question on converting my 3 speed toploader to a 4 speed toploader

Discussion in 'Transmissions' started by 73cometter, Dec 13, 2019.

  1. 73cometter

    73cometter Member

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    Have a 73 Comet that has a 302 with 3 speed manual toploader trans, I want to put in a 4 speed toploader trans , what all is involved with doing this
     
  2. Krazy Comet

    Krazy Comet Tom

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    Assuming you already have a floor shift & correct top loader, can be easy as pulling out the three and replacing with four. Unless clutch has recently been serviced, probably want to check it.

    As far as transmissions, you need a short(24" I believe), small block version. The big block trans have a slightly shorter input shaft, often are too long overall and/or have larger diameter output shaft. Also are long, small block versions.
     
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  3. baddad457

    baddad457 Member

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    Also beware of the 390 specific Toploaders. These have small input/output but the front snout that fits into the pilot bearing/bushing is shorter like the big input transmissions. When used with a smallblock bell, the snout does not reach into the pilot bushing/bearing, this leaves the input unsupported when the clutch is disengaged and the front bearing will fail in a short period of time.
     
  4. dyent

    dyent Member

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    Or you can purchase a "stepped" pilot bearing to be used with the 390 Toploaders, this makes up for the difference in length on the shorter 390 Input snout.
    David
    P1020095.JPG
     
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  5. baddad457

    baddad457 Member

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    Where do you get these ? Doesn't look long enough though. The Boss 302's used a longer bushing as they came with a big in/big out Toploader
     
  6. Krazy Comet

    Krazy Comet Tom

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    I've never seen more than approx ¼" difference in snout of SB vs BB top loader, that bearing should be fine.
     
  7. baddad457

    baddad457 Member

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    I ruined two Toploaders this way in the 80's. The BB input just did reach to the rear of the bushing I was using then (this after I figured something wasn't right) Don't seem like 1/4" would support it as the end of the snout is turned down slightly
     
  8. dyent

    dyent Member

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    I got these from Ford back in the 80's, I would have to dig up the part number, they where quite common when Ford was still into their "Ford Performance" program (60's/70's). I even got a couple from a local speed shop, was looking through their "Dorman" parts bin! The stepped bearing makes up the approx. 1/4-3/8" difference.
    AFAIK, the Boss 302's never came with 1 3/8" larger Input or 31 splined output, just the regular close ratio SB 1 1/16" input/28 splined output, at least on the street versions, perhaps on the race versions may have came with bigger in/out? I have to take a look at my "Boss 302 Modification" book that was sold by Ford Performance or see what Ford racers like Parnelli Jones etc., did on their Boss 302 T/A Mustangs.....
    David

    I used the same stepped bearing behind my 390 Toploader in my 74 Comet 289 for 10 years........
     
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  9. baddad457

    baddad457 Member

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    I've always heard the Bosses came with the bigin/bigout transmissions. Who knows ? Anyway, that was the original purpose of the bushing. Seems like the 4 speed Bronco's used it too. I learned my lesson in the 80's about this with my 67 BB Stang after replacing the cracked O.E bell with one from a pickup truck. Had to get the cracked bell welded to get around this.
     
  10. dyent

    dyent Member

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    I remember when I was rebuilding my 390 Toploader, that I came across a few inputs where the snout tip had varying "chamfers" some had more than others, so I made sure to use the one that had less, so more was engaged into the stepped pilot bushing.
    I think I still have enough NOS parts from when I was still rebuilding them to build 2 or 3 Toploaders, one day......
    David
     

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