~CL500~

Hello everyone. I’m having some braking issues with my 2001 CL500, specifically vacuum/boost related. The problem is intermittent and has been going on for about 2 months now (but never added 1 + 1 until recently). The brake pedal gets very hard and requires a lot of force to stop the vehicle, especially when rolling to a stop with the brake applied. It does not go to the floor by the way. In addition, a hissing sound occurs in the driver foot well when the brake is applied, kind of like air releasing and it only occurs when the pedal is hard to push. After troubleshooting this, it appears the brake booster is not receiving sufficient vacuum or it’s leaking vacuum pressure somewhere. I changed the check valve and vacuum line going to the booster thinking that the check valve might be faulty. While doing this, I checked the vacuum line going to the intake to see if it had sufficient vacuum, which it did. I didn’t have a vacuum tester to verify it, but it felt pretty strong. Immediately after I changed the check valve and booster line, I went for a drive to test the results. Everything worked great for about 5 minutes, but then the problem resurfaced.

I changed the brake pads about 2 months ago, shortly after first experiencing the problem and was planning on changing the brake fluid as well, but am holding off until I resolve this issue, in case further work needs to be done.

So my question to the experts or anyone for that matter that experienced an issue like this: Do I have a bad brake booster or can it be something else? I don’t want to jump and change the brake booster if the problem will still exist, especially since the boosters are pretty expensive.

I stopped bringing my kids in the car after this. Things can get pretty hairy without brake boost

Thanks!!!!

mleskovar

Different car manufacturer, identical problem (except for the hissing sound - that definitely sounds vacuum related).....new booster didn't fix it, new brake master cylinder fixed it.

~CL500~

Thanks mleskovar. That actually did cross my mind initally, until I noticed the hissing sound (helps when you mute the radio). This one really has me stumped.

Anyone else have any ideas? Please?!

sosh

Had a similar problem with a BMW years ago and it was the brake vacuum accumulater that they referd to as the "brake ball" new one solved the problem.

~CL500~

Thanks for all the feedback guys.

After thinking about this further, I'm probably gonna pull the trigger on the brake booster. I don't see the problem anywhere else. The hose to the booster has vacuum and the car does stop pretty well when I press hard enough on the brake pedal. Stopping is pretty linear as well. Also, if I keep my foot on the brake long and hard enough, my idle gets a bit rough. Everything keeps pointing to the booster. I will post my results after I change it.

Thanks again for all your feedback.

Love thy CL, for better or for worst.

vettdvr

You can have a crack in the diaphram that opens when you depress the brake pedal. Then the vac would dump. Only way to fix is R&R.

~CL500~

Well, I finally did it this weekend. It was in fact the brake booster. Thanks again for everyones advice.

What a PITA to replace! I for one hate working upside down in footwells.

It took me about 5 hours on Saturday to replace the booster and on Sunday I bled/flushed the brake fluid with some fresh ATE Super Blue using my Motive power bleeder, which works as advertised by the way. Excellent tool to have.

Due to lack of space in the area surrounding the booster, I had to disconnect the brake lines and master cylinder just to get the booster out. It really tested my patience, but at the end of the day I had results and some bonding time with my CL.

I'm gonna pass on posting the procedure because 1.) Brake boosters rarely fail and 2.) Its tooooo much typing. If anyone were to ever need some pointers, please PM me.

The bleed procedure has some value though. I will post that up shortly.

mleskovar