Another 57 rear disc swap question

[Limey57]

My 57 Ranchero has the factory 9 inch axle, but the brakes are shot & need rebuilding.  If I swap to discs will there be issues with the rear brakes locking up before the fronts?  The front has a disc conversion kit.  I've read on here that late Crown Victoria's are a straight swap, but Crown Victorias are few & far between over here, a more common swap on a 9 inch is to use late 80's Mercedes discs & Ford Scorpio rear calipers on custom made brackets, but my concern is the brakes locking up due to the lighter rear end on a Ranchero.

Thanks

[Frankenstein57]

Gary, I'd go with an adjustable proportioning valve so you can dial it in. I got one online a CPP. They have all kinds of brake kits too.  Mark

[shopratwoody]

I didn't have good luck with the adjustable and was advised to use a stock Ford type.
Worked much better for me.

[Ford Blue blood]

Big thing with the dual master cylinder is if you don't have the factory (or similar after market) proportioning valve in there you still only have a single jar master cylinder.  The factory valve does do the proportiong but more importantly is it contains a piston that slids to the failed side (front or rear) and gives you brakes to the working side.  It turns on a light (brake) in late model cars to say you have a failure.  Most all master cylinders for dual systems have only three seals in them, they rely on pressure from the rear side to seal the front (maybe vicey verse) and without the slide to seal the failed part it will not give you brakes.  Those adjustable proportioning valve are meant for a two master cylinder system, one for the front and a second for the rear and allow adjustment to get the perfect balance.

[shopratwoody]

^^^ good answer^^^

[RICH MUISE]

Bill...I'm glad Ron repied to this today, because I was going to back when you posted it and got sidetracked. I never knew about the sliding piston being in the proportioning valve..I wrongfully assumed the dual cylinders had two seperate systems that functioned that way within the master cylinder itself.
Great explanation...and maybe would save someone some heartaches down the road.
Do all, or most of the aftermarket proportioning valves have the safety piston, or do you have to watch what you're buying?  Rich

[Frankenstein57]

I've been chasing a problem lately where my brakes start dragging on the front discs. They came in hot the other day, so I cracked the line at the adjustable pressure valve outlets to the fronts. The car relaxed, but it happened again. My buddy says I should run the fronts right off the master, (power dual) and use the adjuster for the rear drums only. Shouldn't that separate the front & rear?     Mark

[Ford Blue blood]

Rich the after market blocks that are designed for replacement parts will have the slider in them, the electrical terminal on the block is a sure sign.  I have not purchased one from the many vendors that do brakes so I can't speak of them but the picture of the master/booster/block from ECI has the terminal on it.

Mark running the line through the block gives you the split system, as stated earlier that ol slider valve needs to be there.  You might try looking at the push rod length, if it is too tight the master will not return to it's rest position.  This is the push rod between the booster and the master cylinder.  Many are adjustable and have been know to come loose and cause dragging brakes.  There should be between .01 and .015 minimum with everything at rest.  It is critical on disc systems because disc run primarily on pressure and require very little fluid movement.  The disc pads ride almost on the disc so there in no movement required to energize them.  As soon as you push on the rod the piston moves forward and covers the hole between the bowl and the piston.  What fluid you have in the piston bore is all that is used for operating the brakes on that stroke.  The other item to look at is the booster, a common failure there is for it to hold the brakes on when it has vacumn.  Easy check here, just remove the vacumn line a drive it, no dragging, good bet (still need to check the push rod).

[shopratwoody]

I got one pro valve at junkyard. Work fine on my bros car. I bought mine
from ABS in Orange Ca. Works way better than the one u adjust by hand.

[Frankenstein57]

Bill, as I stated on a different thread, I had too much adjustment between the master and booster. I also shortened up my linkage into the booster,drove it all over the place after work. Seems like that was it, thanks for your input.   Mark

[Ford Blue blood]

Glad you got it Mark.