Saginaw 4 to M-21 conversion.

What all is required for this switch. Does any one know if it is a direct bolt in other than reqiring a new shifter? Or does the drive shaft need to be lengthened. Is the input and out out shafts the same splines? This is going in to 62 Chevy with a 327

 

Why are we doing this swap? (curious)

I have one of each... I can pop out and take measurements if you want.

I'm *fairly* sure that they mounting boss on the tailshaft will line up and that they're the same length.

Now- I'm not sure why you think you'd need to replace the shifter... you should need only to replace the shift linkage rods, because reverse on the saginaw is on the maincase and the reverse lever is on the tailshaft for the muncie.

 

I currently have the m21 and have found a saginaw 4 with the overdrive installed, I am wondering if the switch is worth it. And what all will be required. I know the muncie is a stronger transmission bit the 30% reduction for overdrive would be nice.

 

I would go for it in a flash.
In fact I have been looking for the same setup for my Saginaw. The OD switch is just a direct replacement of the tail shaft from the OD three speed to your 4 speed if is the same as I want to do.
No length change on the Saginaw.
Here is a link that explains it...
Cheers......
http://www.chevytrucks.org/tech/overdrive.htm

 

Reduction is .85 and there is no provision for a shifter mount on the overdrive housing. You will need to fabricate a mount or modify a Hurst Saginaw clamp on mount. It can be done.

overspray

 

Input and output spline count could be different, might have to change the clutch disc and the front drivshaft yoke.

 

Your the second person to tell me .85. Did they offer different o/d gear ratio's. The seller says all saginaw od's were .75. Is there any way to tell for sure?

 

Like is mentioned, your real battle will be the shifter, there is nowhere on the tailhousing to bolt a shifter on. So your either setting up a column shift or creating a shifter mount from scratch.

 

I've got an old Hurst Syncro-Loc shifter for a '66-'71 Saginaw overdrive transmisison; if anyone gets far enough on this to need to see what sort of bracketry they used to mount a shifter, let me know and I'll dig it out and take some pix.

 

Both should be coarse discs and the output is the same, mounts the same. The fly in the ointment will be the shifter, agreed. At one point in the '70's, the only decent Saginaw shifter was made by Mr. Gasket and had the bracket that mounted off the tail housing ears.

Bob

 

Hdonlybob gave the link to the article about adapting the 3sp OD to the 4sp Sag.
There was an article in HotRod (I think) that had pictures.
The article refers to a hole that has to be drilled and a tab that is needed.
It is not just a bolt on.

I remember either meeting someone who had done it or read about it and they said it really gave you an 8 speed as you could use OD in any gear.

I always liked the old ODs. My dad had one in his 327 250 hp '62 Rambler Ambassador wagon with a 4.11 posi.
I scared the daylights out of myself when the trans downshifted at 93 mph one of the first times I drove it on the highway a month after I got my license!

 

The only reason for drilling the hole is for a rod that locks out the O/D when you're in reverse, since damage can be done to the unit if you back up with it in overdrive. If you thought that you could trust yourself to never be stupid and do that, the hole drilling operation wouldn't be necessary.