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So you want BIG Brakes on your Plymouth?


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For some time I've considered how to get really big brakes on my Plymouth.

It wasn't so much that I felt a need as I realized that you could.

My Plymouth P17 has 10 inch brakes, a similar year DeSoto has 11 inch and Chrysler Windsors have 12 inch.

Let me tell you a 12 inch Chrysler drum fills a 15 inch wheel!

I've read about other people's adventures putting disc brakes on Plymouths and it just seemed to me to be more work and engineering than it was worth.

Chrysler across its line of cars had a continuity of design. As cars got bigger and heavier they placed bigger brakes on them of exactly the same design.

Thus a Plymouth uses the very same hydraulics as a Chrysler. Which for the company meant lower costs of stocking parts. For service it meant there were no surprises or re-training for technicians. For manufacturing it meant associated parts could be the same thus again lowering costs. Because high volume cars like Plymouth and Dodge paid the engineering costs, the company could afford to make better DeSotos and Chryslers.

That is the real beauty of Mopar cars.

Since Chrysler Brakes CAN be put on a Plymouth, you knew somebody WOULD. And I am certainly not the only one who has done this.

I studied the shop manuals and parts supplier's sites and found that the king pins in the front were the same but the Chrysler spindles had Torrington Needle Bearings in the top (thus a different P/N for the King Pin Set). Torrington discontinued the bearing Chrysler used decades ago. I found an NOS King Pin Set for my project at a reasonable price with the needle bearings. In retrospect I think one of the reasons the bearings were discontinued is that they tend to get stuck and they skid more than roll. One supplier sells a kit with a thick bushing in place of the needle bearing (at a good price too) and this may be a better choice.

Speaking of bearings, even the wheel bearings and seals are the same.

If you are on a treasure hunt you will need the spindles, backing plates, drums and the tubes from wheel cylinder to wheel cylinder. Being kind of picky I bought a left handed 1/2 x 20 tap & die to clean up the threads on the left side for the lug bolts (most tap & die sets have right handed 1/2 x 20 in them).  I sand blasted everything and put some paint on them just to keep the rust at bay.

Tomorrow I begin to install the front brakes.

 

 

6BB2C2CC-563E-4F8F-8FA6-F7DB6613C9A9_1_201_a.heic

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I'm very interested in this conversion, although here in Oz we never got anything other than the standard Plymouth based brakes even in the Dodge and DeSoto versions as they were just essentially badge engineered here with basic sheetmetal, badging, moldings and trim changes....proper DeSoto & Chrysler vehicles were only special imports and quite rare.........look forward to the info & details..............andyd  

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2 hours ago, Sniper said:

According to this interchange  http://www.jholst.net/interchange/

 

The 49-54 Plymouth and the 51-53 Chrysler/Desotos use the same spindles.  So that may eliminate part of the treasure hunt.

 

Well I can tell you with 100% certainty that you will need the spindles.

The anchor points for the brake shoes are a part of the spindles. When they increased the size of the shoes it required a change to the spindles. Therefore there are three different spindles. All will fit the uprights on the cars however.

 

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1 hour ago, Loren said:

 

Well I can tell you with 100% certainty that you will need the spindles.

The anchor points for the brake shoes are a part of the spindles. When they increased the size of the shoes it required a change to the spindles. Therefore there are three different spindles. All will fit the uprights on the cars however.

 

What you are calling an upright is called a spindle in the interchange. 

This is the problem when people use their own terminology for stuff.  It confuses thing.

In the factory parts book the "upright" is called a support.  The "spindle" is called a knuckle.  The supports are the same part number, the knuckles are not. 

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Eleven inch brakes make a significant improvement especially with regard to "fade"  and as Sniper points out, you need the knuckle which matches the backing plate.    Should you choose 12 inch brakes, the Plymouth  15 inch wheel will not fit, but the 15 by 4  1/2 Chrysler and Desoto will.  Dodge USA drums have a flat flange and use a wheel with a different offset but all could be used under a Plymouth.  I once bought a 54 Plaza which had been a police car and am still using its eleven inch brakes.  ( or parts of them anyway)

 

As for the Torrington needle upper bearing, Canadian built Plymouths  also used these, possibly to offset the extra weight of the longer engine.  In my many many years of servicing these cars, I have never found one worn out.     I wish I could say the same for the bearing which actually carries the weight.

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10 hours ago, Sniper said:

What you are calling an upright is called a spindle in the interchange. 

This is the problem when people use their own terminology for stuff.  It confuses thing.

In the factory parts book the "upright" is called a support.  The "spindle" is called a knuckle.  The supports are the same part number, the knuckles are not. 

 

I am sorry for the confusion, my training did not come from the Mopar parts book.

For clarity what my Plymouth manual calls a “Knuckle” would be called a “Steering Knuckle” or a spindle elsewhere. Which seems more descriptive to me.

The part I called an “Up-right” is indeed called a “Support” in the Plymouth manual. Again being the only vertical suspension member, “Up-right” seems more descriptive than “Support”. If you said “Support” to me without knowing you were referring to a Plymouth front suspension part I would think you were talking about some kind of bracket.

Since they made the car they can call them whatever they wish.

I will be more careful to use the Plymouth nomenclature in the future rather than generic terms.

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18 hours ago, dpollo said:

Eleven inch brakes make a significant improvement especially with regard to "fade"  and as Sniper points out, you need the knuckle which matches the backing plate.    Should you choose 12 inch brakes, the Plymouth  15 inch wheel will not fit, but the 15 by 4  1/2 Chrysler and Desoto will.  Dodge USA drums have a flat flange and use a wheel with a different offset but all could be used under a Plymouth.  I once bought a 54 Plaza which had been a police car and am still using its eleven inch brakes.  ( or parts of them anyway)

 

As for the Torrington needle upper bearing, Canadian built Plymouths  also used these, possibly to offset the extra weight of the longer engine.  In my many many years of servicing these cars, I have never found one worn out.     I wish I could say the same for the bearing which actually carries the weight.

 

Okay news I did not want to hear!

This morning I put a wheel on the drum I finished mounting yesterday. When you tighten the lug bolts on the Safety Rim Wheels the assembly won't turn!

An investigation found the problem, the centers of the Safety Rim Wheels at the dips closest to the outside diameter of the drum just touch the drum enough to distort the drum locking the brake. Since the steel center of the drum is flexible there is no harm done and it springs right back. PHEW!

I had planned on changing the Safety Rim Wheels to a wider rim anyway but this has to be acknowledged for those interested in doing this modification.

Of course a little work with a grinder could knock the corner off the dips to provide clearance. Which is what I will have to do to get my car off the jack stands while I prepare a set of wheels.

 

The Torrington NB-15-OH (Chrysler P/N 681378) needle bearings as I said before are no longer made.

The ones I got were sealed in the original rust preventative paper and grease, but they were stuck.

An hour with PB Blaster and a box cutter got them to wiggle a little but not move.

Two hours in an ultra sonic cleaner in Diesel Fuel broke them loose.

If they had been installed stuck they would have stayed stuck forever. Now I am hopeful.

 

On another topic, I am interested in your Police car.

My Grandmother had a 1951 Ford Police car that was built for the Pasadena PD but remained unsold. This thing had enough torque it went through gearboxes pretty quickly  which is why she got a new Ford in 1955. However it would out run the new CHP Oldsmobile 88 overhead valve V8s for top speed by a wide margin. People give their cars names and her's was always "The Police Car."

Fun to know what Plymouth did for the Police Package!

Police cars after their service (around 100,000 miles) usually become Taxi cabs so there's a lot of heavy duty stuff in them.

 

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3 hours ago, Loren said:

 

Okay news I did not want to hear!

This morning I put a wheel on the drum I finished mounting yesterday. When you tighten the lug bolts on the Safety Rim Wheels the assembly won't turn!

An investigation found the problem, the centers of the Safety Rim Wheels at the dips closest to the outside diameter of the drum just touch the drum enough to distort the drum locking the brake. Since the steel center of the drum is flexible there is no harm done and it springs right back. PHEW!

I had planned on changing the Safety Rim Wheels to a wider rim anyway but this has to be acknowledged for those interested in doing this modification.

Of course a little work with a grinder could knock the corner off the dips to provide clearance. Which is what I will have to do to get my car off the jack stands while I prepare a set of wheels.

 

I had a somewhat similar experience with a later model situation.  My daughter hit a chunk of steel on the road and blew a tire on their 3rd Gen MoPar minivan.  (It was winter, and she actually hit it on purpose, because it was covered with ice, and she wanted to crunch it - said the sound it makes is cool....)  Anyway, so I went out there where she was stranded & took her on into work then went back with a wheel off of a 2nd gen minivan.  It fit and turned just fine until I set it back on the ground.  It ground and skreeched all the way back to my shop. (It was just about a mile, and it was cold, so I just kept going, driving slow.)  Turns out that just the weight of the vehicle changed something enough that it rubbed on the inside of the wheel.

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An update

There is a cheap quick and dirty solution to the wheel fitting problem. 

A wheel spacer (oddly to fit disc brakes on some cars) can be had to give enough clearance.

With some testing I am going to determine the exact thickness needed.

I will pick some up this week at Summit Racing when I go back to Nevada.

 

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I found most of the issues on later pre 90's wheels  (last rear wheel car by MM was 1989) were the bulge of the radial tire or the offset right at the very tie rod end...based on maker of tie rod would also alter clearance...one was so close only the balancing weight hit....the thin spacers are nice and really not an issue in geometry like some adapter/spacers can be.

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What PA says is true.  I fitted a set of 15x7 cop car rims, from an 87 Diplomat, to my 51 and the rim was so close on the pass side, I believe, that it would rub the outer tie rod slightly when spinning, rim was bent a hair.  Good thing those are just roller rims for fitment purposes.  If there were balancing weights on the inside lip they would hit.  Then the bulge would hit the upper pivot bolt, forward part of it, when approaching lock.  A spacer would fix both issues, or proper backspacing. 

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2 hours ago, Loren said:

An update

There is a cheap quick and dirty solution to the wheel fitting problem. 

A wheel spacer (oddly to fit disc brakes on some cars) can be had to give enough clearance.

With some testing I am going to determine the exact thickness needed.

I will pick some up this week at Summit Racing when I go back to Nevada.

 

Not sure I understand exactly where the interference is with your 15" wheels.  (Stock, right?)  So my car, being a 46, has 16" wheels.  Do you think the same problem would exist with stock 16" wheels?  

 

Oh, and another question, Did you happen to weigh the different parts, to establish how much this modification would add to the unsprung weight?

Edited by Eneto-55
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1 hour ago, Eneto-55 said:

Not sure I understand exactly where the interference is with your 15" wheels.  (Stock, right?)  So my car, being a 46, has 16" wheels.  Do you think the same problem would exist with stock 16" wheels?  

 

Oh, and another question, Did you happen to weigh the different parts, to establish how much this modification would add to the unsprung weight?

 

I have looked the wheels over with close attention to what exactly is going on.

It will require a spacer 1/2 inch thick. They make them but I think I am going to go wheel shopping. Wheels do flex on hard cornering so what clears while standing might not clear while they are being used.

 

I am pretty sure a 16 inch wheel will clear. It's the drop center that bumps where the center meets the rim (at the riveted portion).

Yes the unsprung weight does increase. There is simply more iron involved. I don't believe it would be noticeable and considering the benefits it's a good trade off.

Comparing the weight increase versus Vented Disc Brakes, I would have to think the drums would be less.

 

Now I am on another treasure hunt...

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3 hours ago, Loren said:

 

I have looked the wheels over with close attention to what exactly is going on.

It will require a spacer 1/2 inch thick. They make them but I think I am going to go wheel shopping. Wheels do flex on hard cornering so what clears while standing might not clear while they are being used.

 

I am pretty sure a 16 inch wheel will clear. It's the drop center that bumps where the center meets the rim (at the riveted portion).

Yes the unsprung weight does increase. There is simply more iron involved. I don't believe it would be noticeable and considering the benefits it's a good trade off.

Comparing the weight increase versus Vented Disc Brakes, I would have to think the drums would be less.

 

Now I am on another treasure hunt...

Thanks. I'm not a fan of disk brakes, so if I do any brakes upgrade, it will be either larger drums like you are doing, or self-energizing.  (I haven't looked into this at all, just keeping it in mind if I find that the stock brakes seem under-performing to me.  I don't use the brakes nearly as much as other people I've ridden with - never have.  Maybe it's coming from the country, I don't know.  Our family car is a 2009 Dodge Journey, and "everyone" on the Journey site goes off on the smaller brakes on that first-year model.  Neither I nor my wife, who uses the brakes more than I, have found them to be deficient.  The upgrade they do means that they can no longer run the stock 16" wheels - you have to go to 17's or 18's.)

 

But some actual figures on the difference in unsprung weight (especially the over-size drums compared to the common disk upgrade) would be really interesting to see.

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On 8/8/2021 at 6:37 AM, Loren said:

For some time I've considered how to get really big brakes on my Plymouth.

It wasn't so much that I felt a need as I realized that you could.

My Plymouth P17 has 10 inch brakes, a similar year DeSoto has 11 inch and Chrysler Windsors have 12 inch.

Let me tell you a 12 inch Chrysler drum fills a 15 inch wheel!

I've read about other people's adventures putting disc brakes on Plymouths and it just seemed to me to be more work and engineering than it was worth.

Chrysler across its line of cars had a continuity of design. As cars got bigger and heavier they placed bigger brakes on them of exactly the same design.

Thus a Plymouth uses the very same hydraulics as a Chrysler. Which for the company meant lower costs of stocking parts. For service it meant there were no surprises or re-training for technicians. For manufacturing it meant associated parts could be the same thus again lowering costs. Because high volume cars like Plymouth and Dodge paid the engineering costs, the company could afford to make better DeSotos and Chryslers.

That is the real beauty of Mopar cars.

Since Chrysler Brakes CAN be put on a Plymouth, you knew somebody WOULD. And I am certainly not the only one who has done this.

I studied the shop manuals and parts supplier's sites and found that the king pins in the front were the same but the Chrysler spindles had Torrington Needle Bearings in the top (thus a different P/N for the King Pin Set). Torrington discontinued the bearing Chrysler used decades ago. I found an NOS King Pin Set for my project at a reasonable price with the needle bearings. In retrospect I think one of the reasons the bearings were discontinued is that they tend to get stuck and they skid more than roll. One supplier sells a kit with a thick bushing in place of the needle bearing (at a good price too) and this may be a better choice.

Speaking of bearings, even the wheel bearings and seals are the same.

If you are on a treasure hunt you will need the spindles, backing plates, drums and the tubes from wheel cylinder to wheel cylinder. Being kind of picky I bought a left handed 1/2 x 20 tap & die to clean up the threads on the left side for the lug bolts (most tap & die sets have right handed 1/2 x 20 in them).  I sand blasted everything and put some paint on them just to keep the rust at bay.

Tomorrow I begin to install the front brakes.

 

 

6BB2C2CC-563E-4F8F-8FA6-F7DB6613C9A9_1_201_a.heic 1.53 MB · 25 downloads

Im blown away! You kick serious butt. Thank you for this presentation. MIT needs you! (Seriously). We were fortunate to have metal shop< wood working and and Auto shop class in our HS. I chose metal and it became a career for me. I hope you chose a career in education Loren. Thanks!

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I think a 16 inch wheel has a bigger center if i remember correctly 13 and 1/4. This will also let you have this center put in a later 15 inch (whoop) wheel so you can have your hub cap ( clips )and the clearance we will need for big drums or disc brakes.

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Maybe I'm missing something here as I just glanced over this topic. But to use the bigger Chrysler brakes aren't the front wheels going to need to be changed because the bolt pattern won't be the same? I thought Chrysler didn't have 5 x 4 1/2 bolt pattern. Also I couldn't open the download. No big deal, I'm running Disc, just curious what what was in it.

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3 minutes ago, YukonJack said:

Maybe I'm missing something here as I just glanced over this topic. But to use the bigger Chrysler brakes aren't the front wheels going to need to be changed because the bolt pattern won't be the same? I thought Chrysler didn't have 5 x 4 1/2 bolt pattern. Also I couldn't open the download. No big deal, I'm running Disc, just curious what what was in it.

 

I thought I knew everything to get this job done but it seems there are some nuances to this project which I have overlooked.

You can drop the drums into the wheels and everything looks fine until you tighten the lugs.

So...yes you will be changing the wheels....Chrysler Windsor 12 inch brakes have the right King Pins but the wrong upper bushing (or needle bearing).

The steering arms bolt right up but they are now lower than the Chrysler ones. I am still trying to work out wether this could be a problem or they will need to be changed.

Big Chrysler Knuckles have bigger King Pins and therefore are not being used for this mod (they might possibly work if you changed the Supports. Which is not a job I'd tackle unless I was rebuilding the entire front end). The wheels however can be used as they have the same bolt pattern.

 

Bottomline: Once I work out the kinks and get all four wheels on the ground and fully tested, I will put together a new bill of materials and a procedure on how to get satisfactory results. I have to admit this is a work in progress.

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