Transmission case cleanup.

Now let’s face it—Green was a field truck, a cheap, disposable work vehicle. Grandpa certainly was not going to drive his Lincoln Town Car sedan to the field.  He has had only marginal maintenance since at least 1973 and none at all since 1987 (Green, not grandpa). “Deferred maintenance” has been the truck’s lot and there is a lot to do, beginning with basic cleanup.  Plus, as I work I am learning what is connected to where.

Since Green isn’t exactly “auto-mobile” at this point, that will mean doing a fair bit of cleanup by hand.  This past couple weekends, with new snow and the wind howling outside, I decided I might as well start with the superficial stuff—and that means dealing with the accumulations of rust, dirt, dust, grease, seeds, webs, and hair (from the raccoons that used Green as an apartment). Frankly, the undercarriage is fully rusted across the exposed surfaces and any place that leaks fluids (and there are a lot of them) is clad in a thick crust of oil and Great Basin dust.

I figured I might as well start with the transmission, since I am not yet ready to tackle the motor and even a cursory glance underneath shows the transmission case could use some love and attention.  Plus, there is a serial number on it.

Green has amazing access.  One fills the break master cylinder through a hole in the cab floor.  The battery is accessible from a panel underneath the passenger’s feet. To get at the transmission, the transmission cover plate—on the floor of the cab, do you see the pattern?—has to be removed.  About half a dozen  odd sheet-metal screws did it, all of them flat-heads, which were the only screws made at the time.

Once the cover was off from the floor of the cab it was clear there needed to be a cleanup before anything mechanical could be done.  In the photo above you can hardly tell that there is a square fiber gasket around the base of the shift column to seal off the transmission from the cover plate.  It doesn’t seal much in this condition.


Transmissions have always been long, cone-shaped things in the cars I have driven.  Despite all the years I drove Green in the past I never really paid too much attention to the drive train.  I was a bit surprised to see his transmission as a blocky cube, but there it is.

Part of the goal for this exercise was to locate the serial number for the transmission.  Since it was pretty clear that any number was well buried, I took an old flat screwdriver, a steel brush, and began to apply a generous helping of elbow grease to the accumulated grime. The transmission would not have been painted and the cast steel casing has a coating of surface rust beneath the oily rime.  That rime was not soft at all.  Getting it off of some parts was like chipping tar off a road surface.

The 1949 Chevrolet trucks had component serial numbers in addition to the vehicle number. Unfortunately there are several numbers cast into different components.  The photo below is the left (driver’s) side of the transmission. You can see the number in the casting that I thought was a clue to the serial number.


Driver’s side of the transmission (the wire at the right is the speedometer link); you can hardly tell there is a cover plate bolted to the housing directly below the number

I should have taken a photo before starting on the gunk, but didn’t.  Notice that there is a 4 above the “GM” in the photo?  I’ll talk about that in a second.  To the right of it, right beside the 4 on the driver’s side of the case, is another number that looks like it has been screwed on.  According to one site I’ve seen, this is the casting date code.  The number here is “A 20 9”.  If that statement is correct, this one indicates exactly when the transmission case was cast.  The code would therefore indicate that this transmission case was cast A = January, 20 = 20th, 9 = 1949. If this one really is a component manufacturing date, that bit of information squares with what I know about Green’s vehicle serial number.  It tells me the transmission case was manufactured only a few weeks or days before the truck was assembled.

So what is that embossed number that is clearly part of the casting?  According to the Vehicle Information Sheet, the GM suggests that the transmission was manufactured at Saginaw Metal Castings Operations.  SMCO began producing metal castings in 1919.  It was the major supplier of cast casings, forged steel components, and machine finishing for General Motors’ three- and four-speed manual transmissions for over half a century. Green has a four-speed in him. I suspect (based on reasons given below) the number “591665” is a component number, but I can’t say for sure at this point and will keep looking.

Back to that 4 above the GM:  on the opposite side of the transmission c2017jan14-5ase is another number, a single “4”. Since the case was cast in one piece from a mold of interlocking halves (there is a vertical casting joint visible right down the centerline), I think that 4 may be a mold number for each half.  I understand that the castings were not made individually but rather in gang molds (I would guess either four or eight) and then the sprues were cut and ground off during finishing.


Then there is a second set of numbers on the top plate, or transmission cover.  The one on the right side looks like a casting date code again.  This one is “A 6 9”, or as I read it speculatively, January 6 1949. The GM shows up on the left side of the plate, again over a six-digit number, this one “591566”. Together with the code on the case I am willing to bet that the transmission cover also constitutes a major component. There does not seem to be a code on the cover plate bolted on the left side of the transmission case (power take off cover, the service manual says), so it was likely not considered major. If I am right, it would be reasonable to conclude that the major components would carry the record of the manufacturer.

Anyway, over the past couple of weeks when I could grab time from work and Scouts, the transmission case has been scraped off and looks pretty good, and I can’t resist a few before and after shots.

I did find the transmission serial number in the process.  That one, it turns out, is stamped in small numbers on the back of the case on a spot near the top that has been milled flat. In case you can’t read it, the number is 32467.  Other than maybe an ordinal serial count as a finished transmission assembly, I have no idea what it may mean—but there it is.


The next transmission work will be to drain the fluid, open up the power take-off plate, and see what it looks like inside.  That might be awhile, so I’ll probably do something else first—like the brakes.


One thought on “Transmission case cleanup.

  1. Pingback: Engine-block Numbering. | The Green Truck

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