Rear end ratios

[52b3b Joe]

I know its been talked about before on the forum, but I can't seem to find it using the search feature (I think I might have even asked before but I can't remember). I would like to change from the 4.11 my truck has to a 3.73 ratio. I've never had a rear end apart (mine was already rebuilt when I bought it). I would like to just swap the center out (don't know the correct terms) using the same axles and housing. Basically just want a direct swap. I know certain year cars with certain engines will work. I just don't remember what they are. Also, how many spline is my truck? I am going to a junk yard full of old mopars early next week and I would like to get the right one. Just thought I'd ask before I spend money on the wrong one! Its a 52 b3b. Thanks in advance - Joe

[1952B3b23]

Joe im not to sure about your rear end question. But you did mention that you're going to a mopar junkyard. I also have '52 B3b and im looking for a bed for it. Could you let me know if you see anything that looks half way decent? Then i could call them up and see what they could do.

Thanks,

-Chris

[52b3b Joe]

Joe im not to sure about your rear end question. But you did mention that you're going to a mopar junkyard. I also have '52 B3b and im looking for a bed for it. Could you let me know if you see anything that looks half way decent? Then i could call them up and see what they could do.

Thanks,

-Chris

Yeah, I'll see what they have....I'm looking for bed parts too (mainly tailgate)

[tom'sB2B]

Try searching "rear diff swap" in the forum. There are a lot of good threads on this subject

You are looking for late 40's early 50's dodge, chrysler, desoto, plymouth cars.

The differential ratio is stamped on the bottom of the pumpkin. Not all the carriers are the same size and not all carriers have the same bolt pattern/number. You may have a 11 bolt battern or 10 on your truck. There are two different spline counts out there too.

You are going to have to pull the axle shafts out of any car before you can pull the differential. You may want to buy the axle shafts too so you have the right spline number (if there the right length), unless you want to disassemble your rear axle first to know your spline count

These are some of the question/problems I ran into and I'm still looking for one.

good luck

[wayfarer]

I think that is a very small ratio change considering the amount of work involved. What do you expect to gain?

http://ctny.audiworld.com/mark/s4/gears/gear_calc.html

[52b3b Joe]

I know its not much, I'm just trying to get the RPM a little lower for driving 55-65. I was just curious.

[Dodgeb4ya]

The 3.73 should be a good enough ratio to make you happy.

[Plymouthy Adams]

try this link........

http://www.angelfire.com/fl/procrastination/rear.html

 

 

 

Edited August 8, 2017 by Plymouthy Adams

[Merle Coggins]

I've said it here many times... I've got a 3.73 diff from a '50 Plymouth in my truck. I'm very happy with the results. I can cruise easily at 65-70 and can push 80 if needed.

I don't recall the spline count on my truck but it fit perfectly.

Merle

[52b3b Joe]

I've said it here many times... I've got a 3.73 diff from a '50 Plymouth in my truck. I'm very happy with the results. I can cruise easily at 65-70 and can push 80 if needed.

I don't recall the spline count on my truck but it fit perfectly.

Merle

So you didn't have to change your axle shafts with the 50 Plymouth?

[Merle Coggins]

So you didn't have to change your axle shafts with the 50 Plymouth?

Nope

[HanksB3B]

Merle,

How about the spring perches?

Hank

[Merle Coggins]

Merle,

How about the spring perches?

Hank

What about 'em? I only changed out the diff assembly. I've never had my axle removed from the truck.

[HanksB3B]

That's the way I want to do it too!

Thanks,

Hank

[B1B Keven]

Are the axle shafts the same length between cars and trucks?

Say '50-'50 or there abouts?

[Jeff Balazs]

Hi Guy's;

I am interested in this "partial" swap as well. It seems like a really good solution.

I have a 10 bolt 4.10 rear in my truck.

According to the parts book I looked at last night there was even a 3.73 set available for these? I suppose finding one of these would be equal to finding the holy grail.

My question is how do you go about finding the right donor these days?

I don't know much about old Mopars. They are not too thick on the ground in this area. I understand the ratio stamps but beyond that does potential donor axle housing look the same as the one I have? or as I suspect looks different and just matches up internally? If this is the case what model and year cars would the donor axle be in? Surely someone can shed some additional light on this.

Thanks, Jeff

[Young Ed]

Actually its the opposite. Externally they look very similar excluding the driveshaft pinion. Internally the trucks have more heavy duty parts. I swapped a plymouth 3.90 into my 46.

[HanksB3B]

I think if I asked Tim one more time it might turn into this senario. "Differentials...

So to save yourself some grief here are a few threads:

http://www430.pair.com/p15d24/mopar_forum/showthread.php?t=11168

http://www430.pair.com/p15d24/mopar_forum/showthread.php?t=25479

http://www430.pair.com/p15d24/mopar_forum/showthread.php?t=28798

Hank

[Merle Coggins]

I hear that the ratio is stamped into the housing at the top of the diff. Probably not the easiest place to see with the axle in the car. I would probably search late 40's - early 50's Mopars. The Dodge, DeSoto's and Chryslers with the semi-auto trans would most likely have the lower ratios, but I've heard that the larger 7 passenger sedans and limos may have a larger diff. The same would likely be true to the 8 cyl powered Chryslers. It seems that the 4.10 ratio was also common on the Plymouths of that era.

I got lucky. I happeded to be one of the first to read a post from a former member here. He was looking for a 4.10 diff for his '53 Plymouth Suburban (wagon) and he purchased an axle from a '50 Plymouth thinking it had a 4.10 diff only to find out it was a 3.73. He was asking if anyone had a 4.10 diff they wanted to get rid of. I had a parts truck with a 4.10 diff, so I offered to ship my truck diff to him and if it would work for him he just needed to ship his 3.73 diff back to me. It was an even swap and only cost us shipping. Before shipping I sent him some pics. Because the cars use a different type of driveshaft u-joint I ended up pulling off the drive flange before shipping my diff. He did the same with his car diff before shipping it to me. I replaced the input shaft seal and reinstalled my truck drive flange. Then it was just a matter of pulling the diff on my truck and bolting in the 3.73 diff. the only problem I had was with no bed on my truck, at the time, the driveshaft didn't have enough spline movement to get the u-joint clear of the flange. I added some weight to the frame to squat the springs and all was good. Here's some pics. I wish I had taken more of the process. One other thing I remember... When he got the diff from my parts truck (B-2-C) he mentioned that it had the "finer" spline for the axle shafts, which was perfect for his car. Unfortunetly I didn't make note of the spline count on my truck's axle, but the axles fit perfectly into the car diff.

4.10:1 Diff from my parts truck

A look at the differential assembly of the 3.73 car diff

A look at the differential assembly of the 4.10 diff from my truck

3.73 car diff installed in my truck's axle

Adding a "little" weight to the chassis to compress the springs so that I could connect the drive shaft.

[Young Ed]

Merle your pictures show the two different types I mentioned. Your truck one has that drum inside it.

[Jeff Balazs]

Thank you Merle;

That is most helpful. I like your weight!

So basically it looks the same from the outside and has the 3,73 ratio.

Sounds fairly straightforward assuming one can find the correct donor.

I will just have to beat Hank to it.......

Jeff

[HanksB3B]

try to find two. I'm off to the junkyard now with Merle's pictures in tow. (Except for the one with the Catepillar D8 bucket...too hard to explain)

Hank

P.S. I'll keep you in mind.

Merle: How lucky can one guy get.

Edited March 9, 2012 by HanksB3B

[Jeff Balazs]

try to find two. I'm off to the junkyard now with Merle's pictures in tow. (Except for the one with the Catepillar D8 bucket...too hard to explain)

Hank

P.S. I'll keep you in mind.

Hank; that's what I am worried about.......

Finding one is going to be pretty tough......finding two?

Jeff

[Merle Coggins]

Caterpillar? You shouldn't swear like that on this forum. It's an Esco bucket for a Volvo excavator. EC460B I believe.

These are the kinds of toys I get to play with every day.

[Desotodav]

I checked about 9 diffs that I have in the shed today trying to see if any one of them was a better ratio than the other one for use in my latest project. The manual indicates that there is supposed to be a perfectly stamped '4.1' on the flat section under the diff assembly - If only life were so simple!

What do you guys make of this mixed bag of numbers on some of my diffs?... I'm thinking that the extra numbers may be like a diff make/serial # of some sort. They all appear to have the number '4' in there somewhere...