[germangs]

Hi, the brake pedal feels soft when braking. It is only on the first attempt. The second press feels the right way. I am replacing brakes, brake pads sensors and rear rotors tomorrow. But I think that it is the time to replace the Master Cylinder. Is aftermarket good enough or should I go with OEM. Please tell me your experience and where should I shop for aftermarket for mine 99 S420?

 

[Check Codes]

If it were the MC, the pedal would not firm up (and if you have pressure and hold it firmly, the pedal will slowly fall).

You describe air in the lines. A good bleeding should take care of it. If you are doing the work, do not just simply push the old fluid back up the lines. Instead, open the bleeder valve at the caliper, then compress the piston. When it bottoms out, snug the valve. After you change all four in this manner, then bleed enough to FLUSH OUT all of the old fluid, not just to get rid of air bubbles.

 

[MBTECH3]

Check your front wheel bearings

If your wheel bearing(s) are loose on the front, the rotors will not rotate perpendicular to the brake caliper pistons causing the pads to be pressed out from the rotors. Imagine taking a screwdriver and putting it between the brake pad and rotor, now pry on it a little bit. Same difference, the pedal would have to be pressed to get the pads back in full contact to the rotors. Hope this helps.

 

[bayhas]

drain your lines first...

 

[iss]

if your Master Cylinder have a gold valve on a side---its very expensive parts!!!

 

[bayhas]

if your Master Cylinder have a gold valve on a side---its very expensive parts!!!

if the car is BAS equipped, you mean?

 

[iss]

if the car is BAS equipped, you mean?

Hm His car did not have a BAS ? I thought that all w140 1998-1999 have BAS

 

[mbenzz1]

Soft Brake Pedal Feel

Also experiencing soft brake pedal feel (brake pedal goes low). Have replaced rear rotors and brake pads. Resurfaced front rotors. Bled brakes as best as I could (elimiated bubbles). When ignition and engine is turned off, brake pedal works as it should (brakes engage right away). However, when ignition is turned on, brake pedal goes low.
Thanks for your help in advance.

 

[glenlloyd]

My pedal travels too far for my liking. I purged the old fluid but that seems to have made little difference. My next task will be to replace the old rubber hoses, front and rear, but also will likely pull and drain / clean each caliper.

There's no guarantee that bleeding will eliminate all the old fluid, it may seem so when clear fluid comes out but I would rather be sure by pulling and draining off each one. It may seem laborious but I would rather be sure that all the old brown skanky crap is out of there.

Steve A

 

[c4791p]

Soft Pedal 2001 SL500 48K mi

After replaced pads and rotors all around 3k miles ago, just had dealer flush, drain and refill and they claim all in specs. But I just don't get the same firm brake feel as in my previous SLs and even my wifes 2004 C320 Wagon. Still way soft to my mind. Admittedly car starts to stop, but I can just keep pressing pedal -- not all way to floor though -- even after car has stopped.

Ideas?

 

[Benznoob26]

Also experiencing soft brake pedal feel (brake pedal goes low). Have replaced rear rotors and brake pads. Resurfaced front rotors. Bled brakes as best as I could (elimiated bubbles). When ignition and engine is turned off, brake pedal works as it should (brakes engage right away). However, when ignition is turned on, brake pedal goes low.
Thanks for your help in advance.

did this just start after you did the brake job? whenever mine needed bleeding i would have to press it lower but it would still feel firm once i got low enough. im pretty sure MC feel soft to the floor

 

[napaAl]

When I bought my car last year, The pedal was soft. My Indie described high moisture, and bled the brakes. Perfect since.

 

[PetrFin]

I changed my rotors and brake pads around a year ago. Everything was working fine, I could make about 2 or 3 thousands miles since then. But lately I feel how the brake pedal is soft to the first half, but if I press it strong it brakes good. I remember it didn't work this way. My friend recommend master cylinder but not the one in engine. He says there is something underneath the pedal? What is it? Thanks.

 

[samosali]

underneath the pedal or next thing after it in direction of car's front end there is brake booster. from the engine bay it is visible as black cylinder ca 30 cm in diameter, from the cabin you can see the lever and the piston (white plastic ca 5 cm in diameter) covered with gray plastic = dust protection. I doubt that this piston can be purchased separately from the brake booster but i am really not sure. so most probably your friend talked about brake booster.

to be completely honest, what you described sounds totally normal to me. every brake is soft first and harder after that.

 

[PetrFin]

underneath the pedal or next thing after it in direction of car's front end there is brake booster. from the engine bay it is visible as black cylinder ca 30 cm in diameter, from the cabin you can see the lever and the piston (white plastic ca 5 cm in diameter) covered with gray plastic = dust protection. I doubt that this piston can be purchased separately from the brake booster but i am really not sure. so most probably your friend talked about brake booster.

to be completely honest, what you described sounds totally normal to me. every brake is soft first and harder after that.

It didn't do before. It was braking in the first half, I just gently touched the pedal and it started braking. Now it brakes good but only if I press it harder.
I'll ask him about the brake booster. What the brake booster do?

 

[samosali]

only you know the car. and it is difficult to discuss such things over typing text

brake booster uses vacuum from engine. there is one input = vacuum from engine. over a diaphragm this vacuum is used to move an axis in the middle of brake booster. this axis moves master brake cylinder. that's why braking is easy and soft. so once you only slightly depress the brake pedal brake booster knows (there is a valve) that you need assistance and it helps you to depress the master brake cylinder. so you actually not perform all work necessary for braking by your leg but let's say only 20% of it. as soon as your foot stops the brake booster stops working too. Actually it is similar as in power steering. there the media is fluid, here (braking) the media is air.

 

[Peatryp]

Hi, the brake pedal feels soft when braking. It is only on the first attempt. The second press feels the right way. I am replacing brakes, brake pads sensors and rear rotors tomorrow. But I think that it is the time to replace the Master Cylinder. Is aftermarket good enough or should I go with OEM. Please tell me your experience and where should I shop for aftermarket for mine 99 S420?

I have a 96 S320 and the brake pedal is soft and I am preparing to change the master cylinder to stop the soft braking. You don't need a OEM you can get a good after market one save a few dollars and it will be fine.

 

[PetrFin]

I changed my rotors and brake pads around a year ago. Everything was working fine, I could make about 2 or 3 thousands miles since then. But lately I feel how the brake pedal is soft to the first half, but if I press it strong it brakes good. I remember it didn't work this way. My friend recommend master cylinder but not the one in engine. He says there is something underneath the pedal? What is it? Thanks.

The my problem was air in the lines. It's sad that in the Keys nobody knows how to bleed W140.
In Miami did that, but then they did not know how to fix my heat.
I hope shops here in California know W140 better.

 

[willys]

Hi, the brake pedal feels soft when braking. It is only on the first attempt. The second press feels the right way. I am replacing brakes, brake pads sensors and rear rotors tomorrow. But I think that it is the time to replace the Master Cylinder. Is aftermarket good enough or should I go with OEM. Please tell me your experience and where should I shop for aftermarket for mine 99 S420?