The Stovebolt Site Forums The Shop Area The HiPo Shop differrence between master cyl of disc and drum

I'm trying to determine which master cyl to get.I will have 4 drum brakes in my 53.Is there a difference between a 4 disc and a 4 drum master cyl.I'd like to go to my local Napa dealer and know what to ask for.I was thinking of getting a 73-77 4 wheel drum brake master cyl/booster.Is that what I should be asking for?Does it need a flow control or any thing else?
Thankyou, Lothar

there is a differance. i cant remember exactly how to word it but the disc brake master one of the resiviors is bibber than the other where the brake fluid goes. the res. for the front is bigger. on the drum drum master both are the same size.if you are mounting it under the cab in the stock location you probably will need three risidual valves i belive 2lbs presure? hopefuly someone will know the correct answere on that.hope that helps

Are you sure that you can get a 73-77 drum brake set up? I'm fairly sure everything in that era was disc/drum. I also question that this booster would fit under the floor. As 53chev says there are some physical differences but the main internal difference in the disc/drum and drum/drum master cylinders is the residual valve(s).
Fred

The master cylinder for a drum brake system generally uses the same volume for both front and rear brakes; a disc brake uses a higher volume hence the different size reservoirs. A disc frt/drum rear system uses a metering (frt. hold off) valve usually holds off pressure to about 110 psi as the disc brake applies quickly and drums slower at start of stop. All drums don't use this valve. A disc/drum or a disc/disc usually has a valve in the rear system called a proportioner to slow down the pressure rise to the rears (prevents early rear skids from weight balance (light rear) and/or drum self- engergization). Master cylinders should match the volume of the wheel cylinders.

Many of the aftermarket suppliers use a Corvette master cylinder for disc/drum conversions which has the same size reservoir for F&R. I have been using this system successfully for about 7 years and installed several of them on other conversions.
A Corvette MC can also used with a disc/disc application.
It is important to purchase these components from a competent supplier and let them know what type of system you plan to use. Many parts will bolt together but may not be compatable with your system and achieve the desired result.
Fred

i once put a vacuum assisted master cylinder on a manual brake car... it worked, but not very well.. it felt like you were stepping on a brick... i put in the correct master cylinder, and it worked fine.

So if a vacuum assist is not that good and the Corvette one is for disc/drum which one is good for drum /drum?

Here's what i did with this problem on my 52pu with drum/duum. Go ahead and use the corvette mc, position in the same place as your original under the floor. Span the gap with a bolt, washers, double bolted with a cotter key. You'll need 2-10 lb residual valves for drum/drum and the the mc will work fine if you later want to go front disks. I run from wildwood residual valves. Install the 10 lb valves as close to the mc as possible. I like the brass ones from Engineered Components, Inc Vernon Ct. call them as 860-872-7046. Ask for EC-655 3/16 brass. Verify the pn as it may have changed since 2003. I'd also get a 2 lb valve for the future front disk upgrade at the same time. Good luck.

Thanks 52pu, what year of Vette is that?

Do you have any pictures?

I crawled under the truck just now. I know its a corevette mc and i think i got it thru classicperformanceparts.com. I also have the support bracket from them. So go on their web site and fish around. The support bracket is bolted up in the original location. Another option is to use a 69 ford mustang drum/drum mc with the 10 lb residual valve. I'm sorry I do not have the capability to take pictures.

Thanks,I'm in the same boat with pix,I'll see what I can find there 53pu

It seems all the oldtruck suppliers have a conversion"kit" what they don't say and we find here as well is that residual valves are needed. I heard some talk of not enough vacuum to operate the power booster from a 235. Is this true, what is the vac level required?
Wizard 50

Depending on the size of the booster, you will need 13 -18 inches of vac. to have any assist. I ran into this problem with another project, the brakes will work, but the boost will not be ample to make that big of difference. So I decided to go manual. I purchased the "kit" from Classic Performance products online. Came with dual disc/drum(in my case)master cyl. and a pre set prop. valve already plumbed with the support bracket for mounting in the stock pedal location. I will of course need to purchase residual valves for the front and rear. Cost was around $180. no guess work involved. I will be using the stock 235 and a T-5 trans.