44-9F non-locking, free running hubs, 3.50 ratio, 3500 lb capacity

 

the axle code i believe is F140 H2 PRANS K

 

thanks a bunch!! its hard for me because im not actually at home.my dad just gave me the numbers he could find.

thanks again!

 

Im curious why you are changing the ring and pinions if you didnt know what the ratio was?

 

Model F140= F150 4WD pickup 6050 Lb GVW
H2= Ford 9" Locking 3.50 ratio, 3750 Lb Capacity
Trans K= automatic transmission

 

im changing the ring and pinions because i tore apart the 9 inch to find the second bearing blew apart,damaging my pinion and my case is done from the damge too.so i'm rebuilding my rear diff and thought mite as well put bigger gears in it because im running big tires and use the truk for mud drags,mud bogs and eventually daily driving.i was curious to see what my gear ratio was before i change them.and i'm also putting a spool in the rear end and a locker in the front,not sure what kind yet.

 

I have a 4x4 with 3.50s in the pumpkins and 33'' tires, how big are your tires and did you feel it was too high geared? I ask because I'm wondering what mine would be like with maybe 35''s on it.

 

42 teeth on the ring gear divided by 12 teeth of the pinion is 3.5. Thats a ratio of 3.50:1

The same procedure is used for any ring and pinion set so the 42 teeth divided by the 10 will be 4.2 and this is a problem. Its a problem because it is very rare to find a 4.2:1 ratio. This is actually a 4.22:1 but again, it does not make sense why it would be in there.

I am not a real fan of looking at tags, door plate numbers and the like for this exact reason. You can clearly see that the tags have been removed, and this indicates that somewhere or at sometime the ring and pinion has to have been changed at some point or another.

To verify 100%, physically count the ring gear teeth and divide by the number of teeth found on the pinion. This is the only true method.
Since you have this thing apart already, this will be a snap.