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1947 Plymouth p15 drum brake upgrade


Pooshoe

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I have a 1947 Plymouth speical deluxe p-15 and I wanted to upgrade my drums to bigger front drums . I had a 1948 Chrysler Windsor that had bigger drums and I did not know if something like this could be done or not? Thanks

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I personally approve of this upgrade!

Thanks to Chrysler's commendable policy of interchangeable parts and continuity of design you can in fact up grade to 11 inch or even 12 inch brakes.

My copy of "Plymouth 1938-1954 Part Interchange Guide" gives you lots of options you might not have thought of.

Also Andy's has a chart of bearings and seals you can check for free to see what fits.

Just be aware that 12 inch drums might require different wheels than the 15 inch wheels found on 1949-1954 Plymouths.

 

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I'm pretty sure that the backing plate bolt spacing on the spindles is different from one size to another so you'd need everything from the spindles out including spindles. I'd think a disc conversion would be easier, more effective, and probably less expensive unless you have a donor car.

Edited by MackTheFinger
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38 minutes ago, MackTheFinger said:

I'm pretty sure that the backing plate bolt spacing on the spindles is different from one size to another so you'd need everything from the spindles out including spindles. I'd think a disc conversion would be easier, more effective, and probably less expensive unless you have a donor car.

 

I know everybody has an opinion on drums vs disc brakes.

On some collector cars you have very little choice as to brake system improvements. Sometimes it's a challenge just to make them drivable.

One of the things that has bugged me is picking a good improvement, then not being able to find the replacement parts or what they came off of originally.

I've seen many posts about "What kind of rear end and brakes are these?"

The neat thing about the Plymouths I know and love (1949-54) they use hydraulic parts that are readily available (reproductions of course) and are the same for all the MoPar cars. So if you can find a 1951 DeSoto 12 inch drum set up it's no challenge to repair or restore it and they really stop good.

 

Being an old racer I've noted that drum brake cars race in a class of their own with other flatheads and 6 cylinders. Once you modify a car with disc brakes it runs with other modernized cars which includes OHV V8s. That may mean next to nothing for the vast majority of people but it is a consideration of mine. (example: La Carrara Pan Americana revival of the Mexican Road Race)

On my Plymouth (a 1952 Suburban) I have gone out of my way to keep it all period MoPar (within 5 years update or backdate). The idea being that it is an example of what could have been done during the time it was considered a "late model" car. A Hot Rodder's Hot Rod of the 1950s.

 

Cutting frames for better steering and brakes are only one step away from installing an SBC V8. When you do that it really changes the character of the car and takes away from the charm of it. For my money it would be better to let Detroit do the work and just order a new car. You'll get more for your money and one day in the future your kids will own a "collector car" that was once their Dad's. (think of what a nice Challenger will be worth in 20 years!)

 

The Old Car hobby is all about having fun. Do what gives you the most enjoyment. I've been able to buy lots of highly desirable parts from guys who went the modernization route...cheap! So I do appreciate their version of the hobby. To say a disc brake conversion is easier, more effective and less expensive may or may not be true. Consider the many posts regarding "residual pressure valves" and "dual circuit master cylinders" on this site alone! If there is that much handwringing over disc brake conversions it does not seem easier and less expensive to my mad mind.

Finding the right drums and backing plates isn't an engineering project. You're not changing the design at all. Just the size of the brakes. Part of the fun is the hunt!

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5 hours ago, Loren said:

 

I know everybody has an opinion on drums vs disc brakes.

On some collector cars you have very little choice as to brake system improvements. Sometimes it's a challenge just to make them drivable.

One of the things that has bugged me is picking a good improvement, then not being able to find the replacement parts or what they came off of originally.

I've seen many posts about "What kind of rear end and brakes are these?"

The neat thing about the Plymouths I know and love (1949-54) they use hydraulic parts that are readily available (reproductions of course) and are the same for all the MoPar cars. So if you can find a 1951 DeSoto 12 inch drum set up it's no challenge to repair or restore it and they really stop good.

 

Being an old racer I've noted that drum brake cars race in a class of their own with other flatheads and 6 cylinders. Once you modify a car with disc brakes it runs with other modernized cars which includes OHV V8s. That may mean next to nothing for the vast majority of people but it is a consideration of mine. (example: La Carrara Pan Americana revival of the Mexican Road Race)

On my Plymouth (a 1952 Suburban) I have gone out of my way to keep it all period MoPar (within 5 years update or backdate). The idea being that it is an example of what could have been done during the time it was considered a "late model" car. A Hot Rodder's Hot Rod of the 1950s.

 

Cutting frames for better steering and brakes are only one step away from installing an SBC V8. When you do that it really changes the character of the car and takes away from the charm of it. For my money it would be better to let Detroit do the work and just order a new car. You'll get more for your money and one day in the future your kids will own a "collector car" that was once their Dad's. (think of what a nice Challenger will be worth in 20 years!)

 

The Old Car hobby is all about having fun. Do what gives you the most enjoyment. I've been able to buy lots of highly desirable parts from guys who went the modernization route...cheap! So I do appreciate their version of the hobby. To say a disc brake conversion is easier, more effective and less expensive may or may not be true. Consider the many posts regarding "residual pressure valves" and "dual circuit master cylinders" on this site alone! If there is that much handwringing over disc brake conversions it does not seem easier and less expensive to my mad mind.

Finding the right drums and backing plates isn't an engineering project. You're not changing the design at all. Just the size of the brakes. Part of the fun is the hunt!

 

I must have overlooked the part where the OP mentioned he was running in the Pan American. I wish him well. The only pertinent information in your initial response was the possibility of needing different wheels. My response was intended to hopefully provide information  beyond, "Oh, yeah! Lots of Mopar parts will work." Your second response mentions problems identifying mis-matched parts and then recommends Desoto brakes for a Plymouth. While they are from the same manufacturer and some parts are interchangeable from Plymouth to Desoto it could still cause some head-scratching if the next owner doesn't possess an enyclopedic knowledge of Chrysler products. So while I understand your position and agree with some of your observations I'd respectfully recommend you keep your lectures to yourself. Self-aggrandizement is never an endearing quality.

 

 

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I think I’m going to look for Chrysler wheel assembly from the junk yard and rebuild them . I’m pretty sure if I got the hole spindle assembly I should be fine.
Disc brakes are the way better up grade but I don’t want to deal with a master cylinder and Portioning valve just never had luck with them . So if 12 Chrysler are “bolt on” then that’s the way I’m going to go.

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15 hours ago, Pooshoe said:

I think I’m going to look for Chrysler wheel assembly from the junk yard and rebuild them . I’m pretty sure if I got the hole spindle assembly I should be fine.
Disc brakes are the way better up grade but I don’t want to deal with a master cylinder and Portioning valve just never had luck with them . So if 12 Chrysler are “bolt on” then that’s the way I’m going to go.

 

I found a set of DeSoto drums and backing plates that are 12 inch for $250. I am going to pick them up Monday. My research says 1950 to 1954 should work (except the Station Wagons. I think they use heavier bearings) I am told Chrysler Windsor 6 cylinder brakes fit as well. Once I have them in hand I will take some measurements and see what is possible. There are some parts suppliers out there that think these things are made of gold. I saw one outfit asking $600 for a "reconditioned" brake drum! MoPar drums have a center piece riveted to them that makes them MoPar only. The drum itself is a pretty standard affair, so you could drill out the rivets and replace just the drum. I have a chart of standard drums but I won't limit myself to one brand. So more to come...

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This photo illustrates why I believe Chrysler/DeSoto brakes might be a good solution for an upgrade.

I am way early in my project but I can see some merit in it. Compared to the Plymouth 10 inch drums these things are massive!

The rears should be an easy swap, the fronts may require some work, I just don't know yet as my Plymouth is buried in storage. Excavating it is my project for next week.

The donor car in this example was a 1950 or 51 Chrysler Windsor. I had forgotten how huge these things were! Looking it over I remembered my Great GrandFather had one which I rode in once to go get my first bicycle. He had a long narrow driveway so he must of had some skills to manage that big car!

D80DC5E1-C0C6-491F-B6E7-D11BB768E273_1_201_a.jpeg

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I believe that you will find if you use the hubs and drums that the Chrysler wheel bolt pattern is 5"  Dia. versus the 4 1/2" Plymouth.

 

New/used wheels 5" or re-drill and tap to smaller pattern if possible?  Wheel center hole opening size the same size?

 

DJ

Edited by DJ194950
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I went out and checked just to be sure. The bolt pattern and center hole are exactly the same.

There is still a question about the Plymouth wheels fitting over the Chrysler/DeSoto brake Drums, but I've never heard anyone mention that.

I am not keen on changing wheels on this car as it might change the appearance more than I'd like. It's going to be somewhat of a "Q-Ship" in character.

 

When I went to get the parts the temp was 109 degrees, so I wasn't into swapping parts they had laying around to make sure stuff would fit.

After playing around trying to get the rear drums off I determined I need my "Hot Wrench" to break the rusted taper loose.

I ended up buying the whole rear axle just to get outta there. The car had been stored without wheels in a wet or flooded area so there was plenty of rust.

At first I was disappointed to see it had a 3.9 ratio but then it's one more ratio to have on the shelf. My tape measure says it is nearly the same width as the 54 Plymouth rear axle I have.

 

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  • 2 weeks later...
  • 2 weeks later...

The drums in the photo are 12 inch.

I got everything sand blasted and painted (drums and backing plates and spindles). The hardware I wire brushed and then soaked in "Evapo-Rust" solution.

I finally got my order of parts from a well known supplier. They kept a record of my car and when I ordered 12 inch brake shoes they called me up to make sure I knew what I was ordering. When I got the box one of the wheel cylinders had fallen out thru a hole and I was sent Plymouth 10 inch shoes! So now I am waiting for the second round.

In cleaning the hardware I decided I was going to replace all the split ring lock washers (as everyone I looked at had a crack in it) and all the common nuts (6 qty). There are some special nuts but they looked good (4 qty). Easier said than done! At first I thought they were 1/2 x 20, not so. Locally you can get 1/2 x 20 but the anchor bolts are bigger than 1/2 and smaller than 5/8....they're 9/16 x 18 so I ordered them from McMaster-Carr.

The lug bolts are 1/2 x 20 thread both right and left hand, so I have taps and dies to clean them up. I also labeled the drums so as not to waste time guessing what side they go on.

Once I get the brake shoes I'll turn the drums and arc the shoes to fit.

The Chrysler Windsor weighed about 600 lbs more than the Suburban and was intended to have better brakes as a premium car should. So I am expecting a nice improvement. 

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Hmmm

Unsprung weight isn't thought of much when it comes to passenger cars. (and not at all in Pickup trucks judging by the weight of the steel spare vs the aluminum road wheels)

There is certainly a little more weight going up and down with the wheels but not as much as a disc brake conversion.

It's my opinion the suspension is plenty strong enough to handle the extra weight. Where it might show up is in the action of the shock absorbers.

Wheels and tires make up the majority of variables in unsprung weight. A change in brand of tire or size can really change the weight. Then there are the wheels.

I've seen an out of balance tire overheat and explode a shock (luckily it didn't catch fire).

I'd say the difference between 10 and 12 inch brakes can't be more than a pound or two and less than Disc Brakes. If no one has complained about the extra weight of Discs then I think we're safe. Besides I have great faith in the engineering of the ZSB team.

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5 hours ago, Loren said:

Hmmm

Unsprung weight isn't thought of much when it comes to passenger cars. (and not at all in Pickup trucks judging by the weight of the steel spare vs the aluminum road wheels)

There is certainly a little more weight going up and down with the wheels but not as much as a disc brake conversion.

It's my opinion the suspension is plenty strong enough to handle the extra weight. Where it might show up is in the action of the shock absorbers.

Wheels and tires make up the majority of variables in unsprung weight. A change in brand of tire or size can really change the weight. Then there are the wheels.

I've seen an out of balance tire overheat and explode a shock (luckily it didn't catch fire).

I'd say the difference between 10 and 12 inch brakes can't be more than a pound or two and less than Disc Brakes. If no one has complained about the extra weight of Discs then I think we're safe. Besides I have great faith in the engineering of the ZSB team.

I just wondered about it because I am also on a forum for the Dodge Journey, as that is our family car, and it is a common 'customization' on especially the first year Journeys, to put on larger brakes & larger wheels.  (We have that first year model - the 2009, actually built & sold by mid 2008.)  They do talk about unsprung weight on that forum, and some at least say that it is hard on the struts, etc.

As far as aluminum vs steel wheels, I have an aluminum trailer, and I compared weights of an aluminum wheel as opposed to a steel one, and I was surprised how very little difference there was. 

So anyway, just wondered.  I hadn't thought about the additional weight in a disc conversion (and don't have any interest in it anyway).  I'm planning to stick with the 16" wheels (originals), so I assume that your larger brakes would fit inside those wheels just fine, correct?

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16s make it even better as there is more cooling space around the drums.

With 15s it is a close fit but they do fit.

I am sure you don't plan to haul trailers in the mountains or race the car so you could get by with 15s if you had to (for tire availability).

 

With a disc brake car the bigger the discs the better and when you go bigger you need larger wheels to fit them into.

You know large diameter wheels are for styling only, when they still put small discs inside.

Bigger discs are also heavier (along with the wheels to accommodate them) so that's where the unsprung weight discussion starts.

Disc brakes are more weight dense than drums and I think 12 inch are about as big as they go for domestic passenger cars.

Personally I am not fond of strut equipped vehicles. The reason they exist is they are cheap to build. They do not make a better handling car.

Struts have all sorts of issues like binding when they should be responding to road undulations.

Factory struts most of the time can be drained and heavier oil can be put in them. Once they've been changed to the sealed cartridges that option is gone.

Still I wouldn't worry too much about unsprung weight. Automobiles are compromises on every level. You trade suspension longevity for better braking and that's a good deal.

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  • 1 month later...

I have done this several times.  Plymouth wheels fit 11 inch drums  but I had trouble with the 12 inchers,  and had to use Chrysler wheels

 

 Spindle must match the drum size  . Cylinders are the same.   King pins are the same.

 

  Be sure to adjust toe in after changing spindles.

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  • 2 weeks later...
  • 1 year later...
On 9/9/2020 at 3:01 AM, Loren said:

The drums in the photo are 12 inch.

I got everything sand blasted and painted (drums and backing plates and spindles). The hardware I wire brushed and then soaked in "Evapo-Rust" solution.

I finally got my order of parts from a well known supplier. They kept a record of my car and when I ordered 12 inch brake shoes they called me up to make sure I knew what I was ordering. When I got the box one of the wheel cylinders had fallen out thru a hole and I was sent Plymouth 10 inch shoes! So now I am waiting for the second round.

I

I'm trying to order wheel cylinders & master cylinder from Rock Auto. For the wheel cylinders they only list 12" brakes. When I measure the inside diameter of my drums they are 11".  The backing plate is exactly 12".  Measured inside diameter of my wheel cylinders are 1 1/8". Look exactly the same as RA pictures.   Anybody can answer this?

IMG_5241.JPG

IMG_5245.JPG

IMG_3687.JPG

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