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Old 05-24-2018, 12:06 PM   #1
Burt Lake Barn
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Default Trans identification (year)

I recently acquired a 3 speed toploader transmission. The person selling it told me it was a 1939 Merc transmission. When I went thru it, I found it had a later style synchro set in it (may have been updated along the way). At any rate, I wondered if anyone might be able to peg the year for me. On the trans housing above the inspection plate I found the number 7 H C 6 0 7

The shift top plate cover has a number 81-7222

Any help would be appreciated. Thanks in advance.
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Old 05-24-2018, 01:07 PM   #2
rotorwrench
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Default Re: Trans identification (year)

The serial prefix doesn't match US or Canadian numbering system that I'm real familiar with. The 81-7222 casting number indicates it is 81A or production beginning in 1938 (double detent housing) and it's a good one. The serial number really doesn't matter all that much and you may have a transmission from a late 1947 or early 1948 pickup with an H model six cylinder engine but I haven't seen the VIN for those. As long as it has the 78 case then it's usable. If it is original to a pickup, it will have the open drive rear housing set up. These have a different main shaft than the ones made for closed drive but they can easily be converted either way. There were two types of synchronizer used in the 1939 thru 51 light duty 3-speed transmissions. One has the ball & spring plate detents and the other has the spring rings and flat plate detents but they are interchangeable.

Last edited by rotorwrench; 05-24-2018 at 01:14 PM.
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Old 05-24-2018, 03:36 PM   #3
Burt Lake Barn
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Default Re: Trans identification (year)

You mentioned that it may have the "open drive rear housing set up" - it did in fact have a rear transmission mount that is different than my '41 mount but I had planned on using the '41 mount that I already have that fits in my '41 frame with the closed drive shaft / torque tube set up. When we removed the rear trans mount bracket we noted that the main shaft had a gear on it to facilitate the speedo gear that was built in to the trans mount bracket assembly. I also noted that the speedo gear that is on that transmission shaft actually acts to hold in the whole shaft assembly with a slip ring holding it in position. I was hoping that I would not have to take that off and replace it with some type of spacer over the shaft in place of that speedo gear. I suppose this sounds familiar eh? Do you know if it will simply fit into my standard '41 rear trans mount, or will I have to change some things afterall???
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Old 05-24-2018, 04:47 PM   #4
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Default Re: Trans identification (year)

Always be aware of what gear ratios are in the transmission and the rearend.

How many teeth are on the Main Drive Gear ... the small top gear at the front of the transmission on the input shaft. And, what is the rearend ratio?

Knowing this ahead of time will help in your decisions.
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Old 05-24-2018, 05:26 PM   #5
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Default Re: Trans identification (year)

7HC is a prefix for a few 1948-50's 6cyl truck parts numbers.


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Old 05-24-2018, 05:48 PM   #6
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Default Re: Trans identification (year)

The conversion from open to closed drive requires the replacement of the rear retainer-mount assembly and the main output shaft. If you have another transmission such as a 1941 side or remote shift type, you can use all of the gears & shafts from it to build up a top shift transmission. As Hoop mentioned take care if you only want to transfer partial pieces & parts. 16 tooth input shafts have to mate to 28 tooth counter shaft cluster gears(both front meshing gears). The tooth counts vary and there are four or five different ratio sets. This depends on what you are putting the final assembly into. If you have a good cluster & input set, the 1st/reverse slider and the second gear are all basically the same with a few exceptions. The main output shafts for all the car transmissions with closed drive are basically the same after 1939 or at least they are interchangeable if you have the correct 2nd gear with the correct shaft. The pickup or open drive output main shaft is longer and will only work for open drive.

I'd suggest you get a copy of Mac VanPelt's light duty 3-speed transmission booklet. It tells you everything you would need to know on these old cog boxes and helps ID stuff that will interchange and stuff that won't. It's invaluable to have for the early Ford cars & pickups
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Old 06-03-2018, 06:31 PM   #7
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Default Re: Trans identification (year)

If it is the gear I am thinking, it is a 29 tooth so I understand that makes this a 1950 or earlier tranny gear set and therefor can be converted back to a closed drive by replacing the main shaft with an 81A-7061 shaft. Not positive on the rear end ratio but it came in the original 1941 Ford car. Sorry for the delay on my response.
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Old 06-04-2018, 10:11 AM   #8
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Default Re: Trans identification (year)

The 15/29 set is OK for light body car with a 3.54:1 rear axle ratio. The 16/28 set works well with the 3.78:1 ratio in about any application light or heavy but will run higher engine rpm at the same speeds. The Lincoln gear sets were used with 4.11:1 or greater ratio rear axles and many Lincoln car transmissions had the overdrive but the inputs and clusters will fit the 78 case.

As long as it has a 78 series case, it will fit anything that was made to fit in there.
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Old 06-10-2018, 01:43 PM   #9
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Default Re: Trans identification (year)

Thanks all, I think I am on the road to recovery. I did get with Mac at VanPelt sales and am in process of replacing the main shaft with an 81A-7061 shaft so I can use this with my closed drive shaft/torque tube set up. There are a lot of things to be aware of and fortunately many combinations that can work together, and of course, some that don't. Thanks for your input.
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