The Stovebolt Site Forums The Shop Area Driveline 1950 SM 318 tear down & parts

Any tips , pros, cons on tearing my 1950 SM318 3 speed apart please let me know. Also, rebuild kits, (Most seem generic to ALL 3 speeds from 1948 thru like 1964).
The transmission would hardly go into 2nd gear or 3rd gear. It would not shift from either 2nd or 3rd. On the bench it seems to be "Locked up" when I put it in gear by hand. If I slide it out of gear it turns no problem.
Picture of SM318 on my bench ready for a tear down.
Thank you,
Todd

In addition to the bearing kits that everyone sells, you may need a synchronizer drum and shift forks. Your 1950 will use the 2 lug drum. A 1953-1954 synchro can be used by grinding off two of the lugs. The synchros are getting hard to find. I don't think the shift forks are being reproduced so you will have to find NOS.

IDoes the counter gear in the bottom of the tranny sump turn freely?
The synchronizer drums are all the same from the3 sp cars or trucks to the end of the torque tube era as are the reverse idler gear end countershaft gear.
The small parts kits contain the necessary needle bearings as well as thrust washers through 64. I got syncronizers from one of our usual suppliers. Gears are used or NOS.
The clutch shaft can be found online for a 53/54 Corvette.
The1st-3rd shifing fork can be rebuilt by a reputable welder.
John Deere had the main bearings as cheap as anyone else.
I rebuilt mine in 2020 for 350 bucks. Everything.

Beware, car tranny cluster and 1st-rev gears use bushings, not needles
55 2nd and up 2 piece trannys have different drums and sliding gears. Only counter gears and 1st-3rd idler are a swap. That's when the 318
became a 319.

Once you figure how to deal with needle bearings, they are eady to work on.

Is the bottom circled in Red the counter gear?
The Blue sliding gear, when I slide that forward or rear onto a gear Nothing moves , Locks up? Is that supposed to be or is that a problem?
When the sliding gear (Marked in blue) is not engaged the whole gears turn smoothly including the bottom gears.
Hope that makes sense.
Todd

Before you start tearing the tranny down, take lots of photos and continue to take photos of every step of the teardown. Makes assembly a whole lot easier.

Great Idea.
I have started taking lots of pictures.
On another note does anyone know how many needle bearings are in my 1950 sm318? Both the small and large?
So I can count them as I go. The Manual does not give a number.

14 big ones and 24 little ones.
In the pic, the drum is all the way forward in 3rd gear and the blue 1st/rev slider is in neutral. Pop the drum all the way to the rear is 2nd gear. With the drum in neutral you then can slide the blue slider gear into 1st or reverse.
Slide it to mesh with the drum in gear is how you lock the gears to remove the yoke bolt.

Should you need to replace the clutch shaft bearing, you will need a special tool. I made one from 1/8” steel plate. My scrap wasn’t wide enough so I welded two pieces together. Problem solved!

Thank you for added Info.

Jethro in Va :do you have the John Deere bearing numbers?

Phak1: do you know the Wrench size (opening)? So I can fabricate one. The bearing turns, no wobbles, but It should probably be replaced..

Sorry, but that was five years ago. I’m not at home so I can’t measure it, I failed to document it (shame on me) and my memory is not that good.

Fortunately it’s easy to measure with a caliper.

The pivot shaft for the 1st./reverse idler gear has a lock pin that must be driven INTO a hollow spot in the shaft before it can be removed. After the locking pin falls into the shaft, the shaft, containing the captured lock pin can be tapped out of the case.
Jerry

Looking at my notes. I got the clutch shaft bearing from Carquest... National # 207L. Also, ND#43207L.

The mainshaft bearing came from Deere...
JD7696. Cost now is $47.46 from JD. The ND# is 43305L.
I modified the tang of a long file to open the snap ring.

In 2022 I found a NOS clutch shaft/gear on Ebay for about $150, 3699251 for a Corvette. Also a 3699250 will work. NORS Perfection # WT 242-16A.

Mainshaft #3699259 was about $125
NORS mainshaft #WT242-16E,

Hope this helps. Jethro.

Great Info. Thank you.
Is there not a video out there on a 1948-1954 sm318 tear down & rebuild?

I made this from pvc to keep the needles in place while I drove the shaft home. Worked like a charm.

Here's some YouTube videos for your learning pleasure by "The Jayhawker".

Part 1: 1937-1954 Chevrolet 3 Speed Transmission Rebuild - Disassembly

Part 2: 1937-1954 Chevrolet 3 Speed Transmission Rebuild - Reassembly

He has a ton of other videos if you check out his YouTube Channel.

Dan, Thank you.
I watched the first one. It did shed light on my transmission.
The rear on my 50' sm318 is different. Otherwise it was great info!
Todd

Yeah - The 3 speed in the video is the car version that has a shorter output housing and related parts, but otherwise the main internals I believe are the same.

Glad you found it helpful!

Ok, after cleaning some of the transmission I found this:::
I'm assuming it's the area where the Reverse Idler shaft lock pin would be?? Welded up?? See picture.
Is this case a Lost Cause now (** If they have issues*)
Removed main shaft , looks a bit "Worn",...Thoughts?
Also the Syncronizor Drum looks bad. The 2nd gear side it is Missing the two "Tangs" as part of the ring? See pictures.
Thank you,
Oh I have not figured out how to remove the " Rear Bearing support) #18 on GM Transmission 7-7. Any hints?
Todd
Added: the Manual calls those "Syncronizing Cones" .

Additional pictures:

If I recall correctly, there is a hex shaped pipe plug on the top of the rear of the tranny that doubles as a bearing support retainer and is pictured in this diagram as item #12. Once removed use a “J” hook to coax it out.

I removed the hex-pipe plug. I put a "J" hook piece of metal on it and tried to pull it. It did not budge. I will try again.
Thank you.

I have one lead on a shop on the Syncronizor Drum, any other suggestions please let me know. Mine is toast for sure.

Also Is there a GM part number for the Syncronizor Cones?

Todd

Ok, got it off. It was just stuck in there.
I made a 1 5/8" "tool" for the clutch gear to remove the bearing.
I also made a diamond shape tool to open the Main snap-ring to remove that bearing.
The main shaft rear bearing. Federal 1305-CG.
Clutch gear bearing: New Departure 43207.

Nice set of tools! I’ll have to update my photo with a measurement. Thanks!

Ok, I am confused someone shed light on the Needle bearings (small ones like 25 per manual).
When I removed the main shaft it had both large (14) and small loose inside (The Clutch shaft gear). I have NOT removed the counter gear yet. Why is there a set of small needle bearings there?
Am I missing something in the manual? It only says 14 roller on page 7-11 #5.
Thank you.

Phil's picture from the Master Parts Book with the exploded parts view shows two (2) sets of needle bearings in the "Clutch Shaft Gear" where the "Main Shaft" meets it (See Item 7). The main shaft is stepped, with 2 bearing surfaces for the different needle bearings to do their support job. The farther forward (smaller shaft step) of the two surfaces should be for the smaller larger diameter (14 count) bearings and the larger diameter step for the largersmaller diameter bearings (24 count) according to the below paragraphs in the GMC SM318 Rebuild Manual.

Edited to correct previous info.

Dan,
that makes sense. It's just not in my manual.
Thank you.

Is your manual the GMC SM318 book, or something else? I have a PDF of the GMC SM318 Unit Overhaul Manual (1955.2 Series and later open drive version) which I could email you if you like. The main case components are the same for your earlier SM318 closed driveline version. Can't remember where I found it on line many years ago, but can't seem to find it available for download anymore.

I've found that GMC Manuals seem to be better detailed than many of the corresponding Chevy books, even though they share the basic same design and parts for the most part.

Let me know if interested in the PDF.

I would be interested in that manual. I’ll PM you my email.

Phil - I have your email. A copy on the way.

A copy already sent to Shaffer's 1950.

Todd,
Check with Anaheim Gear 800-477-1103 for a rebuilt Syncro assembly.
I sent you a PM.
Fred

Fred,
Thank you. I have a Syncronizor Drum coming from another Bolter ( Twin Jimmys). I ordered a set of synco rings. I should be ok for now.
I will update with my progress.
Todd