56' Custom Royal Ring & Pinion

[rodney]

Repairing 3.73 and need help sourcing Ring & Pinion pn 1567900. 315 cu in 3 spd manual. Any suggestions appreciated.

[Loren]

There are loads of good used ones around.

The nice thing about Mopars is you can use parts from all the divisions.

Someone said a certain ratio was hard to find and in 10 minutes I found 4 in one year of one marque in one wrecking yard on eBay. I have seen new 3.73 on eBay. Just because they are new makes the sellers jack the prices up. A little more of a rarity is the 3.54, I bought a 56 Dodge 3rd member on aBay for $250 so they are around.

[rodney]

Thanks Loren, good advice. If I found a different gear ratio 3rd member, will this fit/swap out directly in my carrier? Dodge also used the 3.9, would that be a good option too? pros/cons?

[Loren]

When they change the ratio they sometimes have to change the differential. The third member or pumpkin stays the same.

If you want economy go to a 3.54. If you want acceleration go the other direction like 3.9 or 4.1.

If you choose to change your axle ratio be sure to grab the speedo gear from the donor car’s transmission ( 1 1/16 th 12 point socket fits).

3.73 is a good all around ratio so unless you want the car to perform differently I would stay with it.

 

The rear axle didn’t change until 1957. They call that one the 8.75....which is the diameter of the ring gear. Up to 1956 the ring gear was 8.25. The Mopar 8.75 is considered one of the most desirable axles there is, Second only to the Ford 9 inch in popularity. Basically the 8.25 is a very close cousin to the 8.75 so in my opinion it is a very good axle.

The 8.75 has more ratios and limited slip differentials so I don’t know why people who want to swap rear ends go with anything else. They are pricey, which is probably the reason. Unless you are making enough horse power to break your 8.25, I see no need to change it and I’ve never seen one broken, only worn.

An added plus, the 8.25 was used in all the Mopar cars, but all you need to change is the pumpkin. You don’t have to buy the whole axle, so that means you don’t have to even think about widths.

[Sniper]

6 minutes ago, Loren said:

When they change the ratio they sometimes have to change the differential. The third member or pumpkin stays the same.

You are going to have to clarify what this quote is saying.

 

Differential, third member and pumpkin are all the same thing.  Maybe you mean the housing varies with the application.

[Loren]

The differential is the rotating part that contains the differential gears and mount the ring gear. The differential gears allow the outside wheel to rotate farther when cornering.

The reason the differential can be different is the offset required for different ratios. When you make the pinion larger the ring gear has to move away from the pinion’s center. This is accomplished by making the ring gear thinner until it would lose strength if made any thinner. The fix is to move the flange on the differential. That’s why I said the differential could be different.

We use a short hand when describing the parts. Differential has been used for the entire axle when it actually is only the part containing the differential gears and mounting the ring gear.

Folks call the “differential carrier”, the pumpkin or 3rd member which are names which don’t appear in any shop manual.

Automotive terms do vary from place to place and for the most part depend on who invented what. Sometimes things were invented at the same time in different countries, then confusion reigns.

Some examples of who invented what, tapered roller bearings are measured in inches (because an American company invented them. Timkin) while ball bearings are measured in millimeters (a European company was the major manufacturer of them SKF) the threads on spark plugs are measured in millimeters for the same reasons even though they might have an inch wrench sized hex. Ford used pipe threads until superior spark plugs made their way from Europe.

 

Just to clarify my M.O. when determining if a particular part may fit another, I look for the associated gasket. If a differential carrier gasket fits across the Mopar range then it’s likely you can swap the carriers between axle housings. Stuff that doesn’t have a gasket means you have to start measuring and fit the various parts or dig into the parts book. I use A.B.’s online catalog a lot because they list all the cars side by side that fit a particular part like gaskets. It’s a kind of quick reference.

Sometimes a kit has a different part number between cars such as the king pins. I wanted to put 12 inch Chrysler brakes on my Plymouth but the Chrysler spindles had a different part number for the king pin kit. Digging deeper I found that the king pin was the same but the Chrysler had needle bearings on the top instead of a bushing. Therefore the Chrysler spindles would fit the Plymouth uprights just fine with the Chrysler king pin kit. A post on that project to follow.

[rodney]

Excellent info and kudo's for the explanation and your perspective. You have a lot of knowledge. As I am a little new to this, I had the same question of several names often used interchangeably to mean the same thing. I really just need the differential then, and I'll seek out 3.73 and keep it the same. Or if I'm lucky enough to find the ring gear and pinion and buy separately.

[kencombs]

31 minutes ago, rodney said:

Excellent info and kudo's for the explanation and your perspective. You have a lot of knowledge. As I am a little new to this, I had the same question of several names often used interchangeably to mean the same thing. I really just need the differential then, and I'll seek out 3.73 and keep it the same. Or if I'm lucky enough to find the ring gear and pinion and buy separately.

It's interesting how language can be such a problem on the 'net.  Rear end/differential terms seem to be specific to countries (Crown wheel or Ring gear?), regions (hogs head or center section), etc. 

The names in this pic are the ones I've always used. I couldn't readily find a pic of one with a drop out center section like Mopars and some Fords use.  That complicates things a little as the 'third member' is separate from the 'axle housing'.

The term differential can be used to specifically mean the internal assembly that provided the named action, or the drop out center section, or the whole shebang.   Now I'm confused, see what I mean?

 

 

In the Mopar, Ford 8 or 9" world, swapping that center section, third member or differential assembly is by far the most common and expedient way to change ratios or repair internal faults.  Changing ring and pinion gears requires a much more detailed setup procedure.

 

back in the day I Had  a little '65 Dart 273 high po.  It had the 8 3/4" and I had more than one third member complete with different ratios.  4.11 for weekend or local use, a 3.55 for most driving and a 3.23 or higher for long commutes or vacation travel.

 

Of course, changing it out was not the chore back then that it is now at this age.

[Loren]

I feel your pain Ken!

I can’t even imagine climbing under a car now days to set up a ring and pinion in one of integral housing axles!

Yet folks on this site crow about their new Ranger or whatever rear axle. Just seems to me to be going backwards and bragging about their “improvement”.

If a person does not have the skill/experience (or the time) to set up a ring and pinion, it’s not a blemish on one’s character to take a differential carrier to a shop that does. At least with a Mopar axle you don’t have to take apart half the damn car.

You might get the idea that really I like the original design and I do. The only other axle I would consider is the 8.75 and the only reason I’d change it would be if I somehow made enough horse power to break the 8.25 (and that only happens in my dreams!).

[Los_Control]

Whole lot of information to be learned about setting up a rear end here.

Whats the goal ... is it going to be original and taken to shows ... thats one way.

 

What if you installed a 7:3/4 rear end .... A great rear end if not giving it any power.  Like a flathead 6?

What if you went up to a mopar 8.75 rear end ... do you really need the strength for the engine you running?

 

@Lorenadvice is good. But finding good replacement rear ends or transmissions on older mopar are out of range for many.

They mentioned a Ford Ranger rear end which I think is a 7.25 ... and 4" to narrow. Nobody ever did that swap and not get laughed at.

 

Mopar rear ends are incredible finds today ... you have a mopar you going to need that rear end to be build specific.

 

https://www.facebook.com/marketplace/item/539265763775191/?ref=search&referral_code=marketplace_search&referral_story_type=post&tracking=browse_serp%3Ac52760e9-10fd-4f63-9e9e-55194bcea884

 

@Loren Just saying, I think this is a scam but I have no proof. While a decent rear end from a Ford or Jeep will run for $200 or less.

Everything works the same ... the Ford is stronger & it is cheaper. More availability.

Then we know Mopar never built their own rear ends in this crisis.

So we just using what works for us in our cars today. Yeah the $2500 car just send your pay pal and fix you right up.

[Sniper]

19 minutes ago, Los_Control said:

https://www.facebook.com/marketplace/item/539265763775191/?ref=search&referral_code=marketplace_search&referral_story_type=post&tracking=browse_serp%3Ac52760e9-10fd-4f63-9e9e-55194bcea884

 

I dunno, slant six car with a blown engine.  Probably all drums, 7.25 rear axle, no interior shots and though they say it's all there it is probably trash.  Probably no AC either, not even one that doesn't work.  Might be a $1000 car to me, $1500 if they throw in the trailer.  But I have what I need to get it on the road again as a beater daily driver.     

[wagoneer]

21 hours ago, Loren said:

When they change the ratio they sometimes have to change the differential. The third member or pumpkin stays the same.

If you want economy go to a 3.54. If you want acceleration go the other direction like 3.9 or 4.1.

If you choose to change your axle ratio be sure to grab the speedo gear from the donor car’s transmission ( 1 1/16 th 12 point socket fits).

3.73 is a good all around ratio so unless you want the car to perform differently I would stay with it.

 

The rear axle didn’t change until 1957. They call that one the 8.75....which is the diameter of the ring gear. Up to 1956 the ring gear was 8.25. The Mopar 8.75 is considered one of the most desirable axles there is, Second only to the Ford 9 inch in popularity. Basically the 8.25 is a very close cousin to the 8.75 so in my opinion it is a very good axle.

The 8.75 has more ratios and limited slip differentials so I don’t know why people who want to swap rear ends go with anything else. They are pricey, which is probably the reason. Unless you are making enough horse power to break your 8.25, I see no need to change it and I’ve never seen one broken, only worn.

An added plus, the 8.25 was used in all the Mopar cars, but all you need to change is the pumpkin. You don’t have to buy the whole axle, so that means you don’t have to even think about widths.

 

Hi @Loren

 

Are you saying that differential assembly in my 48 Windsor  similar to your 49 business coupe, or my 50 b2b is interchangeable with other higher ratio differential assemblies from Plymouth or dodge this solving one of the most frustrating limitations for many of us — highway cruising .

 

I didn’t think our older ones are 8.25 but something even smaller. Have you any offhand examples of differential assembly swaps you have yourself successfully completed or seen for our older mopars? That would be a valuable list. 
 

my b2b needs something higher than 4.1 (like 3.5 or 3.73), and my Windsor could use 3.5 to really be useful in fourth at highway daily speeds.

 

 

[Loren]

I have admit there’s somethings I do not know and won’t knowingly send you down the wrong path.

 I will tell you my experience. My Suburban and my Coupe came with 3.73 gear sets. My research found that the 8.25 axle had many ratios but the lowest numerical one is 3.54. Now that is not a big change but it is noticeable if you’re towing a trailer or other heavy loads. My Coupe is the lightest Mopar of 1949 and I don’t intend on towing a trailer so I am going to put that ratio in it for a trial. I have already installed an R10 Overdrive so this car will really have some highway gears!

So where do you find 3.54 gears? The default answer is eBay because it is so easy to shop. The differential carrier I got was from a 1956 Dodge and I paid $250 delivered for it. Somebody challenged me on that so back to eBay I went and found 4 potential candidates at one wrecking yard. You only had to ask one question to know what you were buying, does the donor car have an automatic transmission? If yes push “Buy it now”

Happily in looking at the ads I saw a 6 volt positive ground Delta Mark 10 ignition box. I wrote to the seller and they said they would sell it to me. Since I know a guy who can test and repair them I bought it. My repair guy said he had only seen one of them in 10 years! I think he was looking in the wrong place. Lol

Anyway, I do not have any experience in trucks or pre-1949 Mopars (with the exception of the 1940 and later transmission. I know you can get an optional ratio for second gear the old time hot rodders liked). Again if it uses the same carrier gasket then it will fit. If the axle splines don’t fit, then change the side gears to the ones from your old differential.

Hope that helps. Please report back and you will be expanding the knowledge base.

[rodney]

I found a used differential with 4.3 for sale, any thoughts on this gear ratio, for this car? Seems like a big change. I believe that was equipped for transmission with overdrive. I have 3spd.  Don't know if that makes a difference. Right now I'm trying to keep this car rolling and enjoy it for it's standard configuration. Doesn't have to be restored to exactness. With the 315 2bbl, is this gear ratio a good solution? Also, without the potential part in hand, how would I know if it uses the same carrier gasket?

[Loren]

4.3 to 1 is for drag racing.

on the highway your engine would be screaming.

A 3.73 is a good all around ratio. If you do mostly highway in flat country 3.54 would be better.

Any change will require the speedo gear from the donor car transmission.

If you need a 3.73 differential carrier complete (no rebuild needed) they are around. The one in my coupe has 38,000 miles. If you want one to have rebuilt I have one disassembled and cleaned too. If you want a 3.54 I can tell you where to find one (they’ll have 3.73s as well).

[rodney]

Prefer 3.73 then. Sure, any sources where I can find one would be helpful. I don't mind rebuilding, but let's first focus on complete carrier.

[Bryan]

On 7/29/2021 at 10:44 PM, Loren said:

4.3 to 1 is for drag racing.

on the highway your engine would be screaming.

A 3.73 is a good all around ratio. If you do mostly highway in flat country 3.54 would be better.

Any change will require the speedo gear from the donor car transmission.

If you need a 3.73 differential carrier complete (no rebuild needed) they are around. The one in my coupe has 38,000 miles. If you want one to have rebuilt I have one disassembled and cleaned too. If you want a 3.54 I can tell you where to find one (they’ll have 3.73s as well).

I was trying to understand more about my car, a 1948 Dodge sedan.   When I look at Rock Auto, it lists an 8.75 carrier bearing.   My service manual doesn't even mention a ring gear size..nor any info on pinion gear end spline numbers, inner axle spline numbers, nothing except gear ratios. Where do you find info that states ours is a 8.25 R & P?  In a couple of years I probably would change mine to a 3.54 ratio if I could.   What does one search for on Ebay, and know it's right?   And lastly, what the heck is a 7 passenger sedan?  3 in front, stuff 4 in back?

[Sniper]

Too many parts listings these days are inaccurate and those inaccuracies are from the manufacturer, the data is wrong, incomplete or misleading in their catalogs.  The parts store, Rock Auto, NAPA, whatever, isn't going to know that and can do nothing to change it.

 

Best bet on those bearings is to get the Mopar part number and cross that rather than go by application.  So I did just that.  All Chrysler products from 1937-1954 use the same differential carrier bearing, as it's called on the RA screenshot, PN 698404.

 

The BCA listing shows that 698404 as an "Alternate/OEM Part Number" it crosses to.  So while the RA listing for the part is accurately done for your vehicle the notes in the parts listing themselves are inaccurate, while it will indeed fit the 8.75 it also fits a lot of other Mopar applications, includiing our axles.

 

Oh, for the answer to the question of 7 passenger, 2, 2, 3.  2 front seat, 2 in jumper seats, 3 in back seat.

[Bryan]

Thanks..know it sounds silly sometimes but I just don't know..  Was just looking thru Ebay and ran across this, but wish I could find a 3.54. Not ready yet, got too much ongoing now.  NOS Mopar 1946-1961 Plymouth Dodge Desoto Chrysler 8-1/4" 3.90 Ring and Pinion | eBay

[Sniper]

Oh trust me I have learned the hard way.  Years ago, when I got out of the Navy I was a parts store manager and I tried to get a part application corrected, to no avail.  At least back then we also had the books and could annotate them.

[James_Douglas]

I am going to suggest a couple of things. One is that the literature om MOPAR's consistently states that they came out with the 8-3/4 inch rear end (Ring Gear) in 1957.

 

This is something of a mistake. The ring gears in my 1947 Desoto Large Wheel Base car are in fact 8.75 inch in diameter. As was the Chrysler Town and Country and the Imperials. Some of the Dodge trucks also used them.  They are NOT interchangeable with the later 8.75 rear-ends.

 

It is correct that nomenclature can get in the way of discussions.  Technically...

 

1. The "Housing Assembly" is the steel housing the holds everything. We commonly call this the rear-end. We should all call it "The Housing Assembly"

2. The "Carrier Assembly" is the cast iron part that holds the ring and pinion gear and their bearing and many of us call it the pumpkin.

3. The "Carrier Case" is the part that the ring gear bolts to.

 

One thing Loren said I think needs clarification. On my Housing assembly, the thing that MOPAR did to deal with the different thickness of the ring gears was to have TWO different Carrier cases. One fits the 3.73 and numerically lower ratios and the second fits the 3.91 and numerically higher ratios. I found out the hard way last month when I had my very hard to get 3.36 Carrier Case right next to my 3.91 Carrier Case. The bolting flange is in a different place to make up for the ring gear thickness difference. Also, on these units you have to slip the Carrier Assembly in with the ring gear parallel to the floor and rotate it. It will not go straight in.  That is why they used bolts and not studs on this particular Housing Assembly.  I cannot speak to the post 1955 issues. My '64 Chrysler 300's all had 3.36 and I never changed them. With Ram Induction...why would one except for all out racing!

 

I also have the tools to set up the rear end myself here. I will be doing that soon on the NOS 4.3 set I have. I know people said that this is only a "drag race" gear but I would qualify that to folks with V8's. With my 5000 pound Desoto and the flat 6, I am finding I like the 4.3. With the overdrive it is fine. If I still had the M6 in it it would be too much I think on the freeway.

 

Now the above said my '49 Convertible is about 800 pounds lighter and has the same 251 in it. With a 3.91 rear-end. It will go up a hill just fine whereas the big Desoto could barely make it without down shifting. It all comes down to HP to weight with the small engines as to what ratio is best suited.

 

James