Brake question. Servo?

[John_Mc]

My brakes generally work very well. Occasionally, however, when I put firm pressure on them to make a quicker slow down than normal I feel and hear a pop (sort of a "PFFFT!") and the pedal depresses further and I lose stopping power. One quick pump usually restores it. I noticed once that after the "PFFFT", rather than pump the pedal, I kept it depressed and I continued to hear a steady hiss. Anybody know what these symptoms are telling me? Initially I thought my PWDA was the source, but the hiss has me thinking it has something to do with the vacuum assist servo. Anybody been down this path before? As always, TIA.

 

[Brosky]

PWDA is purely hydraulic, the pfff is probably from a vacuum leak in the booster.

 

[DNK]

Check the drivers seat. Sure it didn't come from the driver?

 

[RonMacPherson]

Paul was right on. Hissing noise is vacuum leaking. First check the one way check valve in the vacuum line, then check the rubber line/hose make sure it is not cracked, leaking anywhere.

Then do the classic booster performance test.

i.e. with the brakes working normally. Stop the engine. pump the pedal 5 or 6 times to release all vacuum, then holding foot on pedal start the engine. Pedal should drop some and hold steady. If it doesn't the booster is fongoohlahed.

 

[John_Mc]

Check the drivers seat. Sure it didn't come from the driver?

Okay, let me clarify...I heard an ADDITIONAL "PFFFT!" :eeek:

 

[jclay]

Woody at the Wedge Shop can have the vacuum booster rebuilt for you! He did mine and I am very happy with it and he supplied the brand new master cylinder.

jclay

 

[tdskip]

Check the drivers seat. Sure it didn't come from the driver?

LOL

 

[John_Mc]

Paul was right on. Hissing noise is vacuum leaking. First check the one way check valve in the vacuum line, then check the rubber line/hose make sure it is not cracked, leaking anywhere.

Then do the classic booster performance test.

i.e. with the brakes working normally. Stop the engine. pump the pedal 5 or 6 times to release all vacuum, then holding foot on pedal start the engine. Pedal should drop some and hold steady. If it doesn't the booster is fongoohlahed.

To follow up here, everything above checks out okay. I don't see any cracks in the hose-it looks to be in pretty pristine condition. I also noticed when I experienced this problem at idle, it causes the engine to run rough, a sure sign of a vacuum leak. I'm guessing the problem is inside the servo. Must this be sent out for repairs? Are there no rebuild kits like there are for cylinders? I can't seem to find any servo diagrams although I recall having seen one before. Maybe that was in my Haynes Manual. Hmmmmm...have to check that.....