Brakes not working - brake pedal sinks

[das_peikko]

With that type of one-man bleeder you have, you run the risk of getting air sucked in passed the bleeder threads when you let off the brake pedal. I wouldn't trust that thing. Pressure bleeders eliminate that risk.

 

[tookien]

das_pelko,

I canceled out the brake lines altogether.

the way i did it is cap the master cylinder ports.

in this case, when pumping the brakes the pedal should go firm, as air doesn't have anywhere else to travel, but it doesn't.

i tried this with multiple master cylinders, all of which were bleeded out successfully with a couple of squeezes.

the pedal still goes down and the booster still makes the hissing noise on depressing.


and the way i see it, there is no way that push rod inside the booster can deliver pressure to the master cylinder.

the rod inside the booster must have either offset somehow someway or broke, as the diameter on the end I don't see how it conforms to the diameter on the m/c.


this would explain why bleeding out the brakes is such a PITA and takes so long.

there is no pressure at all coming from the m/c.

and since the chance that 3 master cylinders would be borked (2 come from the junkyard) is small.

when I bleed out the master cylinders, there is LOTS of pressure on both lines.


so the diaphragm/something else on the booster is borked, therefore the booster needs to be replaced.

the problem is the brake booster 99%.

I'll pickup another m/c from the junkyard just in case though (1%).

I'm going to pick up a couple of boosters and master cylinders from the junkyard, and if all is well I may just invest in new ones in the near future.

 

[tookien]

das,

I know what you mean about the one-man bleeder, it's a reasonable concern.

with those, i find there is a mid-point that needs to be catched.

when you see the fluid moving towards the container as fast as possible, that is the optimal point.

when you see the fluid returning, that means the valve is either loosened or tightened too much. when it's loosened too much that's where the air leak will happen.


when you eventually see a consistent fluid with no air bubbles, that's when you know there is no air come back to the system.

people use these successfully if you observe and play with it a little.



but in my case either bleeding methods didn't work, so bleeding is not the problem here.

 

[tookien]

Final conclusion:

brake booster had missing pushrod adapter/seal to push the master cylinder.

it must have fell and went inside the booster or whatever (either way I had to get the new booster because that part is not sold separately, dumb)

either way problem is now solved.

I got a new master cylinder as well just because it's never been replaced before and car has 200k. bench bleed it before I put it in (as before likely the m/c had air in it which is why I could not bleed out the system).

I just did the installation this morning, took my about 2 hours in total to do everything.


The hissing noise from booster is now gone, idle good and pedal is nice and firm.

 

[das_peikko]

I'm still going to recommend the Motive Products pressure bleeder anyway. Eliminates a lot of variables.