Brake LIne Pressure Question

[Argess]

Well... before I start I must admit to a lot of confusion with trying to diagnose my brake issue.... and so the saga continues.

I tried my method of using a piece of wood to hold the brake pedal slightly on, blocking the compensation/fill port and then using my Mityvac applied a vacuum to the caliper. I took the calipers off the steering knuckles and manipulated them around so the enlarging air bubbles could rise. I also tapped the calipers with a hammer to loosen bubbles. I also did something else I'll get to shortly.

So it worked. I got more air out, but not very much. Mind you, it did make a difference. The pedal felt firm right away.... like it should.

So now the "something else". One thing I did to help release trapped air, was to remove the calipers and pump the pedal a bit to get the caliper pistons to come out a bit hoping this might help release trapped bubbles between teh bore and the piston.

And here's the rub.... I used my caliper piston resetting tool to push the piston and back in and it seemed to take more force than I thought it should although it was going back in. Then I remembered I had left that piece of wood between the pedal and the seat. I removed it and the piston went back easily.

Hmmm.... now why did the piston go back at all if the port was closed off? It must be fluid seeping past the MC seal... but I just put a new seal in it....

So another test. I monitored the reservoir level and pushed on the brake pedal. Sure enough, the level stayed constant until the pedal started to sink and then the fluid started getting past the seal and caused the reservoir level to rise. This confirms the seal is passing fluid.

Despite the bore looking perfect (although I didn't measure it) and all new guts installed, something is still wrong, so I ordered a whole new MC. I hope this will resolve the issue, but I have doubts. With only 9000 miles driven and the old piston and seal looking perfect, what would a new MC do for me... unless the original MC had a manufacturing defect?

Once I replace the entire MC and still have the same problem, all that's left is the fluid (maybe because viscosity of DOT 5 is lower than 3,4 or 5.1), which is the last thing I want to change (imagine the work needed to deal with the rear inboard brakes).

It will probably take some time to get this done. Summit was out of stock on the MC so I had to go with E-bay. I expect at least 2 weeks delivery time.