Brakes Pulsates during brake application

hello guys.

i need some help from the experts..

my blazer 2wd 4.3Lt Z 1990

has the BRAKES light on in the dash.
when make stop in some where, while i push the pedal to stop the pedal sometimes dont have like pressure.and sometimes when i make a stop the pedal go down normally but a 20% of the times go down doing some pulsates. and other times go normaly and then jump down almost totaly.

this is about the 20 to 30% of the time.

ok, i already replaced this. the master cylinder,rear brakes,the plastics of the pistons of the rear brakes. so a man sayd that this problem would be like the presure valve(combination valve) or the booster.

but i would like to know what do you think.

thanks ..

Nalgman

Sounds like the ABS system needs to be checked out.

ok.. i have the haynes manual. and have done put the clip to the H and the A terminals (jump) and the book says that the Brakes light will show the codes..
so here is my code..
6 .. the brake light flashes 6 times. so the code is the Speed Sensor.
the manual says this " erratic brake action at low speeds and pedal pressure is a sign of a fault in the speed sensor or speedometer circuit."

ok.. this code causes my BIG problem? ... ok there's too much coincidence..

in this model of blazer where is located this sensor.??

i would thank you help..

Nalgman

You need to remove , clean and reinstall the fron speed sensors.

ok ok .. one question.
this model of the blazer 90 2WD
has front speed sensors??
The manual says that RWAL (2WD) has the speed sensor in the tranny.
the 4WAL has 4 sensors.in each wheel.
emm. this is my question...

my 2wd blazer has sensors in front??
or just in the tranny?

can be cleaned?

Nalgman

The speed sensors being refered to are the abs sensors. They are located in each dust shield on the front. To get them, first you need to remove the hub (clean the teeth on the gear drive for that) and then pull the dust shield. Realize though, the sensor is more likely bad than just dirty, but as suggested, try cleaning it up first. Also make sure that your rotors aren't warped.

You can remove the speed sensos without removing the hub.

The speed sensors being refered to are the abs sensors. They are located in each dust shield on the front. To get them, first you need to remove the hub (clean the teeth on the gear drive for that) and then pull the dust shield. Realize though, the sensor is more likely bad than just dirty, but as suggested, try cleaning it up first. Also make sure that your rotors aren't warped.


ok
i'll try to find it tomorrow..
well.. i dont have any idea how looks this sensor. :eek7: but i'll analize the front wheels.

thank you so much.
:iceslolan

Nalgman

look at the dust shield, you will see a wire coming off of it, that's the sensor ring..

1990 - its a RWAL system, not 4WAL, no sensors in the front. RWAL's don't have an "anti-lock" light, just the "brake" light comes on for both regular brake system and the RWAL ABS system. To make sure that its the ABS causing the problem, disconnect the RWAL system by unplugging it and taking it for a drive. If you now don't have the pulsing or pedal drop, then you do have a ABS problem. Check your vehicles speed sensor that is located on your outsput shaft, usually they take a shit, and give you problems like that.

1990 - its a RWAL system, not 4WAL, no sensors in the front. RWAL's don't have an "anti-lock" light, just the "brake" light comes on for both regular brake system and the RWAL ABS system. To make sure that its the ABS causing the problem, disconnect the RWAL system by unplugging it and taking it for a drive. If you now don't have the pulsing or pedal drop, then you do have a ABS problem. Check your vehicles speed sensor that is located on your outsput shaft, usually they take a shit, and give you problems like that.

yes! my blazer is a RWAL .

where is located the RWAL system?
the manual don't show where is it.
the speed sensor can cause that??
emm. my dash don't show my speed.somethimes the speedometer runs and 90% not.
maybe this is the problem???

in the test with jumping the pins A & H of the socket to hook up the computer to read the codes.. the Diagnostic for ABS says "speed sensor"="6 blinks"

Thanks :D:D:D

Nalgman

The RWAL system is located beside the brake fluid resevoir, to the right looking from the front of the truck. Its a black box that jets out from the master cylinder. There are two plugs that plug into it, unplug them both, then take it for a drive. IF its now not pulsating, then the mechanical system is working, and the ABS system has the problem. Now, you mentioned that your speedometer is not always working.....thats most likely your problem, the VSS, or speed sensor. The speed sensor(VSS) gives information to the RWAL system for rear wheel lock-up, it also provides information for the spedomoeter-the speed of the car. If your speedometer is not working, the RWAL will also not be getting the right information. Change out the speed sensor, or VSS sensor, also make sure connections to and from the speed sensor are good and not damaged. The truck will also have trouble getting the TCC into lock-up because the ECM uses the same sensor to know when to lock up the TCC too. Either way, take a look at the speed sensor and all its connections, that should correct your problem.

The RWAL system is located beside the brake fluid resevoir, to the right looking from the front of the truck. Its a black box that jets out from the master cylinder. There are two plugs that plug into it, unplug them both, then take it for a drive. IF its now not pulsating, then the mechanical system is working, and the ABS system has the problem. Now, you mentioned that your speedometer is not always working.....thats most likely your problem, the VSS, or speed sensor. The speed sensor(VSS) gives information to the RWAL system for rear wheel lock-up, it also provides information for the spedomoeter-the speed of the car. If your speedometer is not working, the RWAL will also not be getting the right information. Change out the speed sensor, or VSS sensor, also make sure connections to and from the speed sensor are good and not damaged. The truck will also have trouble getting the TCC into lock-up because the ECM uses the same sensor to know when to lock up the TCC too. Either way, take a look at the speed sensor and all its connections, that should correct your problem.


THANK YOU!!!

the conectors are OK i cheked the cables with my multimeter and it's ok.
i cleaned the sensor and do the same thing. and always has a little transmission oil,but not too much. but i guess that i need to replace it..
in 15 years that kind of things was never changed by the past owner..

Thank you again..
:)

Nalgman