The 1947 - Present Chevrolet & GMC Truck Message Board Network - View Single Post - Info Needed-3spd overdrive

**basketcase** · 11-03-2002, 02:51 PM

Hi Bill,

First you need to be sure which overdrive trans you have. Through the '50s and into the '60s they were an iron case with no syncro in 1st. In the mid '60s they switched to a Saginaw trans that used the same aluminum case as the all syncro 3 speed and Saginaw 4 speed found in Chevelles, Novas ect with low horse V8s. One slick trick, covered in Hot Rod Magazine many moons ago, was to remove the o.d. unit from the back of a Saginaw 3 speed and mount it on a Saginaw 4 speed. Now you have an 8 speed trans.

Sounds like you are missing many small parts that have long since been discontinued by GM. The solonoid that actually shifts the o.d. in and out is located on the side of the o.d . unit. It is controlled by a switch through a relay. The switch is mounted on the carb. When the o.d. was ingaged, by either having the cable pulled out or pushed in (I can't remember which) you would accellerate as normal. You would then let clear off the gas pedal and when the accelerator linkage returned to closed it would hit the switch. The switch would activate the solonoid either engaging the o.d. or disengaging it, depending if you wanted to shift up or down. You could do this in any gear. Also with the o.d. engaged your car/truck would freewheel like pushing in on the clutch when you let off of the gas; the engine didn't help slow the car down. With the o.d. disengaged the 3 speed functioned as a normal 3 speed.

When we used to put these things in our '55-'57 Chevy cars back in the early '60s (we couldn't afford 4 speeds) we would junk the cable and carb switch contol. Then wire the o.d. lever in the engaged position and hook the relay to a push/pull switch mounted on the shift lever. Then you could just split gears like in a big truck without all of the adjustment problems associated with the carb switch and cable. Hurst made a 3 speed floor shifter with the proper mounting brackets for the o.d. trans.

I sold a pile of this stuff about 12 years ago. I found a solonoid for an iron trans a while back in a box when I was moving into my new shop. It won't work on the Saginaw though. If your customer wants to proceed you will need to get a Hemmings and start calling vendors. Going to be a long search I fear. A better solution would be the Tremac 3 plus overdrive available in the late '80s up on 4.3 v6s and small v8s. It has a top shift floor lever and a conventional 4 speed shift pattern. 3rd gear is 1:1 and o.d. or 4th in the pattern is about .67:1.

Good luck in your quest,
Tom

P.S. solonoid part number for '66-'69 3886326
switch part number 1998130
relay part number 1115812

11-03-2002, 02:51 PM	#2
basketcase Senior Member Join Date: Oct 2001 Location: Edgerton OH USA Posts: 633	overdrives Hi Bill, First you need to be sure which overdrive trans you have. Through the '50s and into the '60s they were an iron case with no syncro in 1st. In the mid '60s they switched to a Saginaw trans that used the same aluminum case as the all syncro 3 speed and Saginaw 4 speed found in Chevelles, Novas ect with low horse V8s. One slick trick, covered in Hot Rod Magazine many moons ago, was to remove the o.d. unit from the back of a Saginaw 3 speed and mount it on a Saginaw 4 speed. Now you have an 8 speed trans. Sounds like you are missing many small parts that have long since been discontinued by GM. The solonoid that actually shifts the o.d. in and out is located on the side of the o.d . unit. It is controlled by a switch through a relay. The switch is mounted on the carb. When the o.d. was ingaged, by either having the cable pulled out or pushed in (I can't remember which) you would accellerate as normal. You would then let clear off the gas pedal and when the accelerator linkage returned to closed it would hit the switch. The switch would activate the solonoid either engaging the o.d. or disengaging it, depending if you wanted to shift up or down. You could do this in any gear. Also with the o.d. engaged your car/truck would freewheel like pushing in on the clutch when you let off of the gas; the engine didn't help slow the car down. With the o.d. disengaged the 3 speed functioned as a normal 3 speed. When we used to put these things in our '55-'57 Chevy cars back in the early '60s (we couldn't afford 4 speeds) we would junk the cable and carb switch contol. Then wire the o.d. lever in the engaged position and hook the relay to a push/pull switch mounted on the shift lever. Then you could just split gears like in a big truck without all of the adjustment problems associated with the carb switch and cable. Hurst made a 3 speed floor shifter with the proper mounting brackets for the o.d. trans. I sold a pile of this stuff about 12 years ago. I found a solonoid for an iron trans a while back in a box when I was moving into my new shop. It won't work on the Saginaw though. If your customer wants to proceed you will need to get a Hemmings and start calling vendors. Going to be a long search I fear. A better solution would be the Tremac 3 plus overdrive available in the late '80s up on 4.3 v6s and small v8s. It has a top shift floor lever and a conventional 4 speed shift pattern. 3rd gear is 1:1 and o.d. or 4th in the pattern is about .67:1. Good luck in your quest, Tom P.S. solonoid part number for '66-'69 3886326 switch part number 1998130 relay part number 1115812 __________________ '69 swb stepside in progress. '59 Corvette lifetime project Last edited by basketcase; 11-03-2002 at 03:01 PM.