Hey there, Duck cruzin' with a heavy foot again? Wear the boots with the brake linings...........

Stargazer had a note on here (I think?) about using a different divorced brake booster. Apparently, we are (as usual) being victimized by vendors on account of wanting the "original" parts - when another nearly duplicate part is available for less (and looks just like it).


 
 Steve Metzger       Tucson, Arizona

Seems that anything short of a full-on disc conversion is a 50/ 50 proposition, at best and would come at the expense of losing my power assist. I'm not really in a position to let go of all that $ to do a conversion right now, either. I think I'll just have my booster rebuilt, and buy a big anchor w/ 50 ft. of good heavy chain, in the meantime 'til I can scrape up the coin to do it right. I am still going to send my wheel cylinders out to be sleeved w/ .304 this week however. /Duck

BOO- YA!!!

So the brake warning switch (isolation valve) does most of the work protecting you from brake failure, that's what was told to me and is now confirmed by the link provided by Mark.

I wonder what would happen if you installed an isolation valve (see I learned a new term today) on a single master, split the brake system front to rear and pipe it to the outlets then connect the 2 inlets to a stock single master cylinder. Would that protect from any failure on the down stream side of the valve?

Sure you could still have a master cylinder failure but I have never seen one fail without warning such as sinking pedal or leaking at the pushrod

If the brake system has been opened not using the lock out tool and the isolation valve has gone off center and either the front or rear brakes won't bleed, here is the way to recenter the pressure differential valve. Make sure all four bleeders are closed. Have a helper sit behind the wheel with his foot on the brake but not pushing it down. Open a bleeder on the system that system that will bleed (front or rear) while having the helper very slowly press the brake pedal down until a pop is heard or felt in the brake pedal travel and hold it in that position without moving it. Close the bleeder. The isolation/differential valve is centered and the warning light should be out. I had to do this as an apprentice a few times before I listened to the journeyman explain, once again, how and why to use the lockout tool. I still have mine from 1979.

57 Black Tbird 312/auto

Here is a good description of the brake system function including the pressure differential switch/isolation valve.

http://www.classicperform.com/ShopTalk/

There is a tool to use when bleeding or servicing the brake system to keep the pressure switch/isolation valve centered. Before the hydraulic system is opened, the pressure differential switch connector on the combination valve is removed. In its place, the tool is threaded into the port which has a small pin on it to hold the isolation valve in the centered position.

http://www.npdlink.com/store/products/tbird_brake_pressure_differential_valve_switch_lock_tool-178818-6444.html

57 Black Tbird 312/auto

I had the same situation as Charley, on two different cars. Both have combination valves and dual master.

54 Victoria 312;  48 Ford Conv 302, 56 Bird 312
Forever Ford
Midland Park, NJ

I like to have thought that, too. But that's not what happened. A, fortunately, very low rate of speed in my driveway and the parking brake stopped it. Hydraulics were doing nothing.
There is more too it than simply the master cylinder. I don't know enough about it to say what, and I don't want to contribute to the mis-info.


Lawrenceville, GA

If i ruptured a brake hose, i'd like to think that with a dual circuit master cylinder, two wheels would at least slow me down.


South Australia

There is a lot of mis-info related to brakes. Mine with the dual master cylinder is no safer than a single. That I can tell you as a fact. Something that was mentioned to me is perhaps the pedal travel is not sufficient to engage the safety feature. I haven't taken the time to research this for myself but it should be easy to get an idea if yours is sufficient by finding a travel spec for the vehicle that the master cylinder is intended for and then verifying that yours can achieve the same.

At this point, I'd advise you to not expect the "safety" that everyone claims of a dual mc on a vehicle for which it was never intended. If you install it, maybe it will be safer and maybe it will not. I guess that chance could make it worth the cost.

Here's a fairly recent thread to give you a little more to think about.
http://forums.y-blocksforever.com/Topic90139.aspx


Lawrenceville, GA

To make it even more confusing I have heard that you must use the brake failure switch (4 ports) as it contains a shuttle valve that not only turns on the brake warning light but blocks the line to the failed system to maintain almost normal pedal hight during a system failure.

Nothing says you have to wire the warning switch but a cutaway view of the switch I have seen looks like it does block the failed ports on activation. If you have ever bleed a dual master right at the ports the pedal drops almost all the way to the floor when any line is cracked so there may be something to using the switch.