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disc/disc or disc/drum MC?
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udoittwo
Posted 2014-11-20 8:19 AM (#462341)
Subject: disc/disc or disc/drum MC?


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On my 1967 Disc/Drum master cylinder that I'm using on my AAJ brake conversion, the rear[firewall] reservoir is the larger of the 2 reservoirs and the larger always is used for the Disc because the calipers require more fluid. Every Disc/Drum MC that I have seen, the rear reservoir is the larger. The new pre-plummed MC & proportioning valve kits for Disc/Drum that I've seen, have the rear reservoir line going to the rear brake port of the proportioning valve. By the picture and looking at the cap of these new MCs, it looks like it might have the same size reservoir front & rear?
I've been looking but can't find any info on this. Could they be using a Disc/Disc MC? I guess a Disc/Disc MC would work fine for Drum/Drum? The drums wouldn't care how much extra fluid is available maybe just the bore size. For Disc/Drum, is there a progression of the MC piston that has to make one apply first or is that what the porportioning valve does?
Hope this makes sence and someone has an answer.
Karl.
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Mopar1
Posted 2014-11-20 11:02 AM (#462353 - in reply to #462341)
Subject: Re: disc/disc or disc/drum MC?



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You need to match what you have. The front brakes do most of the stopping & should have the larger reservoir. drum/drum is just a splitter. Aftermarket proportioning valves should have instructions as to how to plumb them.
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57chizler
Posted 2014-11-20 1:41 PM (#462362 - in reply to #462341)
Subject: RE: disc/disc or disc/drum MC?



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One of the more popular MC's is from a 4-wheel disc GM, with equal sized reservoirs it doesn't really matter which MC outlet port feeds which system. The main difference between them and the disc/drum MC's is the absence of a residual pressure valve (RPV).....a disc/drum MC will have a RPV in the front reservoir for the drums.



(Vette MC.jpg)



Attachments
----------------
Attachments Vette MC.jpg (7KB - 127 downloads)
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udoittwo
Posted 2014-11-21 7:36 AM (#462421 - in reply to #462362)
Subject: RE: disc/disc or disc/drum MC?


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That's what I thought. I run an in-line valve anyway.
Thanks.
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55coronet440
Posted 2014-12-05 2:42 AM (#463671 - in reply to #462362)
Subject: RE: disc/disc or disc/drum MC?



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57chizler - 2014-11-20 12:41 PM


One of the more popular MC's is from a 4-wheel disc GM, with equal sized reservoirs it doesn't really matter which MC outlet port feeds which system. The main difference between them and the disc/drum MC's is the absence of a residual pressure valve (RPV).....a disc/drum MC will have a RPV in the front reservoir for the drums.


I found out that the drum port on my M/C (bought one for a '72 Plymouth) didn't have the RPV so I got a 10 lb. Wilwood inline valve from a friend. Have yet to get the new line plumbed to the rear that will also have the MP adjustable proportioning valve and the RPV installed. I'm planning to just run the line from the M/C disc port down to the distribution block and on to the calipers, and run the drum line straight to the prop valve, then add the RPV right where that line connects to the rearend's rubber hose. The rear outlets on the dist. block will be plugged.
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udoittwo
Posted 2014-12-05 9:58 AM (#463698 - in reply to #462341)
Subject: RE: disc/disc or disc/drum MC?


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I've been talking with Summit racing and they had no ideas why my car doesn't stop but suggested that my MC bore might be too large. I kept going larger and it made no difference, so I found a new[not rebuilt] disc/drum MC with just under a 1" bore instead of the 1 1/32". I found a set of NOS return springs for the rear drums as one was not releasing very well and while I'm at it, I'm going to replace the old rear brake lines with nice copper/nickel lines.
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ttotired
Posted 2014-12-05 5:54 PM (#463749 - in reply to #462341)
Subject: Re: disc/disc or disc/drum MC?



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Not sure copper lines are a good idea Karl

Copper has a lower burst point than the steel lines that were there orriginally

You should be able to get the right pipe (pipes, 3 sizes if memory serves), its called bundy tube here, but its easy and cheap to get

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Beltran
Posted 2014-12-05 7:44 PM (#463764 - in reply to #462341)
Subject: Re: disc/disc or disc/drum MC?



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Chevy put the larger reservoir in front and Mopar put it in the rear next to the booster. The one that Chizler posted up there is the unit I have, it is mated to a Wilwood valve set up.
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udoittwo
Posted 2014-12-06 6:22 AM (#463797 - in reply to #463749)
Subject: Re: disc/disc or disc/drum MC?


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From all that I've read, copper/nickel[not pure copper - 90% copper/10%nickel] brake line was tested to be superior to steel in bursting strength and corrosion resistance. It has a bursting strength of 3200 lbs. The one article said that figure is technically multiplied by 3 or something to get actual strength at nearly 10,000 lbs. Didn't understand that part. It doesn't corrode nearly as fast and is MUCH easier to bent and flare than steel. It is more expensive. I went to Advance Auto where they stock and sell a lot of it and paid $52 for 25" roll of 3/16" but on eBay, found same roll + 15 3/16" fittings for a little over $42[free ship] so I took back the Advance stuff. Coated steel which is less than 1/3 the price but with the copper/nickel you shouldn't have to worry about your lines again and 25" should do 1 car. It is used on many high-end cars[Rolls Royce, Lamborgini, BMW, Audi, fire trucks, ect.]. Its much easier to work with than stainless and it has a sort of appealing brass/steel color but can be painted if needed.
Might be something for you to check out if you need to do any brake work.
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57chizler
Posted 2014-12-07 5:41 PM (#463908 - in reply to #463797)
Subject: Re: disc/disc or disc/drum MC?



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It's worth noting that the 90/10 copper-nickel alloy is far different from the copper tubing you buy in the hardware store.
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60 dart
Posted 2014-12-07 6:26 PM (#463911 - in reply to #463698)
Subject: RE: disc/disc or disc/drum MC?



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udoittwo - 2014-12-05 9:58 AM

I've been talking with Summit racing and they had no ideas why my car doesn't stop but suggested that my MC bore might be too large. I kept going larger and it made no difference, so I found a new[not rebuilt] disc/drum MC with just under a 1" bore instead of the 1 1/32". I found a set of NOS return springs for the rear drums as one was not releasing very well and while I'm at it, I'm going to replace the old rear brake lines with nice copper/nickel lines.



the larger the mc bore , the more pressure needed . a smaller bore will give one better stopping power and a much harder pedal feel but one
doesn't want to go too small ---------------------------------------later
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jimntempe
Posted 2014-12-07 11:08 PM (#463941 - in reply to #462341)
Subject: Re: disc/disc or disc/drum MC?



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The smaller the bore the longer a stroke will be needed.
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udoittwo
Posted 2014-12-08 10:49 AM (#463975 - in reply to #462341)
Subject: RE: disc/disc or disc/drum MC?


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I believe the MC that AAJ suggested when I installed the kit was a 15/16" bore. At least that was the first size I got. Then I kept going bigger looking for any improvement until I got to 1 1/8" but that was all before I added the proportioning valve and the 10 lb check valve. Now I have added those 2 items and after talking with Summit I am going back to a smaller bore.
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