2nd Gen Non-Engine/Transmission New master cylinder hissing

[KRStone]

New master cylinder is hissing. Fittings are tight, no leaks, but it's hissing when depressing the brake pedal.

Also, the pedal travels further to stop then prior to the replacement.

I don't know if the noise is normal or not; never listened to the other one.

KRS

UPDATE: is the hissing a bad seal inside master, or the booster making noise? I have never had someone push the brake pedal down while i was listening unser the hood.

 

[BigPapa]

Which truck is this on?



If it's the '96 with the vacuum booster, are you hearing it inside the cab? Is it a "hiss" or is it a "whoosh", "bellows" type sound?



Sounds like the booster's bad to me.

 

[KRStone]

My apologies, it's the '96.



Hearing it with engine off, with head right by master cylinder.

 

[jelag]

The hissing is a power booster problem... you've got vacuum leaking. . Its possible for the stroke on the new one to be different then the old one... that's why the pedal feels differently... put a vacuum gauge on the supply line and see of you have minimum of 23" of vacuum at the booster... also even though the rear brakes are self adjusting take a minute and raise the rear wheels, and adjust the star adjuster until the shoes just start to drag... .

Often drum brakes don't adjust up like they should with the self adjusters. . only because we don't stop fast enough in reverse for the adjuster to move as it should

Is the unit you purchased a Cardone Reman unit?

 

[KRStone]

I just redid the rear brakes completely, adjusted them on the stands. Probably need to adjust them again since I've driven it. Need to get them just dragging.



The master is in a NAPA box, M3290 is the part number

 

[ILIANBG]

Did you bleed the master cylinder? When I had mine replaced I saw the guy bench bleed it first. I know he said that's how it's done. No problems after that.
Ilian

 

[KRStone]

LOVE the instructions on bench bleeding [sarcasm intended].



I followed the directions.



Except, the directions kind of end at "when finished bench bleeding, install port plugs and the master cylinder is ready to install".



What the instructions don't say is if you try to set the M/C in place with the plugs in the ports, you can't get the plugs back out because the hard lines to the combi valve are in the way. So, you need to remove the plugs and lose fluid while lining up the M/C, moving the combi valve and rwal brackets away from the booster studs, getting the M/C in back of the brackets and then onto the studs, start the stud nuts, then get the hard brake lines threaded in... .



NOT a process that is done quickly.



So, I'm guess a fair amount of bench bleeding gets undone.



KRS

 

[jelag]

The reason for bench bleeding is to save the time in bleeding the brakes... bench bleeding is not a requirement if you do a good job on bleeding the brakes...

 

[KRStone]

Jim I've heard that before and I agree in theory. I have a hard time in practice thinking air bubbles could be pressed down (against their will, so to speak) through the brake lines, and out the bleeders. Seems like they would find a way to let fluid by (down the line) and remain in the line. People do it successfully though, so it's just a skill I haven't developed.