Brake problem - low power, pedal skinks at 1st time
 

Hello!

I have a C220 2008 with 220000km. It's a reliable car, never gave me big problems, only necessary to keep the recommended maintenance. No major costs, given that it was me doing the maintenance.

But the past two weeks, there is a problem in the brakes. When I need to pedal the first time the brake pedal sinks more than normal. It does not give me the braking power I need. If I pedal hard, the brakes respond well. Without any problem. But if I want to control the speed with the brakes or if I pedal slowly, the pedal sinks fast, does not give me a safe braking and have to pedal again to gain braking power.

I googled on this subject and found maybe something similiar: https://mbworld.org/forums/c-class-w...ml#post3857128, which i will follow first if i can resolve the problem before more great adventures.

I changed front brake pads and surface front rotors at 198800 km, but only now, after 210000 km, it came up with this problem. I didnt change rear pads, as they were good at that time.

But since then, with my window open, in more rough streets, i can hear the brakes shaking, as if they are not tight to the rotors. Maybe the brake piston need some fix. Dont know if that is relate to this problem.

Well, i am giving myself an anwser, but if someone can give me a different idea of ​​this, i appreciate.
My car vin is WDD2042081F278198.
I will keep this post updated.

Sounds like air in the lines. When was the last brake fluid flush?

Well, i bought the car used in 2010 and never flushed the brakes.

I will flush today the brakes.

That's a good place to start. It's possible that was never bled since new and if so that's a long time and a lot of miles for brake fluid to be in service.

ATE recommends 3 years on their standard brake fluid, 2 years on the low viscosity variant which is what I think the W204 uses.

Well, i flushed the brake fluid on all 4 corners. I even checked the brake pads at front and rear (the wear is even in all 4). And checked for leaks. None at what i saw. And the brake pistons are working.
But the problem is still there... :(

https://mbworld.org/forums/c-class-w...placement.html

this is Glyn's post you can read the full thread in the link

See pad break-in procedure on the Stoptech website.

This is a common problem with 2 main causes - Calipers over returning or changing the front pads without doing the rears. So tell us - did you change all the pads? If not - do so & then do the break-in procedure

The pistons in a brake caliper depend on the distortion of the D shaped seal to return them to the brakes off or resting position. When changing pads on these cars great care should be taken not to push the pistons back too far in the caliper to get the old pads out. You should just push them back sufficiently to release the old pads. If you don't do this, stiction of seals on the caliper bore can cause the piston to move forward but not bring the seal with it down the bore surface & cause the piston to over return when you release the brakes. You then need more fluid to bring the pads back in contact with the disc (rotor) which gives you a low or mushy pedal.

There are two ways to fix this - one laborious & the other risks popping the pistons out of the calipers so be carefull.

If replacing all pads does not fix the problem - then you need to remove all pads. Make up some wooden or similar spacers about the thickness of a brake pad backing plate. Insert these or old backing plates with no friction material on them into the calipers & stomp on the brakes to move ALL the pistons forward in their bores. Then push back gently until you can just slip the new pad in & you should should have cured the over return.

The alternative is to strip & dry all fluid out of the braking system. Reassemble the calipers with pads, shims, pins & all. Blow the pads against the discs with compressed air & then bleed the braking system.

Good luck - I hope your problem is just not replacing all the pads at the same time.

Ya, i saw that post. Thanks anyway!
Well, will try around the pistons 1st. Do the procedure. If that doesnt solve the problem, will change all pads. But as from i saw today, the pads are all even and with low wear.
Dont know...

So today i did what is describe in https://mbworld.org/forums/c-class-w...placement.html and the problem is still there...

What may be more??

A leak /kink /blockage in your vacuum line to the master cylinder?

Vacuum leak in the brake booster?

Any check engine lights on the dash?

There is no engine light. No other problem. Just the brakes are mushy at slow brake. In that situation, the brake pedal goes deeper than normal. Is like it looses power during a slow brake or controlling the car velocity with the brakes... If i brake a little hard, the brakes does the job.

I havent notice any leak or malfunction. Just notice today when i brake, i can hear next to the pedal a low sound, as a vaccum loosen... Is that normal? Is just the pedal working? Never heard before that sound but in the other hand i never search for that sound or been so close to the pedal..

Maybe a silly question... how to check for vaccum leak in brake booster?!

With the engine running & bonnet open check pipe from vacuum pump at front of engine to the brake booster. Listen carefully you should be able to hear a bad leak. Check at pipe joints too. .

So the brakes after all, got better next day after doing the piston procedure. Its not all perfect but is a safe car now, for daily driving..

Thanks to all.. :)

Will change rotors and pads in a few months, as rotors only have a 1mm thick till limit.