[cdoggy81]

So just to verify all this off the m13 can be swapped over to the m20 correct?
I assume the bellhousing, clutch fork, clutch, flywheel, & driveshaft.

Looks like I will need to still get these items correct?
Longer speedo cable plus the shifter & linkage?

Thanks everyone who has positively contributed :-}

[Held for Ransom]

As long as you're not swapping out the 10 bolt rear for a 12 bolt, you're fine.
Not sure if the current speedo cable work or not, but for sure you need a shifter and linkage that will work for the '70 Firebird. I don't know about the shifter arms working with the studs, but would think they should be fine.

[cdoggy81]

Thanks Ransom. Its a 70 with the stock 12 bolt. You think that will be an issue?
Any ideas / best places for shifter & linkages? I assume just find a good used set.

[Held for Ransom]

Weird. A Firebird 350 should not have had a 12 bolt, oh well.

The shifter, rods and arms, as well as one year shifter plate, will cost you.

[cdoggy81]

I will double check but I could have sworn I counted 12 last time I was down there looking :-)

Do the shifter, rods, arms, & one year shifter plate all have to be from a 70? I’m not worried about originality or year correct. Just looking to get one in there for him is all

Thanks!

[Held for Ransom]

The shifter plate is 1970 only. 1971 went to the larger output shaft and things were redesigned. Plenty on eBay, just make sure all the welded square nuts are there.
Shifter body, arms and rods are the same for the Camaro and Firebird Muncie. Shifter handle may be different for '70. Shifter grip (ball) was another '70 feature. Reconditioned set up can be found here on eBay. Looks to have everything but it's not my auction so I'm not guaranteeing anything. https://www.ebay.com/itm/154872875487

[unruhjonny]

I guess it was just a matter of time before I came across this thread....

Originally Posted by cdoggy81

Good info & thanks guys!
Now the hard questions…. :-)

If I have the m13 3spd in it now what all would I need for the swap?

What is it worth? $300-$400-$500?

Are the current m13 ratios 2.54-1.88-1.00 ?
If so going to the m20 ratios of 2.52-1.88-1.46-1.00 should make a nice street cruiser behind the Pontiac 350 (2800 cam) & a 3.08 posi I would assume.

The standard three speed manual transmission for the inline six and 350(2bbl)was a Saginaw sourced three speed.

With the base/inline six it came as a column shift;
The V8 required floor shift - and floor shift was optional on the inline six.

The 'Heavy Duty' three speed Muncie (RPO: M13) was available for to the powered cars.

I believe that all saginaw cars recieved an ITM shifter - so the stick would be bare;
I understand that the Muncie three speed cars all came with a Hurst shifter - so it would use the same chrome stick that was used in a factory four speed car.

If the car has an aftermarket shifter,then you need to look at the side cover;
The saginaw has a centrally mounted raised bolt boss, while the Muncie has two raised "ears" for bolt bosses:

Saginaw:


Muncie:


Using the RPO code can be confusing, because for many years and applications the RPO 'M13' was actually a saginaw transmission;
My understanding is that often the RPO M13 indicated the base three speed for a gvenyear & application - while some earlier PMD applications used M12 for the same equipment.

The Saginaw three speed came in three different gear sets;
The Muncie came in two;

The 1970 Firebird I-6 Saginaw (3spd) used the following gear ratios: 2.85 / 1.68 / 1.00
The 1970 Firebird 350 Saginaw (3spd) used the following gear ratios: 2.54 / 1.50 / 1.00
The 1970 Firebird Muncie (3spd) used the following gear ratios: 2.42 / 1.58 / 1.00

Lastly, a 1970 Firebird (floor shifted) Saginaw OR Muncie is a direct swap in for a pre-1971 Muncie four speed;
They both use the "TH350" driveshaft input, and both use the same transmission input gear setup.

The only parts that change on a three or four speed manual transmission car are those for the reverse light activation;
The rods were different and the "dongle" that the reverse rod attaches to actually flips differently.

If you do identify that transmission as a Muncie 'SM-330', I am pretty sure a couple people on this forum are looking for one...
I would be interested in a spare,but I am guessing shipping would make it too cost prohibitive for me.