Low Brake Pedal
 

Hello everyone. After reading around the existing posts regarding this situation, I wanted to post my question. The car stops fine but the travel of the pedal seems excessive, it is near the floor.
I purchased brake pads thinking that it was the issue but upon removal of the tires, the pads are in excellent condition (silly me!).

Anyways, this started to happen within a short while, I have not had any work done on my car recently so it is happening on its own. This is a 2001 S80 T6 with about 74K miles on it. I am sure there is a wear item at fault here but I wonder which it is. When the engine runs, the pedal goes down but when it is off after a few pumps it goes back up.
So, I am wondering if the master cylinder could be bad or if the booster. I do not drive this car hard so I cannot say I have felt theABS kick in recently. Anyways, as always, your help is appreciated.

regards

Jim

RE: Low Brake Pedal
 

This isnormal. The booster works on a vacuum system created by the engine. If the engine is not running there is no way to keep the vacuum, therefore, the pedal 'hardens'.

Has the brake fluid been changed? It is recommended that it be changed every second year or at 30,000 mile intervals. There may be air in the system or, worse still, moisture, asbrake fluid is hygroscopic. This could cause the excess travel on the pedal.

RE: Low Brake Pedal
 

Hello Bill, thanks for the message. I understand the method of operation of the booster, I mention it as means to suggest that pedal does not travel slowly to the floor when pressed with the engine off, which may (may being the operative word) suggest that the master cylinder is operational. I say may since it could be that one of the stages might be failing.

The fluid has not been replaced recently, I have had the car for almost a year now and I purchased it from a dealer. I will look into it and will also try that. Do you have any tips regarding bleeding the brakes? Anything to watch for?

I have the car still up on stands since I also want to replace the strut bearings so it will take some time for me to finish it.

again , thanks for the response.

regards,

Jim

RE: Low Brake Pedal
 

Check this one: https://volvoforums.com/m_65619/tm.htm.

The rear bleeding is slightly different. If you wish to do this I can post the instructions.

Bill.

RE: Low Brake Pedal
 

hello, I had my brake booster replaced / master cylinder replaced, and a key thing I noted about mine, when it needed to be replaced was that after using the brake pedal a few times there would be a hissing noise, as if air is commin out of the brake pedal area. this hissing noise is continuous, and my brake booster/ master cylinder was changed by the delearship after i explained that to them.

When I had this problem, the pedal felt really weird and had that air leaking/hissing noise, which only stopped after i shut the car off.

RE: Low Brake Pedal
 

Bill, thanks very much, that is good information. If you could post instructions, that would be great. Also what the difference is between front and back. Maybe that is what is giving most people the results they are getting.

regards,

Jim

RE: Low Brake Pedal
 

Hello Gordon, thanks for your message. That hissing noise is defintely a problem with the booster for sure. Your dealer did the right thing in replacing it. The booster had a leak and the vaccum was not constant and uniform which is likely the cause of the weird behaviour of the pedal. I hope I do not have to replace both things.

regards,

Jim

RE: Low Brake Pedal
 

Instructions for bleeding/replacing brake fluid to rear wheels.

Who thought up this system?



[IMG]local://upfiles/4491/012F87699A8B4C2E86CC14477F9F38B0.jpg[/IMG]

RE: Low Brake Pedal
 

Thanks for the info Bill. This is awesome.
As to who thought it up, I would imagine someone with a lot of time in his hands ;)

regards,

Jim