Proportioning valve or no for 65 Dart disc/drum brake conversion.

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Stumpy

Stumpy

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Finally getting around to converting to front disc on my 273 hipo 4-speed 65. Car currently has 10” drums and 14” rallyes. I was thinking about going Pirate Jack for manual disc brakes. I have already converted to dual master and have the new disc brake compatible master. I’m guessing I don’t need a proportioning valve. Am I wrong?

Also, I think this kit doesn’t need new ball joints and the current 14” OEM later A rallyes will fit.

Good kit or is there a better kit that isn’t overkill?
 
What are you looking for in a conversion? Keep the 5x4 bolt pattern? Link to the kit your looking at?
 
Hey @Stumpy There are a few discussion threads down in "Brakes for your Classic Mopar" that break down the various kits that are out there including Pirate Jack.

What would you consider to be "overkill" on a kit?

I am maintaining my SBP 14" and 9" rear drums so that really limited the options as most require moving to a 15" wheel.

Best of luck
 
I don't know anything about the kit but with disc up front and drum in the rear some type of proportioning valve is needed.
 
Dana67Dart said:
I don't know anything about the kit but with disc up front and drum in the rear some type of proportioning valve is needed.
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I’m already using a new distributing block for the current dual master setup. Early disc brakes with drums didn’t use a proportioning valve. Why is it needed in this case?
 
WV64Signet said:
Hey @Stumpy There are a few discussion threads down in "Brakes for your Classic Mopar" that break down the various kits that are out there including Pirate Jack.

What would you consider to be "overkill" on a kit?

I am maintaining my SBP 14" and 9" rear drums so that really limited the options as most require moving to a 15" wheel.

Best of luck
Click to expand...

I consider “overkill” the more expensive performance kits. I want to stay well under 1k for the kit.
 
Stumpy said:
Yes, I’d like to keep the 5x4 rather than drop more cash on new wheels and tires too. This is the one I was thinking of getting. Comes with lower ball joints.

DBK6272A-40-B - 1962-1972 Mopar A Body Small Bolt Pattern Standard Disc Brake Conversion Kit w/ Powder Coated Black Calipers
Click to expand...

I'm "PRETTY" sure it's a rebranded MBM front conversion kit....

Most every retailer gets them from MBM I found in my exploration. (the images match across multiple sites). I went with a power conversion kit from Classicdiscbrakes in Texas and they drop-shipped from MBM in Asheville, NC

DBK6272A-40-B - 1962-1972 Mopar A Body Small Bolt Pattern Standard Disc Brake Conversion Kit w/ Powder Coated Black Calipers
 
Stumpy said:
I’m already using a new distributing block for the current dual master setup. Early disc brakes with drums didn’t use a proportioning valve. Why is it needed in this case?
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Yes they did. I don't where you got your info. It's incorrect.
 
Stumpy said:
I’m already using a new distributing block for the current dual master setup. Early disc brakes with drums didn’t use a proportioning valve. Why is it needed in this case?
Click to expand...

"I'm not an expert"

The proportioning valve allows for balance of braking action between the front and the rear especially as the disc and drum combination would be out of wack.
 
Before you pull the trigger on a kit, contact Cass (Dr. Diff) and see what he offers. The plus side is he is well know and recommended for his excellent customer service and will support you after the sale with any tech questions.
 
RustyRatRod said:
Yes they did. I don't where you got your info. It's incorrect.
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I thought I read that proportioning valves were in later a bodies.

So I will need the distribution block and the proportioning valve or does the valve replace the block?

I won’t be doing the conversion, I’m taking it to a shop but I want to correctly source all parts to make sure that the Dart doesn’t sit there taking space waiting for a part I didn’t order.
 
Stumpy said:
I thought I read that proportioning valves were in later a bodies.

So I will need the distribution block and the proportioning valve or does the valve replace the block?

I won’t be doing the conversion, I’m taking it to a shop but I want to correctly source all parts to make sure that the Dart doesn’t sit there taking space waiting for a part I didn’t order.
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The proportioning valve serves as both. You CAN use an aftermarket adjustable proportioning valve installed in the line going to the rear brakes. Mopar Performance used to make a nice one. I would just use an appropriate factory replacement one.
 
I installed ‘73 - ‘76 big bolt pattern front factory disc brakes on my ‘66 Dart with the small bolt rear 9” drums along with an adjustable proportioning valve .
With this set up the p.v. is set wide open , the 9” drums don’t seem to need one .

Later when I get around to installing my 8 1/4” axel with large bolt pattern 10” drums the p.v. may come into play .
 
What most call a proportioning valve is a pressure restrictor. The best way to increase/decrease the effectiveness of the rear brakes is through the diameter of the wheel cylinders.
 
C130 Chief said:
What most call a proportioning valve is a pressure restrictor. The best way to increase/decrease the effectiveness of the rear brakes is through the diameter of the wheel cylinders.
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Well that's funny. In the HUNDREDS (maybe thousands) of technical manuals and service manuals I've read in my life as a professional dealership mechanic, I have never once seen it referred to as a restrictor. Always proportioning valve. Every single time. Although what you say makes sense, I think if the factories wanted to call it a restrictor, they would have.
 
RRR,
You are right, a prop valve. For the OP: it is needed with disc/drum combinations because discs need about 50% more line pressure than drum brakes, so pressure to rear brakes is 'proportioned'.
 
Sort of yes because the servo type drums multiply the braking power.
But that could be addressed by the wheel cylinders and brake size.
Its more about maximizing initial braking and then proportioning to prevent lockup during hard braking as wieght transfers off the rear.
Just like the factory pamphlet describes.
 
I have taken several Combination valves apart, and concur that they are just a hold-off valve . The idea being exactly what @C130 Chief said in post #18. It's just a valve with a spring. I can't speak as to the pressure required to blow it off tho.
And IMO, Chief is also right about w/c size being a better anti lock-up plan.

Stumpy said:
I’m guessing I don’t need a proportioning valve. Am I wrong?
Click to expand...

The answer is yes and no. With four same sized tires and 10inch rear drums, you may get premature rear wheel lock-up, so in that case yes you are wrong. Premature Rear Wheel lock-up must be avoided at all costs because as soon as the wheels stop turning, the back-end is already planning to come around , and you may have only milliseconds to avoid a spin-out or a collision.
But if you have bigger tires in the back, you may be able do better proportioning with smaller brakes and or fine-tune with w/c size.

For example; I run NO Proportioning at all on the back of my car.
It has 10x2 drums on the back, 7/8ths w/cs, and 295/50-15s.
on the front are KH 4-pots and 235/60-14s.
The M/C is a 15/16ths, and yes I run a large single-diaphragm Booster.
When I brake hard, it's like I imagine it would feel to throw out a 'chute at speed; the car just hunkers down and stops without any drama. Because it works so well, I sometimes drive stupid because I know the brakes will be there for me.
I gotta admit tho, that she burns off more than double the sets of rear shoes to one set of front pads..... In other words, the rears are doing a lot of the light-pedal work. And I like it that way, cuz in 1999 when I built the car, there was no way of knowing if I would ever be able to procure another set of rotors. So I stocked up on pads at least.
 
WV64Signet said:
I'm "PRETTY" sure it's a rebranded MBM front conversion kit....

Most every retailer gets them from MBM I found in my exploration. (the images match across multiple sites). I went with a power conversion kit from Classicdiscbrakes in Texas and they drop-shipped from MBM in Asheville, NC

DBK6272A-40-B - 1962-1972 Mopar A Body Small Bolt Pattern Standard Disc Brake Conversion Kit w/ Powder Coated Black Calipers
Click to expand...

MBM and Pirate Jack are one in the same, and in the same building....so you are correct. They are maybe 10 miles from where I live.
 
A hold off valve is usually called a metering valve. It's used on the front brakes (of some cars) to reduce front lock up at low speeds on icey pavement and similar.
 
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