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Discussion Topic:
Rear axle swap from '40 Passenger to '40 1/2 ton
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Carcheologist |
06-10-2022 @ 8:10 PM
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A friend purchased a complete 3.54 rear axle assembly from a local swap meet and was told it came from a '40 Ford Passenger car. He wants to swap the existing rear axle in the truck which is a 3.78 for the swap meet unit, but has run into a couple of fit problems. His truck is a 1940 1/2 ton factory stake bed on 112" wheelbase. The overall length of the swap meet torque tube unit seems to be roughly 3" longer than the one currently in the truck. We're at a loss as to what he has and if he can use it. What things should we be looking for to make sure he has the right axle assembly to fit his truck? One difference we noticed right away was the radius rods on the swap meet unit are a good 19" shorter than the one in the truck now. Looking for some clues!
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kubes40 |
06-11-2022 @ 4:55 AM
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The 3:54 did NOT come out of any 1940 Ford. The differential can be installed in your friend's '40 but it will require some modification. You'll need to determine just what it came from first. My guess? A later model, perhaps post war. If later, the axles are probably longer than the '40 axles. Have you removed the torque tube as yet? Axle housings?
Mike "Kube" Kubarth
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Carcheologist |
06-11-2022 @ 6:17 AM
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Kube, Thanks for the info - didn't know that a 3.54 was not available on '40 Fords. My advice to him was to remove the torque tube and drive shaft on the 3.54 unit and swap them with the torque tube and shaft currently in the truck. What other modifications can you think of need to be done to make everything fit up right? As always, appreciate your precise and helpful information!
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Carcheologist |
06-11-2022 @ 6:25 AM
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Kube, Oops, forgot to respond to your other questions. No, we haven't removed any of the axle housings or torque tube from the donor unit as yet. I think you're correct about being a later axle assembly since the torque tube is 3" longer and the radius rods being a different length. Another thing that threw me was the fact that the brake backing plates have the 2 lower brake shoe adjustment bolts. I thought that ended with '40 passenger cars. Please advise.
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TomO |
06-11-2022 @ 8:05 AM
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My guess, without seeing photos, is that your friend has a 39-40 Mercury rear end. If this is the case, he probably will not be able to switch drive shafts. Most Merurys had the pinion gear pressed on the drive shaft, while Ford used a coupling to mate the drive shaft with the pinion gear.
Tom
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Carcheologist |
06-11-2022 @ 9:41 AM
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Tom, Thanks for your comment. I sure didn't know that about the Mercury having a pressed-on pinion gear. Looks like we may have hit a brick wall on this swap.
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ford38v8 |
06-11-2022 @ 7:16 PM
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I agree with TomO, with a guess that it's a Mercury. Your dead in the water if there is no coupling there there. Bottom line applies to all Swapmeet finds, and many vendor offerings: Know what you are looking at by your own research, don't put your faith in what you're told by any seller ...And if you think about it, that's a good plan for all sorts of transactions.
Alan
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Carcheologist |
06-12-2022 @ 12:57 PM
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TomO, Not doubting your information here, but just want to make certain about this rear axle before we decide to forget this whole swap idea. I've been looking in the big Green Bible (28-48 Ford parts book) and I can't seem to find any reference to a drive shaft or pinion gear that identifies use specifically for Mercury or a vehicle with 116" wheel base, which is Mercury. It lists the following drive shaft and it's the only thing close that I could find : 68 4605-B Shaft (drive)-solid-use with axle having 6 spline pinion Pass, Comm 37-41 Were ALL Mercury driveshafts one piece with a pressed-on pinion gear? Is there even a remote possibility that it just might have a splined collar like Ford used? We would have to remove the torque tube to verify. Again, not casting doubt on your information, but just would like to confirm, if nothing else but to expand my own education! If you have any further corroboration it would surely be appreciated.
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TomO |
06-13-2022 @ 7:07 AM
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The Green Book shows the FORD chassis parts and does not list Mercury only parts. After WWII Ford created the Lincoln - Mercury Division and the last catalog to carry both Ford and Mercury parts was the 1946 Chassis Parts catalog. This lasted until sometime after 1953 when they combined the catalogs again. As I said in my previous post, MOST 39-40 Mercury drive shafts have the pinion gear pressed on the drive shaft. I have never seen one that wasn't, but some people have claimed they have seen them with the splined drive shaft. With Ford manufactured parts, I never say ALWAYS or NEVER, because someone out there has an exception. The 39-48 Mercury parts catalog lists the gear set as "99A-4209A Ring gear and drive shaft with pinion, matched set 3.54 to one ratio." My identification of the rear end is just a guess. There may be other drive shafts other than 39-40 Mercury ones that are longer than the stock Ford, I just don't know of any. Pulling the torque tube is not a big job, so you could do that and verify if it is a Mercury rear end.
Tom
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Carcheologist |
06-13-2022 @ 2:15 PM
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Thanks Tom, I really appreciate your helpful info. This exercise has shown me that the parts books only help so much. Beyond that, we have to rely on the experience and expertise of knowledgeable folks in our hobby like you. You've been most helpful! I will recommend to my buddy that he remove the torque tube just to satisfy our curiosity.
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