I'm putting a 350 in my 1947 Fleetmaster that has a muncie sm-420 in it. What bell housing will I need to use to bolt a 1978 Chevy 350 that was pulled from a Camero in? Also if you know any issues I may run into and any extra info on the transmission that would be great. Thanks! Also what would be a good gearing for my rear?
you really want to put one of these huge truck transmissions in a car? It will fit on most Chevy car bellhousings, although the lower bolts go in from the front, so you'll need to drill out the threads in the bellhousing (make it not so useful for future use in front of a car transmission), and install the bellhousing and transmission as one unit. Or use a 55-67 truck bellhousing, which is open underneath, and has the holes already not threaded. But I'd look for something else... as for rear end gearing, high is 1:1 like all the other non-overdrive transmissions. Gear ratios from low 2s to mid 4s would be appropriate, depending on what kind of driving you do--all highway, to only racing. Most guys settle for something in the 3.0 to 3.5 range.
I think I would drill out the transmission. Then you could mount it to a closed bottom bellhousing. If you used a truck bellhousing with no threads in the bottom holes its bolt and nut time. Back in the day when I was using my 65 PU with a 327/350HP to grenade the little 3 speeds, I couldn't always get a truck case, so I did the bolt and nut thing regularly.
I think the reason they use the setup they did, is because it's not easy (actually impossible) to get that one lower right side bolt in from the back...take a look at the transmission case, again, from another angle I also used a few car transmissions in truck bellhousings, with nuts.
Agree with Squirrel on the trans choice - those truck transmissions are pretty bullet proof but shifting is like rowing a boat with that long stick. Its a 4 speed, but you drive it like a 3 speed - 1st gear is super low and non-synchronized. Though, I just read your post again and it sounds like this transmission is already in the car so you already know the above - did someone swap in a 216/235 and SM420 from a truck at one point, and now you're yanking the 6 to put in the 350? In the interest of a budget and the trans already being installed in the car, its fine to leave it there, but if it were me, I'd be looking for a more driver friendly trans, something in the Saginaw/Muncie/BW 4-speed lineup.
50's Ford pickups with 4 speeds had two bolts that go in from the trans side, and two studs on the bellhousings with nuts for easier access. Also makes heaving that 100+ lb trans a little easier to hang on the studs. You (or he, or whoever) could also install a stud or two and drill the trans. Would make trans removal a little easier when he decides that big clunky transmission should not be in his car .
yup thats exactly what happened will the clutch linkages link up nicely on transmissions you mentioned? Money is an issue at the moment
You may have a ground clearance issue. I would look for the bellhousing Squirrel mentioned, you'll need the truck starter too, it bolts to the bell. Since the SM420 has no provision for a tailshaft type mount, I would fab up mounts to go from the bellhousing to the chassis. The combo with the clutch and flywheel has to be over 230 lbs. You can either fab clutch linkage, I'd probably go hydraulic since it makes things easier.
The clutch linkage on the stock setup should work with the 55-59 and 63-67 truck bellhousing, use the fork that is already in the car. But without seeing exactly what you have now, I'm just guessing....so, show us some pictures
will do as soon as I get it apart. Im putting the 350 together at the moment. I still have the original starter on it. I figure I wont be able to use it with the 350.
I've installed a couple of these trannys into Jeeps and they work perfect. Not so great though in a car I'm thinking.
1st gear is like 7:1, that why the crawler guys like them. 2nd is around 3:1. I've put thousands of miles on those boxes in trucks. It may work in a car but there are better choices.
Agree, that trans has the super low 1st gear of 7:1 ratio. Granny low is what that gear is commonly called. It was designed for heavy truck to get going. You don't have that problem with a car, so you effectively have a 3 speed using 2nd-4th. In trucks you start in 2nd gear as well unless the real heavy load. 4x4 guys like that trans for the super low crawling in 1st gear. It's just not a good choice for a car, there is a reason GM never put it in cars. However if you are tight on money, it can work and will certainly hold up behind a 350 SBC. Since 4th gear is straight 1:1, like any non-overdrive trans, you should use a rear gear ratio that works with that in mind. Using the 350, a ratio around 3.00 will be fine in that car.
Fleetmasters are pu's right? Not mentioned but you might have firewall issues, cars did. 47 was a closed drive line so your rear is probably 4.11's. I believe the same rear was used thru 54 for sure maybe later I don't know. Hydramatic trucks had 3.90's. What ever you do do not go to Patrick's in Az. for his 3.54's. You can read about him on the HAMB. Someone else may step up with them. If yo end up changing completed rears then the enclose rear trans will leave too. Good luck.
The car already has the SM-420 trans in it. So it also has aqn open drive conversion done and is not running the stock torque tube. OP wants to swap in a 350 SBC engine. Even if the trans is not the normal choice, it is already in the car as it is built now.
I have a few of those transmissions and bells. The proper bellhousing will be made of cast iron. Passenger car aluminum bellhousings will not work the bearing retainer hole is too small. All the truck bells I have run across have bellhousing crossmember mounts. Denny
The SM 420 did not have a provision for a mount off the tail and hung free and clear in the air is why the bell was cast iron...The aluminum car bell couldn't take the weight. When GM came out with the SM 465 that was done away with and a proper mount was added to the tail of the transmission Also reverse change sides on the SM 465 was over to the right and down. And some time in the 80's GM got rid of 1st on the shift knob and put a "L" for LOW and 2nd now was first. The SM 420 was used thru 1967(rare in that year) in 67 GM came also came out with the SM 435 that lasted till 1972 In 1968 the SM465 came into existence also. For some reason GM in the trucks the transmission hung free till 1967 (manuals) but cars got a mount on the tail ?
Are you sure about that? From my experience, the SM420 has the "small" bearing retainer, while the SM465 has the "large" bearing retainer. The 465 replaced the 420 in 1968. Both of these transmissions are huge truck 4 speeds, but the 465 is huger than the 420 (it also has synchro in granny gear)
Yes the 420 does have a SMALL bearing retainer you are correct.. I remember doing a 465 swap on my 65 c20 and was a BIOTCH ! to find a bell with the feet Think I got one out of a later c50
Some bearing retainers will swap, I forget which ones. I've turned big ones down in a lathe and made rings to use small retainers. I agree on using nothing but a steel bellhousing with the SM420, they weigh 150 alone, 2x what a M21 weighs. I have a lot of truck bellhousings stashed, a '55 to '62 car one will work, not sure if the mount pads are the same as the truck.
The sm 465 uses a large retainer, because it had a big tapered roller bearing on the input shaft, iirc. Sent from my Trimline
On a different tangent: The Tight Money Thing: I believe your SM420 is worth money or at least a good trade to the right guy. A relatively unabused SM420 in a light street car on smooth pavement would be a good find. Have a look through any of the 4wd/rock crawler/Jeep forums; that 7:1 granny is much sought after (or was 10 years ago when I was in it). Eddie
Ive got a pile of those 420 transmissions. and two of the 465,s. What I like is the slow reverse makes it easier for me to back up especially when backing a trailer. No reason they will not be Ok in a car.
At any rate it would be advisable to run a Cast iron V8 bellhousing be it a car or truck housing. One thing, does this trans have open drive or closed drive as the 48/54 Chev 3100 pickup 4 speeds had a closed drive and torque tube and I think with a bit of parts jockeying you can put the granny 4 speed in front of the car rear. You will need a V8 flywheel that matches the bellhousing. Back when I was in high school one of my uncles drove an early 50's Dodge Surburban wagon with a "big" Chrysler flathead six and a Dodge truck granny 4 speed as his "huntin" rig. That old wagon would climb a brick wall if you gave it the chance. First time I ever had a back strain was lifting the trans while changing the clutch in it a week before hunting season.
So what I have been reading the 420 isnt recommended for my car. What would be a good transmission that would require minimal fabrication for installation? I am planning on putting a new transmission in it in the future so I seems it would be foolish to pay the money for different gears when Im planing on swapping them again when I get the new transmission.
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