Master cylinder

[DieselCash]

For the last couple of weeks my brakes have been acting up. At first I would slow to a stop and as I was sitting at the stop light the brake pedal would very slowly drop to the floor. The last couple of days it got worst to where it would do this on long stops. Today it was doing it on short stops to where I was having to push down on the brake pedal multiple times. When I hoped in my truck to come home tonight it went all the way to the floor and with all my might it would slowly stop the truck.

So, I went to O'Reilly's and picked up a new master cylinder. It was easy to take the old one out and the new one in. Then I attempted to bleed the rear brakes. Nothing, and I mean nothing fluid wise would come out of them. I first tried my one person vacuum bleeder and nothing. Then gravity, nothing. Then I opened both rear ports and pushed on the brake pedal multiple times, nothing.

I then tried the front brakes and they bleed easily.

Any ideas?

I have changed out at least 6 master cylinders on these old chevys and I have never had this problem before.

I am stumped.

 

[dmaxx3500]

try using 2 people,1 to push brake pedal,2nd to open breader,,start by opening breader-then push brake pedal to the floor slowly-then before letting up pedal close bleader,,,repete steps 4-5 times or no air comes out and clean fluid comes out too,,make sure not to run master out of fluid ,,,i know this isn't the way weve been tought to bleed brakes-but this works

 

[DieselCash]

That is actually how I use to bleed my brakes. This time I was using one of those vacuum type bleeders.

Thanks,
I will try this.

 

[Burning oil]

Did you bench bleed it first? I don't remember why as its been along time, but its supposed to be done.

 

[handcannon]

Several years ago I was changing out a bunch of brake stuff on my Toyota FJ40. One item I changed was to a reman master cylinder. I could not get the brakes to bleed, not enough pressure to push the fluid through. I fought that for a long time, then took the MC back for a new, not reman, one. I was able to get that one bled right away. Bad MC problems usually seem to be with reman items, but I guess it could also happen with new ones.

Don

 

[DieselCash]

Did you bench bleed it first? I don't remember why as its been along time, but its supposed to be done.

That is exactly what I forgot. Left out of work early and did it real quick, now the rear brakes are getting fluid. :thumbsup:

It is always the little things. :mad2:

 

[THEFERMANATOR]

The trucks with just rear ABS MUST be bench bleed as they use a 3rd chamber inside the master cylinder. Why I don't know, the only reason I can figure is to keep you from mashing teh brake pedal to fast when the RWAL kicks in. I did a 93 a few years back, and even bench bleeding it took forever to get all the air to purge out of that last port in the rear.

 

[btfarm]

Last time I did one of those a bench bleed kit came with it so it's pretty hard to miss that step.

 

[DieselCash]

Last time I did one of those a bench bleed kit came with it so it's pretty hard to miss that step.

Some how, I did! :rolleyes5:

I hate bleeding brakes. :mad2:

I think I got it, we will find out when I leave to go back to work.