Need help with brakes

[mikem 13]

I had good brakes the last three years after rebuilding or replacing all componets except the power booster and distribution block. I recently noted the pedal going to the floor and checked my m/c. The reservoir that supplies fluid to the rear brakes was empty. I noted leaking at the back of the m/c where it connects to the power booster. I replaced the m/c with another rebuilt one. I also removed the distribution block to clean and recenter the valve. I saw that the flexible line for the back brakes was looking bad so i replaced it too. I bench bled the m/c and then bled the lines in the proper order and manner. I have good fluid blow out of all bleeders. I bled until there was no more bubbles and then went around one more time to be sure. I have good pedal until i start the car, then it goes to the floor. The front calipers were not removed and they are confirmed to be on the correct sides. This is a factory equipped front disc and rear drum car with no pedal changes. The rod sticks out of the booster about 1" and the depth of the plunger on the old m/c cylinder and replacement m/c are the same.

From what i read, there must be an internal leak in the m/c or air in the lines. I replaced the m/c with a NEW one just to make sure. Same outcome. I've always been able to do my own work but this one has kicked my fanny over the last two weeks. Before i have it towed to a brake shop, are there any thoughts on what i could have missed?

[buening 63]

Is the pedal very hard prior to starting the car? The booster will magnify air in the lines when the car is running. Check all brake line connections to make sure you don't have a leak. I just noticed my rear brake line was leaking at the fitting that connects it to the line in the trans tunnel. I can bleed the brakes and they will operate fine, but after a day of sitting the pedal will get soft. Air is slowly entering the system, and mine has similar symptoms as yours. Pedal is somewhat firm but not hard when the car is off, but as soon as the car is started the pedal is very spongy (making the car nose-dive when brakes are applied)

[LoneWolf2U 136]

A MUST is checking the boosters rod lenght to the new master.

A measurement from the masters plunger cup to the masters mounting ears(not the sleeve the slides inside the booster) and the rod lenght is macthed from the boosters face to the rods end minus .005.

 

With this done you can proceed to bleed the barkes again and dispell any air bubbles.

 

The boosters test is pumping the brake petal 3-4 times, then with your foot on the brake start the eng and run it up over 2k, you should feel the petal drop approx 1-2 inchs.

[mikem 13]

The brake pedal is very hard prior to starting the car. I will check the rod length also. I do not see any leaks. I've noted that now when i pump the brakes with engine off, fluid is being pushed out of the m/c lid and down the sides of the m/c. What the heck?

[mikem 13]

Anyone know if pressure bleeding would help?

[buening 63]

Do you have the gasket on the M/C lid? If so, what shape is it in? Fluid should not come out the sides.

 

Also, did you BENCH bleed the M/C prior to hooking up the brake lines to it? I typically bleed it installed to the pedal and have lines going from it's two output lines back into the bowls. After its bled fully, then hook up the brake lines and bleed all lines starting with rear passenger, rear drivers, front passenger, front drivers.

[mikem 13]

New master cylinder and new lid and new gasket. Bench bled the mc. Followed proper sequence for bleeding lines. Let the car gravity bleed for 24 hours to the rr brake only. I saw some dribble down the tire and maybe three drops of fluid on the ground. Fluid level in the mc still appears nearly full. I have an appointment at a shop thats been around a long, long time and the guy is a Ford nut so maybe he has seen it all and can fix it.

[DRASTiK 22]

The above post doesn't specify (unless I missed it) but have you verified that you don't have a rear wheel cylinder leaking?

[Grabber70Mach 107]

Are the front calipers on the correct sides of the car? IIRC the bleeder should be pointed toward the rear of the car. I've also found it necesssary in the past to remove the caliper bolts and clock the caliper to orient the bleeder screw as close to 12 o'clock as possible while maintaining pad contact with the rotor. Bleed as normal while holding it here, then do the other side. When the caliper is mounted on the car the bleeder screw sits about 1:30-2 o'clock thus creating an air pocket that is hard to get the air out of.

 

 

Look about three-quarters down this page.........................

 

 

http://www.mustangsteve.com/granadadiscs.html

[mikem 13]

Thanks for the responses. The front calipers are on the correct sides and bleeder valves pointed toward firewall on both sides. No leaks at all. It has to be air trapped somewhere. I gave up and took it to best brake place in my area so i'm just waiting for the verdict.

[d.reese 13]

I had the same problem with rear brakes once, all I had to do was leave it jacked up over night (rear of car)and the air went high points. Then next day bled rear again and wala, I'm a brake guy!! I left out that my brother(the real smart one of us two) told me what I was doing wrong, LOL!

[mikem 13]

I was advised by the brake guy to do that before i brought it in. I left the back end jacked up with one bleeder open. It dripped maybe six times and quit but i left it up there for 24 hours.

I took it in for the pressure bleeding. It had good pedal initially but by time i hit a dozen stop signs on the way home, it was almost back to where it was before. I can sit at a stop sign and the pedal is maybe a half inch from hitting the floor unless i press a little harder, then it hits the floor pan. No leaks that i can detect and i hate to just start replacing wheel cylinders and calipers when all that was done 3 years ago. The two front hoses were replaced at that time also. I'll keep playing with it but hopefully someone will have an answer. It seems to me it just has to be air trapped somewhere in the lines. Thanks again for any and all suggestions.

[buening 63]

I left the back end jacked up with one bleeder open. It dripped maybe six times and quit but i left it up there for 24 hours.

I took it in for the pressure bleeding. It had good pedal initially but by time i hit a dozen stop signs on the way home, it was almost back to where it was before.

 

This sure sounds like a leak in the system. If there is air in the system it will always have a soft pedal. If it has a good pedal right after bleeding and it gets softer as you drive it, air is entering back into the system from a leaking component.

[danno 128]

Certainly tell us what they found. I am curious myself. The only thing I thougth of that was not mentioned is possibly one of the flex lines to the front wheels is bad. They can blow up like a balloon, with no leaking, and create a similiar problem. But those are usually easy to see.

 

Let us know!

[LoneWolf2U 136]

I took it in for the pressure bleeding. It had good pedal initially but by time i hit a dozen stop signs on the way home, it was almost back to where it was before. I can sit at a stop sign and the pedal is maybe a half inch from hitting the floor unless i press a little harder, then it hits the floor pan. No leaks that i can detect and i hate to just start replacing wheel cylinders and calipers when all that was done 3 years ago. The two front hoses were replaced at that time also. I'll keep playing with it but hopefully someone will have an answer. It seems to me it just has to be air trapped somewhere in the lines. Thanks again for any and all suggestions.

 

 

Well if there is no leakage/fluid loss then there is not much left for it to be but rubber line expansion. Did you replace the rear?

[CarZombie 25]

Could it be the power booster is bad? I have had mine rebuilt twice in the 37 years I have had my Mustang. Trouble is, I can not remember what it did when it went bad.

[69gmachine 15]

I believe Buening is right on this one. Air is entering the system when the pedal is released. When you step on the pedal, it pushes the air back out, but not much if any of the fluid, so the leak is very small and hard to detect. The most likely place for the leak is at the distribution valve. If you have stainless steel lines, they are very hard and do not conform well to make a good seat. You have to tighten, loosen, and re-tighten several times to get them to seal. I don't recommend stainless for brake lines. The seats in the distribution block are fairly soft brass, so they could be damaged preventing a good seal. A fitting could have been cross threaded when you installed it. Wipe the distribution block down with brake cleaner and let it dry, then feel it after pressing on the brake. If you feel the slightest moisture, you've found your problem. Just some ideas to check for.