I have replaced the master cylinder and the booster, bled the brakes and when you press the peddle you think you have good brakes but once you crack the truck up the peddle goes to the floor. What am I doing wrong?
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Re: Brakes won't hold
Check to make sure you have no leak around the tires or from the pistons in the calipers. If all that checks out ok, then I would top off the brake fluid close the top and re bleed the brakes to make sure that you have all the air out. Also make sure that the master cylinder lines and booster lines are tight and no air is getting in.
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start the bleeding process by opening the longest line first. Get a mate to help with the process . Pump the pedal a few times and hold it down while the bleed screw is opened. tighten the screw and pump up again open bleed screw . Repeat process until no air comes out of the screw . Repeat the process back to the last line. Keep the master cylinder reservoir full during the processes.. Operational brakes will work wit or with out the booster . The booster only reduces the amount of energy you have to exert to put the brakes on
Sounds like you will have to bleed your brakes again, but thats not the problem og hard brake peddle, need to check your power brake booster, sit right in back of master cylinder, check make sure it has vacum going to it, also to test it with engine off, press on brake peddle three time, then state engine with foot on peddle, peddle should go down a few inches, also with engine of peddle should feel soft for three pumps, if you have none of this , power brake booster is bad.
Well if you have bled it correctly starting at the farthest out(PS Side Rear) and working to the closest(DR Side Front) and you make sure to close the bleeder valve before letting up and repumping the peddel,then I would say that the seals in your new master cylinder may be bad.When you bled the second or third time if there was no air then I would say you have a bad master cylinder.If there was air then you have another problem.Well hope this helps and good luck.
When you bleed the brakes are you starting with brake furthest from the master cylinder? Also was the master cylinder bench bled? If everything there is okay and you are not getting any air in fluid stream, you could try bleeding the brakes by having some one slowly pump the pedal till it is firm. Then have them let off open first bleeder valve and slowly depress to floor and hold there untol the valve is closed. repeat this at all bleeders. You may want to have car running to do this. Try this and let me know.