OK, I fixed a leaky wheel cylinder on the left rear by redoing everything: new drums, shoes, hardware, wheel cylinders, rear rigid brake line on both sides; reman calipers, new pads and rotors in front. Time to bleed.
I've done this before with no particular issues, other than my truck took 2-3 iterations to bleed fully. So last night my wife worked the brake pedal while I bled each wheel. Started with RR, LR, RF, LF. I never let the master cylinder get low. Procedure: connected a rubber hose from bleeder to a bucket of new fluid, submerged. Told her to press and hold pedal when I say "down" and only release when I say "up." She followed this precisely.
At each wheel I called out "down", then opened the screw, and bubbles from the hose itself came out. Closed screw and called out "up." Maybe once or twice more, got rid of the bubbles. A tiny bit of discolored fluid came out. Didn't really seem like enough fluid or air blew through to account for empty wheel cylinders and calipers. Finished up and the pedal was rock-solid with engine off.
I started up and it did travel a tiny bit more than normal. Cautiously stopped a few times in the driveway, then tried level road. Each time I hit the brakes somewhat hard. The pedal sighed a little, felt mushy but not much longer travel than usual, not as firm as usual. The car nose-dived and stopped, but there were two things I noticed:
1) When I hit the pedal hard, I did not get that hard impact feeling that I should, of the pads making contact. I could not lock up the wheels at all. No ABS.
2) When I released the brake while still rolling, instead of feeling it release and roll more, for about a second I still felt braking action, even with the pedal released.
When I got back home, the rims were very warm to the touch, having hit the brakes somewhat hard for about 15 times within a mile.
I didn't change the flex hoses because they are rusted to the upstream rigid lines and the rubber is in great condition - no cracks or defects at all. If I change them, I have to replace every rigid line in the car. And they were fine just before this job.
Consensus? I believe there's still trapped air, and that when I released the brake pedal, the air was slow to decompress, and so it held the brakes on for just a second. I don't believe the flex hoses are bad and acting as a one-way valve. I just didn't see as much air blow through as I expected. So I will try again.
BTW, it IS a dual diagonal braking system. Should I bleed RR-LF and then LR-RF? I did furthest to nearest. I'll also leave all 4 screws open to ooze, for about 15 minutes before I start. I might then step lightly on the pedal before bleeding, to eject air and fluid from each screw first.
I've done this before with no particular issues, other than my truck took 2-3 iterations to bleed fully. So last night my wife worked the brake pedal while I bled each wheel. Started with RR, LR, RF, LF. I never let the master cylinder get low. Procedure: connected a rubber hose from bleeder to a bucket of new fluid, submerged. Told her to press and hold pedal when I say "down" and only release when I say "up." She followed this precisely.
At each wheel I called out "down", then opened the screw, and bubbles from the hose itself came out. Closed screw and called out "up." Maybe once or twice more, got rid of the bubbles. A tiny bit of discolored fluid came out. Didn't really seem like enough fluid or air blew through to account for empty wheel cylinders and calipers. Finished up and the pedal was rock-solid with engine off.
I started up and it did travel a tiny bit more than normal. Cautiously stopped a few times in the driveway, then tried level road. Each time I hit the brakes somewhat hard. The pedal sighed a little, felt mushy but not much longer travel than usual, not as firm as usual. The car nose-dived and stopped, but there were two things I noticed:
1) When I hit the pedal hard, I did not get that hard impact feeling that I should, of the pads making contact. I could not lock up the wheels at all. No ABS.
2) When I released the brake while still rolling, instead of feeling it release and roll more, for about a second I still felt braking action, even with the pedal released.
When I got back home, the rims were very warm to the touch, having hit the brakes somewhat hard for about 15 times within a mile.
I didn't change the flex hoses because they are rusted to the upstream rigid lines and the rubber is in great condition - no cracks or defects at all. If I change them, I have to replace every rigid line in the car. And they were fine just before this job.
Consensus? I believe there's still trapped air, and that when I released the brake pedal, the air was slow to decompress, and so it held the brakes on for just a second. I don't believe the flex hoses are bad and acting as a one-way valve. I just didn't see as much air blow through as I expected. So I will try again.
BTW, it IS a dual diagonal braking system. Should I bleed RR-LF and then LR-RF? I did furthest to nearest. I'll also leave all 4 screws open to ooze, for about 15 minutes before I start. I might then step lightly on the pedal before bleeding, to eject air and fluid from each screw first.