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Technical Installing a Ford 9 3/8" posi 3rd member in a 9" housing

Discussion in 'The Hokey Ass Message Board' started by karambos, May 25, 2014.

  1. karambos
    Joined: Aug 14, 2009
    Posts: 71


    I bought a 31-spline, positraction Ford 3rd member with 3.50 gears from a swap meet. The guy said that it was from a truck and that it was 9 and 3/8" across so I'd have to grind a 1/16" off each side of the housing to get it to fit in my Ford 9" housing. He said this was quite commonly done and that there are a bunch of videos on youtube showing you how to do this, but I can't find any.

    Has anyone ever done this? Did you have any issues with it?

    My axle is from a 1957 Ranchero and is currently non-posi with highway gears roughly 2.97's (they came with the car so I don't know exactly what they are).
  2. Don's Hot Rods
    Joined: Oct 7, 2005
    Posts: 8,319

    Don's Hot Rods
    from florida

    I remember something like you described, grinding the case to open it up where the ring gear slips through, but I don't remember the details. If you don't get an answer here call Currie Enterprises. I just bought some parts from them for the rear end in my rpu project and they were extremely helpful.

    Here, I found this on the net. Scroll down to where they discuss the 9 3/8 in a 9 inch housing
    . It has the heading 9 1/2 there:

    Last edited: May 25, 2014
    karambos likes this.
  3. 19Fordy
    Joined: May 17, 2003
    Posts: 7,530


  4. 1971BB427
    Joined: Mar 6, 2010
    Posts: 7,353

    from Oregon

    I've seen many guys go the other way and put a 9" differential in a 9 3/8" housing. Haven't heard anyone going the other route as you're looking to do.

  5. lostone
    Joined: Oct 13, 2013
    Posts: 2,028

    from kansas

    Same here, 9 inch into 9 1/2 housing. Infact getting ready to narrow the housing 5 inches.

    My only real concern would be grinding the housing right at the gasket sealing area. Have to be careful or i would think it could be a problem spot for leaks.
  6. uglydog56
    Joined: Apr 8, 2008
    Posts: 331


    My friend Jimmy did it. I don't remember how much grinding was required, but it didn't leak when he was done. He took out a 4.56 spool and put in a 2.80 posi for power tour.

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