Usually a hard brake pedal is the brake booster. Since you replaced that it is out f the picture (unless the replacement was bad). This issue of the pedal going to the floor is troublesome and potentially dangerous. If it is not doing it all the time, it probably soon will. What most likely occurred, and this happens quite often, is that after having had the hoses and calipers replaced, it was necessary to bleed the brake system of air in order to get proper brake operation. This requires depressing the brake pedal numerous times to the floor while purging air from the system. There is a potential problem in this and that problem is that the o-rings in the master cylinder can be damaged by the bleeding process, because the normal stroke of the master cylinder is much shorter than the one used during bleeding. This sometimes results in o-ring damage because the master cylinder bore may have worn a ridge in it where the normal stroke ends. The repeated passing of the o-rings over the ridge will damage them and can cause them to fail. When this happens the pedal will drop to the floor. You really can't blame the mechanic for this but it most likely happened as a result of the work done. Have the master cylinder replaced ASAP. I wouldn't recommend using the vehicle at all in the meantime.. it is a pedal-press away form total brake failure at any given moment.
Hi thanks for the answer but i did change the master cylinder yestarday and wasn't working at all was defected cylinder so i put the old one back
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SOURCE: 1998 chevy s10- brake pedal goes to the floor-
Did you put fresh fluid in the master cylinder? I really think you still have air in the lines. To bleed manually, start with the bleeder the greatest distance from the master cylinder, car running, helper pushing down about half way on brake pedal and releasing 3 times, on 3rd time, holding pedal down to half way depressed point while you open the bleeder valve. Repeat until you are sure all air has been flushed out. Check master cyl reservoir level often, because if it gets low and you **** air into the system, you have to start all over again. Go to wheel next greatest distance from master cyl, repeat above, working your way to wheel closest to master cyl last.
SOURCE: brake pedal dropping to floor
do u have the antilock brake bleeding tool? if not you will need to have the dealer bleed the brakes, the ABS control valve must be electricaly held open to bleed the brakes there of course is a special tool for this.
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SOURCE: how do i know if brake booster is gone ? 2001 gmc
Do you by any chance hear a hissing noise from under the dash? If so, yes, you have a bad booster. For it to do what you're saying, it would almost have to have a vacuum leak. However, if there is a problem with something in the ABS system, you should have an ABS warning light on. Also, ABS can make the pedal fade, but I've never heard of it making the pedal hard. Your diagnosis of a brake booster does sound likely, but I'll admit I can't be sure -- this is an odd one.
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