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Sizing and plumbing new Master Cylinder
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jboymechanic
Posted 2018-05-23 10:13 AM (#563882)
Subject: Sizing and plumbing new Master Cylinder



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Key info:
1960 Plymouth Belvedere
Front disc brakes, 2.9" diameter pistons
Rear disc brakes, 2.5" diameter pistons
1.03125" diameter bore master cylinder (no residual valves in the ports of the MC)

Car stops, but the pedal is very soft and goes near to the floor even for gentle stops. Yes, the brakes have been bled and re-bled several times and the lines are air free. I think the additional volume of the front and rear disc calipers are making the pedal softer than I'd like. So, I'd like to go to a 1.125" diameter bore master cylinder, which should firm up the pedal. This is a MC bore area increase from 0.835 to 0.994 square inches, and increase of just under 20%. I'm hoping this will give me a better pedal feel and provide the 4 wheel discs the volume they need. I want to go to master cylinder Raybestos part number MC39178, which gives me the larger bore, lighter aluminum casting and a plastic reservoir with easy to remove plastic caps (all pluses in my book).

Here is my question, refer to the pictures of the master cylinders below. First picture is my current MC. Larger reservoir closest to firewall is for front brakes, small reservoir is for rear. The second picture is for the MC I hope to use (I have a 4 bolt to 2 bolt adapter). The info page on Rockauto says the primary outlet is 9/16 thread, which would be the smaller reservoir farthest from the firewall. This is just incorrect information on Rockauto, right? I should just be able to swap out MCs and be good to go, no need to switch the brakes lines front to rear and rear to front, correct? Just trying to be sure. Thanks.



Edited by jboymechanic 2018-05-23 10:16 AM




(MC Centric 13063014.jpg)



(MC Raybestos MC39178.jpg)



Attachments
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Attachments MC Centric 13063014.jpg (59KB - 30 downloads)
Attachments MC Raybestos MC39178.jpg (158KB - 40 downloads)
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Mopar1
Posted 2018-05-23 10:46 AM (#563884 - in reply to #563882)
Subject: Re: Sizing and plumbing new Master Cylinder



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it's either wrong, or the size got reversed @ some point. you'll find out when it comes in.
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1960fury
Posted 2018-05-23 1:49 PM (#563893 - in reply to #563882)
Subject: Re: Sizing and plumbing new Master Cylinder



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I have 2 of these MC's, one in continuous troublefree use since the 90s. The large outlet is the FORWARD one. So the fw outlet is for the front brakes.
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Powerflite
Posted 2018-05-23 3:07 PM (#563899 - in reply to #563882)
Subject: Re: Sizing and plumbing new Master Cylinder



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I don't think either of those are intended for 4 wheel disc brakes. You will need to remove the residual pressure valve from the rear brake port.
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1960fury
Posted 2018-05-23 4:28 PM (#563904 - in reply to #563882)
Subject: Re: Sizing and plumbing new Master Cylinder



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Residual valve? Mine didn't have any. I use an inline (external one) for discs.
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1960fury
Posted 2018-05-23 4:34 PM (#563907 - in reply to #563882)
Subject: Re: Sizing and plumbing new Master Cylinder



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Of course the larger 9/16" fitting is for the FRONT brakes as its made for/accepts 1/4" brake line and the 1/2" is for the 3/16" rear brake line.
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Powerflite
Posted 2018-05-23 5:01 PM (#563912 - in reply to #563882)
Subject: Re: Sizing and plumbing new Master Cylinder



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That is definitely wrong on the iron master. The 9/16 fitting has a small 3/16 line coming out of it and is for the rear brakes. You can tell that's true just by looking at the cap. If the aluminum is made for/by Chrysler (and I think it is), it will likely be the same.
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1960fury
Posted 2018-05-23 5:38 PM (#563916 - in reply to #563912)
Subject: Re: Sizing and plumbing new Master Cylinder



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Powerflite - 2018-05-23 5:01 PM

That is definitely wrong on the iron master. The 9/16 fitting has a small 3/16 line coming out of it and is for the rear brakes. You can tell that's true just by looking at the cap. If the aluminum is made for/by Chrysler (and I think it is), it will likely be the same.


It clearly says PRIMARY outlet size 9/16".

The aluminum one came with fittings. 9/16" have a 1/4" opening, 1/2" are 3/16" hole and if you reorder these fittings (I just did) they are still like that, and it makes sense, doesn't it? Why on earth should they use the larger fitting for the smaller lines and vice versa?

And this works for me for 100 000+ miles without any problems.



Edited by 1960fury 2018-05-23 6:25 PM
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Powerflite
Posted 2018-05-23 6:25 PM (#563920 - in reply to #563882)
Subject: Re: Sizing and plumbing new Master Cylinder



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It doesn't make sense, but that's the way they set them up. I am not familiar with the inner workings on the aluminum version. But the iron version is definitely configured exactly as it is shown and as I stated. The 9/16 fitting in the front goes to the rear brakes. These masters were used on many of the cars starting in 1973 (especially A-bodies) and I have used them on multiple older cars. Most of the later Mopar muscle cars are configured that way too so it makes this master easy to swap into them when doing disc brake conversions. The aluminum master replaced the iron version and I believe they kept the same configuration as they had with the iron version. So I would assume that unless you can prove otherwise.

Here is a picture of an older muscle car that came with a drum brake master, that was converted to discs using the iron master shown. You can see that the rear brake port is in the front, (with a 9/16 fitting) just as it was with the original master.

Edited by Powerflite 2018-05-23 6:29 PM




(Muscle car.jpg)



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Attachments Muscle car.jpg (195KB - 28 downloads)
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1960fury
Posted 2018-05-23 6:42 PM (#563922 - in reply to #563882)
Subject: Re: Sizing and plumbing new Master Cylinder



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Again, the 9/16 fittings have a 1/4" hole and the 1/2" fittings a 3/16" hole. When I installed mine 20 years ago, for some stupid reason I drilled the rear one to 1/4" to use 1/4" line like in front. I changed that a couple of years ago and reordered a 1/2" fitting, it had a 3/16" opening like the one that came originally with the MC. I just ordered the same type of MC for my 61 Fury, I ordered it with fittings. The fittings were like that too. LARGE fitting=LARGE line, SMALL fitting=SMALL line. Now use common sense

Edited by 1960fury 2018-05-23 6:44 PM
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1960fury
Posted 2018-05-23 6:50 PM (#563923 - in reply to #563882)
Subject: Re: Sizing and plumbing new Master Cylinder



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But maybe I didn't get it, are you saying that the large line is supposed to feed the rear brakes and the small line the front? Well, that does not make sense to me.
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56D500boy
Posted 2018-05-23 6:57 PM (#563925 - in reply to #563920)
Subject: Re: Sizing and plumbing new Master Cylinder



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Why you guys sort out which is front and which is rear, what about the "T" block that is required for this single to dual circuit conversion?


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1960fury
Posted 2018-05-23 6:57 PM (#563926 - in reply to #563923)
Subject: Re: Sizing and plumbing new Master Cylinder



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A car brakes mostly with the front brakes when driving forward, so my guess is the PRIMARY outlet means front brakes. Here's a Wilwood MC, so the primary 9/16" at Rockauto isn't a typo.

Edited by 1960fury 2018-05-23 6:59 PM




(WIL_260-8555Dia.jpg)



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1960fury
Posted 2018-05-23 7:05 PM (#563928 - in reply to #563925)
Subject: Re: Sizing and plumbing new Master Cylinder



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56D500boy - 2018-05-23 6:57 PM

Why you guys sort out which is front and which is rear, what about the "T" block that is required for this single to dual circuit conversion?




I don't understand the questions. The OE distribution block remains, only the rear outlet is blocked. The smaller rear port of the MC is directly connected with the rear brake line. I use a prop valve and disc residual valve as connector.
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Powerflite
Posted 2018-05-23 7:08 PM (#563930 - in reply to #563882)
Subject: Re: Sizing and plumbing new Master Cylinder



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Wilwood sets theirs up like GM, which is, and always has been backward from Mopar.
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1960fury
Posted 2018-05-23 7:17 PM (#563933 - in reply to #563882)
Subject: Re: Sizing and plumbing new Master Cylinder



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Okay, that makes sense, as I'm not 100% sure if the MC I use is the aluminum one above. It just looks 100% identical. So its possible the Rockauto discription is an error. BUT if it is indeed Large front/small rear I would use common sense when plumbing, regardless what other people do or did.
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56D500boy
Posted 2018-05-23 8:50 PM (#563936 - in reply to #563928)
Subject: Re: Sizing and plumbing new Master Cylinder



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1960fury - 2018-05-23 7:05 PM

56D500boy - 2018-05-23 6:57 PM

Why you guys sort out which is front and which is rear, what about the "T" block that is required for this single to dual circuit conversion?




I don't understand the questions. The OE distribution block remains, only the rear outlet is blocked. The smaller rear port of the MC is directly connected with the rear brake line. I use a prop valve and disc residual valve as connector.


Okay. The OE Distribution block becomes the "T" block that I thought was needed. How do you block the rear outlet? With what?

(I am just trying to figure this out before I dive into it).

Thanks in Advance.



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Powerflite
Posted 2018-05-23 9:45 PM (#563939 - in reply to #563882)
Subject: Re: Sizing and plumbing new Master Cylinder



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You can get a brake flare plug from most parts stores to block it. I don't like them very well because they don't have much of a seat on them, but the ones from Earls at summit are a little better.

Edited by Powerflite 2018-05-23 9:46 PM
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jboymechanic
Posted 2018-05-23 11:54 PM (#563945 - in reply to #563882)
Subject: Re: Sizing and plumbing new Master Cylinder



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Wow, a lot more responses than I expected.

Sid, you are right about the residual valves, Mopar MCs didn't have them as they used separate valve assemblies.

Nathan, I believe you are right about the large 9/16 port being for the rear brakes, that is how my dad's '74 Charger and '79 300 are set up (just had him check today). Not sure why Mopar did that.

The last detail that is odd is that Mopar used a 9/16"-20 thread inverted flare nut instead of the standard 9/16"-18 inverted flare nut. Why?! The MC that was in the car actually had a 9/16"-18 threaded port, so I have to make one new brake line as well when the new MC arrives.

Also, below is a great article about Mopar master cylinders, save it for reference.

http://therammaninc.com/files/categories/Moparts_Complete_Guide_to_...


Edited by jboymechanic 2018-05-23 11:57 PM
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Powerflite
Posted 2018-05-24 1:07 AM (#563949 - in reply to #563882)
Subject: Re: Sizing and plumbing new Master Cylinder



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Yep, they are slightly different, and close enough that you can still get it threaded quite a ways, thinking you are good, just before it jams up in the hole and destroys the threads.
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1960fury
Posted 2018-05-24 8:15 AM (#563957 - in reply to #563882)
Subject: Re: Sizing and plumbing new Master Cylinder



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Okay, I found the instruction sheet for my new WILWOOD (I just bought) MC. It really says large front port secondary rear brakes and small rear port primary front brakes.... WTH? I looked into the reservoir and it has 2 inlets in front and 1 in rear also the fittings are 1/4" outlet front and 3/16" outlet rear and the fewer or smaller inlet are supposed to feed the front brakes? I don't get it and I'm not sure if I'm going to run it that way. If someone wants to swap mine (Mopar configuration) against the aluminum one above, let me know.

Edited by 1960fury 2018-05-24 8:18 AM
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1960fury
Posted 2018-05-24 8:16 AM (#563958 - in reply to #563936)
Subject: Re: Sizing and plumbing new Master Cylinder



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56D500boy - 2018-05-23 8:50 PM

1960fury - 2018-05-23 7:05 PM

56D500boy - 2018-05-23 6:57 PM

Why you guys sort out which is front and which is rear, what about the "T" block that is required for this single to dual circuit conversion?




I don't understand the questions. The OE distribution block remains, only the rear outlet is blocked. The smaller rear port of the MC is directly connected with the rear brake line. I use a prop valve and disc residual valve as connector.


Okay. The OE Distribution block becomes the "T" block that I thought was needed. How do you block the rear outlet? With what?

(I am just trying to figure this out before I dive into it).

Thanks in Advance.





I just welded an old fitting shut but you can get plugs for that purpose.
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jboymechanic
Posted 2018-06-13 11:11 PM (#565125 - in reply to #563882)
Subject: Re: Sizing and plumbing new Master Cylinder



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Just thought I'd give an update here. The Raybestos MC39178 master cylinder is not in the Plymouth. The port closest to the firewall is 1/2-20 threaded and connected to the front brakes and the port farthest from the firewall is 9/16-20 threaded and connected to the rear brakes. The brake pedal feels great and the brakes work well, happy with the switch.
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vinnybagadonuts
Posted 2018-07-30 11:38 PM (#567469 - in reply to #563882)
Subject: RE: Sizing and plumbing new Master Cylinder


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Location: Nashua NH
Hi I did a 4 wheel disc conversion on a 56 lancer using AAJ rear kit and ECI front, All use GM calipers. I have the same problem with the brake pedal. I had 1 1/8 bore manual MC from Master Power. It did not work. I called AAj and he suggested 15/16 MC for increased pressure. I bought the mopar A body from rock auto and pulled the residual valve from the rear port of the master since discs don't need that. It has the front brake reservoir in the back and bolts right up. But I have the same problem.

I isolated the issue to the front calipers by pinching the hoses to the front calipers and the pedal is high and firm. I bled them to death and still the same issue. I have to pump the pedal 3 times to get a pedal and it stops but no panic stop it wont stop.

Did your set up work. At at my wits end.

Thanks

jboymechanic - 2018-05-23 10:13 AM

Key info:
1960 Plymouth Belvedere
Front disc brakes, 2.9" diameter pistons
Rear disc brakes, 2.5" diameter pistons
1.03125" diameter bore master cylinder (no residual valves in the ports of the MC)

Car stops, but the pedal is very soft and goes near to the floor even for gentle stops. Yes, the brakes have been bled and re-bled several times and the lines are air free. I think the additional volume of the front and rear disc calipers are making the pedal softer than I'd like. So, I'd like to go to a 1.125" diameter bore master cylinder, which should firm up the pedal. This is a MC bore area increase from 0.835 to 0.994 square inches, and increase of just under 20%. I'm hoping this will give me a better pedal feel and provide the 4 wheel discs the volume they need. I want to go to master cylinder Raybestos part number MC39178, which gives me the larger bore, lighter aluminum casting and a plastic reservoir with easy to remove plastic caps (all pluses in my book).

Here is my question, refer to the pictures of the master cylinders below. First picture is my current MC. Larger reservoir closest to firewall is for front brakes, small reservoir is for rear. The second picture is for the MC I hope to use (I have a 4 bolt to 2 bolt adapter). The info page on Rockauto says the primary outlet is 9/16 thread, which would be the smaller reservoir farthest from the firewall. This is just incorrect information on Rockauto, right? I should just be able to swap out MCs and be good to go, no need to switch the brakes lines front to rear and rear to front, correct? Just trying to be sure. Thanks.



Edited by vinnybagadonuts 2018-07-30 11:58 PM
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Powerflite
Posted 2018-07-30 11:42 PM (#567470 - in reply to #563882)
Subject: Re: Sizing and plumbing new Master Cylinder



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Sounds like you are barking up the wrong tree. From your description, it sounds like you have a leaking or bad caliper or line. Track that down to figure it out.
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jboymechanic
Posted 2018-08-01 5:13 PM (#567593 - in reply to #563882)
Subject: Re: Sizing and plumbing new Master Cylinder



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My setup works great, my post above should read that the Raybestos MC39178 master cylinder is NOW in the car. Pedal is firm but not too firm, very happy with the setup.
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1960fury
Posted 2018-08-01 6:36 PM (#567600 - in reply to #567593)
Subject: Re: Sizing and plumbing new Master Cylinder



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jboymechanic - 2018-08-01 5:13 PM

My setup works great, my post above should read that the Raybestos MC39178 master cylinder is NOW in the car. Pedal is firm but not too firm, very happy with the setup.


I bought that too, as a backup. Have you connected the large (front) primary outlet with the front wheels, as per instructions, or the "Mopar-way"?
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jboymechanic
Posted 2018-08-08 4:15 PM (#568077 - in reply to #563882)
Subject: Re: Sizing and plumbing new Master Cylinder



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I have it installed the "Mopar way", good so far.
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