Brake Master Cyl not building pressure

Hi all,
I just had my brake master cyl rebuilt by White Post Restorations ($300) as there was pitting on the bore. So they re-sleeved it and put new seals in. Installed today and still no pressure build when I press the pedal.

I Used power bleeder (Motive) like many times before. Have full stream of fluid from each corner with no air. Yet pedal still mushes to the floor and my son can spin the front rotors by hand when brake pedal held firm to the floor.

The only thing is that I used my existing top seals that the reservoir is mounted through on the MC as the new ones from White Post were nearly impossible to seat the tank through the holes. They seemed way to small. Could that be the issue? Old seals leaking where the tank mounts? I don't understand as the cylinder is completely below the level of fluid in the tank, so those seals should not affect the pressure in the cylinder. And there are no leaks of fluid at those seals. But could the old seals (look perfectly good to me) be causing some sort of air leak that is preventing pressure from building up?

White Post said they bench tested the MC before returning to me for installation. I have no leaks that I can find on any lines, calipers or anywhere on the car. But the pedal does not get firm and the discs spin by hand.

Also, what is the blue cap on the top of the reservoir? It has like a small finger pump type unit on top and when I press it, bubbles come up the motive power bleeder line. It seems like some sort of bleeding mechanism that is on the top of the tank where the level sensor wires connect. Frustration is high.. car is ready to drive, but I have not brakes.

Thanks,
GT

 

I'm concerned about the seal sizes as well. The top two seals that the tank nipples go through are much smaller diameter than the stock ones that were in there. Too tight to get tank installed. used old ones (very good condition) and system failed. My question is weather or not those two top seals could cause the problem. My assumption is that the ports for inlet and outlet are below the fluid level line, and that since there is no leakage around those seals, that I should be okay. Going to try to install with the seal they provided, although extremely tight fit on the plastic nipples!

Also, regarding bench bleeding. Very much a PITA on this car. Have to install the reservoir, and bench bleed. Then remove the reservoirto install the MC (bottom corner nut is a ***** with the tank installed). Then put it all together and I pressure bleed the system. I did connect two rubber hoses to the outlet ports with some spare bleeder valves screwed in place. PUt the lines back up into the reservoir and pumped brakes. A few bubbles and then nothing. I was expecting to see a solid stream of brake fluid eventually, but nothing came out of the lines when pumping the brakes. Then when I removed the rubber hoses (black, not clear unfortunately), they were full of fluid. This thing is not pumping out the two brake line ports... Really a PITA!!

 

It's not really necessary to bench bleed if using a power bleed system like Motive. But yes, I "bench bled" it installed on the car as it's not an easy task to do out of the car since you need to remove the tank to install the MC. So it's easier to test when installed.

 

I bled all four corners and bled the MC when installed with two rubber lines from the ports that I had installed bleeder valves. Pumped the brakes with the lines feeding back into reservoir. a Few bubbles, then no pressure.

 

I took it apart. Seals were bad and all gummed up. Cleaned and replaced with new seals. Still did not work. Took it apart again and closely inspected. The Cyl was all marred and pitted. Sent entire unit out to White Post Restorations to have it sleeved and new seals (again) replaced. They would not use the 'new' ones I had installed as they said they risked damage from the cyl pitting that was present. Had it sleeved, sealed and sent back. Installed and same thing, no pressure. Now I'm concerned they used too small of seals or something. But they are top notch and said they pressure tested and vacuum test all of their work. I emailed them to confirm. Going to try one more time tonight before I take this thing off again for the 4th time. What a PITA. Never had any issue like this with ANY other car. No air flowing from all 4 brakes. Has to be an issue with the seals or air trapped in the MC somewhere.

 

Thanks. The reason I chose to rebuild was to prevent the issue with adjusting the length of the push rod on the power booster. Each car was calibrated at the factory. If the length of the new master cyl piston is even a couple mm longer, the brakes will drag and then you have to take it all apart again to turn the screw on the booster pushrod. But since I'm on my 4th R&I at this point, it probably would have been better to spend the $600 for a new one vs. $300 for the rebuilt one and been done with it. Geesh... what a PITA.

 

And what's more frustrating is that this MC failed immediately upon return from the rebuild shop. They said they tested it. But it isn't working obviously. I'm gong to try and bench bleed it one more time while in the car with an assistant pushing on the pedal while I watch for air bubbles from the lines that I will put on the ports. If no air and I cap off the ports, it should build pressure. If not, I'll be chasing for a refund and just buy a new one.

 

exactly

 

To be clear... WP has not denied anything. I just got it back on Friday and emailed them yesterday. I expect they will have good customer experience. Nothing negative to say. Stuff happens... we'll see if it fails when I attempt to bench bleed/test what they say. I'm sure they will want it back to check it out.

 

It should only cause a problem if you have gunk, pitting or issues at the bottom of the bore. SInce this is a new sleeve and seals, it should be fine with pedal pressed to the floor. But I know what you are saying.. for an old MC, it can damage the seals further. Should not be the case with a freshly re-sleeved/rebuilt MC.

 

New Theory... what do you all think?

Is it possible that my newly rebuilt brake booster (rebuilt 2 years ago, and just getting to finishing all the work on the car - brakes are list item) has affected the overall "throw" of the push rod length? Could be that the acorn cap was turned out or the new rubber and springs and outer seals on the booster are different thickness than factor and the push rod extends further out toward the MC now?

Thus causing the MC piston to be pushed in at rest beyond the inlet ports to the reservoir. And when I'm applying pressure 10 to 12psi on my Motive power bleeder, fluid is getting to the brake calipers. But when I remove the pressure, I cannot pump fluid out by using the pedal. No pressure. So my theory is that it may be possible that the piston is too far "in" due to the changed potential changed length on the rebuilt booster push rod thus preventing the MC from getting fluid to the chambers that feed the brake lines?

When I installed the MC the last 2 times, I had to compress the MC piston slightly by hand to get the push rod to enter the MC piston end due to the length of the entire unit hitting the inside of the wheel well area. It was just ever slightly too long to fit straight on the booster push rod. But when I compressed the MC piston to make the overall length of the MC unit shorter, I was able to align the MC to the booster and get it to slide on the push rod/Shaft sticking out of the booster.

So after I use the pressure bleeder to get fluid out of all 4 corners, I make sure all of the bleeder valves are closed and attempt to pump the pedal to stiffen up the brakes (pressurize the lines). But if my theory is correct, is it possible that there is no new fluid entering the compression chamber (ports) in the MC, thus I cannot build up pressure along the length of the brake lines.

BUt I'm still confused as to why I am able to get fluid to flow under pressure, but not flow under no pressure. Is 10 to 12psi enough pressure to force feed fluid from the reservoir, past the seals (that are potentially blocking the fill holes in the cylinder due to longer geometry from the booster push rod)?

Can you visualize what I'm thinking with this description? I suppose the only way to know for sure is to take it out again and try to get it to build pressure on the bench.

 

Also, where is this seal supposed to go on the booster or master cyl. My brake booster rebuild shop sent this seal originally when they returned the unit. However, it do not slide on the MC piston end. Too tight. THen I called them and they sent me an update version (now installed in the car), but it is much thinner like a rubberized washer with a metal insert. I think that is the seal for the booster internals. But now I'm thinking that this seal should be on the shaft which would push the booster pushrod back into the booster by a considerable amount. Could this be the issue? This seal should be on the MC shaft before installing into/onto the brak Image Unavailable, Please Login e booster?

 

Disregard... Just spoke to Booster Steve at Power Booster. The seal in the photo above should not have been put in my box. I did put the "replacement seal" on the shaft that he sent me, but that was to replace an internal seal that is still in the booster. So now I have two seals in the booster on the shaft which could be displacing the MC piston just enough to be blocking the fluid inlet ports I suppose. So... back to the garage to take it out again. Bench test and report back. Fun!