hello everyone
(1985 f150 I6 4.9L)

so I have noticed in the last couple of days that my break pedal goes hard when I brake, and there is a distinct hissing sound that was always there, only now my foot will go almost too the floor with a VERY loud hissing sound, I then will hit the breaks again trying to get any force the the pedal is now rock hard, if I let go and wait 5-10 seconds the above can be repeated

I believe this is a problem with my break booster. the vacuum line is good and dose pull a vacuum.

I have replaced in the last year the front and rear calipers (drum and disk) along with the master cylinder (at this point my breaks were perfect, better than my moms 2008 Subaru impreza) when I got back from summer camp though, my master cylinder had gone bad (again) and was leaking fluid out the back (where the master cylinder connected too the brake booster) so I replaced it (bench bleeding as instructed and bleeding the lines after) but now I have the above mentioned problem. on top of that my new master cylinder seams too be leaking in the same spot as the previous one, but I would have too check again.

maby this is the cause, 4 days ago I put the truck in the ditch, went in nose first traveling down the road almost sideways in the direction of original travel, no damage was done and I am perfectly fine, got the truck out and the brakes worked fine for the next day or 2.

thanks for all the help, I am realy tired of having too fix my brakes.
p.s. sory for the long explanation.

 

Brake fluid leaking out the back of the M/C will destroy the diaphragm of the booster in short order.
Best to replace as a complete unit.

 

talked too my autoshop teacher (mechanic for 26 years)
and he agrees it is my break booster.

the confuseing part is this morning I had hard breaks, this afternoon I had realy soft breaks that almost needed too be floored to get some breaking force and I couldent make them go hard by mumping them, we will see what this evening brings, glad I drive on barren roads, and drive a manual.

 

It sounds like a brake booster gone bad. As for the master cylinder were are you buying them & are they new or remans? I never buy remans for items like brakes BUY NEW.

Craig

 

This morning you had no booster
This afternoon you had no fluid left in the M/C cylinder or the piston seal is finally shot.

 

first one was at napa and lasted 3 months (then it catastrophically failed, like absolutely no breaking ability and a gush out the back of break fluid), think it was a reman, the one I have now has stopped leaking and is a new one I believe, I got it from lordco (I have switched too buying from lordco as they are closer and have been better for parts not breaking on me and better selection where I live) I told them I wanted the premium new one so I am assuming thats what I got.