The Stovebolt Site Forums The Shop Area Driveline MUNCIE M20 swap

i have a 59 3100 truck that i purchased with a 350ci/th350 combo already swapped in. i have located a m-20 muncie id like to install but am unsure of what bellhousing/clutch/ect to look for. i have 2 GM bellhousing sitting in my shop now but don't know if either would work. both are cast iron, one is off a sm465 and the other was behind a 57 283 with a 3 speed.
i think this trans will make for a good swap just not sure on the bellhousing. thanks for any help.

Don't the both have a 1:1 final drive? Just curious why the swap?

i just want to have a 4spd trans. i'm not a big fan of automatic transmissions. i was going to use the 3 speed i have in a 59 3200 parts truck but since the 3 speed doesnt have a tailshaft mount and i'm installing a side motor mount crossmember it wont work.

Cool. I was just wondering. As for the bell housing, I'm an idiot and can't help you. Good luck though.

Back in about 1972 I took the original 3 speed/Overdrive out of a 1957 3100 with a fresh 283 and put in a Muncie four gear from a 1969 Camaro. It bolted right up the the V8 bell housing.

FWIW: I was never happy with the combo and soon replaced that M20 or M21 with an SM 420.

I remember now that it was a dog when starting off, especially on a hill, the first gear ratio not being a good match, even though the stock O.D rear axle was 4.11. Can't remember now what size tires I was running on the 15x 7 or 8 "chrome reverse" wheels.

If it already has a 350 automatic, someone propably altered the original frame mounts for the bell housing. So you are putting side mounts for the motor,a regular bellhousing(alum) from just about any chevy would work, you are going to use a rear trans mount. Just check the size of the hole in the bellhousing against the size of the collar on the front of the transmission.Some of those big 4 speeds had larger collars, you want one that matches the size of the trans you have.

I actually have a sm465 truck 4 speed with bellhousing but I wasn't sure how it would fit under the cab and it seems like the shifter would be way to far forward

if the engine is in the factory V8 position, the SM shifter will be about in the center of the trans floor cover, which would need to be the 'high hump' cover that has the hole for the shifter, the flat cover won't clear and has no hole .... the factory position for the V8 sets back from the rad and requires a shroud

Bill

Well thats where one of my issues comes in. the engine is currently sitting forward towards the rad, i have around 1.5" between my fan and the radiator. right now the engine is using the front support legs and the mount on the tailshaft of the trans. i got the side engine mount crossmember and i plan on moving the engine/trans back 2" to gain clearance for a flex fan.
i'm not sure if moving it 2" will be enough for the shift tower to be in the correct position

sounds like you must have a real long nosed water pump, my 283 mounted on the factory front pegs has 4+" rad-to-fan, and that's with a 2" spacer on the pump .... you could find a different water pump easier than moving the engine, and if it really is mounted as factory, you'll find that moving it back 2" results in interference at the firewall, especially if it has a fat HEI

why a flex fan? not cooling well? 1.5" won't cool well without a shroud, the clearance needed without one is about 1/2" .... or maybe your rad has been misplaced?

Bill

i don't think the engine is mounted where it should be. i have a 59 3200 parts truck with a 283 in it and that has almost no clearance between the dist cap and firewall, and thats a points dist. the 350 in the truck im working on is 4-6" farther forward then the 283 is.

yeah, then someone has rigged the front mounts, they can't be in the right place, should be able to see that from the parts truck mounts .... and unless you move it back nearer the firewall you won't get a SM4xx or a stock 3 speed to work, especially the clutch setup .... here's an original front mount setup

Bill

Rick O is providing some good advice here. I too have a M-21 Muncie in my '65 C10 ( http://talk.classicparts.com/showthread.php?t=13928 ). You'll need at least a 3.73 rear gear, and if you are running oversize diameter tires the 3.73 gears really aren't enough. But anything taller than a 3.73 and you'll lose any chance of highway driving due to increased engine rpm ( http://www.csgnetwork.com/multirpmcalc.html ).

One thing that would help the launch ratio ( http://www.5speedtransmissions.com/startlineratio.html ) is a heavier flywheel, especially if your 350 SBC is healthy and has decent HP.

I like rowing through the gears of a 4-speed too, but I believe you would be much happier with a 5 or 6 speed that has a steeper first gear and an overdrive final ratio.

Well i think i might be changing my plans a bit. for now i'm going to keep the TH350 at least for this summer and maybe tackle the 4 speed swap next winter. now my issue is that since my motor isnt at the exact location as a factory V8 i'm not sure what headers will work. currently the 350 has a ram horn style manifold on the driver side and a rear dump manifold on the pass side. i'd like to run the mid length patriot headers if they will fit. i'm going to be moving the engine back at least 1-2" to gain some clearance for the fan

I'm using the Sanderson headers on my 58 gmc with 350. Made for use on 55 - 59 pickups for $254 at summit. They tuck in close to the engine and don't interfere with steering. Mine is using the steel bellhousing mounted in the stock location. Hope this helps. Larry

Pictures.... pictures.... pictures! Ya gotta show some us some photos LarryW

I hear you John. I tried reading that "Posting images" thing and they use words I don't understand.Larry