Transmisson Gear Set Interchange

corsair_kid1979

corsair_kid1979

Junior Member
So I have started the teardown of the 78-casting, three-speed transmission I acquired and found that at some point in its past it had an earlier ('32-35) gear set installed in it. What gear sets from these later years will interchange with the 78-casting case? I have order the Vanpelt book and waiting on it in the mail, but would like to start putting the feelers out to source another transmission.

I heard the '39-48 ones will work, but is that only for cars or truck transmissions.
 
The "easy-to-come-by" '40 thru '48 side shift transmissions have the perfect, latest-synchro set of gears that fall right into that case. ALWAYS replace gears as a set. You cannot mix 'n match pieces of different-era gear sets. DD
 
I have even done this. Put a set of the later side-shift gears in a '39 case. As long as you have the proper second-third fork, it should be easy. I was a rank amateur when I did it and it turned out fine. I used good used gears with new bearings and synchronizers. The transmission was the only part of the drivetrain I didn't break.
 
corsair_kid1979 said:
So I have started the teardown of the 78-casting, three-speed transmission I acquired and found that at some point in its past it had an earlier ('32-35) gear set installed in it. What gear sets from these later years will interchange with the 78-casting case? I have order the Vanpelt book and waiting on it in the mail, but would like to start putting the feelers out to source another transmission.

I heard the '39-48 ones will work, but is that only for cars or truck transmissions.
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Be advised, there are gear sets within the years of '39-'48 transmissions that have different 1st and 2nd gear ratios, as well as open and closed driveshaft versions. So, you may want to wait until you read Van Pelt's book, and understand those details, before you buy another transmission and wind up with something you don't want or need. Just sayin'.
 
Some parts can be mixed but it's best to have Mac VanPelt's transmission book to ID what you have and fit parts to work with each other. It has gear charts in the back of it that will be good to have. Even some of my old early 51 Mercury transmission parts can interchange back to the mid to late 30s.

Pickup gear sets can be different in the later years. The input shaft gear has to mate with the cluster and this gives the starting ratio. There are pretty standard Ford ratios, ratios that were made for the Mercury cars in 39, and the close ratio Lincoln sets but they work better with heavy car rear axle ratios & overdrive set ups.
 
Stick with an "EASILY-FOUND" '40 through '48 side-shift PASSENGER CAR gear box for your gear set and you can't go wrong! DD
 
Well I think I got lucky today and found someone who has three transmissions for 40 bucks. Think that is a hell of a deal too.

Looks like one of the transmissions has a Borg Warner R10 overdrive on it.
 
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Since you have an early gearset in it now your shiftforks won´t match up with the later gearset...you will need another top or replace a fork in the top to make it work.
The later gearbox with overdrive will not be a good doner for gears...
And the 50- pickup gearboxes while they might look identical at first sight have a different gear setup to.
 
Well I don’t have a shifter yet, so that is not a big deal yet. As for the three transmissions i think there is one I can use, and the others might help offset the costs of the package.
 
corsair_kid1979 said:
Well I think I got lucky today and found someone who has three transmissions for 40 bucks. Think that is a hell of a deal too.

Looks like one of the transmissions has a Borg Warner R10 overdrive on it.
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Does the O/D trans look like this one? If so, it's from a '49 thru early '51 Mercury. That gear set is going to have a main shaft that won't work for your torque tube application, therefore, that set is no good to you. Not a whole lot of demand for those. I've had one layin' around for about 24 years now. What are the other two? Show us pictures of the insides, or tell us the serial number with STARS stamped into the flat, rectangular pad at top, front of trans cases. Those numbers can tell us year of trans. Also, let us know that number stamped into your good case and we can likely figure-out it's origin also.


In the meantime, go play around on Mac VanPelt's (where your manual is coming from) site which I have linked below. Lots of info to get ya started! DD


http://www.vanpeltsales.com/FH_web/flathead_transID_3speed.htm


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The trans with the top shifter looks like a pickup heavy duty 3-speed, the one that says teeth broken is the one you need, the last one is a 1949-early 51 Mercury OD.
 
I'd surely like to know what the case on this side-shift transmission came out of with that cast bolt flange on the rear. Corsair-Kid....can you turn that trans upside-down and look for a ??-7006 number cast-in at bottom rear of case? They may be covered by caked grease. There should be two prefix numbers before a -7006. Can you see TWO prefix numbers like that? Can you read a serial number STAMPED into that flat, rectangular pad at TOP, Front of trans case? DD
 
seems to me they are all cast, no? i'll go look later, but pretty sure i have both widths of rear mounts that are cast
 
That rear mount is like my 46 had, I needed a cluster gear, the only not broken one I found was from a later trans, probably overdrive, but was missing both input gear and tailshaft housinf, had a short main shaft, and a shifter rail sticking out back unlike my 46,probably missing overdrive section, the main drive gear on the cluster had one less tooth, the teeth a slightly different shape, and loose needle bearings, the shaft was missing and many of the needles, local parts store had broken package of needles they sold me cheap, put in just the cluster--- even though wrong tooth count it worked, was quiet and survived a lot of abuse--- at the time I didn't know it shouldn't work
 
cas3 said:
seems to me they are all cast, no? i'll go look later, but pretty sure i have both widths of rear mounts that are cast
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Maybe I'm just seeing that bolt-on bearing retainer all wrong. It looks cast into the trans in his picture. Should be this bolt-on piece below! DD


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That truck transmission is the Canadian type. You don't see those down in my territory much.

The Mercury or Monarch transmission has a usable input gear, cluster, synchronizer, and low plus 2nd gears but you would need a main shaft that would work with the 2nd gear. This is where Mac's book is invaluable. The OD will only work with that case since they have a different casting to work the reverse lock out control plus the overdrive.

The 91A 2nd/3rd shift fork will be needed for a top shift to run any of the 39 through 51 sychronizer set ups. There are three different types and any one of them will work as long as they are complete.
 
V8COOPMAN said:
Maybe I'm just seeing that bolt-on bearing retainer all wrong. It looks cast into the trans in his picture. Should be this bolt-on piece below! DD


57287
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If that piece would have been cast with the housing you should need another bolted on flange in it or getting the rear bearing installed and staying in place would be tough.
So probably just the picture fooling us...
 
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