Another brake bleed/MC/Booster problem thread

[infernosg]

Originally Posted by Pete_89T2

That is odd, although the right rear line is always the most difficult to bleed, since it's the longest line length. Only other thing I can think of is maybe the bleeder screw threads have worn out, or perhaps the new MC is defective? Sloppy bleeder threads would allow air to sneak in and would show up in the bleeder tube while you're bleeding it, but since it's a pressure bleeder, I don't think that air could get pulled into the system from that point or effect pedal feel.

You're telling me. I've never had this much difficulty bleeding brakes and I've probably done them 100 times on this car. I have no external leaks whatsoever. I suppose the MC could be bad but when I bled it I could push the piston in <1/16" using all my strength. I guess I'll pull it off again tomorrow to see if anything is leaking internally. Beyond that I'm out of ideas.

The top bleed screw is the correct one to use for the rear calipers, right?

[RETed]

For dual bleed screws on brake caliper...
1) Bleed mostly from top screw to eliminate air.
2) Bleed a little more from bottom screw to eliminate debris.

I think you should wait till the engine is in the car and running.
Due to physics...
Pressure is defined by mass divided by area - i.e. pounds per square inch.
You have effectively increased the "area" side of the equation due to the larger brake master cylinder bore.
Now you have spread pressure over a larger area...
Thus, the feedback pressure is going to be less back to your feet - i.e. softer pedal feel.

We need the brake booster to be operating to see how effective the whole system is under working conditions.

I think you're just wasting brake fluid and labor at this point.


-Ted

[infernosg]

Originally Posted by RETed

For dual bleed screws on brake caliper...
1) Bleed mostly from top screw to eliminate air.
2) Bleed a little more frombottom screw to eliminate debris.

I think you should wait till the engine is in the car and running.
Due to physics...
Pressure is defined by mass divided by area - i.e. pounds per square inch.
You have effectively increased the "area" side of the equation due to the larger brake master cylinder bore.
Now you have spread pressure over a larger area...
Thus, the feedback pressure is going to be less back to your feet - i.e. softer pedal feel.

We need the brake booster to be operating to see how effective the whole system is under working conditions.

I think you're just wasting brake fluid and labor at this point.


-Ted

Pressure is force per unit area. There's a finite amount of fluid in the system so if the MC diameter is increased it moves more fluid per unit of displacement so less pedal travel for a given amount of braking force. Either way I removed the MC again after systematically plugging off the ports. Even with all the ports plugged I was getting the same pedal feel so I somehow got air in the MC. I've bled the MC again and it's nice and firm installed with the ports plugged. I'll bleed the system the old fashioned way this time around to avoid any issues.

However, before I install the MC permanently and bleed the brakes I want to set the brake booster pushrod clearance properly. The FSM calls for a specific SST, which I obviously don't have. Is there another way to do this or does anyone have access to the SST I can borrow?