KISS. Not advise, just one of the ways I R&R brake master. Working on brakes is at your own risk!
Just some highlights, not whole procedure.
1) To drain or flush reservoir, I:
Key on, press and hold brake pedal, open rear bleeder. Note: Motor is designed for short run times, don't burn it up. Keep runs times under 2 minutes, each time than rest (cool) 2 minutes or more!
My little helper. Never complains and always has time for me. Spring loaded shower curtain rod.
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Note: FSM, recommends pre-prime new master with brake fluid. Which means adding brake fluid to reservoir and working master plunger in and out a few times, until fluid pumps out.
2) Install new master. I take great care not to damage flare male or female threads and seat flare squarely.
3) Add fluid to max line. I do not spill brake fluid on master or body.
3A) Gravity feed with 1 or more bleeders open (key off). But this I may skipped. Depends on how much time I have.
4) Turn key to on (all bleeders closed), until booster motor stops. If engine running, I can't hear when booster motor stops, so I don't start.
5) Turn key off. Pump pedal 40 times.
6) I repeat steps 3) 4) & 6) a few times. This bleeds accumulator.
7) Repeat step 1). But just flush rear bleeder until no more air bubbles seen in clear tube run to catch can. This usually about 1/2 cup or more of brake fluid draining. Keep reservoir above min line at all times now.
8) Move to other rear bleeder and repeat.
9) Bleed air from front lines, one at a time.
For this I use a live helper. Here we pump pedal 20 times key off. Than turn key on, and keep it on until both fronts done.
Pump pedal 5 more times once booster motor stops running, and hold pedal down.
Open bleeder as pedal held and pressed down. Note: never take pressure off brake pedal, while bleeder open. Doing so, suck in air.
Note: FSM has us start bleed at fronts. I can come back and bleed again starting at fronts, but don't find I need to. I use the pump and start at rear to get max fluid or air out first.
10) Repeat strep 9) at front bleeder(s) one at a time, until no air. Usually a minimum of ten bleed repeats on RH side and 7 on LH side. But may take more times.
11) Repeat, fill procedure and time how long booster motor runs afterwards. Spec is 30 to 40 seconds. This is with battery at ~12.4 volts.
12) Test braking in shop, than at slow speed.
13) Go out find a dirt or slick road, and stop hard from 35MPH or more, activating ABS. Repeat 3 times.
14) Inspect level again, look for leaks, check all nuts on and torque, check pedal height and free play.
14) Dry out bleeders and cap them.
Note:
I'm working on a new time test. Or rather a variation of time test. It will be where brake pedal depressed during key on time test (accumulator pressurizing and brake calipers under pressure). I need to play with this on a known good working system, to get base line times. Times, may be just a tad higher??
Reason for this I just had and incidence of time test not revealing a leak.
What happened was; time tested at 38 seconds before and after flush & bleed. Which is high, but withing spec. Volts at battery, were around 11.4 to 11.6. Which is low (weak battery). Bleeder cap RH front would blow off. But not just when key on, which makes sense now that I've pondered it! The key had to be ON, also pedal depressed.
What we found was rig had aftermarket rebuilt caliper. The caliper bleeders female hole threads and bleeders male threads, were damaged. OEM bleeder would not fit this AM caliper, as different size. We replace caliper with OEM. Than time dropped to 34 seconds (now battery even lower at 11.3 volts), shaving 4 seconds. With good volts, we'd likely get even better times.
Clear tube and catch can.
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