Hello to all;
Just took my cat from storage... long story short- on the first drive I've noticed that the brake pedal is hard to press. the DSC Off light on the dash... When I've examined it more - I can hear a hissing sound in the car, near the brake pedal. When pressing on the brake - the sound stops... Is my brake booster done ?? or could be simply a hose ??
If it's a break booster - can it be rebuild or do I have to get a new one ?? Or maybe the problem is somewhere else ??

 

The first 2 things I would recommend:
1. Check brake fluid level.
2. Check, if the calipers and rims are especially dirty (black greasy stuff). This would indicate to me a brake fluid leakage.

Next:
I assume you know that brake fluid should be changed now and then - I can't put a time on it - but after several years.
Reason: Brake fluid (DOT 4 more so that DOT 3, and DOT 4 is the recommended brake fluid for S-Type) draws water from the air and thus, the brake fluid get diluted with water over time. This affects the functionality of the brake fluid.
Apart from the not directly noticeable effect of water in the brake fluid, which is corrosion of brake lines and calipers, is a "spongy brake action". If that is what you mean by "having to press the brake pedal hard", then this is most likely your problem: Water in the brake fluid, and you need to change the brake fluid. When bleeding the system always start at the wheel, which is furthest away from the brake booster and finish at the wheel, where the brake booster is closest. Start with removing the old fluid in the reservoir with a little hose on a syringe, fill in new DOT 4, and do the brake bleeding.

I have currently removed all 4 calipers from my 2.5L X-Type and I have taken those calipers apart and I am replacing the seals. Maybe that is one thing to consider, too?

 

Thanks for update - no - there is no loss of brake fluid - the pedal is not spongy - it's hard to press... and I can hear hiss - like air escaping or maybe pulling it ... so it seems it's something with the power booster... Can it be recondition > or does it have to be replaced ??
Is there a hose in the system that could cause that ??

 

I don't know about how damaged master brake cylinders behave ( I never had a damaged one), but it is possible that if it is damaged that this is also due to water having been absorbed by the brake fluid over time, as the above mentioned corrosion (due to water in the system) can also corrode the brake booster/cylinder from inside.
On the other hand, if the brakes are hard to press, maybe it is an indication that the moving parts in the calipers are kind of :stuck", which again would mean that the other thing I recommended (and what I am doing on mine right at this moment) might help: Cleaning all the parts of the calipers and swapping the seals.
If the calipers are seriously "solid stuck" I could imagine that the generated hydraulic pressure buildup (caused my pressing the brake pedal) is looking for some kind of different "escape route", and wherever that might be it might cause the hissing noise.

Also: You did not mention, if that hissing noise occurs every time or only after driving and braking for a while...: Compressing air and water in the brake lines can cause the water to boil as the temperature can reach 1000 degrees. And then there would be steam, that could "hiss" somewhere, when there is a leak...

 

It sounds like a vacuum leak, probably on the line to the booster, check out the pic of the lines thanks to Joycesjag.

 

Yes, that could be, indeed! ...a vacuum leak - I did not think of that.

Nonetheless: I recommend not to forget about changing the brake fluid, as failure to do it causes brake system corrosion and other problems....

 

A bad Master cylinder will give you a soft spongy or pedal that goes to the floor. The vacuum leak at the brake booster or an internal booster leak will give you a hard pedal

 

read the dsc codes

yes the active booster can fail

 

I agree too. Classic symptoms!

 

Just to close this thread - yes - it was a brake power booster - got it replaced with a used one - so far, so good...