My 55 ate its engine, so while it's out I'm pondering my brake setup. I've pieced this car together over 35 years and attempted to keep it in daily driver status. My brakes are a conglomeration of junkyard parts and ingenuity.. A few years ago, I swapped the rearend and now have four wheel disc. The back has Eldorado calipers and Trans am rotors. Front is...maybe Chevelle or Pickup calipers and rotors. -- My issue is I have no recollection of swapping out the master cylinder. I'm running a power booster from a big Buick (as best I can recall), and I think a Corvette master. I also have a proportioning valve from...something...?? So, I'll probably swap the master only because I'm not sure for sure... Now, do I even need a proportioning valve with a 4 disc setup? Researching this gets me a slew of conflicting answers. Oh yeah..note to self. Start keeping a list in the glovebox of what the hell I install in this collection of miscellaneous rolling parts.
I put a disk brake kit on my 55 a few months back. I got it from speedway but mine are only front disk. When i looked at the brake kits there was one for 4 wheel disk and yea it did come with a proportioning valve. Look them up and you should be able to figure out what you need. Good luck! Sent from my iPhone using The H.A.M.B. mobile app
I did 4 wheel discs on mine as well, but I was fortunate that my master cylinder was already able to work with rear discs. I installed a proportioning valve, even if I didn't NEED one, since it is really nice to be able to dial in the rear bias how I want it. If your rear brakes lock up easily, then yes, I would recommend a valve. Even if you don't need it, there's no harm in having it.
So you have been driving it for a few years now, how does it stop? If the answer is "fine" then leave it alone. The corvette mc is correct for 4wdb. the proportioning valve is ok, it also serves as a distribution block and in fact might be what you have. You know what calipers you have and the rotors are probably not PU truck that would have a different bolt circle not the 4-3/4" that the 55 had. Pat
Not sure what you're trying to accomplish as you didn't mention how your current setup performs, but if your intention is to "standardize" your brake system, I would order a complete kit from a known supplier. If you just want to swap out your master cylinder, look up a 4-wheel disc brake unit from one of the Tri-Five vendors to ensure it's a bolt-in deal. I would use an adjustable prop valve for the rear so you can adjust the bias as necessary, as others have noted.
I guess I should mention that I really didn't notice any real issues with braking, but can't say I ever even had a panic stop. I did have fits bleeding the brakes a while back after changing the front brake hoses because one swelled up and was "wet". After reading y'alls input, I'm going to swap the MC and buy an adjustable proportioning valve. Thanks
There is a valve that installs in the front brake line to reduce the initial pressure. It is supposed to prevent the fronts from locking up and allows the backs to work better. Damned if I can remember what it is called. Not a purporting valve. This might be something to investigate in case of the need for a hard stop.
Metering valve, used in disc-drum applications to delay the front brake application to allow the rear drums to overcome the return spring pressure to start to apply at the same time. Avoids a nose dive situation. Sent from my iPhone using H.A.M.B.
..but if your intention is to "standardize" your brake system.. Yes. good way to put it. Trying to set it up so I know it is correct. Looking now at booster/ MC combo's.
I would defiantly put a adjustable proportion valve, no metering valve.. That master cyl looks like it was from a 60s Corvette four wheel disc brake system..
So shit... is there, or is there not,a difference between MC's for disc/drum vs disc/disc? Shopping sites make no differentiation..
Reservoir size. That’s it Drum masters may have residual valves. Now that’s it Sent from my iPhone using H.A.M.B.
So what difference could reservoir size make? It's a big pool of fluid that sits on top with 98% of it never used unless you have a leak... And what is a residual valve?
I'm glad you added that point Fargo. And Agele55 there is a difference in MC. Like I said before you had/have a working brake system and you want to f#@k with it. I would venture a guess that after you are done listening to all the recommendations that have been given here and change everything you will be back on here trying to find out why something isn't working and blaming defective parts. I hope you have a satisfying result. Pat
This is what happens when I try to outsmart a car as old as I am... I’m starting to lean heavily towards Leave it the F#@k alone...
The reservoir size is bigger for discs as it has a greater void to fill as the caliper pistons extend due to pad wear. The residual valves keep a small amount of pressure in drum brake systems to keep the cup seals sealed upon brake release so they can’t pull in air. Sent from my iPhone using H.A.M.B.
It's not the reservoir size, it's the master cylinder's bore size that you need to be concerned with. Drum brakes take a lot of volume to actuate the brakes, discs require more pressure. That's why these older cars that had drum brakes had 1/4-inch brake lines and we can get away with using smaller, 3/16-inch lines when using disc brakes. Though I run 3/16-inch lines on my Model A with 4-wheel drums and it works great. A larger bore size master will tend to give a firmer pedal feel. Also, as mentioned, some drum brake masters have internal residual pressure valves that will wreak havoc on a disc setup. An early Ford 4-wheel drum setup used a 1 1/16 bore master cylinder, which would be too big for most disc brake setups. Best case scenario, figure out what brakes you want to run, front and rear, whether you want manual or power brakes, and consult one of the vendors regarding master cylinder sizing.
Actually drum brakes take way less volume to actuate than discs. Think about the space behind the caliper piston compared to the wheel cylinder. Once the air is out of the system it there is less than a teaspoon of fluid “flow”. It essentially acts as a solid. A smaller bore master will give more pressure but increased pedal travel. That’s the reason why a larger bore master will give a firmer for pedal as you put it. It generates way less pressure. Therefore we have to push harder. Sent from my iPhone using H.A.M.B.
The Jalopy Journal
