Master Cylinder

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TexinCali

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1972 dart /6 9" drums all around, manual

I asked this in another thread but got no response so want to try again. I will eventually do a scarebird conversion but need the car on the road ASAP while I gather parts.

I need a new master cylinder now. If I replace all of the wheel cylinders, I have read that new wheel cylinders do not need the residual valve, can I use a disc/drum master with all drums until ready for the scarebird.

If not I will just get a rebuilt drum/drum for now but I would rather just do it once if possible.

Thanks!!
 
I am not aware that new wheel cylinders do not need the residual valve or have the valves inside them. I have always seen the residual valve(s) (or check valves) in the MC. So, no you could not use a disc/drum MC, unless you get a separate residual valve to put inline with the front drums for now.

Some info on residul valves types: http://www.mbmbrakeboosters.com/ind...tent&view=category&layout=blog&id=8&Itemid=16
 
For everyone, the linked article states for drum-drum brakes:

Drum brakes require a 10 lb. residual pressure (RPV10) to counteract the spring tension in the drum system which tends to pull the shoes away from the drums. This will give you a longer pedal travel and "spongy" brakes. The residual valve holds a pressure keeping the shoes near the drums giving a higher firmer pedal. Also required a metering valve (PVM) to the front (the metering valve prevents nose dive).


That doesn't jive with what I have read elsewhere. The "... to keep shoes near drum" sounds particularly strange. Our cars have "self-adjusters" that keep the shoes "tight enough". Wouldn't you always want the shoes to return to their mechanical stops, not resting against hydraulic pressure? I am just a mechanical engineer and these MBM guys are ? (shows old guy w/ handle-bar mustache). Anyway, decide for yourself what makes sense.

I understand that only rodders who place the MC below the floor need a residual valve today. Its purpose is to keep the rubber cups at the wheel cylinders tight so air doesn't get past them. The "new style" cup springs (say since 40 yrs ago) have a metal base (or tight-wound spring) that keeps the rubber tight, thus obviating a need for a residual valve in the MC.

The MBM suggestion of a metering valve for the fronts in drum/drum sounds confused also. I understand you only need a metering valve for a disk/drum setup. Its purpose is to hold off actuating the front disks until the rear drums have time (enough volume flow) to contact the shoes. Such a "front metering" is integral in later "combination valves". However, many people have no problem using just a proportioning valve for the rears in a disk/drum setup. Haven't heard of them complaining of "nose dive", but that probably requires a panic stop.

Similar to you, I rebuilt my brakes and want front disks eventually, but drums for now. I used a later disk MC & booster (for 95-99 Breeze) and the brakes work great.
 
You can use the drum/drum master cylinder,, then remove the residual press. valve from the front brakes, using the technique in this video.. only leave it on the car.. and re-bleed//

Brake fluid is excellent paint remover,, so if you get any on the paint,, rinse immediately with lotsa water..

http://www.bing.com/videos/search?q...&mid=FBA26E668FEAF993E5F9FBA26E668FEAF993E5F9

I'd use a 15/16 bore M/C to get the best "feel" and pedal effort..

Rock Auto has them..

hope it helps
 
Hey guys, thanks for the input;

I picked up a 15/16 bore stock replacement today and will probably get it on so I can get on the road but Bill spelled out my thought process exactly, seems to be lots of data that does not stack up, you layed it out nicely, just like an engineer should ( I am an Architect :D) and sounds like it worked fine.

Thanks again for the help, really appreciate it.
 
Just to close out this thread, I got the new Master on this weekend and we are back on the road. I am going to start gathering parts for the disc conversion, and call me lazy but am really thing about going power assist. My '78 F350 has power discs and I don't have to work nearly as hard to stop that beast as I do the little dart, of course they are HUUUGE.....

As has been said before this forum is the best, I would not be able to keep the car on the road without all of the help.

THANKS!!
 
I did do some reading on the capacity issue, seems to be fine if the fluid level is watched. Although when I do the disc upgrade I will probably go disc/drum master anyway. I just had to get it on the road hence the drum/drum mc for now.

Thanks
 
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