4+3 transmission without the OD?
Thread Starter
Tech Contributor
Joined: Jun 2004
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From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
4+3 transmission without the OD?
Just curious, has anybody converted/repurposed a (failed OD) 4+3 transmission into a standard working four speed? I have a general idea what might be involved in doing this, but am interested in any information in the event that someone has already done a deep dive look into this.
Thanks for any constructive information.
Thanks for any constructive information.
Le Mans Master
Joined: Feb 2005
Posts: 6,485
Likes: 566
From: Clearwater Florida
While it depends on the ultimate use of the finished product , and this is strictly my opinion ... the numerically high 1st gear ratio severely limits the torque handling capability of the 4 + 3 transmission .
The same front box ratios were used in the early 3rd Gen F-body 5.7L V8 cars and are what you are looking for in a 4 speed ST-10 trans ... BUT ... as I recall the F-body shifters were body mounted with no provisions for a shifter to be attached to the trans tail shaft ... similar to the 4 + 3 ... and would only need a tail housing swap to accommodate a shifter if you could find a tail housing for the small diameter 27 spline output shaft .
Discarding the 4 + 3 OD unit requires a lot of parts ... everything from the main case back (all of the reversing parts , gears , fork , tailhousing , etc) and the output/main shaft ... changing the mainshaft requires complete disassembly of the main box .
The same front box ratios were used in the early 3rd Gen F-body 5.7L V8 cars and are what you are looking for in a 4 speed ST-10 trans ... BUT ... as I recall the F-body shifters were body mounted with no provisions for a shifter to be attached to the trans tail shaft ... similar to the 4 + 3 ... and would only need a tail housing swap to accommodate a shifter if you could find a tail housing for the small diameter 27 spline output shaft .
Discarding the 4 + 3 OD unit requires a lot of parts ... everything from the main case back (all of the reversing parts , gears , fork , tailhousing , etc) and the output/main shaft ... changing the mainshaft requires complete disassembly of the main box .
Thread Starter
Tech Contributor
Joined: Jun 2004
Posts: 20,911
Likes: 962
From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
While it depends on the ultimate use of the finished product , and this is strictly my opinion ... the numerically high 1st gear ratio severely limits the torque handling capability of the 4 + 3 transmission .
The same front box ratios were used in the early 3rd Gen F-body 5.7L V8 cars and are what you are looking for in a 4 speed ST-10 trans ... BUT ... as I recall the F-body shifters were body mounted with no provisions for a shifter to be attached to the trans tail shaft ... similar to the 4 + 3 ... and would only need a tail housing swap to accommodate a shifter if you could find a tail housing for the small diameter 27 spline output shaft .
Discarding the 4 + 3 OD unit requires a lot of parts ... everything from the main case back (all of the reversing parts , gears , fork , tailhousing , etc) and the output/main shaft ... changing the mainshaft requires complete disassembly of the main box .
The same front box ratios were used in the early 3rd Gen F-body 5.7L V8 cars and are what you are looking for in a 4 speed ST-10 trans ... BUT ... as I recall the F-body shifters were body mounted with no provisions for a shifter to be attached to the trans tail shaft ... similar to the 4 + 3 ... and would only need a tail housing swap to accommodate a shifter if you could find a tail housing for the small diameter 27 spline output shaft .
Discarding the 4 + 3 OD unit requires a lot of parts ... everything from the main case back (all of the reversing parts , gears , fork , tailhousing , etc) and the output/main shaft ... changing the mainshaft requires complete disassembly of the main box .
The OD failed/locked up years ago, and no transmission shop wanted to touch it, and it sat on the shelf under an ever growing layer of dust until I tossed it during one of my moves. I still have the main box under that dust layer, and my curiosity bumps up on occasion when I happen to glance at the remains. I put a Richmond six speed in the car after the 4+3 broke, but for track days it's just more gears and weight than I need. I just keep thinking about putting a basic four speed in the car.
Thanks again.
