I have a Saginaw 3 speed transmission (GM) with the OD unit. I have read that you can take a Saginaw 4 speed, put the gear cluster on the 3 speed main shaft and install the whole thing with the OD in the 4 speed gear box thus creating a 4 speed over drive. So what would I need, parts wise, to convert the 3 speed to a 4 speed? The side cover comes to mind as well as the different main shaft gears for 1st, 2nd, 3rd, and reverse. I can get all the bearings and snycros from a rebuild kit. Do I need a different counter gear ***embly? I have found transmissions on e-Bay, but don't want to spend 200+ for a used 4 speed and then another 75+ to ship it. So far I haven't found anything close by, but I did find some 4 speed parts. Please advise, thanks.
Here you go: Go to www.chevytrucks.org, click on the "technical forum", then click to the "general forum" and you will find "overdrive/mpg"; that will give you the details on how to do the conversion. Butch/56sedandelivery.
Since you need to replace just about everything including the case, cluster gear, and all the other gears, you're probably better off buying a 4 speed, eh?
if you have to buy a 4speed one to look for is one out of a 76 or 77 vega they where the same saginaw that was used in the big cars except they have a lower 1st gear ratio and work great in a heavier car
saginaw 3 speed and 4 speed cases are the same, I believe. the OD unit conversino requires drilling a small hole in the rear face of the 4-speed case if converting that way.
Like I said, the 4 speed saginaws are hard to find. I haven't found one in my area yet and e-Bay prices are $200+. I also already know how to do the conversion. The question is for you rebuilders, what is needed to convert the 3 speed to a 4 speed?
Case, cluster gear, 1st, 2nd, and 3rd gears, synchros, reverse idler gear and shaft, small parts kit, main drive gear, complete side cover. Not much to it!
Maybe I'm missing the point....Wouldn't it be easier to change rear gears than to overdrive a transmission that wasn't that way to begin with? Not trying to be a smart ***...I'm good at that, I don't understand....Thanks. Mike
I did a 4spd OD conversion 4 years ago and have put together many Saginaw 4 spds.3 and 4 spd cases are different like the guy above says.
For what it's worth...I think I first read about this OD conversion in a mid 70s issue of Hot Rod magazine. Don't know the exact issue but I think the cover showed Richard Petty and his crew in overalls around an old barn sitting around one of their 70's Dodge Charger racers. And for some reason I think there was some chickens in the picture too. It was a nice, fun, tongue-in-cheek cover. As for the Vega/Monza Saginaw 4spd ******s, I think you'll find that these units do not have the shifter mounting holes drilled and tapped on the extension housing. The bosses are still in the casting but the Vegas and Monzas had their shifters mounted to the floor pan instead of on the transmission. It probably wouldn't be too big of a job to drill and tap the mounting holes, but this might also help you to I.D. one of these transmissions. I think they also tended to have a big bob-weight bolted onto the back of them too, to help dampen some of the roughness of the Vega engine.
Three speed and four speed main shafts are the same.The OD mainshaft is shorter and must be used for an OD conversion of either 4 or 3 spd.
As for the Vega/Monza Saginaw 4spd ******s, I think you'll find that these units do not have the shifter mounting holes drilled and tapped on the extension housing. The bosses are still in the casting but the Vegas and Monzas had their shifters mounted to the floor pan instead of on the transmission. It probably wouldn't be too big of a job to drill and tap the mounting holes, but this might also help you to I.D. one of these transmissions. I think they also tended to have a big bob-weight bolted onto the back of them too, to help dampen some of the roughness of the Vega engine.[/QUOTE] This doesn't really matter on the conversion, but is good info, because you put the overdrive rear ***embly and tail case on the 4 speed. You end up makin or modifying a shifter bracket and or rods to work. Overdrives are fun and learning some cool hot rod applications is fun also. A 700R4 would be easier and probably much more efficient but not as unique as a 4 speed with a planetary OD unit. The first one of these conversions I saw was at the 77 Street Rod Nats swapmeet. It was completely chromed and I was mesmerized. I wish I could still buy it for the $225.00 asking price. Funny how some stuff sticks in your head forever.
Wider ratio, with my wide ratio, it should be something like a 2.60 first and a .70 od or something like that, should work good on a t-roadster As for saginaws being hard to find, **** i can get em all day at the swap meet for $150, the OD's are a little harder
I used to be able to find saginaw 4 speeds for a buck and a half, but the local supply dried up. Last one I got required buying the 4 cyl 82 camaro it was in.
I have a Saginaw 4 speed in my roadster and I have a couple of questions that might pertain to the thread. I was under the impression that Saginaw 4 speeds were all the same. If they aren't, how do you know which is which? Are there casting numbers to look for? I was told mine came from an '85 Camero V-8. Also, mine is behind a 454 in a maybe 1800 pound car, and I've been told that the big block will destroy the Saginaw in no time. It looks like, with Muncies and Borg Warners being ******ed up by the muscle car geeks who are willing to spend anything for bragging rights, the lowley Saginaw is going to become the four speed of choice for us hot rodders. Thanks, Mike
look for grooves machined on the input shaft, generally the more grooves, the wider ratio it is. Some of them have a first gear of 3.5 or something! A big block won't necessarily destroy a Saginaw in no time, but careless driving will, and a big block can make it happen a lot faster
Gotcha, Squirrel! Hell, I can destroy an anvil with a claw hammer....if I work at it. I balloon foot everything I drive. I've broken too much equipment in the past to abuse what I have. Mine is in the engine right now, but I don't recall any grooves, so that would make it relitivly close ratioed,correct? Thanks, Mike
I guess that's one advantage to living on the east coast---Saginaw four speeds are still at every swap meet around here, and at least half of them can be had for $100.
NEVER DOUBT THE SQUIRREL ! I was only recalling the original Hot Rod article linked in other posts. to wit: "For example, both versions use the same case, and the mainshafts are identical in both transmissions"
Rather than try to find a 3-speed Saginaw with overdrive to start with; the truly hard part of the swap, I'd just go with the Chevrolet/GMC 3-speed+manual overdrive made by MOPAR. It was a reworked 883/833 (not sure of the numbers) 4 speed MADE INTO a 3-speed with 4th being overdrive. Hurst makes the correct shifter for this trans also. Butch/56sedandelivery.
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