Ford 9'' third member question

If you could help me with your 9'' knowledge I would appreciate it.
I wanted to know what year 9'' third members interchange with eachother. I wanted to get a lower gear ratio for my 79 ford 9''
thinking 73-79 should be the same or earlier later?
Also does anyone happen to know what year 9'' fit up under a 51-52 f1oo?

Thank you for your time Paul

 

you need to know how many spline axles you have

 

The third members should interchange as long its using the right number of splines (28 or 31 for a factory third member). I've put the third member from a '78 f100 into a '67 rear with no problems. Some Ford 9 inch rears have a drain plug on the housing , others out the plug on the third member so you might mix parts and have a rear end with no drain/fill hole.

Ford put a tag on the rear with the ratio on it, but the sure thing is count teeth on the ring and pinion then do the math.

Don't know which year would fit a 51-52 f100

Here's good place to start:
http://www.kevinstang.com/Ninecase.htm

 

Late 50's to the late 60's F-100 isalmost a direct bolt in

 

A 9 inch from a 1957-72 F-100 should bolt in. I used a 9 inch from a 1958 F-100 in my '48 F-1. It was a fairly straight forward swap. Read through these threads, they are what I used and are helpful. spudsmania9 is right on about the third members. Good luck!

http://www.ford-trucks.com/forums/127564-rear-axle-tech-article-for-fte.html

http://www.ford-trucks.com/forums/243194-1948-60-f1-and-f-100-rear-axle-swaps.html

 

.....and the size of the U-joint also varies depending on application. Not usually a big problem other than using a different or a 'conversion' U-joint which are readily available.

 

Thanks to everyone who posted I appreciate your help