The Stovebolt Site Forums The Shop Area General Truck Talk Help with drum/drum dual master cylinder

Would like to upgrade old single master cylinder to a dual master cylinder in my 3/4 ton with stock drum/drum. Looked at the past forums, but not much on 3/4 ton trucks where drum/drum is only option.
1. Do drum/drum require a Corvette master cylinder with equal sized resevoirs?
2. Is a porportioning valve required with master and drum/drum?
3. Does booster really help for drum/drum?
4. Does a 3/4ton to 1 ton brake system require larger sized master than a 1/2 ton?
5. Is it cheeper to get the under cab to frame mount/bracket from CCP and salvage a used master cylander. pros vs cons?

Alot of questions but hopefully I will be asking for others as well as myself to make the best combination for this upgrade.

Thanks,

Eric

Howdy crowsgmc,

A while back I asked many of the same questions and folks were kind enough to give me the benefit of their experience, so let me pass some of it along.
1. No, the 'Vette master is not required. There are lots of options, but you do want one for a drum/drum system. A '67 or '68
drum/drum Belair master will work fine.
2. According to Master Power Brakes, no proportioning valve is needed with drum/drum dual brakes.
3. I can't answer this one, I didn't use one, but a booster only "boosts" input pressure. Your brakes will only be as good as your shoes and drums.
4. No, the larger the bore of the master, the harder the pedal will feel. Again from MPB. Stick with no more than 1 1/8." I used a 1" bore master from Sachse Rod shop.
5. Oh, yes! As I understand it, you have to change your clutch pedal,too. That means more expense and hassle. The under floor
bracket is available from many outlets from about $55 up.

My conclusions run like this, to improve braking, you must improve your brakes. This means discs. I didn't want to go that route, so the dual master is for safety. Nothing else that you could do will change anything but "feel," as long as the rest of the system is in top notch shape.

You will also have to "replumb" the brake lines. Not a bad idea anyway on old trucks like ours. There is an excellent article on doing this in the "tech tips" section of stovebolt.com

Best wishes,I hope this is what you are looking for.

I'll throw my 2 cents in on this one too. There is nothing wrong with drum brakes in and of themselves, when they are set up properly. With proper leverage between pedal angle, master cylinder bore, and wheel cylinder bore the leverage on the shoes pushing them against the drums is plenty without unneeded effort. Consider the amount of friction material in a drum brake versus a disk brake. It has substantially more surface area than a disk brake. A disk brake has to grab much harder in a smaller area in order to stop the same vehicle. The only drawback to drums is they retain heat. Once they are warm they tend to stay that way.

Devin

Eric - I put a booster on my drum/drum brakes & it REALLY helps. At the same time time I put a double res. M/C. No prop valve is needed since both axles are drum, there's no need to proportion. I never even thought about resivoir size. Long as you fill it & it don't leak, anything should be OK. I did it all with wrecking yard parts & some mounts I welded up.
Doug

Thanks for your all your advice. Roadmarks...will look into the clutch pedal mod that may be needed. Would like to avoid if possible? But your information is what I was looking for...thanks.
55 Tractor, I saw here in one forum that there is a ceramic drum pad available that is recomended for todays driving, faster stopping and reduced heat, made by PDB. www.praisedynobrake.com.

Desertdog did you go to Desert Valley Salvage here in Phoenix for the used parts, and what did you look for?

Eric

I just did this on 55 2nd 3/4 ton. Do search on 55 2nd 3/4 ton dual master. I replaced all line, master, slaves, pads, springs everything. The master came from Classic Performance Products and includes the adapter bracket, everything else came from the local auto parts store. I recommend new over rebuilt master and slaves, mine were at least 20 years old and were to far gone. I had two issues, I needed a longer push rod from pedal to master piston than was supplied with the kit, and you need to adjust the brake pads as per the manual prior to final bleed. Bench bleed master, bleed longest lines first then shortest on front and rear respectively [separate reservoirs] and then adjust brake pads per manual. This is critical. Then do final bleed.

good luck

Don't get me wrong, I like power brakes. Adding a booster will not and can not change braking if the booster is the only change. A booster will only change the amount of physical input needed to apply the brakes. I did this change on a '75 C-10. After I installed the booster, I went out to a favorite, nearly unused back road and and did a couple of "panic stop" tests. I had a sign post that I had used as a marker before the changeover. At 40mph I nailed the brakes at the sign. The old pick-up stopped at exactly the same spot as before, it was just easier for me to push the pedal. Now I know that this is about as unscientific as things get, but it worked for me.

Maybe one day I will add a booster to my '56. It will make it easier for my wife to drive, but I don't mind the old truck feel.

I don't recommend my tests to anyone else for obvious reasons.

have fun!

I hope this works
I have a 50 3/4 ton which was just updated to dual cylinders etc,etc, on drum drum.
Try this post below.
It contains a lot of information on 3 pages of help and explanation to needs v/s requirments.


https://www.stovebolt.com/ubbthreads/ubbthreads.php/ubb/showflat/Number/241789/fpart/1



I really learned alot about my brakes, resistors, portioning valves, etc..

Hope you can get as much help out of it as I did.