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Technical 4-speed OD Conversion

Discussion in 'The Hokey Ass Message Board' started by MO54Frank, Apr 28, 2019.

  1. MO54Frank
    Joined: Apr 1, 2019
    Posts: 102


    I seem to remember years ago reading a magazine article about installing the overdrive unit from a Saginaw 3-speed into a Saginaw 4-speed. Anybody know anything about that, or did I dream it. Thanks.
  2. oldolds
    Joined: Oct 18, 2010
    Posts: 2,681


    Yes there were articles about it. If I remember correctly you needed to change out the longer main shaft from the 3 spd. and put it in the 4spd.
  3. I have a sag four speed and a sag three speed overdrive. I thought about doing the conversion. I think the floor shifter could be a bit of a hassell
  4. s55mercury66
    Joined: Jul 6, 2009
    Posts: 3,313

    from SW Wyoming

    I know a couple of guys with them, installed behind BBC 427's. Not too sure how much abuse they might actually take.
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  5. That will depend on if you have a R10 or R11 OD unit...
  6. squirrel
    Joined: Sep 23, 2004
    Posts: 42,340


    Most of them were R10 on the Chevys. Not real strong.

    you might also want to drill the case for the reverse lockout rod.
    sunbeam and jimmy six like this.
  7. J. A. Miller
    Joined: Dec 30, 2010
    Posts: 1,139

    J. A. Miller
    from Central NY

    Yeah, that was in an issue of Hot Rod that had one of Richard Petty's stock cars on the cover. Probably in the mid 70s. I think the same article appeared in a truck magazine later on, probably a Peterson publication.
    loudbang likes this.
  8. streetrodder71
    Joined: Jan 15, 2015
    Posts: 290


    I do not know about the sag 4spOD conversion but I have a BW T-10 overdrive conversion in my 34 Ford
    pick-up. It was made by a man named TOM BEATTY. My trans is a 1962 BW T10 with a Ford BW OD
    tail shaft on the rear. It is 39 inches long. It has 8 forward gear and is shifted with lever and a button between lever shifts. Gears are close and I use button most in first or fourth. OD can be locked out
    with a lever and trans can be used as a standard 4 sp. It is unusual and a 5 sp or 6sp would work out
    loudbang and sdluck like this.
  9. miker98038
    Joined: Jan 24, 2011
    Posts: 389


    Probably not much use to you, but a few guys put the BW T-11 o/d behind the Ford top loaders from the mid 60’s. What I’ve read the first top loaders were based on the BW T-85 case, with the reverse gear added on. I think the T-85/R-11 was used as the base trans all the way thru the 406 motors. Today the cost of a T-11 and the machining would be more than a TKO-500 unless you can do all the work yourself.

    The R-10 units in Ford’s were usually (later models) behind the T-86 trans. Ok, but abuse will break them pretty quick.
  10. That was the top option through to the '61 390/401HP, replaced with the T10 in '62 when the 406 came in. Ford wasn't happy with either trans and B/W wouldn't upgrade them as per Ford's request, which is what led to the development of the toploader.
    Jeff Norwell likes this.
  11. 56sedandelivery
    Joined: Nov 21, 2006
    Posts: 5,512


    Go to; that's the article you need for the conversion. Just look in the tech forum. I am Butch/56sedandelivery.
    loudbang likes this.
  12. Like mentioned above, it can be done.

    Remove the three speed gears from the B-W main shaft and replace with the gears from the 4-speed main shaft.
    Hole for reverse lock out, optional. If you want the feature you will need to modify the reverse shifter fork.
    Fabricate a shifter mounting bracket and make some shifter rods.
    Wire up the solenoid, governor, and kickdown switch. The kickdown switch is a momentary ground, so you can make something up vs the "factory" style if you prefer.

    Up side, the transmission will bolt up to your existing four-speed crossmember. And you can use the same hole in the floor for the shifter.
  13. MO54Frank
    Joined: Apr 1, 2019
    Posts: 102


    Thanks for all responses.
  14. MO54Frank
    Joined: Apr 1, 2019
    Posts: 102


    Thanks Butch. I went to and the link labeled Overdrive/MPG is dead. Several other links on their Technical Area are dead. :( I will look some more later. Thanks.
  15. I have a scan of the Hot Rod article, somewhere. When I find it, I'll post it here.
  16. 31Apickup
    Joined: Nov 8, 2005
    Posts: 1,784


    It was the 1975 issue with the Petty charger on the cover, don’t remember the month.

    Sent from my iPhone using The H.A.M.B. mobile app
  17. Fordors
    Joined: Sep 22, 2016
    Posts: 1,831


    The conversion was detailed very well in the March 2014 issue of Hot Rod Deluxe.
    Oh wait, I forgot. A lot of you guys have no use for print publications.:cool:
  18. Jeff Norwell
    Joined: Aug 20, 2003
    Posts: 12,685

    Jeff Norwell
    Staff Member

    Now,..... THATS funny.
    427 sleeper and 42merc like this.
  19. Here's the scans.

    saginaw3-odto4-odp1-50%25.jpg [ saginaw3-odto4-odp2-50%25.jpg
    MO54Frank and Jeff Norwell like this.
  20. I keep all of my print publications, semi-organized, even!
  21. MO54Frank
    Joined: Apr 1, 2019
    Posts: 102


    Thanks Algoma56!
    Thanks all.
  22. I'll disagree with the 'rugged' description (unless you're talking about a four-pinion R11 unit, but those are very rare). I've killed these behind a bone-stock 223 Ford six more than once. But they do make for a fabulous cruising trans if treated with care and installed with all factory hook-ups.
  23. flux capacitor
    Joined: Sep 18, 2014
    Posts: 653

    flux capacitor

    One of the alliance member here on the hamb ‘s brother wrote this article on it for hot rod deluxe. Garage motor sports shop built it . I too built one after their article & love it. I bought another side cover & he had traced it out so I could cut it out so I could gauge where to weld the new fabricated curve onto reverse lever to engage it & prevent “rolling off “ . Great article titled how to get gone with detailed pics . Flux FCD27458-4B8A-48E4-A1E7-0C19B5FDF02B.jpeg
    Here’s end result 489DE90A-9115-42C8-8CB2-4FC2F5D23E0D.jpeg
    79FCB0D1-B0BD-4586-89AD-C3FFB8C70AD8.jpeg If you consider going this route, also be aware there’s no where to mount the shifter. You can go to my slow moving build thread (53 150 Build) to see pics & description of how I fabricated the hurst shifter off a Muncie 4 speed to work on it . Flux
    Last edited: Apr 29, 2019
  24. I didn't remember seeing that article in Hot Rod Deluxe. I'm usually pretty good at recollecting, especially with a hint. Just checked my library; missing that issue. At least I know I'm not losing it. Yet!
    flux capacitor likes this.
  25. MO54Frank
    Joined: Apr 1, 2019
    Posts: 102


    My question was asked because I am interested in putting a Saginaw 4-speed behind a 235-6 in a Chevy A-D pickup. Remember Patrick Dykes torque-tube conversion? I would swap rear axles for an open drive with 4.11 or so gears, limited-slip preferred. With a 3.50 first gear and 4.11 rear it should have enough torque to start with a heavy-ish load or trailer. And with the OD, it could cruise 65-70 lightly loaded without a strain. Thanks again to all.
    flux capacitor likes this.
  26. Here are pdf's of a factory '55 OD harness and mine, plus my shifter and mount.

    Attached Files:

    flux capacitor and MO54Frank like this.
  27. MO54Frank
    Joined: Apr 1, 2019
    Posts: 102


    Thanks Heap.
    Am I looking at your image correctly? Is that a Sag 4-spd with Overdrive? What do you run this in? What engine? Thanks.
    Last edited: Apr 30, 2019
  28. Yes, Saginaw 4-speed and Borg-Warner R-10. This is in my '57 Chevy behind a 327. I put a 3.50 in the rear when I had the Muncie installed, I think I should lower the gear now.

    The shifter mount is forked to allow for the "hump" on the B-W unit. The shifter rods were cobbled together from some pieces I got off of eBay. You will need to move the shifter back to allow for the speedometer cable.

    Instead of a kickdown switch, I have a momentary ground button on the shifter knob. The 6-2 and 8-7 connections on the DPDT relay are normally closed. When the governor grounds, the 87-30 connections close to energize the solenoid. If the lever on the OD unit is in the correct position, then the transmission goes into overdrive. Pressing the shifter switch closes 5-3 and the OD is cut out.
    Automotive Stud likes this.
  29. MO54Frank
    Joined: Apr 1, 2019
    Posts: 102


    Cool setup. Thanks for sharing the info.

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