quote:

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Originally posted by Fastback68:
I'm ignorant here What's the difference between a master cylinder for drums and for discs?

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The disc master has a larger reservoir for the disc pistons. {they take a much larger volume of brake fluid than the drum's wheel cylinders.} It also has a residual check valve which keep a small amount of pressure to keep the disc piston against the disc pad.

Don't use it.

As far as I know residual check valves are only nessesary on cars were the master cylinder is lower then the brake lines or wheel hydralics, Reguardless of if they are drum or disc. Mustang M/C are higher then both the lines and the calipers?

Reservoirs simply provide fluid for the brake system throughout their travel. If the reservoir provides enough fluid for full pedal actuation when the brake pads are worn to limits it has done it's job. The front reservoir can be the same as the rear reservoir or larger. The rear brakes if properly proportioned will displace less fluid thus not needing as large of a reservoir as the front. That goes for disc or drum brakes. The reservoir is just that, a reserve of fluid it does not affect the brake hydralics in any way.

Also, another misconception I keep seeing on this forum and other sites is how bore size affects pedal presure. The SMALLER the bore diameter the EASIER the pedal pressure not the oposite! It's all about mechanical advantage, the easier the work the more room will be needed to get the work done.

Misconseption number 2; "If I use X size master cylinder I don't have enough volume to actuate the brakes, I know this beacause the pedal is squishy."
The way to know if you don't have enough volume for the brake system is as easy as looking at your pedal. Does it hit the floor or bottom out in the master cylinder? If not you have enough volume and look for a problem else were for your squishy pedal!
Not haveing enough volume won't cause a squishy pedal. let's simplify it and say volume=pedal room. If you don't have enough volume then you don't have enough room to actuate the brakes, It's that simple.

Sorry for being a young punk, correct me if I am wrong, god knows it's happened before. But don't, what ever you do, take my word for it and spread misconceptions like wild fire! Read a book, talk to professionals and find out for yourself! While this forum is pretty good, bad advice has been given here and in any case it should be taken as advise not gospel. For gods sakes you could DIE cause some putz doesn't know squat about hydralics! That includes me!
Also, note the above post was in question form because Steve knows his Sh'tuff I was asking if he had just used the wrong word, or got mixed up.
Thanks, and again sorry.

[This message has been edited by SundanceKid (edited 08-24-2001).]

That being said, if Ford calls for a certain characteristic for a master cylinder for certain brake systems, and I'm changing the features of the car by adding power brakes or adding disc brakes, well, I'm going to go with what Ford specified. It is NOT opinion or advice to say "this is a Ford specification." It IS opinion or advice to say "this is not what Ford did, but I've done it this way and it works, or you could try it this way and it will probably work for you."

Its been my experience that people try things that aren't Ford specification because they are tight on money and are trying to cut corners with what they have available. To be melodramatic about it, that is where you put your life at risk dealing with brakes...cutting corners because you can't/won't wait until you have the money/parts to do it right the first time.

For disk brakes, the MOST critical thing to consider is bore size. As Sundance said, you've got to get enough juice to the calipers with an acceptabel amount of pedal pressure and travel. Power assisted M/C's tend to have larger bores, so you need to know whether you plan using a booster before you begin your serach for a M/C.

I found two master cylinders that work for power assisted 4 wheel disk setups: '78 Lincoln Versailles (came with 4 wheel disks....but the MC has port is on the right side which interfered with my 460's valve covers) and a '96 Windstar MC. Yes, a Windstar. It's of the small aluminum design (will never rot and is very light), has ample reservior size, 1 1/16" bore (perfect), and perfect pedal stroke and feel. It also bolted right up to my '67 booster. It required a slight mod at it's end to clear the shock tower. No big deal though.

FWIW,
Brian

Concact me off list if you need help with the 4 wheel disk conversion.

Regards,
Brian Bulow

Mellow, Go with your "opinions" and trust your "guts". Someday when you have a "sinking feeling" and your foots on the floor rushing toward a 300ft cliff.
Don't get mad when the guy at the morg has his own "opinions" about your "guts" and "feels" like he's gotta puke.

But seriously mellow, the only connection to your post and mine, is mine procedes yours and we were both talking about brakes. I was stating the "facts" as I know them, this does not mean I may have had a misunderstanding of the princepals involved and left the subject open to mature debate not a flame war.

In your post you stated:

1. It does have two differant size chambers.

Did you actualy read my post above? or did you stop at "putz" and get pissed and rushed to flame me back?
I also stated that in a properly proportioned system a M/C will have a smaller rear (meaning rear brake) chamber then the front (meaning front brake) chamber because the rear would displace less fluid then the front. This is due to the proportioning valve weither it be adjustable or not.

So what you mean is we agree on this then?

Now to further mess with everyones minds, they can be the same size too. Again restated, if you get you get it, if you don't you don't.
(not directed towards mellow)
As long as there is enough fluid to cover the master cylinder inlet ports and not allow air into the system throughout the pedal/piston stroke at maximum pad wear it doesn't matter what size the reservoir is! And furthermore, as was also mentioned the reservoir are sized over-large in the event the owner of said vehicle forgets to check the brake fluid level. In plain engilsh; It is not nessesary to make the the rear reservoir as big as the front reservoir because the rear fluid volume is not as large as the front.

Mellow, you also said;

2. It does have what appears to be a check valve on th side.

Again did you read my above post?
I said YES you do need a check valve for drum and a few disc brakes with mechanical retraction. The Ford disc system in question DOES NOT need a check valve. If you were to use a check valve you would cause serious premature brake wear and I'd hate to see your gas bill! To simplify it, if you use a 25psi check valve on your system it would be as if 25 psi was constantly being applied to the brakes. If you want to try this out for yourself, drive with your foot rested on the brake pedal, or apply your e-brake with 25 pounds per square inch or force. Drum brake pads are further away from the wear surface (the drum) then disc pads are from the disc. The reason a check valve is used on drums only is because the wheel cylinder seals require a slight amount of pressure to keep them sealed against the wheel cylinder bore.
The 68 M/C you had in front of you had drum brakes right? So it uses a check valve.

So we agree on that point as well?

Remember when I asked Steve if he might of had it mixed up? It was because he stated to use a check valve on disc systems, and that drum brake M/C don't have a check valve. So Mellow you say you saw a check valve? Acording to you you shouldn't, assumeing you still in your "opinion" "think" what Steve said was right.
Also in my experience with early Fords, wich I admit is limited, the brake proportioning was done in the M/C and used a distribution block wich is easily mistaken for a proportioning valve. Like I said I could be wrong, but don't mistake the one for the other or well, as I dramaticaly said you could DIE! The other way to proportion brakes with tandem master cylinders again as stated above is to use differant sized bore for the front and back. With this style system it is not nessesary to use a proportioning valve even, that is unless you want a non-linear pressure drop in the rear system wich is more favorable.

Drum master cylinders actually DO have 10 psi residual valves to maintain pressure against the cup seals in the wheel cylinders and overcome retraction spring pressure. Disc master cylinders have 2 psi residual value if, as you stated, the master cylinder is mounted below the calipers to prevent siphoning of the brake fluid from the caliper to the master cylinder.

Now I'll have to drag out my books, but I distinctly remember being told pressure is maintained in a disc system to keep the disc piston against the pad to prevent the piston from being retracted into it's bore. That is why disc brake systems always have a constant slight drag, and the reason some drag racers looking to eliminate wheel drag stayed with drum brakes for so long when disc brakes became commonplace.

I'll look into this further when I have a spare minute. Hopefully no lives will be lost in the meanwhile.

Now: Yes, I am a shi**y mechanic because I am not particularly fond of grease! LOL! I like assembly, body and fender and painting {no more as the new paints are too toxic} Oh, I CAN do mech things{ I like it right} but I'd rather be doing something else. I have other interests, also. I did do much of the mechainical assembly on my 65, though. After 10,000 miles, I'm still alive! Sorry about that, guy, I'm trying to lighten things up a bit!

To get back to the issue, I still wonder why going in the Ford manner would be harmful. It is a fairly straight forward thing. I look to Stainless Steel Brakes, Master Power Brakes for parts and they follow Ford guidlines with some improvements. Another good company which I know little about is Wilwood. Without being sarcastic, Sundance, why the dramatising about morgues, guts and whatever! If I use the parts that I know are good, and the work is performed by a savvy tech, why would it be dangerous? I have new rotors, calipers, lines, prop valve and wheel cyliners in the rear along with new drums, lining and hdwe.

I do not have credentials to back up my statements but I have relied on the advice of merchants and some people on this site- of ALL ages, I might add! And, in the case of brakes, I traded skills with a good tech. My 68 is going to have EFI/AOD, if I get off my a** and buy the stuff! The person doing it is {hesitate to mention age} a man of 25or 26 who has put blown, bigger V-6's with t-5's in two Ranger PU's. and is currently doing a "secret project" His work is impeccable! Some of the sharpest young men I've had the pleasure to meet are owners of late models in the club that I belong to.

As an opinion, I think that coping to one's age in defense or offense!! in describing a situation/s is a ha*d j*b!! It really can't be taken to the bank! Older people do it, as well as younger. We had a situation where a 17 yr old was WAY out of order and kept throwing up his age! I offer this ONLY as an example. Bottom line, his age made no difference 'cause he still had to take responsibly for his actions. The guy who gave me the idea about the larger drum brakes is a young guy of about 25 and he's a fighter pilot on top of having good mech. skills. Conversely, I am an older person, and I dislike an older person who is patronizing or looks down his nose at others. An older person does have to watch it because it's easy to do. I do know a few things about these cars as I been doing this since 1982, restoring, buying and selling. If I know something, I mention it-certainly not to make myself look good. Being retired has taken that competitive dog eat dog stuff out of this ol' boy!!

I got into this booster gig innocently enough, and I expressed some opinions so I'll have to take ownership of them. Oh well! But, I will take responsibility for them. So anyway, that's it for now, guy and I offer my hand to shake. If you come to the MCA show, I'll buy you a drink! Not the rest of you guys!! LOL!

Steve, As far as I know disc brakes do have a slight drag due to rotor runout (warpage) and no mechanical means to retract them. Drums have springs to retract them and old school drag racers prefered the drums because they could back the drums shoes off with the starwheel for absolute zero drag. I realy wouldn't know cuz, quite frankly it was before my time?
At least back then they didn't stick a coffee can on the exhaust pipe and expect horsepower gains!