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Old 08-25-2005, 06:37 PM   #14
Bruce68SB
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Join Date: Jan 2001
Location: Pomona, CA, USA
Posts: 90
There was a 3-speed with overdrive transmission option on our trucks. It was the saginaw 3-speed with overdrive. The main shaft and main case are interchangeable with the saginaw 3 speed and saginaw 4 speed transmissions. The overdrive unit was internal to the transmission. It was housed in a modified saginaw tail housing. I think they used a governor to tell it when to kick-in. There was the cable control, that basically locked out the over drive from kicking-in if you did not want to use it. There was also a soloniod control that was hooked to a carburetor kick-down switch. Also called a detent switch. In the mid 1970's Hot rod magazine published an article about making a saginaw 4-speed with overdrive transmission, from a saginaw 4-speed and a saginaw 3-speed with overdrive tail unit. Since the main case and the main shaft were interchangeable, it could be done. I actually did this myself. I had alot of fun with punching the trottle on the freeway and having it automatically kick down to 4th gear. The saginaw 3-speed with overdrive is out there, but I have not seen it much in the self-serve junk yards. But I bet collectors and trans shops have them. Hope this helps.
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