Transmission Fun

louisb

louisb

Senior Member
Today I drove the four hours from my house to Ken/Alabama’s place to pick up my rebuilt 36 axle. I also brought my ‘39 style trans as I had tried to get it together a half dozen times and couldn’t figure out what was wrong so I asked Ken to take a look.

We worked on it for a while and couldn’t get it back together so Ken started to compare parts to spares around his shop. All the gears checked out but when we took a closer look at the case Ken noticed the clearance was wrong at the bottom of the case. Even though it is a “78” case it has the wrong clearance for the later gears.

Turns out my case is a 1937 which I guess is different than later cases. I grabbed a junk 78 case and took some pictures that show the difference. Pretty obvious when you look at the pictures. So I guess not all 78 cases are the same.

Thanks,

—louis
 

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Thank you, that is something I didn't know. Might be a good idea when we go to swap meets to take a list of the post 1937 serial numbers to ensure we get a good 78 case. The list would be little lighter than a cluster. Those numbers are in Mac Van Pelts book.
 
thats a new one on me! i always thought a 78 case was a 78 case! good to know, thanks
 
cas3 said:
thats a new one on me! i always thought a 78 case was a 78 case! good to know, thanks
Click to expand...

Me too! Absolutely could not install the front main drive gear with the cluster laying in the bottom of the case. Took it all back out and measured the case from the bottom up to the bottom of the front bearing hole. It measured 3 7/8". Then measured some of the cases I have and they were anywhere from 4" to 4 1/8".
 
I seem to recall reading somewhere on the Mac Vp site about trimming some of the syncro teeth from the input shaft to enable assembly in such situations.
 
I do know there are at least 2 versions of the "78" case, 1 with the continuous rib on the bottom which is "shallower" in the rear under the shaft bosses and the "78" case with the shorter rib which is "deeper" in the rear. It is the deeper case which I thought was for the 29T cluster and was in production by '39. I tend to see the deeper cases more than the shallower cases. Good Luck Louis and let me know if you need a "deep case"
Paul J.
 
I spoke with Mac Van Pelt, whom I purchased the case from, this morning and he is sending me a replacement. Great customer service as always. He said he has seen this before but said it is pretty rare. It sounds like it is basically a 48 case with a 78 number that was produced for a short time in 1937. I could get the 29 tooth gears to fit but since this is my first rebuild I would rather KISS and get the replacement case.

Thanks,

—louis
 
Being a "shoebox guy", I admit I know nothing about this, but I have to ask : Is there enough "meat" in the case in that area to allow a relief to be ground to clear the gears?
 
It is fairly simple to tell. The early 78 cases used the 48 gear shell with the later bellhousing. They have 48 cast into the inside of the case.
 
Following this thread got me thinking. I used later 46-47 side shift gears in my 48-7006 case. I believe it was from a 37 that I had acquired a long time ago with an engine attached. I just crawled under it a few minutes ago and it also had the strengthening rib running the full length of the case. It is running in my T-A as seen in my avatar. But I am not using a 29 tooth cluster. Mac is a big help with these transmissions. Good luck with yours louisb. :)
 
I just delt with this but with a 48 case. Couldn't get the front drive in until I started to polish the inside of the case. I had the cluster in and out number of time as I didn't want to take out more then I needed ...
 
The first version of the 78 case was for simpler gear sets. The second version came out in 1939 for use of the new gear set for the Mercury cars plus the new synchro set up. The later changes were due to limitation of resources for the war effort and finally due to outside manufacturers making them for spare parts. That 78 case had a long run from 1937 up into 1951 for production and a few more years for spare parts.
 
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tubman said:
Being a "shoebox guy", I admit I know nothing about this, but I have to ask : Is there enough "meat" in the case in that area to allow a relief to be ground to clear the gears?
Click to expand...

I had this question too: can a 48 case be clearanced to accept the later gear sets and synchros?
 
The short answer, yes they will fit but there can be problems like this with any of the different cases. The 15/29 set may not. They will go in a 78 case OK unless is is like the subject case. The input gear is smaller but the cluster is larger.
 
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