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thebeebe5

Master cylinder suitability for dual circuit upgrade

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quick background:

1937 P4 coupe, recent complete brake overhaul. All new (edit) nickel copper DOT approved brake lines and rubber hoses. All new wheel cylinders, all new shoes and I rebuilt (probably 25-ish year old foreign repop?) original style master, 1 1/4" bore size with a bernbaum kit specifically for the unit. Car had about 600 miles on it from prior brake redo circa 1980 (per prior owner). Master ID measured 1.2540". Piston measured 1.2505"

I realize per shop manual that's half a mil over spec. IIRC it said .001" to .003"??

the problem:

My complete brake system re-do worked well (2 whole months) until last night's cruise when I lost almost all brake pressure. NO leaks found, reservoir is still full, but pedal suddenly goes nearly to the floor and is quite soft. Ride the brake with gentle pressure and it will go all the way to the floor. Pumping doesn't help. Car will stop with this limited brake pedal pressure. Does not pull or shimmy. Seems as if all wheel cylinders are operational. I'm thinking its the MC. Have not pulled anything apart yet to investigate.

Figure maybe I'll do the dual circuit master swap now. Looking at suitable candidates. I can find a load of 1" bore manual masters in the mopar lineup, but seem to keep finding the 101323M which bears the application description of drum/drum manual. Fits a load of cars/trucks in the late 60's early 70's.

Would a swap from a single circuit 1 1/4 down to a 1" bore provide enough fluid volume to replace that of the larger single? I realize it will provide more braking power but require more travel.

Open to suggestions for suitable tried and successful dual circuit manual Drum/Drum replacements.

Thoughts? Need additional information? I have an entire engine machine shop available and can make anything required for installation.

Edited by thebeebe5

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I sure hope you didn't use copper lines!! Iff you did, you will have to pull them all off as that is highly dangerous and illegal. Copper won't hold up. Use nicopp lines, safe, legal, won't rust and easier to work with than stainless steel.

I used a ECI dual master kit on my 52. Great kit, highly recommend it.

Earl

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Wow! Thanks everyone for thinking of me. I appreciate your concern for my safety! I did use the nickel copper alloy lines suitable for brake line replacement.

Forgive my mistake in my initial post.

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How many miles in those 2 months? Have you checked your shoe adjustment? I would start with checking the adjustment on the front shoes and see if they are quite loose. Way out of adjustment shoes can feel like a bad brake system

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How many miles in those 2 months? Have you checked your shoe adjustment? I would start with checking the adjustment on the front shoes and see if they are quite loose. Way out of adjustment shoes can feel like a bad brake system

thanks for weighing in Young Ed.

About 250 miles in that two-month period of time. After I had assembled the breaks I drove that car about 10 miles, brought it back into the shop and pulled all of the drums. I checked wear pattern on all of the shoes and made corrective adjustments. The shoes now contact the drum this nicely, and the pedal has been high and quite firm since that secondary adjustment. This failure occurred yesterday evening. The brakes were as usual upon our arrival at our first cruise stop. When we left that stop I noticed the pedal was going about halfway down it's travel and the brakes felt mushy. To stoplights later I knew I had a problem, and the brakes were behaving as I described in my initial post. Of course I intend to pull each wheel and have a look, but the abrupt decline of breaking does not lead me to believe that all of the shoes suddenly went out of adjustment. I simply have not had enough time to go through those steps.

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thanks for weighing in Young Ed.

About 250 miles in that two-month period of time. After I had assembled the breaks I drove that car about 10 miles, brought it back into the shop and pulled all of the drums. I checked wear pattern on all of the shoes and made corrective adjustments. The shoes now contact the drum this nicely, and the pedal has been high and quite firm since that secondary adjustment. This failure occurred yesterday evening. The brakes were as usual upon our arrival at our first cruise stop. When we left that stop I noticed the pedal was going about halfway down it's travel and the brakes felt mushy. To stoplights later I knew I had a problem, and the brakes were behaving as I described in my initial post. Of course I intend to pull each wheel and have a look, but the abrupt decline of breaking does not lead me to believe that all of the shoes suddenly went out of adjustment. I simply have not had enough time to go through those steps.

 

I agree with that description its not the adjustment. Sounds like you lost a line or a WC somewhere.

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I agree with that description its not the adjustment. Sounds like you lost a line or a WC somewhere.

No line breaches. No leaking WC IMO. I've lost WC before on 4w drums and its definitely not the same. And the fluid is to the top of the reservoir.

Wondering about how this dual circuit MC would work as a replacement.

http://m.summitracing.com/parts/aaz-10-1323m

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Considering the suddenness of the change in braking ability, I wonder if a small particle of rust or something got in between the cup and the bleed back ring inside the MC.  (It's been many years since I had one open, so I can't be more descriptive.  The diagram Don posted should help in understand what I'm getting at.  It might be what is called the Stop in the diagram.)

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thebee,

In regard to the split/tandem system conversion, I have used the NAPA NMC M2534 M/C with success but in systems that used a 1" bore to begin with. The 2534 is spec'd for a number of Chrysler products (at least it's common and still in the family) and has a 24mm bore. The displacement difference is of no concern there (about .946" instead of 1") but, when compared to a 1.250 bore, the 24 mm bore difference is substantial, yielding only ~57% of the original amount. Pedal effort would be almost half but the big downside is that the travel to deliver the needed volume would certainly bottom-out the piston. Yikes!

You need to find one with similar or equal bore size and, preferably, one that has a removable reservoir that you can mount up on the firewall where it belongs. Underfloor M/Cs suck.

Frank

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thebee,

In regard to the split/tandem system conversion, I have used the NAPA NMC M2534 M/C with success but in systems that used a 1" bore to begin with. The 2534 is spec'd for a number of Chrysler products (at least it's common and still in the family) and has a 24mm bore. The displacement difference is of no concern there (about .946" instead of 1") but, when compared to a 1.250 bore, the 24 mm bore difference is substantial, yielding only ~57% of the original amount. Pedal effort would be almost half but the big downside is that the travel to deliver the needed volume would certainly bottom-out the piston. Yikes!

You need to find one with similar or equal bore size and, preferably, one that has a removable reservoir that you can mount up on the firewall where it belongs. Underfloor M/Cs suck.

Frank

I was thinking the same thing, Frank. A lot less volume and they're just might not be enough brake pedal travel to actuate the brakes effectively.

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I think I found the problem…

The piston cup rubber is deteriorating rapidly. I have a new kit from Napa and the components look of better quality. The supplied piston is considerably too long, but all of the rubber parts are the same. Plus, the Napa piston cup actually has a piston washer embedded in the crown of the cup itself. I do have a question about this thick rubber washer that came in the kit. When I disassembled this master cylinder originally this rubber washer was underneath the valve. And other words, it was the first component installed onto which the valve was placed, then the spring, piston cup, and piston. I do not see this thick rubber washer in the schematic in my manual. Is that something that is necessary? Could it be that that just increases the spring return ability? Wondering if I can leave it out completely...?

No everything is still nice and clean on the inside except for the deteriorated piston cup. New it had to be something severe as rapidly as the brakes quit working. When I pulled the master and put it on the bench to test it pushing the piston in just blew fluid out the holes in the bottom of the reservoir and did not advance anything through the brake line. No surprise there… Especially after opening it up

post-8133-0-10662000-1463108931_thumb.jpeg

Edited by thebeebe5

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Thebee,

I don't know where my last post disappeared to so I'll give it another try.

The 10-1323 M/C is several 60s and 70s Chrysler products but is a 1" bore. That would yield a displacement at only ~64% of that put out by your original 1.25" cylinder. Pedal effort would be substantially decreased for a given system pressure but the greater piston travel necessary to achieve the same volume output could result in over-traveling and "bottoming out" of the piston. Very bad.

Look for a cylinder with a bore size closer to the 1.25", preferably one with a detachable reservoir so that it can be firewall mounted, as God intended. If it isn't easy to check, it doesn't get checked.

Also, a residual valve in each circuit (10 psi for drums, 2 psi for disc) is recommended if the M/C is <24" above the W/C elevation. With the reservoir up on the firewall, they shouldn't be necessary, although I have installed them anyway without issue.

Frank

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I think I found the problem…

The piston cup rubber is deteriorating rapidly. I have a new kit from Napa and the components look of better quality. The supplied piston is considerably too long, but all of the rubber parts are the same. Plus, the Napa piston cup actually has a piston washer embedded in the crown of the cup itself. I do have a question about this thick rubber washer that came in the kit. When I disassembled this master cylinder originally this rubber washer was underneath the valve. And other words, it was the first component installed onto which the valve was placed, then the spring, piston cup, and piston. I do not see this thick rubber washer in the schematic in my manual. Is that something that is necessary? Could it be that that just increases the spring return ability? Wondering if I can leave it out completely...?

No everything is still nice and clean on the inside except for the deteriorated piston cup. New it had to be something severe as rapidly as the brakes quit working. When I pulled the master and put it on the bench to test it pushing the piston in just blew fluid out the holes in the bottom of the reservoir and did not advance anything through the brake line. No surprise there… Especially after opening it up

Wow.  You're not kidding about severe deterioration.

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Many years ago, I installed a small bore 86 Dodge MC to my 38 Coupe.  

The MC did ok for about 10 years.

Several years ago I installed a large bore MC from a 94 Bronco.

I believe the 94 has a 1.25 bore.

The 94 has done good the past few years.

The foot pressure feels about the same to me.

I used my original pedal assembly on both installs..

post-1465-0-33389200-1463229082_thumb.jpg

post-1465-0-94562100-1463229118_thumb.jpg

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Many years ago, I installed a small bore 86 Dodge MC to my 38 Coupe.

The MC did ok for about 10 years.

Several years ago I installed a large bore MC from a 94 Bronco.

I believe the 94 has a 1.25 bore.

The 94 has done good the past few years.

The foot pressure feels about the same to me.

I used my original pedal assembly on both installs..

Excellent! You still have 4 wheel drums Robert?

Quick search on RockAuto says 1 1/8" bore, but that's going to be pretty close. Is the front disc/rear drum MC useable? And a power boosted MC is fine w/o a booster?

Edited by thebeebe5

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There is a guy I got my dual master set up for a 49 Studebaker called" Turner Brake" out of Indiana ,he's on the net,or 317 8770453 after 6 pm turnerbrake.com

He had a kit with a dual master kit for the Stude that was under the frame mounted ,and some tasty rear disc set ups ,

Some folks make there's it's bitsty boosters for disc set ups but the smaller the booster the more vacumbing it takes ,which is problematic if you have the low compression inline 6

On the Plymouth you have room on the firewall for a good sized (8"-9")booster with a hanging brake pedal and could put in a front disc kit

There's a company called (?)power brake something, on orange street in Southern California 'that makes the parts for everyone's kits and they're universal kits fit great and wow what a stepping difference ,I put this on a heavy Packard touring car and was real happy

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There is a guy I got my dual master set up for a 49 Studebaker called" Turner Brake" out of Indiana ,he's on the net,or 317 8770453 after 6 pm turnerbrake.com

He had a kit with a dual master kit for the Stude that was under the frame mounted ,and some tasty rear disc set ups ,

Some folks make there's it's bitsty boosters for disc set ups but the smaller the booster the more vacumbing it takes ,which is problematic if you have the low compression inline 6

On the Plymouth you have room on the firewall for a good sized (8"-9")booster with a hanging brake pedal and could put in a front disc kit

There's a company called (?)power brake something, on orange street in Southern California 'that makes the parts for everyone's kits and they're universal kits fit great and wow what a stepping difference ,I put this on a heavy Packard touring car and was real happy

 

This place..... http://www.abspowerbrake.com/ I have used them before, somewhat local to me.

Edited by deathbound

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Excellent! You still have 4 wheel drums Robert?

Quick search on RockAuto says 1 1/8" bore, but that's going to be pretty close. Is the front disc/rear drum MC useable? And a power boosted MC is fine w/o a booster?

I have 37/38 drums/shoes on the front, that I riveted Granada linings to.

I have a 1995 Ranger rearend with drum brakes.

I used the Ranger park brake also, attached to my 38 park brake cable.

I have not needed a power booster, even in hilly Virginia

 

The small bore Dodge MC did ok also for many years...

post-1465-0-93036700-1463314707_thumb.jpg

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Replace master cylinder with a new one. Period.

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I have 37/38 drums/shoes on the front, that I riveted Granada linings to.

I have a 1995 Ranger rearend with drum brakes.

I used the Ranger park brake also, attached to my 38 park brake cable.

I have not needed a power booster, even in hilly Virginia

 

The small bore Dodge MC did ok also for many years...

do you have more pictures of this brake master mod? or a link to your build?

thanks in advance 

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