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1940 Plymouth truck differential


Mertz

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I just started work on my truck and doing a lot of investigation into what I have and how things go together. Yesterday I wanted to check the rear end ratio. I turned the drive shaft and neither wheel turned. Both wheels turn freely by hand. I assume there is no “free wheeling” in the differential. I checked to see if I could loosen the bolts on the differential and the drive shaft and I could. Earlier I tried to remove the driver side brake drum (it was wobbling when I towed it) but could not get it off. My dodge truck manual says I need a drum puller. They show a picture of the puller but I have never seen one. Is there a trick to getting the drum off?  I assume I need to pull both axles to remove the differential. 

 

Thanks in advance for the help. 

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Interesting that the axles did not turn. I am curious to see what others have to say .... Could be the reason previous owner parked it years ago.

 

You need a good drum puller. Life is to short to remove the drums without one. I bought mine from ebay for $80 + shipping.

A quick search for ebay automotive hub pullers   I found this one for $65.

https://www.ebay.com/itm/TruePower-20-2029-Universal-Hub-Puller/383254053924?hash=item593bb8c424:g:9vEAAOSw8Sddw1mc

 

s-l1600.jpg

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Good news...I got the passenger side off and the backing plate. The axle is held in by the bearing which is a bit worn. The brakes look terrible but will be easier to rebuild off the truck. The seals have failed and the brakes are covered in grease. 

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Glad you got it off.  Question is why does the drive line not turn the axles? To me this suggest internal damage of the rear differential. Like something major has broken inside.

You will need to pull the drums and axles to drop the differential and look at what is broke ....  My feeble carpenter mind thinks you have a broken pinion, but what do I know, may be a keeper or a clip or something small. Thats why I am curious to hear what others have to say ... I think is major damage, always pleased when someone steps up and suggest a simple fix.

 

IMHO, I suspect you may be searching for a replacement rear end. I would not be worried about seals and brake shoes just yet  ..... You really want to see useable brake drums. The drums will be the hardest parts to find. You will need to find used drums in good shape.

 

At this stage, you need to decide how authentic of a restoration you want to do. A lot of people will install a modern 90's jeep cherokee or a ford explorer rear end.

3:73 gears seem to be the sweet spot for the flat 6, you get modern brakes, you can use the E-brake cable from donor and modify to use with original Hand e-brake.

Because a lot of people do this, you really should be able to find a stock rear end fairly easy ... shipping will be a cost to include.

 

Myself, I am building a driver. I found my seals were not leaking, shoes are in good shape, 1 drum seems new, 1 drum shows a small amount of wear. I replaced the hydraulics cylinders on them. If I can live with the 4:11 gears, just cheaper to keep er.

Otherwise I will do a rear swap on it, and the stock rear end I would expect zero interest in someone buying it, and offer it for free if someone would use it.

Others might do the same, I really think you could find a stock rear end ... you may want to consider updating now.

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Thanks for the info. I have access to a complete drive train for the truck engine, trans and rear end.  He put a new frame and Chevy engine in his. That rear end will probably need the same work as mine but I might buy it anyway since the price is right. I want to keep this as original as possible. This will not be a show car but I want it as nice and original as possible. I just watched a YouTube video of an all original 1930 Franklin Airman. I would give up all my cars for that car and I would do nothing to it but care for it and drive it. 

 

Once I get the other drum off and both axles out, I will pull the differential. I completely agree that something is broken inside. That might not be all bad since I want to change gear ratio to 3.73 anyway. 

 

I got the brake assembly for that side apart to check to check the inside of the wheel cylinders. 

 

I was was disappointed yesterday but I’m back to being excited about what I’m doing today. 

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Enjoy the process. It is very possible you can find a period correct car rear end with 3:73 gears in it. May be a few other changes required but very possible to do this.

The side bearings and teeth count from the differential & axle may be different. You can swap them.

 

I really think this should be a hobby and enjoy what you are doing,  You will need to do research, and then search, the whole process is a adventure.

I can imagine disappointments along the way, as long as we are learning and having fun .... shrug off those disappointments and wear a smile  :)

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It may not be as bad as you think.  Usually a broken gear set will make noises when turned by hand.  Since you didn't hear any of that, the next most likely thing IMO is a broken axle.  that would produce the symptoms you mentioned and would be an easy fix, assuming a replacement axle is found.

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22 hours ago, Mertz said:

 Earlier I tried to remove the driver side brake drum (it was wobbling when I towed it)

 

I was thinking same thing as kencombs. Broken axle or stripped spline? Perhaps it was the axle wobbling on the driver side and not a bent drum? Let us know what  you find.

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Based on the fact that the drivers side wheel was wobbly when I moved it around and that side had a fat and larger washer on it and that it is stuck would to me point to a broken axle. There is no jamming of gears inside the differential. If it had broken teeth it would jam.  The other option could be a broken pinion gear shaft. 

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Now that I have the driveline off I did another check. If I turn either wheel the opposite wheel turns. If I turn at the differential the passenger wheel turns but I can hold it to stop it. Turning the differential will not turn the drivers side wheel and drivers side wheel will not turn the differential. I guess the pinion gear is ok and the passenger side is acting normally. I don’t think the axle is broken but the splines are stripped but holding enough to turn the other side. 

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11 minutes ago, Mertz said:

Now that I have the driveline off I did another check. If I turn either wheel the opposite wheel turns. If I turn at the differential the passenger wheel turns but I can hold it to stop it. Turning the differential will not turn the drivers side wheel and drivers side wheel will not turn the differential. I guess the pinion gear is ok and the passenger side is acting normally. I don’t think the axle is broken but the splines are stripped but holding enough to turn the other side. 

At the red statement, if  you continue to hold the passenger wheel and then turn the dif,what happens? 

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As mentioned above the driver side wheel does not turn when the differential is turned. The only time it turns is when I turn the passenger side wheel. By resistance I mean like a very weak clutch. I can feel it trying to turn but can easily hold it. I imagine it’s like running a car on jack stands and both wheels turn but you can stop the non drive wheel but not the drive wheel unless it has posi. 

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I get confused easily, but I'm not following exactly.  ?  I'm just a shade-tree mechanic. 

 

I believe this is the way to check:  ?

 

Standard open differential - With both rear wheels off the ground,  rotate one of them, the opposite wheel should spin in opposite direction.

 

Positraction / limited slip differential - With both rear wheels off the ground, rotate one of them, the opposite wheel should spin in the same direction.

 

If you have a standard open differential (which is likely), place a block of wood or something under one of the rear tires and lower vehicle so opposite wheel is free. In this case, if you rotate (pinion / driveshaft) the free side should rotate. You could then mark the axle and (pinion yoke / driveshaft) with a paint stick and then count the turns to approximate your gear ratio. If the wheel does not spin in this scenario, I would think something definitely wrong.

 

Being your vehicle has set for so long, I would suggest removing both drums before checking again. Rusted surfaces might be giving you the "resistance" you're referring too? 

 

Does anyone know if and what years Mopar installed limited slip differentials our trucks?

 

 

 

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I have done what you suggested and I have a standard differential with wheels spinning in opposite directions. The reason I found this problem was I was checking the gear ratio as you describe but the differential was not turning when I turned the wheel or visa versa. 

 

I got the drivers side drum off and did a recheck. Now if I hold the passenger side and spin the differential the drivers side will spin. My guess is that the brake drum drag didn’t allow it to spin and the side with the drum off had less resistance so it was the one spinning. So I think the differential is ok. The wobble could still be what I originally thought was a bent wheel. 

 

One concern are the bearings so i might pull the axles anyway. I have about an 1/8” back and forth play on each side. 

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Now that I know a little more about the rear end I’m still going to pull the axles to replace the bearings and seals. Looking at the diagram and cross section of the rear end it appears to have an inner and outer bearing and seal. If I pull the axle and the inner bearing is pressed on does it come out with the axle?  Are the bearings the same size?  Does the cup stay in and if not how do you reinstall it? 

 

I’ve watched a number of videos and none talk about an inner bearing. The willeys Jeep videos are pretty close to the same rear end and they don’t show an inner bearing. 

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There is a bearing pressed onto the axle. That's the one you want to check carefully. There are also bearings in the diff which I would pull and inspect but not disassemble the unit. 

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  • 3 weeks later...

Got the axles out using my homemade slide hammer. I used a couple of short pieces of pipe one in the other and 2 pipe reducers over a 5/8” althread. I had a heavy turn buckle left over from hanging cables between buildings to hang a Christmas tree over the intersection downtown Spokane. 82C162CF-5C82-4068-8D1A-63F1F4258C1B.jpeg.478a24491a2f65c718baee4af63ffe81.jpeg

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Slipping the brake drum loose on the axle shaft leaving the key off..put the nut on a few turns ...use the drum as a slide hammer.

The axle will come right out.

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I’m a woodworker and have clamps that I can change from pull to push. I tried that with the brake drum on with no movement. One side was really tight after 40 years. I taped the other side in with a hammer to see if I could take up the slack and think I loosened it so it came out easier than the one I didn’t. Anyway it’s out and I have a slide hammer to pull the seals after I make the correct piece to attach to the end. Life is good 

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