1954 Plymouth Rear Axle Swap

[rahowell154]

I inherited a 1954 Plymouth 2dr hardtop several years ago and now have the time and money to start making some modifications. I plan on having the flathead rebuilt and have purchased an Edgy head. I plan on installing a dual intake manifold, converting to 12 volt, and rebuilding the stock transmission. I keep reading that in order to achieve more comfortable highway speed a rear end swap or an overdrive transmission would be beneficial. From what I can see, a rear end swap would be more cost effective. I'm looking at possibly trying to find a Ford Explorer rear end but need advice on the best gear ratio. It looks like these rear ends have several options; 3.27, 3.55, 3.73, and 4.10. What ratio would give me what I'm looking for and what year(s) of Explorer should I be trying to find. Any advice would be greatly appreciated.

[Plymouthy Adams]

with Indiana being fairly flatland....the 3:55 would be a good choice.....the 3:27 would like be needed a bit of clutch feathering.  Your driving habits will also be part of this...if you rather heavy on the foot on takeoff....you may want to keep what you have....terrain of operation and driving habit only you can rightly decide what is best.....as for the year Explorer...sorry others will pop in for that maybe as I still work with Mopar retrofits...and don't ask which Mopar as these are a bit beyond stock retros.

[Booger]

go to carnut.com/specs/rear.html for axle widths

R10 ODs are gold. good luck

Edited September 15, 2021 by Booger
speling

[Loren]

I am the devil's advocate here.

Why do folks want to work so hard changing rear ends?

Your 54 very likely has a 3.73 ratio stock. You can get a 3.54 and I've heard that there are 3.26 ratios are available for the Mopar 8.25 rear axle.

Find the ratio you want and just swap the Differential Carrier NOT the whole damn rear axle.

No engineering, no welding just a parts swap and an easy one at that!

 

A Plymouth Overdrive transmission is transformative! They have a 30% Overdrive where the others are 28%.

They are Automatic and very easy to drive. Again, no engineering, no cutting, no welding, just bolt the damn thing in and wire up the throttle switch, the relay and GO!

 

When you find a Differential Carrier be sure to get the speedometer gear from the transmission. It will fit the Overdrive and that will be one less thing you have to worry about. If you keep your car ALL MoPar then all you have to do is swap parts. No engineering, no cutting, no welding and no Bravo Sierra!

For alternate ratios to fit your 54 axle look at the spec sheet for any Mopar 1940-56 (V8s and automatics are most likely candidates). For Overdrives 1952-59 (unless it has been retrofitted to an earlier car 1940 or later) Overdrive prices are high but not prohibitive. Do not spend over $1,100 to 1,200 depending on condition and extra parts. Axles will cost $150 to 250 from a retail wrecking yard. FREE from someone doing a garage clean up.

Just sayn'

[Sniper]

Because no matter how hard you polish that stock rear axle you are still stuck with very old tech drum brakes on it.  They are neither self adjusting nor self energizing.  If you are planning to cruise the freeways odds are real good that at some point some clueless driver playing with their cell phone will end up causing you to have to brake real hard.

 

Not to mention parts price and availability is much better on a newer axle.  Same exact reasoning for me to add front disc brakes to my 51 rather than try to hunt up some 12" drum others are so fond of. 

 

Our rides have a lot of designed in defects that can be addressed using newer parts.  The drum brake system I mentioned.  Then there is the bump steer caused by having one real short tie rod assembly and one real long one.  Wheel hop in the rear is real, real bad.  The front shock setup is mediocre at best.  Trans mounted parking brake is no longer used for a reason. 

[Plymouthy Adams]

these old cars are not necessarily flawed design....just an earlier one and at the time they were top line....but as we run the cars harder in more traffic and contend with other idiots out and about....the margin for safety is thin and while there is not a need to upgrade IF you keep your stock at peak performance....the overall ease of maintenance, as Sniper said the cost and availability for an improved system has merit.  Loose a shoe 300 miles from home and or blow a cylinder......you pretty much stuck a bit unless you carry spares or top line towing on a road service policy.  I have my disc on standby for when the time comes to service mine...until then...these are good....I rarely am in traffic.  I will fault no one for keeping it stock anymore than I will for those that upgrade.....I find fault with those that try to push their philosophy on others as being the absolute method...

[Booger]

3 hours ago, Loren said:

I am the devil's advocate here.

Why do folks want to work so hard changing rear ends?

Your 54 very likely has a 3.73 ratio stock. You can get a 3.54 and I've heard that there are 3.26 ratios are available for the Mopar 8.25 rear axle.

Find the ratio you want and just swap the Differential Carrier NOT the whole damn rear axle.

No engineering, no welding just a parts swap and an easy one at that!

 

A Plymouth Overdrive transmission is transformative! They have a 30% Overdrive where the others are 28%.

They are Automatic and very easy to drive. Again, no engineering, no cutting, no welding, just bolt the damn thing in and wire up the throttle switch, the relay and GO!

 

When you find a Differential Carrier be sure to get the speedometer gear from the transmission. It will fit the Overdrive and that will be one less thing you have to worry about. If you keep your car ALL MoPar then all you have to do is swap parts. No engineering, no cutting, no welding and no Bravo Sierra!

For alternate ratios to fit your 54 axle look at the spec sheet for any Mopar 1940-56 (V8s and automatics are most likely candidates). For Overdrives 1952-59 (unless it has been retrofitted to an earlier car 1940 or later) Overdrive prices are high but not prohibitive. Do not spend over $1,100 to 1,200 depending on condition and extra parts. Axles will cost $150 to 250 from a retail wrecking yard. FREE from someone doing a garage clean up.

Just sayn'

you have spoken the truth, Kimosabe

[Young Ed]

4 hours ago, Loren said:

I am the devil's advocate here.

Why do folks want to work so hard changing rear ends?

Your 54 very likely has a 3.73 ratio stock. You can get a 3.54 and I've heard that there are 3.26 ratios are available for the Mopar 8.25 rear axle.

Find the ratio you want and just swap the Differential Carrier NOT the whole damn rear axle.

No engineering, no welding just a parts swap and an easy one at that!

 

A Plymouth Overdrive transmission is transformative! They have a 30% Overdrive where the others are 28%.

They are Automatic and very easy to drive. Again, no engineering, no cutting, no welding, just bolt the damn thing in and wire up the throttle switch, the relay and GO!

 

When you find a Differential Carrier be sure to get the speedometer gear from the transmission. It will fit the Overdrive and that will be one less thing you have to worry about. If you keep your car ALL MoPar then all you have to do is swap parts. No engineering, no cutting, no welding and no Bravo Sierra!

For alternate ratios to fit your 54 axle look at the spec sheet for any Mopar 1940-56 (V8s and automatics are most likely candidates). For Overdrives 1952-59 (unless it has been retrofitted to an earlier car 1940 or later) Overdrive prices are high but not prohibitive. Do not spend over $1,100 to 1,200 depending on condition and extra parts. Axles will cost $150 to 250 from a retail wrecking yard. FREE from someone doing a garage clean up.

Just sayn'

If the original poster was just looking for some top speed I'd agree with you. However with their large list of other mods why keep the stock diff and brakes? Disks up front and maybe even in the rear sounds appropriate to me. 

I've got a 48 plymouth with a 3.73 swapped in and an overdrive too. I've also got a 47 dodge 1/2 ton with a modern rear and a 5spd.

[Loren]

Being the Devil's advocate here I fully get the position of "new-er" vs the stock old.

Just remember Newer will become Old and obsolete very quickly and then where will you get parts?

Who is going to keep track of all your mods? Let see an axle from here, a transmission from there, brakes from some other place and pretty soon nobody will know what you have.

Rather than do the detective work to figure out what something is, the mechanic in 2050 will likely junk your car. After all where in the parts book will he find what you've put in the car?

Disc brakes are not the panacea people think they are. I've driven cars that had them and found them horribly lacking. Some cars with 4 wheel disc brakes I've driven can not be stopped smoothly. Their stopping power is not linear and can't be modulated. Its always herky jerky.

My Dad refused to buy a new car after they changed from the Lockheed style brakes to the Bendix style "self energizing" type because he said they locked up. I think he was right in that the self energizing feature deadens the feel and the modulation you CAN (I didn't say DO) get from the Lockheeds.

YES, working on the older stuff takes some knowledge, tools and skill but isn't that what the hobby is about? Honing your knowledge and skill?

There's not much bragging rights to "I put new pads in my Disc brakes this weekend" vs I got my 12 inch Chrysler brakes to stop straight and quicker than your Disc Brakes.

I am old school of course. The old car hobby to me is about bringing back the simplicity of 1950s. No electronics, no plastic. I grew up in Southern California and my Dad knew all the guys who hot rodded before the war and came back from it with new knowledge and skills. SoCal was THE car crazy place then. Getting the most from those old cars was the science of the day and those guys did pretty good. Lee Petty found a 49 Plymouth could beat a new  V8 Oldsmobile in a stock car race. On paper OHV V8 beats L head 6 every way you look at it but he found a way to make a living doing it. (and others followed him)

Everything that I have suggested is in the Mopar parts book.

Everything that I have suggested is less work to get the same results.

Nothing I have suggested will reduce the value of a car.

All of the replacement parts are being reproduced right now and thus MAY be available in the future.

That can't be said for the strange parts suggested by others.

There is no standard for performance with strange parts and components.

Going from a Plymouth 3.9 final drive to a 56 Dodge V8 automatic 3.54 final drive is a known quantity.

Going from a Plymouth 3 speed to a 30% overdrive Plymouth transmission is a known quantity.

Going from Plymouth 10 inch brakes to DeSoto 11 inch or Chrysler 12 inch brakes is a known quantity.

There are entrees in the Plymouth service manual regrading the service of all these components.

When any of them start making a funny noise you can inquire at this very site.

With a strange part or component, who you gonna call?

Ghostbusters?

Just sayn'

This is how I do my car and if asked this is what I will tell you.

Your car can and should be your own. Do what you want.

 

[dwest999]

I appreciate everyone's passion on this forum... it's such a great asset to all of us... good and respectful debate... thank you Loren, PA, Sniper, Ed, and Booger.

[rahowell154]

I appreciate everyone's input. It has provided me options to think about. Booger, the link you provided was very helpful if I decide to go through with the explorer rear end option. Prior to making this post I attempted to search this topic on the site using various terms and the search results also had a ton of unrelated topics and I really couldn't find the answers I was looking for. I apologize for taking part of beating a dead horse if that it is what it seemed. Thanks for all the replies! I'm new to the site and the hobby, just trying learn as much as I can.

 

The plymouth I inherited was purchased by my father a few years prior to him passing away. It is the same year, make, model, color scheme, etc. that he owned when he married my mother. My son and I are making this a project together. l'm looking forward to making memories with a vehicle holds such sentimental value. 

[Sniper]

14 hours ago, Plymouthy Adams said:

these old cars are not necessarily flawed design

 

When they were built, maybe.  Though it could be argued otherwise to some extent. 

 

Every issue I mentioned was known to the industry in general well before. 

For example, the earliest SAE paper I can find on self energizing brakes dates from 1928.

 

I suppose you could say they were built as cheaply as could be gotten away with.  Today if you want to play on the roads, especially the highways, that philosophy won't cut it. 

 

 

 

 

[bamfordsgarage]

Thirty-five states, three provinces, Atlantic Ocean, Pacific Ocean, Gulf of Mexico, Beaufort Sea, Pikes Peak, interstates, blue roads, dirt roads, no roads, deserts, -35F, 95F, heavy traffic, no traffic, whatever…

 

Stock brakes, stock suspension, stock rear end, 6-volts +ve ground and original engine.  
 

Definitely not for everyone but it can be done — and it sure works for me ?

 

 

[Happy 46R]

Seen the car and the pictures so what he says is true. I keep my 46 Coupe stock because I want an authentic ride and feel. I am sure there are those that disagree with that sentiment but I am sure there is some bent sheet metal with all the bells and whistles as there is with original parts. Personal choice never is wrong. 

[Los_Control]

21 hours ago, rahowell154 said:

I keep reading that in order to achieve more comfortable highway speed a rear end swap or an overdrive transmission would be beneficial. From what I can see, a rear end swap would be more cost effective.

My humble opinion, the 3:73 gears is the sweet spot for a stock 218/230 flathead/3spd Very possible you already have a 3:73.

I would inspect the brake drums on it. They are not so easy  to find. I know of one person making new ones, seems they were $300-$400 each. Shoes are available along with hydraulics. You can buy used drums.

 

So that was my deciding factor, the condition of the drums ... if bad replace the rear end now.

If good and mine are, then repair the brakes, replace any obvious leaking seals, use the rear end as is. Now concentrate on the motor/trans/clutch/steering and drive it.

Then make a educated  decision from experience if you want to swap the rear end for better gearing.

 

You want your  rear gears to  match your engine. Since you are going with a edgy head, dual carbs .. headers I assume, what about a custom grind cam or ???

Your stock rear end will give you a baseline or a starting point, you may find you want 3:55 I have heard of some using 3:23.

If you find a overdrive trans, kinda spendy ... you may now want 3:90 gears for it.

 

A T-5 trans from a S-10 or mustang is a pretty common swap, not nearly as expensive as a good usable factory overdrive.

Might be a good swap while you have the motor out. Again the stock rear end may be perfect already.

 

So, this is why I am keeping my stock rear end for now.

[Booger]

4 hours ago, rahowell154 said:

I appreciate everyone's input. It has provided me options to think about. Booger, the link you provided was very helpful if I decide to go through with the explorer rear end option. Prior to making this post I attempted to search this topic on the site using various terms and the search results also had a ton of unrelated topics and I really couldn't find the answers I was looking for. I apologize for taking part of beating a dead horse if that it is what it seemed. Thanks for all the replies! I'm new to the site and the hobby, just trying learn as much as I can.

 

The plymouth I inherited was purchased by my father a few years prior to him passing away. It is the same year, make, model, color scheme, etc. that he owned when he married my mother. My son and I are making this a project together. l'm looking forward to making memories with a vehicle holds such sentimental value. 

that is so freakin cool. Dads looking down on you with joy