I replace my hissing Brake Booster yesterday on my 02 S-80. While it took me the better part of the day to complete everything went well. After compete, the brakes were very soft. I bleed all 4 four brakes but now, the pedal is super firm. The brakes work and stop the car well but it takes a lot of pedal presure to get it stopped.

Any sugguestions?

Thanks in advance for your help!

 

Make sure there is not a leak outside by the brake booster.(Vacuum leak)

 

Thanks for the tip. Are you talking about the vacuum hose that connects on the engine side of the fire wall? Could it also be if the booster is not tight to the firewall? I battled with those 4 bolts for a long time to get them tight.

Again, thanks for you tip and help.

 

The hose that goes to the brake booster and the back of the master cylinder. There is a rubber seal between the master and booster. Sometimes the seal will fall off or the master is not seated all the way causing a vacuum leak.

 

Thanks! I know what seal you are talking about. I replaced the seal between the new booster and the master cylinder. I'll double check it tomorrow to make sure there is not a leak.

Thanks a lot for your sugguestions and help!

 

Your welcome!

 

Thanks for the advise on this. Just an update for anyone else that has a smilar problem. Indeed I did have a vacum leak on the connections to the brake booster. It took a small amount of silicone sealer and everything is working great...with no hissing!

Thanks for the support.

 

Glad it is good now.

 

I have a similar issue after replacing the booster on my 01 V70. I have bled the brakes 3 times, but every time I find new bubbles in the fluid. That means air is leaking in - is the main sylinder bad? BTW, there is some green gooey stuff in the top where I refill brake fluid. Is it just dust and small particles that have loosened? Do I need to take it out and clean it?

 

Go to the Dollar store and get a turkey baster. Remove the fluid with baster... use a non-lint cloth to clean inside the master and refill.
Be careful with the fluid...it can remove paint and eat through wires. Wash any mess with Simple green and water.

Cb