The Stovebolt Site Forums The Shop Area Driveline Installing A SM420 Transmission In Big Bolt Trucks 1947 And Older!!!

I may have the answer for you, installing a SM420 trans without all the cost in Big Bolt trucks. I needed to replace my original 1942 235 engine as it had a broken crankshaft. I installed a 1962 235 engine with low miles, along with 1948-53 truck bell housing and SM420 transmission behind it for no more double clutching. I made an adapter plate to this bell housing to accept the original clutch and brake peddle. No need to have the piece with the three bolt holes from your old bell housing welded to the 1948-53 truck bell housing. Will post it as a Tech Tip at some point. If I say so myself it turned out great. If anyone would like to add a SM420 trans to their truck call me for the details will be happy to help. Pictures are posted at xxxxxxxxxxxxxxxxxxxxx Phone number 1-262-392-2989 or mribbich@wi.rr.com

I SEE PEOPLE ARE HAVING TROUBLE FINDING MY POSTING THE BEST WAY OF GETTING THE INFORMATION IS TO CALL OR E-MAIL ME I AM ALWAYS HAPPY TO HELP. THANKS!!!

Marv.

Moderator Edit: The above noted "picture" link was removed as it is no longer a valid source. To see the first batch of pictures for this fabricated bracket, see this later post and then the ones below it for all the rest of the pictures/drawings involved.

I should mention that the truck I did this to is 1-1/2 ton it my not work on smaller tonnage units.

Marv.

I had to double clutch my SM420 into high gear. I found that if I paused for an instant in neutral w/o the second clutching before continuing the shift into high, there was no grinding. The pause is no longer in time than the double clutch would take.

Also, my left knee appreciates it.

Marvin,

If you email photo(s) to me, I will host them and post links to them.

Wally,

You have double-clutch into 4th gear to avoid grinding - an SM420?

Moderator Edit: The posting of pictures has been done in this later reply post.

Tim,

My SM420 (4-speed, granny gear, right?) would grind with a reasonably brisk single clutching. Doubling clutching solved the problem but just pausing an instant in neutral on the way to high gear also works so that's what I do now.

i've driven several trucks,(if not a dozen),of SM 420's through the years. if the synchro's are good,every gear should shift like butter. You just have to shift into "Granny",and reverse, when truck is parked,(or completely stopped),to keep from grinding gears. That's my experience.

I have never had any grinding when up-shifting any of the SM420s I've had in my trucks.

However, Wally, your technique works for you and might help someone with worn synchronizers. What weight gear oil do you use in your transmission?

"I made a adapter plate to the bell housing to accept the clutch and brake peddle no need to have the piece with the three bolt holes from your old bell housing welded to the 1948-53 truck bell housing." Marvin Ribbich

Here are some pictures from Marvin

Here are more pictures from Marvin

Here are the last pictures from Marvin


Moderator Edit: These new links were used to replace the no longer valid original picture source link.

Thanks for posting some pictures, its sure going to help people wanting to do the same.

Tim,

I'm 700 miles distant from the truck with family, but I'm pretty sure I use the 80W-90 gear lube.

Wally,

That gear oil is good, unless it is synthetic oil or hypoid oil.

Here is Novak Conversions' recommendation:

When filling your 420 with gear oil, we recommend that you select a conventional mineral oil or a para-synthetic in lieu of a full synthetic oil. Properly assembled manual gearboxes do not have the thermal strains seen by combustion engines or hypoid gears. Synthetic fluid in these gearboxes, while not harmful, is probably an economic waste.

Hypoid gear oil is sulphurized higher than transmission oil and can be mildly corrosive to the non-ferrous alloys used for synchros, bushings and thrust washers in these transmissions.

An 80W-90, API-GL5 or MT-1 rated fluid is very good. Some claim faster shifts from using a 50W engine oil in their transmission and we do not consider this to be contraindicated unless you operate your vehicle in a very warm environment.

I had a few bolters call with questions about the 3 holes in the original bracket that the 1" shaft goes through. They need to be taped with a 3/8"X16 tap. No need to drill the holes before tapping as they will tap just fine. Again any questions on the making or installation of the adaptor just give me a call. 1-262-392-2989

Marv.

Marvin,

Change your gear oil to straight 90 weight mineral based gear oil. This usually cures the double clutch problems 90% of the time, unless you have syncho problems. Got the straight 90 weight gear oil at NAPA.

Hope this helps.

Tim

Has anyone tried to make and install this adapter on there truck???

Marv.

I considered doing it. My son is putting a 1954 235 into his 1946 2 ton truck. I wanted to keep everything from the 46 motor kept together as I did not want to mix and match parts between the 54 and the 46.

Being the 54 came with the clutch housing I thought about having the adapter plate you designed made and used. But I did not think I would have enough time to have one made. Being my son uses his truck for his catering business I did not want to delay getting his truck back on the road.

Turns out the machine shop took so long to do the rebuild I could of had a truck load of adapters made.

So I am using the 46 clutch housing on the 54 engine.

I am going to put the 54 clutch housing on the 46 engine so I can mount the 46 engine on a 1945 1/2 ton rolling chassis. As soon as I can find a front motor mount. Jeffrey

Your adapter plate is why Stovebolt is a great place. I learn about great things that I may not use but is great to know because one never knows when and what he will come across in the future. Jeffrey

Hy 32vld, just to let you know the 1954 and 55A series trucks use an angled mount at the bellhousing to frame connection, the earlier trucks use a flat mount, so the later bellhousing will not mount into the earlier chassis, hope that helps.

I am the guy who came up with the bracket so that you can mount your clutch and brake pedal to the bell housing. This bracket is for the larger trucks not 1/2 tons. If any one has a interest they can call or email me, I can send pictures. 1-262-392-2989 or mribbich@wi.rr.com

Marv.

PM sent to you Marv.

I will post your pictures on this site Marvin, I will send you an email.
Steve

Uploaded pictures of the adaptor.

More pictures:

more still

All credit goes to Marvin Ribbich -- thanks. This pdf if printed on letter 8.5x11 should be to actual size.

New guy question.... if installing a SM420 into a 1940 replacing the crash box, will I have to change the torque tube to an open driveshaft at the same time?

I don't think a SM420 was ever used with a torque tube plus your bell housing need to be changed to except the SM420 if I remember right the bell housing need to be from a 1948-54 engine. My guess the answer to your question is yes. Thanks for asking!!!

Marv.

Marvin,
I believe you could get a sm420 in 1/2 and 3/4 ton trucks from 48-54, all had torque tubes bells connected to them.
The question is would his wheelbase change and would his existing torque tube bolt up the the sm420 bell mount.

See the picture for an example of an SM420 with the torque tube bell adapter.

Any SM 420 transmission can be adapted for torque tube vehicles by changing the rear bearing retainer casting which has the pivot for the torque tube ball. The tricky part is finding the front half of the universal joint which bolts to the transmission output shaft. Those items are very scarce. Making the torque tube from a truck that was originally equipped with a crash box transmission fit the 420 transmission might require some fancy footwork, however. I seem to remember some trucks that had a short torque tube, and then an open driveline to the rear end, which might be one possible option.
Jerry

Yes you are right. I actually have that exact setup in my storage room. It was out of a 53 3600 if i remember correctly with a 3 speed tree shift trans. Front half torque tube to a carrier bearing then open shaft to diff. Which was a ho52.

Glenn,

While you are going to do all that work, why not put in a 4500, single driveshaft if it isn’t too long or difficult to adapt to the diff, then you will also be able to cruise.

Ed

I agree. But im not da 1 with da project. I was just commenting on the tubed/open driveshaft availability.

Marv,

Just a note here that after a lengthy review earlier today, your info included throughout the thread is being considered for being made into a Tech Tip for possible addition to the Driveline Forum "Tech Tips" subforum.

While that process goes on, we are going to lock the thread so everything currently included can be kept undisturbed and used to gather and build a draft Tech Tip for review by the Tech Tip HQ Team.

While that is going on (may take a little while), feel free to drop me a PM if you have questions or additional information you would like to add to what is already here.

Best Regards,

Dan