47-55.1 Drums to Disc, What master cylinder to buy?

[CombustionSociety]

I am in the process of converting my rusted out and missing drum brakes in the front of my 53 GMC 150 and replacing them with Disc Brakes (from 2007 Savana) using this forum thread. https://67-72chevytrucks.com/vboard/...d.php?t=647049

What new master cylinder should i purchase? Brake Booster? I know I want a dual master but I dont know what bore or size. Any help is appreciated.

[mr48chev]

Mechanicsman is still active on here but hasn't been on the board since Jan 22.

I don't know what he used for a master cylinder but he does have a build page on that truck that is seveal pages long when you include posts from the rest of us and I'd take time to go through it and see if he tells what he used. https://67-72chevytrucks.com/vboard/...d.php?t=562068

[dsraven]

will the master be under the floor like stock or on the firewall?
disc/drum?
gotta figure the size of the original master would be worth looking at. maybe get one from a savanna that had disc/drum if thats your plan too. a hydroboost would likely work well for you if you're going power brakes.

[mr48chev]

All I can say is match your master cylinder to the rest of the brakes,

Simply meaning check and see what the bore size of the master cylinder for the rig that your calipers and wheel cylinders or rear calipers came off. I'd have to think that a lot of guys get in trouble by buying an aftermarket booster, master cylinder kit that when all is said and done has a master cylinder that doesn't match the volume of the calipers and the rear wheel cylinders.

Truthfully that can go either way. either too small of master cylinder that can't move the volume of fluid needed to work the system or in the case of my truck back in the 80's a master cylinder/booster combo that was a bit too much for the Camaro calipers and rear wheel cylinders. That truck has always been a one man horse anyhow but then the brakes were super touchy and would lock up if you hit them a bit harder than you needed to.

[mick53]

I agree with mr48chev. I would use or match the original master and booster. If you call Wilwood they can probably look it up for you. They are great guys and speak American. When they designed my 12.88" 6/4 brake system they determined I needed an 8" duel diaphragm booster. So I have to figure out how to fit that under there. I'm running a vacuum pump because I have no manifold vacuum. Just about anything can be done but it all needs to play well together. It's brakes. Thank you for your time.

[dsraven]

a brake vacuum booster will be a little bit of a squeeze under the floor unless you buy one of those small diameter ones that a lot of people have problems with, thats the reason why I suggested a hydroboost and also why I suggest to figure out the goal of the whole thing as a unit before putting together a disc/drum set up. if borrowing a disc set up from a savanna then also borrowing the master cylinder makes sense if the savanna had disc drum as well. it probably also had a hydroboost so grabbing that whole system at the same time makes sense. grab everything down to the brake hoses and frame brackets for them. installing a hydroboost under the floor isn't much different than installing a vac booster except there is the power steering pump to deal with. that is do-able. lots of guys on here have made the frame brackets or adapted a frame bracket to install a hydroboost further back on the frame to allow room for other things like transmission bellhousings etc. to avoid also installing a vacuum pump to run the vac booster a hydroboost may be th way to go and will give awesome boost all the time. it also allows for a power steering system upgrade later if that is something you may be thinking of. sorry if I sound like a big hydroboost fan, I am just saying that there have been a lot of questions from guys who buy an aftermarket frame mounted dual diaphragm brake booster and master cylinder kit and then they have nothing but problems with it and spend a lot of time trying to get it to work, talking to the "tech line" wondering if they got the right parts etc etc. if you get all the parts from a savanna with a disc/drum set up and grab an adjustable proportioning valve so you can set up the brake bias you will likely have less problems.
your truck, you decide. just build it safe.

[CombustionSociety]

Originally Posted by dsraven

a brake vacuum booster will be a little bit of a squeeze under the floor unless you buy one of those small diameter ones that a lot of people have problems with, thats the reason why I suggested a hydroboost and also why I suggest to figure out the goal of the whole thing as a unit before putting together a disc/drum set up. if borrowing a disc set up from a savanna then also borrowing the master cylinder makes sense if the savanna had disc drum as well. it probably also had a hydroboost so grabbing that whole system at the same time makes sense. grab everything down to the brake hoses and frame brackets for them. installing a hydroboost under the floor isn't much different than installing a vac booster except there is the power steering pump to deal with. that is do-able. lots of guys on here have made the frame brackets or adapted a frame bracket to install a hydroboost further back on the frame to allow room for other things like transmission bellhousings etc. to avoid also installing a vacuum pump to run the vac booster a hydroboost may be th way to go and will give awesome boost all the time. it also allows for a power steering system upgrade later if that is something you may be thinking of. sorry if I sound like a big hydroboost fan, I am just saying that there have been a lot of questions from guys who buy an aftermarket frame mounted dual diaphragm brake booster and master cylinder kit and then they have nothing but problems with it and spend a lot of time trying to get it to work, talking to the "tech line" wondering if they got the right parts etc etc. if you get all the parts from a savanna with a disc/drum set up and grab an adjustable proportioning valve so you can set up the brake bias you will likely have less problems.
your truck, you decide. just build it safe.

I'm really digging the idea of a hydroboost and usings a proportioning valve to dial it in. Now i need to figure out how to rig up the power steering pump. Thank you all for your help. The Savana has a bore of 44mm and the 53 150 has a bore of 1 inch if anyone was curious.

[dsraven]

I suggest to grab as much stuff from your donor vehicle as you can so it all matches. Even the combination valve. Cut off the steel brake lines and leave the fittings in each accessory part so later you have the flare nut sizes required.

[dsraven]

1 inch converts to 25.4 mm
44mm is 1.73 inches
bigger bore displaces more fluid but is harder to push so the result can be less pressure actually applied to the brakes with the same amount of pedal effort. that is a factor to consider, remembering that the pedal mechanical advantage could be different between the 2 vehicles. the length of the pedal from it's pivot and where the pushrod attaches to the pedal are factors to compare.
for the hydroboost there are brackets you can buy to fit the old style trucks with the master cyl on the frame and there are youtube videos showing how guys are installing them. there are guys who have used that bracket and a hydroboost from a wreck and put them together on the frame and they work fine. cheaper than buying the whole kit. one build I recall, kim57, has the master cylinder mounted further back on the frame with a longer pushrod from the bracket and that gave him better access and room for other stuff in the area where the master cylinder would usually go.
here is a link to kim57 build. the master cylinder stuff starts on page 3 post 54, with the frame bracket and pedal. there is a few other build stuff mixed in before he gets back to it around post 73, then back again at post 161, the master cyl being mounted at 171, then post 200 shows the whole set up mounted. anyway, some stuff to consider. a different truck but the same theory.
http://67-72chevytrucks.com/vboard/s...=283107&page=3
another hydroboost thread using an astrovan hydroboost, also has some info from ogre's build where he used one from a mustang I think. anyway, you can look that stuff up if you go to the search box at the top of the page and type in what you want, then click the 67-72 spot instead of google and then hit enter.
https://67-72chevytrucks.com/vboard/...d.php?t=815582

[mr48chev]

Master cylinder bore Diameter on the 3500 series vans and trucks that the parts he used came off = 2010 is 1.5 inch. Most of those rigs run a hydroboost. Having a 77 1 ton with Hydroboost I can say that as far as booster goes that is the way to go.

Looking it up, the master cylinder for my 77 1 ton has a 1-5/15 bore.