Bleeding Master Cylinder

[mark69sportsroof 31]

Hey All,

 

What is the best way to bleed the master cylinder when it's in my 69 Sportsroof. I have disc up front and drum in the rear?

 

Thanks Mark

[Brian Conway 264]

Well your not going to like this;  disconnect the brake lines to the front and rear bowls.  Screw in the plastic plugs to the same two holes.  Next I suggest you get a someone to watch the MC while you slowly pump the pedal repeatedly until the bubbles stop.  Will take some time so be patient and bring a magazine.  Brian

[Rsmach1 71]

+1 with Brian, or just take it out and bench bleed it, one man operation that way.

[mark69sportsroof 31]

Thanks for the info. When I remove the 2 existing mc lines will the fluid in the bowls drain out?

 

Thanks Mark

[Rsmach1 71]

Yes

[RPM 1,190]

Put a towel under the master cylinder and when the plugs are removed hook up the lines. Only a small amount will leak.

[mark69sportsroof 31]

I bled the mc in the car. After 45 minutes the front disc brake bowl would only dribble out. I put in a new mc

and bled it again. Great fluid from the front and rear bowls. I bled all brakes and the brake pedal would be firm at

1-2 inches when pushing it down. Finally normal functioning brakes. I start the car and the pedal goes to the floor with about

10% pedal pressure. I noticed to 2 brake line connections barely dripping. I tighten them up. Any ideas on what to do

next?

 

Thanks Mark

[Rsmach1 71]

If you found leaking lines after you bled, you need to bleed again, if fluid can leak out, air can get in. Have you done any other work to your brake system? Changed calipers? Wheel Cylinders?

[mark69sportsroof 31]

Everything is new on the brake system. it has about 70 miles total the car. Just got done with a 4.5 years

restoration. I will bled again tomorrow and update all.

 

Thanks Mark

[Ridge Runner 1,113]

I havent bought a master cylinder in quite a while ,they used to come with two plastic plugs with nipples on them that you attached ruber hoses to .The two hoses go into the bowls while they are full of brake fluid .Pump the master cylinder untill air bubbles are no longer visible .The master cylinder is now bled . attaching the brake lines back to the master cylinder will sometimes allow some air into the lines so the entire brake system will need to be bleed .

[RPM 1,190]

I bled mine like Ridge Runner explains, but used old lines and fittings cut to fit into the reservoir. It's a simple one man job.

[Rsmach1 71]

Have you had the bad pedal since you replaced everything, or did it just start?

[Rsmach1 71]

Something to check if you've had trouble bleeding the brakes sine changing out the calipers. Also be sure the rear brakes are properly adjusted.

[mark69sportsroof 31]

I doubled check the calipers and they are mounted correctly as shown in the picture above on the left side. The pedal

pressure has always been the same. The brake booster was rebuilt. The pedal has good foot pressure then when I start it

no pressure.

 

Thanks Mark

[Rsmach1 71]

OK, well your booster sounds like it is good, when there bad the pedal will be hard as a rock with the engine running. When you said "NEW" master cylinder it's not a rebuilt one correct?

[mark69sportsroof 31]

Its from NAPA and the box says Premium New Master Cylinder.  Before replacing the mc, the pedal had about 10% resistance and if you pumped it 2-3x it

was about 70% pedal pressure.  After installing the new mc, I have hard pedal pressure at about 2 inches moving to toward to the floor.  It feels normal pressure.

Then I start the car and the pedal goes to almost no pressure.

 

I was reading the mc instructions and I believe I might have messed up.  When I bled the MC in the car.  I attached 2 old mc line to the mc and bent them to drain

back into the mc.  The instructions say to keep the lines submerged in the mc fluid so it doesn't suck air back into the mc.

 

Any thoughts?

 

Thanks Mark 

[Rsmach1 71]

Did you keep the lines submerged? If so were you able to verify there were zero bubbles coming out of the lines?

 

Edit, on a side note I ALWAYS bench bleed master Cylinders, never in the car, over the years I've had a few that leak out the rear seal. Doing it on the car you might not notice as it will leak into the booster.

[Brian Conway 264]

I got a MC from NAPA 3 years ago.  Part number M1929 is a 1" bore and works just fine.  The brake system is a closed hydraulic system.  Simply put; all fluid and no air in any of the separate parts; MC, lines and wheel cylinders, at anytime,  or it won't work.  The MC is a separate part and must be purged, emptied, cleared of all air usually before installing. .  This is done on the ' bench '.  If you are going to bleed the  MC the lines and the wheel cylinders as one unit be prepared for a lengthly process.  It seems this is all new to you and your working it out.  It is a learning process that we all have gone through.  When I learned how to bleed brakes it was a two person process.  I still do it that way.  When you get this worked out you will need to get that pesky brake warning light to go out.  Another adventure.  Brian   

[Ridge Runner 1,113]

Buy the distribution block centering tool before you attempt to bleed the brakes as a unit ,that is if you have front disk brakes ,it will save you lot of head aches trying to re center the piston in the block .It screws into the brake light sender in the distribution block .It can be unscrewed ,fluid will not come out of the hole ..

 

Some times the brake light sender will stick if the distribution block piston has tripped ,you can push the center pin back down with a test light ,the center pin simply makes  a connection completing a circuit and turning the light on .

[mark69sportsroof 31]

Thanks for all the help.  This is new to me.  I don't always have a second person to help so I try to do it in the vehicle.  I will try again and keep you updated.

 

Thanks Mark

[Rsmach1 71]

If your by yourself, just bite the bullet, pull it out and do it on a bench.

[mark69sportsroof 31]

I agreed. I have decided to pull the new mc and bench bleed it.  On the brake light switch I'm confused on the pin situation as described by Ridge Runner? Please clarify.

 

Thanks Mark

[Ridge Runner 1,113]

the pin is in the switch .It may not be stuck but if it is the light will stay on ,when you remove the switch you will see the pin on the bottom of the switch .

[mark69sportsroof 31]

I k the mc off and bench bled it. It had a lot of bubbles. Re installed it and will bleed the brakes tomorrow when I have some help.

 

Thanks Mark

[Rsmach1 71]

Cool, make sure you start at the farthest point and work forward. Pass side rear, d/s rear, pass front, d/s front. Be sure you have no leaks in any of the fittings.