whistling noise from brake vacuum boost system...

[dingus]

Manual Transmission Drivers-(Survey) What rpm range do u drive in?

hey all,

i'm stumped by this! (94 XJ Sport, 5 speed, non-abs brakes)

When i first hit the brakes, something under the hood (or maybe on the brakes themselves...?) starts whistling, almost like a squealing belt but i replaced my serpentine belt with no avail. This picture is of what my best guess is but the noise has not given up:

I tried running a bead of silicone around the master cylinder because when i pull on that hose while its running it leaks air... so i figure that while i'm driving the pressure builds to the point that it sucks through elsewhere or just broke my seal where i can't tell. Has anyone had this thing apart? Usually, the whistling won't go away until i start moving again... this appears to be some sort of vacuum-assist setup for the brakes, correct?

 

[90Xjay]

RE: Manual Transmission Drivers-(Survey) What rpm range do u drive

That is your vacuum assist line from the booster to the intake where it gets vacuum. The hard plastic peice going into the booster may be a check valve, it has been awhile since I messed with that.
the squeal is more than likley a vacuum leak with a high pitch because of air volume being sucked into the the intake.

 

[dingus]

the squeal is more than likley a vacuum leak with a high pitch because of air volume being sucked into the the intake.

good description of my problem

 

[redrooster]

Replace the plastic peice and the hose. It should stop. If not it may be the booster itself (the large round black object). If you want to narrow the search then get the whistling to happen again and spray WD-40 around the area. It will quit momentarily when you spray over the leak. THis needs to be repaired ASAP or you may loose your power brakes at a critical moment.

 

[Inspector-Gadget]

Re: RE: What I didn

Hi-Ya, dingus,

Too many possibilities for me to venture a guess, but for trouble isolation purposes only, try disconnecting the brake booster vacuum hose at the manifold end of the hose and then sealing the manifold nipple.

Then take that red hot chili-pepper XJ for a ride and see if the noise has vanished.

Careful please! although you will still have manual brakes, you won't have power or vacuum assisted braking.

If the noise disappears -- well, I don't think I need to explain.

Regards,

Divide and conquer, Gadget

 

[dingus]

Re: RE: lockers on a YJ

thanks for the suggestions guys, i will look into this mess this weekend (when i have time to sleep) and will get back to you. it seems that my worst case scenario is a new brake booster huh?