I have a 1991 Mazda Navajo and put a new master cylinder on it and now I have brake pedal fade .
It has new brake lines, new master cylinder now after bleeding the system the ABS and brake light comes on and if you are stopped the brake pedal will fade to the floor. Is there some secret to this? How can I fix this, I have done every thing that I can think of?
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There may be air in brake lines. While changing pads probably it got air from oil cap to inside. I assume that i was opened while putting new pads. You should flush brake fluid first. It should fix the problem
their is an old trick. have someone help you have them pump the brake about 5 time allowing the pedal come up each time have them hold the pedal down as you loosen the brake line at the wheel cylinder the tighten it up before the pedal come up and repeat till the brake feels good,keep an eye on the mastercylinder level
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
You still have air in the brake system and this becomes evident when the operation of the booster allows the pedal to do down as it is compressing the air in the lines more efficiently than what you can do with your foot. Try starting the bleeding procedure but undoing the lines at the master cylinder and priming the unit first to get the air out of both sides of the unit. Tighten the lines and with the help of a assistant start at the longest line first and work back to the shortest. Booster failure will result in no assistance or engine stopping from a massive vacuum leak when the valves are opened. The abs is just a motor driven pump that supplies pressure to the brake system when the wheel sensors come into operation otherwise the brake pedal pressure is operating through the ABS unit to the brakes. (An ABS is only there to keep the brake pressure constant as the sensor opens and closes a valve to stop the wheel skidding . If it is not working then pressure from the pedal may bleed back leaving you with no brakes.)
The master cylinder and the wheel bearings are completely un realated parts. The first thing to check is the brake fluid level. If it's full and you have zero braking and zero pedal then you may well have a dead m/c. If you find an empty reservior, fill it and then figure out where it went. A leak anywhere will have the same result, no fluid, no brakes. The ABS issue may or may not be related but you need to solve the no pedal problem first.
first did you perform a bench bleed on the master cylinder? if not bench bleed the master cylinder. had a neighbor with a similar problem with a ford truck. did some reaserch and found the ABS system needed to be bled. one way to bleed air out of it is to connect the diagnostic computer and perform an ABS bleed and then bleed the brakes like you normaly would. The other way was to take the vehicle somewhere you can slide around safely and slam on the brakes causing the ABS to activate. do this a few times and then perform the normal bleed method.
try bleeding your ABS block first, if that doesn not work could need a master or proportioning vavle. Some scan tools are capable of bleeding the ABS system on some vehicles, and some you have to bleed manually.
if your brake master cylinder has four separate lines to feed all four brake components separably check the out put at that outlet by cracking the fitting loose and applying brake pedal pressure slowly if no brake fluid (Dot 3 or Dot 4) comes out then you need a new master cylinder if there's only two lines and your dealing with only one brake cylinder not getting fluid then its your pa-portioning valve usually located down stream from the brake master on the fire wall
those of us who are not fortunate enough to have access to a power
bleeding tool, the manual brake bleeding procedure will quite adequately
remove air from the hydraulic system. The major difference between the
pressure and manual bleeding procedures is that the manual method takes
more time and will require help from an assistant. One person must
depress the brake pedal, while another opens and closes the bleeder
In addition to a length of clear neoprene bleeder hose, bleeder
wrenches and a clear bleeder bottle (old plastic jar or drink bottle
will suffice), bleeding late-model ABS systems may also require the use
of one or more relatively inexpensive combination valve pressure
bleeding tools (which are used to depress one or more valves in order to
allow component/system bleeding). To fully bleed the late model ABS
systems, a scan tool should also be used to run the system through
Clean the top of the master cylinder, remove the cover and fill
the reservoirs with clean fluid. To prevent squirting fluid, and
possibly damaging painted surfaces, install the cover during the
procedure, but be sure to frequently check and top off the reservoirs
with fresh fluid.
Never reuse brake fluid which has been bled from the system.
The master cylinder must be bled first if it is suspected to
contain air. If the master cylinder was removed and bench bled before
installation it must still be bled, but it should take less time and
effort. Bleed the master cylinder as follows:
Position a container under the master cylinder to catch the brake fluid.
Do not allow brake fluid to spill on or come in contact with the
vehicle's finish as it will remove the paint. In case of a spill,
immediately flush the area with water.
Loosen the front brake line at the master cylinder and allow the fluid to flow from the front port.
Have a friend depress the brake pedal slowly and hold (air and/or
fluid should be expelled from the loose fitting). Tighten the line, then
release the brake pedal and wait 15 seconds. Loosen the fitting and
repeat until all air is removed from the master cylinder bore.
When finished, tighten the line fitting to 20 ft. lbs. (5 Nm).
Repeat the sequence at the master cylinder rear pipe fitting.
During the bleeding procedure, make sure your assistant does NOT
release the brake pedal while a fitting is loosened or while a bleeder
screw is opening. Air will be drawn back into the system.
Check and refill the master cylinder reservoir.
Remember, if the reservoir is allowed to empty of fluid during the
procedure, air will be drawn into the system and the bleeding procedure
must be restarted at the master cylinder assembly.
On late model ABS equipped vehicles, perform the special ABS
procedures as described later in this section. On 4 wheel ABS systems
the Brake Pressure Modulator Valve (BPMV) must be bled (if it has been
replaced or if it is suspected to contain air) and on most Rear Wheel
Anti-Lock (RWAL) systems the combination valve must be held open. In
both cases, special combination valve depressor tools should be used
during bleeding and a scan tool must be used for ABS function tests.
If a single line or fitting was the only hydraulic line
disconnected, then only the caliper(s) or wheel cylinder(s) affected by
that line must be bled. If the master cylinder required bleeding, then
all calipers and wheel cylinders must be bled in the proper sequence:
Bleed the individual calipers or wheel cylinders as follows:
Place a suitable wrench over the bleeder screw and attach a clear
plastic hose over the screw end. Be sure the hose is seated snugly on
the screw or you may be squirted with brake fluid.
Be very careful when bleeding wheel cylinders and brake calipers. The
bleeder screws often rust in position and may easily break off if
forced. Installing a new bleeder screw will often require removal of the
component and may include overhaul or replacement of the wheel
cylinder/caliper. To help prevent the possibility of breaking a bleeder
screw, spray it with some penetrating oil before attempting to loosen
Submerge the other end of the tube in a transparent container of clean brake fluid.
Loosen the bleed screw, then have a friend apply the brake pedal
slowly and hold. Tighten the bleed screw to 62 inch lbs. (7 Nm), release
the brake pedal and wait 15 seconds. Repeat the sequence (including the
15 second pause) until all air is expelled from the caliper or
Tighten the bleeder screw to 62 inch lbs. (7 Nm) when finished.
Check the pedal for a hard feeling with the engine not running. If
the pedal is soft, repeat the bleeding procedure until a firm pedal is
If the brake warning light is on, depress the brake pedal firmly. If there is no air in the system, the light will go out.
After bleeding, make sure that a firm pedal is achieved before attempting to move the vehicle.