My car just got this problem yesterday. When I apply the breaks it makes hissing sound and idle goes up. I also loose vacuum assist. Pretty obvious it is a vacuum leak.

The sound is coming from inside the car somewhere on top of the pedal. I could not get myself underneath to take a good look.

Anyone had this problem? Any suggestions on what I should do now?

Thank you?

 

Sounds like valve or diaphram is shot, Hissing sound will be entering through brake pedal box.

 

Thank you.


Does it worth taking thing off and looking what is broken, or I should just buy new part and replace?

 

Might be diaphram or valve or both. I am not sure what is available but both may be part of a rebuild kit anyway. What model and year is your car?

 

It's 1985 XJS, looks like part number is CAC1227.

 

Hello,

does anyone have procedure how to replace break booster / servo?
it does not appear as an easy job...

Thank you.

 

Assuming it is like the V12, then because the indent in the wing bodywork is about 1 inch too short, you cannot remove the brake servo on its own, because you cannot get it off the pedal box studs. You have to unbolt the entire pedal box and lift it out, pedals and all. On your car you will have a clutch pedal in there as well, and you may or may not have to disconnect that fluid line as well. The box does not have to be raised that much to clear the booster's exit path.

So what you do is disconnect the brake lines from the master cylinder, also the lines from the fluid reservoir, and undo the two bolts that hold the reservoir fixing bracket, and disconnect the vac line from the booster, so then the pedal box and brake booster (servo) and master cylinder are free of all attachments.

Then, if you look carefully, there are four bolts that fix the pedal box to the sloping part of the bulkhead. Undo these and you can carefully lift up the box and pedals enough to get the brake booster off its fixing studs. You can see three of the four the pedal box fixings, and the pedal box bulkhead hole, and the pedal box itself, in the attached pics.
Greg

 

Thank you! Will probably leave it as is this weekend - too hot...
I figured I need to pull out pin that attaches pedal to servo from inside (or it can be done after lifting pedal box?)
I am surprised my manual does not address replacing servo...
Thanks again.