Bleeding Master Cylinder

[skidmarky 50]

Still think there is fluid in booster, did you check when the MC was off?

[mark69sportsroof 31]

I still can't get the mc off.  Even pulling it up and toward the engine the mc will not come off.  I checked the brake boost 2 bolts and both are snug.  The front of the mc

hits the shock tower when trying to pull it off.  The driver side of the mc moves to the end of the threads on the bolt, the passenger moves about half the distant. 

 

It's not hard to get in but hard to get off because of the shock tower and bolts.  I thought about cutting the bolts off about 1/2".  I can't get the brake boost off with  

the mc still on.

 

Any tricks on getting the mc off?  Can some one measure the bolts from the brake boost to the end of the bolts?  I would like to verify their length.

 

Thanks for your time and patience.

 

Mark

[Brian Conway 283]

Total distance from face of booster to end of bolt in picture is 1 & 3/8".  Master Cyl. mounting flange is 5/8".  Brian

[1969_Mach1 335]

If the MC went on, it must come off.  They barely fit and need the right combination of movements to get it off.  I think like others have mentioned, the booster has a lot of brake fluid in it and the new master cylinder is not leaking.

 

If you have drum brakes, the brake shoe adjustment is critical for proper brake pedal feel.  If they are adjusted too loose the pedal will be low.  If they are adjusted too tight the pedal will be high but the brake shoes will very likely burn.  For rear drums, a quick test is apply the emergency brake then push on the brake pedal a couple of times while the E-brake is still applied.  The brake pedal will be higher and feel more solid if the brake shoes are far out of adjustment. 

 

Also, if the pedal is slowly going to the floor with the engine running, inspect the entire brake system for leaks.

 

My brake pedal is lower, but not nearly to the floor, with the engine running than with it not running.  I don't understand the details of how the booster operates or why this happens but the brakes still operate fine.

[skidmarky 50]

Probably should also check to see if your booster is working, if it has a bunch of fluid in it it may not be. Easy test, with the engine off pump the pedal a few times and hold it, start the car, if the booster is working the pedal will drop some.

[mark69sportsroof 31]

Brian, thanks for the pics. I have the same measurements on the bolts and mc mounting bracket. Can you measure the mc unit itself. I believe mine is 7 1/4 inches. Also can you estimate the distant from the front end of the mc to your shock tower.

 

I checked the mc I got from NAPA and it's the same one you have the M1929. All three have leaked from the back. They are made byUnited and made in the U.S. NAPA manager said if it leaked again he would change manufacturer. I will stop by in the morning to discuss it with him.

 

Thanks Mark

[Brian Conway 283]

     The MC length is the same 7 & 1/4" and the MC to shock tower clearance is no more than 3/16".  You will need to remove your shock tower to firewall brace.    As suggested, with the MC removed,  get the brake fluid out of the booster.  You can do this using some paper towels.  Brian

[mark69sportsroof 31]

Thanks Brian, I am trying a new mc from the local mustang shop. How do I dry out the brake boost with paper towels? All I

see is the gasket in the opening and the push rod. I don't know if the gasket can come out in order to get the paper towels

inside to dry it out.

 

Thanks again, Mark

[Brian Conway 283]

Mark, my error forget, the paper towels.  That only works on a Midland Booster.  If the Bendix forward seal is in place your good to go.  When bench bleeding your new M1929 MC you will see if it is leaking or not.  Remove the shock tower brace, because you need the room, and install the MC and carefully install all your brake lines.  I install the lines and fittings using a repeated tighten, loosen, tighter, loosen and retighten firmly procedure.  The hydraulic fittings need to be re-seated and this method works for me.   Brian 

[mark69sportsroof 31]

I finally got the mc off by pulling, yanking and anything else. I dented the shock tower right in front of the mc so I can get it

off in less then 2 hours. I got my 5th mc from the local mustang shop who got it from O'Reilly's surprisingly enough. I'm at the

point of I don't care as longs as it works.

 

The brake boost push rod came out along with the rubber seal in the midst of the removal. I place a clean rag down inside the brake boost and no fluid on the rag, so I don't believe any brake fluid got inside.

 

I will get a new rubber seal for the brake boost and try everything again.

 

Thanks Mark

[mark69sportsroof 31]

I got a new brake boost seal from the guy that re built it.  I checked inside the boost again and no evidence of fluid leakage.  I bench bled the new mc and did it by the instructions.  I will let it sit overnight on the work bench then check for leaks.  If all is well, I will bolt it on the brake boost and let it sit overnight, then check for leaks again.  If all goes well then I will bleed the brakes again. 

 

Thanks Mark

[Rsmach1 71]

I have my fingers crossed lol, you've had a hard time with this and I hope you get the issues solved.

[mark69sportsroof 31]

Thanks.  After bench bleeding and sitting over night no leaks.  I attached the mc to the brake boost.  I will let it sit over night and check for leaks before attaching the 2 lines.  One step at a time. After 5 months of having no brakes, I'm ready for some good news and some driving time.

 

Thanks Mark

[mark69sportsroof 31]

Another update.  Got the latest mc bench bleed.  Installed it on the brake boost and no leaks.  Did the brake bleed at the tires.  Pedal is good and hard.  Moves less

then an inch and gets firm.

 

Start the car and little to no resistance.  I have to pump the brakes 3-4 times to get 50-75% normal brakes.  I think I am going to have to do the aftermarket proportional valve or add inline  pressure equalizier valve.

 

Frustration continues but it was sure nice to drive it.

 

Thanks Mark   

[1969_Mach1 335]

Another update.  Got the latest mc bench bleed.  Installed it on the brake boost and no leaks.  Did the brake bleed at the tires.  Pedal is good and hard.  Moves less

then an inch and gets firm.

 

Start the car and little to no resistance.  I have to pump the brakes 3-4 times to get 50-75% normal brakes.  I think I am going to have to do the aftermarket proportional valve or add inline  pressure equalizier valve.

 

Frustration continues but it was sure nice to drive it.

 

Thanks Mark   

What exactly does that mean?  Does the pedal go to the floor with the engine running?  Do the brakes work okay but it feel like the pedal is too soft with the engine running?  Does it stop okay but the pedal just has more travel with the engine running?  Is pumping the brakes 3-4 times depleting the vacuum from the brake booster so now the brake pedal is more firm like without power brakes resulting in a firmer brake pedal?

 

From the description it's kind of difficult to determine if something is wrong or what you are experiencing is normal for these cars.

[danno 128]

You certainly have a frustrating problem.  I am following the novel that is getting written on it, and wonder if you have a problem somewhere else?  Suppose you had a flexible brake line with a soft spot  or bubble?  Everything works fine until there is pressure in the system and the pressure expands a portion of the brake hose and so you cannot get good pedal feel. Examine all three flexible brake lines while someone is pushing the brake pedal.  I replaced mine a few years ago, I did not have any problem, I just figured it was time after 46 years, they could be bad. Maybe something other than the master cylinder is the problem?

[1969_Mach1 335]

Good point danno.  I too don't think it's a master cylinder or proportioning valve issue.

[mark69sportsroof 31]

Ok let me clarify.  With the car off I got very good brake pressure.  It moves less then an inch then get hard.  When I start the engine the pedal will go to the  

floor with little resistance.  When I drive it I have to pump the brakes 3-4 times to get good pressure to stop.  Every thing is new on the brakes including hoses.

 

Previously I disconnected the front rubber lines and pumped the brakes to check fluid flow through the metal lines.  It was good, then I attached the 2 front rubber lines and checked the fluid flow through the rubber hoses and it was good.

 

What do I look for when checking the 3 rubber brake lines while someone is pumping the brakes?

 

Thanks  Mark

[LoneWolf2U 136]

With each new master cyl, have you rechecked the booster rod for proper length?

The booster is working as when you start the engine the pedal should drop only 1-2 inches and full brake pressure to wheels.

the going to the floor is not correct and rod adjustment is in question for your complaint.

 

As for the rubber hoses the visual inspection is looking for ballooning when pressure is applied.

you stated they are new so it would not be my first place to look.

 

Have you tried to bleed the system by pressure or suction from another source other than pedal pumping?

Pumping the pedal with the booster with no vac can feel like it has a solid pedal but you are working against the booster rubber diaphragm.

 

My 2cts is in the improper booster rod measurement to the master plungers depth, it would be my first place to look and verify.

[danno 128]

One more item...  I seem to remember that  you can have the left and right front wheel cylinders reversed. If you do this, everything will work fine except that you cannot bleed all the air from the front brakes.  There is a certain amount of air trapped in it.  Verify that with them, the air bleed valve is at the top, as high as it can be. 

 

Maybe I am wrong on this, but I seem to remember something about it. I will have to take a look at mine.

[buening 69]

You mention being able to drive it.  Does the car nosedive when applying the brakes?  If so, you likely have air in the line that goes to the rear of the car or something misadjusted (or issues with wheel cylinders) with the rear brakes. If it is the front, sometimes it will pull to a certain side (indicating that side is working up front).

[1969_Mach1 335]

I'll say it again, it doesn't make sense.  Having to pump the pedal makes me believe there is still air in the system, or the rear drum brakes are far out of adjustment.

 

Is there something wrong in that rebuilt booster?

 

With the engine off and the brake pedal feels good, will the wheels lock up when stepping on the brake pedal?

 

Have you very carefully tried to stop the car with the vacuum source to the brake booster disconnected and plugged, thus, eliminating any power assist.  If your brakes are bled and all is okay it should stop with a lot of pedal force by your leg.  Put the rear wheels on jack stands and carefully run the engine with trans in drive so the rear wheels rotate.  Then apply the brakes and stop them with the vacuum source to the booster still disconnected and plugged.

 

This maybe far fetched, but I wonder if there is air in the system and something is wrong with the booster giving you a false good pedal feel with the engine off 

 

NOT ANY OF MY THUMBNAILS

[mark69sportsroof 31]

A few months ago the local automotive shop did vacuum bleed the brakes.  Since then I have replaced the mc and proportional valve a couple of times. 

 

When I drive it the nose doesn't dip nor does the rear brakes lock up.

 

I haven't adjusted the booster rod since the original mc

 

It seems to pull to the right sometimes if I press hard after the 3-4 pedal pumps.

 

Is there a way to check if the brake boost is working correctly while mounted in the vehicle?

 

Thanks for all the advice.

 

Mark

 

Not my thumb nails

[Brian Conway 283]

I know I asked before about your brake pedal; you replied the pedal is correct and you got your stuff from the local Mustang shop. So that set up; pedals, pedal support and pro/dist block is not original to the car? I gotta think something in that assembly is the problem. I am using the same after market brake booster and master cylinder as you with no problems. The rest of my power front disc brake system is stock 69 OE equipment. To answer your last question; With the engine not running the brake pedal will be firm. Apply steady/firm pressure to the brake pedal and start the car. The pedal will sink about an inch or so. That is the booster test. Brian

[1969_Mach1 335]

The OP mentioned in one post he got a new brake booster seal from the guy that rebuilt it.  From that I understood the OP had the original brake booster rebuilt.  I am also thinking the car is an original power brake, front disk/rear drum car.  Is that not the case and there might be miss matched components?