brake trouble need answer ASAP

[icanfixall]

Another overlooked reason for a sinking brake peddleis the rear brakes are way out of adjustment. Whats happening is the front brakes are doing all the stopping. Then the peddle pressure is attempting to fill the rear wheel cylinders. Then the peddle sinks to the floor. Try this but do it on a safe side street. Apply the parking brake peddle about 1/3 the way down. then dirve it. See if the brake peddle is acting further up and if it sinks... Make a manual brake adjustment to the rears and test drive... The self adjusting rear brakes never reallydid function correctly.

 

[93cc7.3]

ya i adjust them regualry but the thing is when i do that i have an abs light on so the rears lock up real fast when adjusted tight but once the truck is stopped holding light pressure keeps the truck stopped but if i push the pedal will still slowly sink to the floor plus i can see where the master has dribbled down the front of the booster where they meet this week it will have a new master and booster put on

 

['94IDITurbo7.3]

old vac pump only put on 5 inches of vacuum new used one 25 inches of vacuum brakes work better now still sinking but thatll be fixed soon atleast i have power assist back

Did you hit the brake pedal with the vac gauge hooked up? My old pump helds steady at 25 inches at idle but if you hit the brakes once the vac would drop down to ~10 and take at least 35-40 sec to get back up to 25. if i hit the pedal multiple times the vac would drop all the way down to ~5 and take all of a minute to pump back up to 25.

I replaced my vac pump and now that is good but my pedal is still soft and low. i will have to check my rear brakes.

 

[93cc7.3]

Did you hit the brake pedal with the vac gauge hooked up? My old pump helds steady at 25 inches at idle but if you hit the brakes once the vac would drop down to ~10 and take at least 35-40 sec to get back up to 25. if i hit the pedal multiple times the vac would drop all the way down to ~5 and take all of a minute to pump back up to 25.

I replaced my vac pump and now that is good but my pedal is still soft and low. i will have to check my rear brakes.

no i was only able to pull the hose out of the booster and plug the gauge in that hose i didnt want to chance ripping a vac plug it was late and had to work at 5 am so both readings were just at idle i know this (new) used pump isnt perfect because 4 full pumps rapidly will drain the vac but 10 secs its good again this week i might throw a vac can on it as well to help have more vacuum storage

 

[Compu Doc]

it sounds like your Vacuum assist Brake booster is doing its job. I suspect you Brake Master Cylinder is leaking internally and causes the pedal to sink

Ok here we go again. What your describing is what a so called mechanic did to my truck when I did not have the time to work on the truck myself and needed the job done. The so called mechanic puts on a new master cylinder then decides thats not the problem because the pedal is still sinking to the floor yet charges me for the labor and part that was no even the problem, He then figures rabs valve and replaces that. Now the pedal was no longer sinking to the floor.

Not only did that happen once with this mechanic but it also happened another time with another so called mechanic in a different shop I did not have the time to fix the truck myself and that story can be found here : http://www.oilburners.net/forums/showthread.php?t=19805

Look for my insertion on page one titled "Pep Boys Good and Bad"

Now here is the proper way to diagnose the problem of a sinking brake pedal:

http://www.asashop.org/autoinc/dec99/techtips.htm

Note: This is titled "The fading Bronco brake pedal" but applies to our trucks as well as it does to any vehicle with a RABS system.

 

[93cc7.3]

compu doc i assume the abs light on would be from the rabs valve? should i be concerned with the leak on the front of the booster

 

[Compu Doc]

Yes you should be concerned with the leak on the front of the booster but the RABS light does not necessarily need to be on to indicate the RABS valve is bad. Even in the first instance I mentioned in my response above the RABS light was not on. It's an idiot light just like the rest of the warning lights in our trucks.

The point I am trying to make is that when people have a sinking brake pedal they automatically assume that it is the master cylinder when it could be another malfunctioning part.

Would you want to replace your master cylinder only to find out that you had a bad RABS valve?. Why throw parts and money at something without properly diagnosing the problem first.

A master cylinder can leak but not show it is leaking also. Also the RABS light can be on in a truck but not have a bad RABS valve as what happened at Pep Boys with my truck with a new RABS valve after they diagnosed the problem incorrectly and the only problem was the idiot mechanic did not adjust the rear brakes properly.

 

[93cc7.3]

well i drove it again just now then i push the pedal it will sink all the way to the firewall its firm but will not stop before the pedal maxes out im going to continue to adjust the back in see if that changes pedal movement

 

[Matrix37495]

Any of you guys know if my OBD1 code reader will read ABS codes? Or any other way to figure out the light?

I forgot about the RABS valve being a common nuisance....