Tonight, I decided to try a master cylinder with a smaller bore. The one I've been using is for a 1968 corvette with power brakes, 1 1/8" bore. The one I want to try is for the same vehicle with manual brakes, 1" bore. I have manual brakes.

Anyway, I got it installed, and the front brake circuit would not bleed. I tried the two person method - 1 handling the screw, the other handling the pedal. I also tried a vacuum pump. I also noticed that the master cylinder would not make a little fountain in the reservoir when the pedal is pressed.

Both cylinders allow the pedal to travel to the floor so they aren't bottoming out. The 1 1/8 cylinder might require 1/3 of the available pedal travel to stop the truck and so there should be plenty left for the 1" bore.

I think it's a bad master cylinder. What do y'all think? have manual brakes.


Lawrenceville, GA

Did you fill and bleed the master cyl before you installed it?

Glen Henderson



Freedom is not Free

Letohatchee, AL

Charlie:

Do you have a little bit of "free play" when the pedal is all the way up?  If not, the actuating rod may be too long and not allowing the cylinder to back up far enough to take in fluid.

John - "The Hoosier Hurricane"

I don't think so. How do I do this?







There is some free play.



Lawrenceville, GA

charlie

i may have an answer for you if the master is second hand check the bottom piston is not stuck in the bore i have had this happen on master cylinders before usually the front wheels wont bleed & no fountain in the resevoir you cant feel it pressing on the brake pedal it will feel like both pistons are moving as the spring between the 2 pistons will still compress have also had it happen on a new master cylinder that had sat on the shelf for a while at the parts store & was bench bled.

moz. geelong victoria australia.

graduate 1980, bus, truck, car, hot rod, boat, submarine, hovercraft, hydrafoil, firetruck, mobile home, jet, helicopter, cruise ship, motorcycle, bicycle, santa's sleigh, clock, alloy bullbar, alloy fuel tank, lens, dr who's tardis, matter - anti matter warp drive buffer & y-block lover

It's a remanufactured master cylinder. I was thinking about taking it apart to see if anything is apparent. I haven't taken one apart before. Are there any parts that like to jump out and dive into the black hole under the work bench?


Lawrenceville, GA

  This is called "bench bleeding" and is VERY important, Charlie.

Simply take the M/C to your bench and install plastic tubes (or old brake lines) from the brake line outlets back to the reservoir.  Fill both sides at least half way, then pump the piston at least thirty times.  You will see tiny air bubbles in the fluid, so the idea is to do this relatively slow.  Keep pumping until the bubbles stop.

The M/C has lots of nooks and crannies inside.  Doing this on your car will require LOTS of brake fluid (because the tiny bubbles  keep coming for many strokes).  On your bench, return tubes recycle the fluid so there's less waste.

You are smart to go down from 1-1/8" piston.  That's a lot of area, and I never met a brake system that required so much volume.  Reducing the bore to 1" will give your foot a 20% easier pedal.  Reducing to 7/8" will ease the pedal by 40%!  My '55 Customline came with a 7/8" M/C.  It pushed four shoes without a power booster, just fine.  If you keep up with your brake adjustments 7/8" is the way to go.

Hope this helps.  - Dave

Royal Oak, Michigan (Four miles north of Detroit, and 12 miles NORTH of Windsor, Canada).  That's right, we're north of Canada.

Ford 292 Y-Block major overhaul by simplyconnected

not really once you remove the circlip the washer & first piston may pop out but they shouldnt goe flying under the bench. as its remanufactured it could be possible a cup is on  the piston the wrong way ive had that happen as well you know put together at 4.45pm on a friday

moz. geelong victoria australia.

graduate 1980, bus, truck, car, hot rod, boat, submarine, hovercraft, hydrafoil, firetruck, mobile home, jet, helicopter, cruise ship, motorcycle, bicycle, santa's sleigh, clock, alloy bullbar, alloy fuel tank, lens, dr who's tardis, matter - anti matter warp drive buffer & y-block lover

I've never heard of that. But if it's a good thing to do, then perhaps I should start doing it. Sounds like an excuse to make another tool. I haven't had problems the way I've been doing it - perhaps until now.


Lawrenceville, GA

Charlie, you can use old 3" brake line ends.  Just bend them up, back into the reservoir (like a "C").  Some instructions make it clear to end the hose below the liquid surface, in case the brake fluid wants to suck back into the M/C.  I find old brake line works better than clear plastic.  When bending the line, metal tends to stay put.  Plastic needs clips to hold it down.  Here's what MBM includes for bench bleeding, with the purchase a M/C:

It's a couple clear tubes with hard plastic tapered ends (you just shove them into your output holes).  Here's another set:

This kit has "exact fittings" but it's the same thing, two little plastic tubes.

Put the M/C in a vise and start working the piston in and out, like I said, about thirty times.  When the bubbles stop, you're ready to mount it in your car.

-  Dave

Royal Oak, Michigan (Four miles north of Detroit, and 12 miles NORTH of Windsor, Canada).  That's right, we're north of Canada.

Ford 292 Y-Block major overhaul by simplyconnected