Heads up to those that install a 2 bolt aluminum master cylinder.

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Kern Dog

Kern Dog

Build your car to handle.
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With the prices of these being about the same as a new or rebuilt cast iron 4 bolt MC, the aluminum units are a great option. I've found a small glitch though.
In 2012, I wanted to convert my power brake '70 Charger to a manual MC setup to shed weight and to reduce clutter. I had problems with getting adequate stopping force after trying 4 different MCs. I gave up and put the power booster back on.
In June, I pulled the engine for a rebuild and decided to try again with a few changes to ensure that it would work right.
It did not. Once again, I was disappointed. Braking at low speeds was fine but above 20 mph, it wasn't. With some unresolved angst, I put the power booster back on but was still curious about why I couldn't make the manual setup work right. I have driven several manual disc-drum A body cars and was always impressed with the braking. These always had the stock iron 4 bolt master cylinders though.
In the Charger I have the Dr Diff 13" front brakes and the 11.7" rear kit so the car should stop.

I felt that something was wrong and I may have stumbled upon it.

Today I got the manual MC out and the booster in. As I was bench bleeding the 1 1/8" MC, I noticed that the front port got the fluid first and the bubbles first. The rear port only started pushing fluid about 1/3 the way into the stroke. Usually, the front port serves the rear brakes while the rear port serves the front.
With the brake lines connected the traditional way, the REAR is getting pressure before the front.
This can't be right.
I tested a stock iron 15/16' MC and front and rear get pressure at the same time.
I tested the Dr Diff aluminum 15/16" MC and it was exactly like the larger 1 1/8" version: Pressure and bubbles at the front port before the rear.
There was no tech sheet in the box with these master cylinders but Mancini Racing includes this sheet:

892 R.jpg


The ports are REVERSED.
Is this common knowledge? I am no expert but I'm a decent mechanic on these cars. Reversed ports aren't completely unusual. I had a '78 Trail Duster that had a MC with reversed ports like this.
Just a warning to those that may run into the same problem.
 
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Thanks for the heads up! I use those a bit. Haven't run into it yet, but, I bet I will soon. Thanks, again!!
 
Well, ****. I'll have to redo the brake lines on my project car. I assumed the two bolt masters had the same configuration as the old ones. Great catch and thanks for the heads up!
 
I had no idea that they were reversed, I'll keep that in mind when I install mine in the future. 65'
 
Well **** howdy !!!!!
I have had an aluminum MC on my 65 Dart for years !!!!!
Would have been nice to know. So are we saying there is different pressures, or timming during braking ?
 
Interesting! I have always thought the same thing. My 4whl discs don't stop quite right.

I'd be interested in what Dr. Diff has to say about this.
 
On automobiles the front brakes are primary because they do 75% plus of the braking power. On trucks medium and heavy the rear/drive axle brakes are primary; this includes air brakes.
 
One more thing that I have to check now. That master is on the car that I bought last year. Stops OK , will check.
 
I have one on my car from Ehrenburg and am happy with it.

I remember him saying that just any aluminum MC will NOT do, and to NEVER use a FWD one. Maybe this is why he warned against it? Not saying it is, just wondering if there is a correlation.
 
Super thanks for this. My brakes are just not that great and I have been through 2 master cylinders and have bleed enough fluid through to make me cry, but the brakes just arnt great. Even the pedal doesn't feel that good. I'm running Wilwood disc's all round and figured the car should stop on a dime. I guess I'm doing some brake investigation today!
 
I'm running the aluminum master from Dr Diff on mine. The rear port on it controls the front brakes. I have my line lock plumbed into the line coming off the rear port and it works as intended controlling the front brakes.

I have the 15/16" version.

Mopar Aluminum Master Cylinder Kit
 
I think some may find the 1 1/8" master is not a good choice for manual brakes and very hard to stop. Most prefer 15/16" or 1" which will provide good braking with much less leg.
 
MomsDuster said:
Cass got back to me.
No. The front port feeds the rear brakes like all Mopar master cylinders.

Cass
Click to expand...
He responded to you yet I emailed him last night and have yet to get a response.
If he thinks the ports are traditional, what is the reason for the front port getting pressure and fluid first? Why should the rear brakes get pressure before the front?
 
Go to a parts store and buy a master cyl for a 1979 Dodge Ram manual brakes. I could put someone through the windshield at 100mph. If installing it in an a-body with and adapter use a E-body or B-body brake push rod . This gives the extra length to make up for the adapter.

DSCN1676.jpg
 
I have a Mancini (made by Strange) aluminum master cylinder. The instructions that came with it say it is for 4 wheel disc brakes only. I will be using rear drums, so ended up purchasing an aluminum master for a 1980 Volare with manual disc/drum brakes. I checked the plastic reservoir and the large side of the reservoir is in the rear, which would be for the front brakes. I never checked the Mancini master to see if both sides of the reservoir were the same size.
 
Oldmanmopar said:
Go to a parts store and buy a master cyl for a 1979 Dodge Ram manual brakes. I could put someone through the windshield at 100mph. If installing it in an a-body with and adapter use a E-body or B-body brake push rod . This gives the extra length to make up for the adapter.

View attachment 1716014192
Click to expand...
This is the part number for that unit. It shows the different port thread sizes. The rear port on mine does have the smaller threads so it does have the traditional arrangement.

RAYBESTOS MC39178 Specifications
Number of Ports2
Primary Port Thread A1/2"-20
Secondary Port Thread A9/16"-20

I'm still curious as to why I'm getting fluid to the rear brakes first.
 
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It could be as simple as it bleed out sooner. I also read the rear channel doesn't have a residual pressure valve in the aluminum master cylinders and the Iron ones do, could that cause a variation in bleeding?

See Post 28.

www.forbbodiesonly.com

Anybody using a 15/16" bore master cylinder

I just measured my pedal as I'm in the garage working anyhow. My pedal is 6" at rest off the floor, and if I stand on it as hard as I can it's 2 1/2 off the floor. I can't go that additional 1/2.
www.forbbodiesonly.com www.forbbodiesonly.com
 
qkcuda said:
I have a Mancini (made by Strange) aluminum master cylinder. The instructions that came with it say it is for 4 wheel disc brakes only. I will be using rear drums, so ended up purchasing an aluminum master for a 1980 Volare with manual disc/drum brakes. I checked the plastic reservoir and the large side of the reservoir is in the rear, which would be for the front brakes. I never checked the Mancini master to see if both sides of the reservoir were the same size.
Click to expand...
These plastic reservoir units have two fill caps but I've found that if you fill one side, it fills the entire reservoir. There is probably a divider inside but also an open space to allow the fluid to equalize.
 
Kern Dog said:
He responded to you yet I emailed him last night and have yet to get a response.
If he thinks the ports are traditional, what is the reason for the front port getting pressure and fluid first? Why should the rear brakes get pressure before the front?
Click to expand...
I contacted him through his website. All I know for sure is that it was a pan in the arse getting it bench bled.
 
Mine bled out fine.
Maybe if I understood fluid dynamics and hydraulics it would make sense to me. My mind spins when I don't have a clear understanding...I go off and think some "way out" scenarios when no clear explanation is available.
 
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