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No pressure in brake line

9K views 17 replies 7 participants last post by  Tomvw 
#1 ·
hi guys, need some help here. I was replacing rear brake pads/rotors and had issue to push piston in. So I had to remove caliper from brake line and get a garage to fix it. Now I got caliper back, installed it, and tried to bleed brake system. First, no pressure at brake pedal. Second, no brake fluid coming out of the bleeder. Seems master cylinder was full, and brake fluid was not going inside the mc if I topped the fluid.

Any suggestions? I think there must be air in the brake line, but do I need a pressure bleeder?
 
#3 ·
Well, I'm going to guess that you pushed the pedal several times to try and get the fluid to flow; you'd think that the fluid would show up pretty quickly, no matter how much air was in the system. If that's true, you have somehow blown your MC, but I must admit I've never heard of an MC so hosed it can't even bleed brakes.
 
#5 ·
The brake booster isn't a hydraulic part; it's a pneumatic one. And failure leads to a hard pedal, not a limp one. Do you mean the ABS controller? As long as you never ran the MC dry, there shouldn't be any air in the ABS pump unit. Did you neglect to plug the brake line while the caliper was off?
 
#10 ·
Providing the ABS pump hasn't been run with air in the system, you shouldn't need to use VCDS to run the pump.
Replace the hoses you may have damaged.
Get a pressure bleeder or use the standard 2 man method one to operate the pedal while the other operates the bleed screw.
 
#16 ·
yup, that's the procedure.

not familiar with the HF bleeder, but the better ones pressurize the master cylinder reservoir rather than apply vac on the bleeders -- the latter can draw air in to the caliper pistons. There is nothing better than a 2-person brake bleed and in this case I would do it that way. You really don't want to take any chances. If in doubt a shop can do the work for not a whole lot, given what is at stake.
 
#17 ·
Update: did vacuum pump method, then 2-person bleeding method, finally got brake pressure back. Used about 6 bottle of brake fluids.

I also tried ABS bleeding using VCDS, no luck, VCDS showed group 001 or 002 not available. Not sure why.

Now the problem, brake light flashes and beeps, "Stop Brake Fault Service Manual" message showed up. No codes by checking VCDS. Did a lot of research and it seems a lot of people have the same problem, and it's pretty much the problem of brake fluid sensor. So I full the sensor plug off then message gone. Plugged back and message showed up again, which approved that it's the problem of brake fluid level sensor. The sensor is buried in reservoir, so should I replace the whole reservoir? tired with brake bleeding so just dont want to go through it again.

Any suggestions? I found somebody said it's the problem of the magnet float inside the reservoir. Anybody ever fixed it yourself or rebuilt it?
 
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