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11-07-2010 12:24 PM #1
Trouble bleeding brakes - soft on 1st press OK aft
I did a bunch of work on the car (98 528i sport MT) yesterday including rear pads, rotors, p-brake replacement, caliper rebuild, and bleed through from ATE Super Blue to ATE Type 200. (More on this later, I have some helpful hints and general rants)
I had no pedal issues going in, now the brakes are soft on first application but great on immediate reapplication. I know these are the same symptoms as for high rotor run out. I feel no vibration including braking up to 130kph and when the new parts were all mounted and I turned by hand there was even scuffing of the anti-corrosion coating all the way around the swept surface of the rotor - not ssh....ssh....ssh... I used Textar pads and COATED Balo rotors (my first time trying the coated).
For bleeding I used the old fashioned two person method with a brick under the brake pedal to limit travel. I don't think I made any mistakes - tapping the caliper piston with a rubber mallet occasionally (esp the rears which were taken apart), bleeding through until the colour changed and then the final couple of bleeds were at higher pressure, several open/close cycles (break bubbles free and squirt them out) and I didn't let the pedal bottom out against the brick to make absolutely sure no air was sucked in at the bleeder.
The only possible screw up I can think of is that after I drew most of the fluid out of the reservoir with a turkey baster I got interrupted and when I returned I set up the brick before adding the new fluid. I pressed the brake pedal onto the brick a couple of times by hand before I clued in and filled the reservoir back up. I know that "losing prime" in the master cylinder is a big problem but I didn't think I did and the entire bleed went completely routine (even the clutch) after that point.
Also I replaced the caliper slide boots on both sides. One of them was tough to get in but I don't think I mangled it permanently. It looked distorted for a bit but when I test fit the pin it was snug and felt like the other 3.
I know the first thing to do is bleed some more. I'm running low on the 1L of Type200 I bought and I can't get anything as good as that off the shelf around here. I know anything DOT4 is good enough but I'd like not to waste the expense on nice Type200 by following up with whatever house brand is at the local parts store. However if it was simply "bleed some more" I'm surprised by a second rapid brake application feeling fine - this isn't what I expect from bubbles.
I checked the fluid level after some driving and I haven't lost any. The brake pedal doesn't seem to fall when holding pressure (i.e. leak or torn master cylinder seal).
Any ideas other than bleed more? Anyone ever had bubbles cause the second-application-is-fine behaviour? Any chance my interruption mistake got a bubble into the ASC/ABS side of things that could have this weird effect?
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