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keithb7

Differential ‘38 Plymouth

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Axles and diff came out tonight.  Easy-peasy and quick. As I loosened the first housing  bolt my wife poked her head in the garage and said “Dinner is ready”. 5 mims later I sat down to eat. Removal was done. I love the simplicity. 
 

It feels tight. No slop. No noise. No clunking. Gears look great.  No complaints. I have no idea how old the bearings are.  I figure there must be something I can do, I’m in this far. Perhaps I will install all new bearings and a pinion seal? 
 

I’ll get to reading and learn more about this before I go any further. I understand it. Why and how, it does what it does. I get tooth pattern and bearing pre-load. My knowledge however is just text book reading. In terms of hands-on diff rebuild experience, zipola. Never been in one myself. It’s a great model to learn on I figure.  Like my tranny, it’s time I learned. 
 

I just jacked up all 4 corners and used jack stands. I don’t have a proper hoist. The diff was easily manipulated by myself without the aid of anything. I just lifted it out by hand.  It felt heavier than my tranny. Could be because I actually had to get under the car and work with my arms up.  I stole the bathroom scale. It checked in at 57 lbs. I can’t recall for sure, but think the tranny was about 50lbs. 
 

Questions to come. 

 

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Edited by keithb7

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good looking  gears.  probably 4,1 to 1.   Talk to me if you decide to change the ratio.    These gear sets  gave very little trouble.

 

if it ran quietly, put a new seal on it and reinstall.  Use a Hypoid high pressure oil  80  os 90 SAE

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I’ll clean up the housing and see if I can find the stamped ratio. I do climb a fair hill back home. The 4.1:1 sounds like it may give decent performance. Saying that, I am up from the 201.7 engine to a 228. Hmm. 

Edited by keithb7

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the ratio will be written on the crown gear.

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Also have a look at the post labeled "Rearend"

I put a photo of where to look on the case for the ratio.

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Don't take it apart as Dave says if it's quiet...

Maybe do the pinion seal.

Carefully prick align punch the pinion nut, end of pinion shaft and yoke to re-assemble exactly as originally built.

The nut can be tightened a whisker beyond your prick punch just.so you can still get the cutter pin in.

I also use blue loctite on the nut threads.🙂

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Here's a pic of the gear ratio stamped into the ring (crown) gear. Once you get it cleaned up it should be easy to find. Also look for the ratio stamped on the outer housing.

I also agree with the others regarding leaving it together. If the gears look good after cleaning, and there is no abnormal bearing noises, I would replace the pinion seal and call it good.

You could practice measuring gear backlash and gear pattern if you want to learn a bit about differentials, but otherwise don't tear it down unless necessary.

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I cleaned up my crown gear and found 4.1-1 stamped on it. OK by me. I'll get out my dial indicator and measure backlash. Maybe I'll try and see if I can record the gear contact pattern. Then go from there.

 

I will indeed change the pinion seal at a minimum. Seems like reassembly as the bearings are now, will suffice based on everyone's input. I have not had much considerable driving time with the car yet. It's only been around the block on some test drives. So I guess I cannot say for sure there won't be any gear noise. I never noticed any in my brief test drives. The diff was easy to get out, and pretty quick. If I have to go back in, it's not a big deal. Wheels, drums, brakes, backing plates, axles, then the diff...It's not a daily driver, so I'm not concerned.

 

I think back to last May when I bought this car. It was barely running. It was very sick. Barely drivable. I've learned so much. The car is so much better now and running healthier! These old Mopars are war horses.

Edited by keithb7

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You don't want any deep pitted gear teeth for sure.

That issue if there were one can or will cause noise and possible tooth failure depending on depth and location of pits.

You probably are safe ....rear end doesn't look too bad.🙂

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I cleaned everything in solvent. Then put it in a hot industrial type dishwasher at work for 15 mins. I was able to inspect the gears better when clean. I cannot find anything of concern. Backlash measured in at .007 inch. Spec is from .006 to .010 inch. Seems like it’s all good to go back in. I’ll put then new pinion seal in when the diff assy is bolted back in the axle housing. Easier to keep the pinion from turning, by putting the wheels back on the ground. 
 

My 82 year old gears look pretty good!

 

 

 

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Beautiful looking g gear set!

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I was somewhat surprised by how much the centre thrust block can move around. I’m trying to understand its purpose. 
 

The axle gets pushed all the way in until it bottoms out against the block. Then we tap in the outer bearing cup. However we leave a few thou clearance by shimming the brake backing plate. Then tighten everything down. The centre block acts as a stop for the axle. Is that right? It wiggles around a little does it? Pushed back and forth, left to right during turns a few thou? Is that right? The few thou clearance we leave when we push in the cup is it to allow for heat expansion? 
 

Thanks. 

Edited by keithb7

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It’s kind of hard to explain in words, but if you think about it, there is only one bearing per axle, and as it is a tapered roller bearing you need to have a way to keep the two pieces in contact. When everything is fully assembled the axle shafts work together with a bearing at each end and a thrust block in the middle. When setting your shims you need to have both sides assembled and you are shimming the whole assembly. The thrust block allows the inner ends of the axle shafts to be able to spin independently while holding the outer bearing cones into theIr bearing cups. 

Edited by Merle Coggins

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