Thinking of swapping transmissions

[Stephen717]

Okay so I've always wanted to swap from the three on the tree Saginaw that's in the truck to a Muncie M21 close ratio 4 speed. My question is, what is the difference in dimensions between the two transmissions. Am I going to have to get a new drive shaft due to the difference in length or will everything bolt right in place. Thanks in advance for the advice.

[LockDoc]

Originally Posted by Stephen717

Okay so I've always wanted to swap from the three on the tree Saginaw that's in the truck to a Muncie M21 close ratio 4 speed. My question is, what is the difference in dimensions between the two transmissions. Am I going to have to get a new drive shaft due to the difference in length or will everything bolt right in place. Thanks in advance for the advice.

I ran one in a '67 stepper years ago and used the column shifter with a choke cable mounted under the dash for reverse. I don't remember now if I had to cut a shaft or not. there are a few threads on the board about it but most do not have a lot of info about the swap.

http://67-72chevytrucks.com/vboard/s...d.php?t=664562

LockDoc

[AussieinNC]

I am assuming you are thinking of a floor shifted conversion....

Most Muncies will have the same input shaft, only the M-22 close ratio and the 72 up units have a different input shaft configuration. (Even then you just need to change the clutch disk).

The original trans and the "common" Muncies are 10 spline shafts, the others are 26 spline. If you get a 26 spline shaft all you need to do is replace the clutch disc with one that has 26 splines.

The output shaft on the original has 17 splines, the Muncie will have 27 splines, unless it's a 72 up which has 32 splines.

You can just change the yoke on the front of the driveshaft to the right spline, it will be compatible with the u-joint if you get the right yoke.

I believe a TH 350 yoke will work fine....

The trans will bolt up without any issues, both into the bell housing and the trans mount.

Driveshaft length is same...

BTW...buckets seats will almost be essential...but I believe Hurst may have a shifter for a bench seat installation.

Hope this helps...

[Stephen717]

Thanks for the info. I already have a set of bucket seats from a 1969 Camaro and was actually looking at putting a Hurst pisol grip shifter in it. Yes I know it's a Mopar accessory but I've never seen it done in one of these trucks and I love the way they feel when shifting gears.

[Mike C]

Muncies shift great and are fairly durable, but you will hate the 2.52 and/or 2.21 first gear in a truck. Unless you are building a real hot rod with 4.10 or 4.56 gears IMO.

[volksworld]

drove mine for 20yrs with a muncie...3.73 rear and 10/31 15's....was great...the muncie exploded 1st gear when i put in the big block...the saginaw 3 went back in with absolutely no changes other than the shifter....so whatever model muncie i had was same length, same yoke and same clutch disc spline...i really dont want to put in a turbo 400 but i own one already and around here used muncies go for damn near a grand

[AussieinNC]

454's just love Muncies...for Breakfast !!!!

[Stephen717]

I can honestly say that I don't know what is currently in the truck for gears. I know that it had a 307 long before I got it and it now has the 250. It is the original transmission to my knowledge. And I know it has the standard pickup truck 12 bolt rear in it. But I am not sure of what gears are in it or if it's a posi rear or a limited slip. I am going to have the trans rebuilt with heavy duty m22 gears and am going to hold off putting it in the truck while I build the 350 I have for it. I would love to eventually put a 427 in it but I don't know if I ever will. also have a 454 laying around that I thought about building but I don't know if I'm going to build that or let my cousin put it in his 69 camaro. eh I'm ranting now though.

[Mike C]

I wouldn't have a bunch of new expensive parts put in the used case. Look into an AutoGear M23z. It has a 2.98 first gear and 1:1 4th. It is stout and let's you run a 3.07 gear and still have some acceleration out of the hole and cruise at a decent RPM.

That and it's all new parts. Delivered. I HIGHLY recommend Jody's Transmission as he will give you service second to none after the sale. He is a dealer for AutoGear.

[WorkinLonghorn]

They made a close ratio 4 spd for these trucks called the New Process 435. For some reason they get very little/no mention on this forum. The 1st gear, 4.56, is for starting a heavy load, but with 3.07 gears out back it would be absolutely usable as a normal 4 spd. It's toughness rivals that of a 465. The one in my hard-working longhorn is original from 1969 with no problems ever except that one of the syncros is a little sketchy. Smooth-shifting, short-throw, bullet proof drop-in replacement. -BA

[Stephen717]

OK, the plan is building the 454 that was in my old work truck, adding a 12 bolt posi rear from a chevelle, and I am scrapping the idea of rebuilding a used transmission as I found https://www.5speeds.com/ this guy sells brand new muncie 4 speeds and has the m22x I'm looking for. I have heard of the np435 but don't know if I would go that route

[WorkinLonghorn]

You should consider it. You would want the NP 435A with the 4.56 1st gear. some others had a 6.68 granny.

http://www.novak-adapt.com/knowledge...s/manual/np435

https://www.hemmings.com/magazine/hm...n/3749160.html

[Mike C]

Originally Posted by Stephen717

OK, the plan is building the 454 that was in my old work truck, adding a 12 bolt posi rear from a chevelle, and I am scrapping the idea of rebuilding a used transmission as I found https://www.5speeds.com/ this guy sells brand new muncie 4 speeds and has the m22x I'm looking for. I have heard of the np435 but don't know if I would go that route

The NP435 is a close(r) ratio truck 4 speed. But it is still a big honking, slow shifting, truck 4 speed. It just has less first gear than some of the other big honkin' truck 4 speeds which are great in a truck that is used offroad or for hauling big loads.

If you are building a hot rod, get a hot rod transmission. You will not regret buying from Jody's Transmissions as you will probably have some questions and his support is second to none. The AutoGear trans quality appears excellent. I'm helping a guy swap one into a big block Camaro and Jody has been a great resource.