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Best case scenario bad vacuum pressure to the brake booster. Worst case bad abs control module or valve body/motor the abs system works by add and removing hydraulic pressure through valves and electric motor. Try using block off plugs at the master cylinder( remove lines plug outlets at master cylinder) check if brake pedal position and pressure is good(if there is no change problem is master cylinder or brake booster/ vacuum) if plugging at master cylinder solved issue repeat procedure at abs valve body after reinstalling lines from master cylinder if your problem returns your issue is in the abs valve body if plugging at the abs solves problem reconnect at the valve body bleed each line one by one testing between each line until you find the problem
is the abs light on?the abs system only effects the pedal when you are stopping quickly to activate the system. you still have a hydrualic brake pressure problem. are the rear brakes shoes or pads? rear shoes out of adjustment can cause a low brake pedal.even though the master cylinder has been replaced doesn't mean you got a good part.if the part was a remanufactered part very likely it is bad. to determine if it is the master cylinder, plug off the lines from the side off the master cylinder and hit the brake pedal. if the pedal stays up look for a problem elsewhere in the system. if the pedal drops the the master cylinder is defective.
if a master cylinder is bad and you are sure you have all the air out and no leaks.pedal will go to floor , running or not. if booster is bad it will cause a hard pedal. but if master cylinder is bad it will turn on a brake light on dash if it works. make sure the wheel cylinders are not leaking. I beleive that the master cylinder is bad, or you have a leak somewhere. If the master cylinder is functioning properly, the brake pedal will depress to a certain depth and no further.
SOME SPRINTERS HAD RECALLS ON MASTER CYLINDERS YEARS 2006-2009 CHECK DEALER FOR MAYBE RECALL,IAM NOT SURE WHY YOUR BLEEDING THE BRAKES IF YOU HAD OPENED A LINE OR CHANGED A CALIPER THERE MABE AIR IN THE LINES-I ALWAYS USE A PRESSURE BLEEDER OR YOU CAN GRAVITY BLEED SYSTEM BY OPENING EACH BLEEDER SCREW UNTILL GOOD FLOW THEN CLOSEING-IF BLEEDING FOR MUSHY PEDAL CHECK BRAKES AND THICKNESS OF ROTORS-ARE THEIR ANY CODES -IS THE ABS LIGHT ON-IF ALL CHECKS OUT GO TO MASTERCYLINDER
i suggest a bad master cylinder, but 1st answer this, when you apply brakes firmly and keep pressure on the brake pedal, does pedal go down while you're holding pressure on the pedal? if so, the master cylinders bad. and also have you checked the vacum to the brake booster?
Try changing the brake booster. The abs has nothin to do with the brake pedel. All the abs does is electronically adjust pressure applied to each wheel to keep the wheels from lockin up and sliding. You've either got a bad master cylinder or your brake booster is bad
have one person in the blazer pumping the brake pedal and then hold to the floor, crack the bleeder then tighten, release pedal, repeat till all air is out one side at a time, if this does not work then your ABS unit is bad witch if u follow your lines from your master cylinder u will find a black box with a motor on it, or the master cylinder itself is bad, it also can cause u to have no pedal, replace the master cylinder first, most likely cheaper.