Star diag - inspect brake system for air
 

My braking is poor. The car stops fine, but I believe I need too much foot pressure to do it. The previous owner just put on Akebono ceramic brake pads before I bought it. Some searching here suggests people seem to be very happy with them.
I would try bleeding the brakes but I noticed there is a star diagnostic routine to check for air in the system. I did it this morning and all the tests passed, however, I had use some serious foot power to get them to pass.
This test in particular. You press the brake slowly and evenly til you get to the green area on the chart. The chart changes scales a few times until you finally get to this scale that I have in the picture. It was very difficult to get to the green area here. I was able to do it but I had to push very very hard on the pedal.
It just doesn't seem right that I should have to push so hard to get it to pass.
Anyone else have experience with this test?

https://cimg6.ibsrv.net/gimg/www.mbw...3a7ff2d7d2.jpg

I will suggest that it's the Akebono pads. I put them on my CLK550 and hated them. Stops got longer and they would squeal in reverse. I replaced them with OEMs and everything was fine.

Something else is very likely wrong.
I changed my own pads and flushed the brake fluid. The system is very resistant to being bled out fully
I bled out of the lines for longer than any other car I've ever worked on.
Another issue could be the procedure of flushing and how precise or high tolerance the ABS pump and the ABS ECU controller is.
Did you unplug the ABS ECU before you bled out the system?
I also used the STAR to perform the same brake check. You shouldn't have had to push as hard as you described to do that.
Ceramic pads are used by most manufactures now and are rotor friendly and shouldn't effect pedal pressure to the level your describing.

I replaced pads using a Ceramic compound, pedal pressure and feel are normal and stopping power is better than the Corvette C5 with Kevlar Carbon and braided lines we had previously

when following instructions on the pressure test follow instructions exactly. i had to press on the brake very hard for a while. also i had to bleed my brake a few times to get a firm pedal feel. make sure you have your motive bleeder pressurized right and make sure you have everything in place like tools and bleeder hose. was my first time doing it took about 3 tries for me to get it right.

I haven't bled the brakes. I completed the star "air in system test" to see if I need to bleed the brakes. All tests passed, so if I were to trust this test, there isn't any air in the system. Having to press the brake pedal so hard to get the tests to pass is what bothers me, so the question is why so much effort is needed on the pedal? Bad master cylinder possibly? An adjust to the pedal assembly, maybe a marginal sensor?
I don't know much about SBC brakes so I don't know where to look. I can certainly rule out the brake pads as far as this test goes. Maybe the fluid is very old and needs to be changed. I'd love to hear a good theory....

SBC works by an electric motor pressurizing the system. The system then looks at where your brake pedal is at electronically tells how much pressure to then apply to the brakes (much like a drive by wire throttle system). Any brake pedal feel is artificial as pushing the brake pedal does nothing other than tell the computer how hard you are pushing it. (the exception being emergency mode when the manual backup brake system starts working, but only on the front 2 brakes and with no power assist). The problem you are experiencing is most likely the pads. You are having to push a lot more with the ceramics compared to the softer compound OEM pads to get the same amount of braking. I have done the test you are speaking of and yes you have to push fairly hard and yes it is very difficult to get it exactly in the green area.

Here's a nice little video explaining how SBC works

The SBC system should not be bled using traditional procedures such as pressing the pedal with the drains open or using a vacuum/pressure assist one-man bleeder. You must uses SDS to activate the bleeding functions within SBC.

Excellent!! that is what I needed to hear. Pads it is. I already have a set of new oem pads, just wanted to make sure it wasn't something else.

The test does say something to the effect that the sbc is disabled and you are using the back-up system. With no assist it probably explains why it is so hard to push.
Thanks everyone for the replies!!

You have to have both STAR and a motive pressure bleeder in order to fully bleed the system. You can partially bleed the system with just the pressure bleeder, but you won't get everything out and pushing the pedal does nothing for the main brake system.

Thank you carguyshu.

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It is SUPPOSED to be done with star, but can actually be done without. the sbc system would need deactivating, and a pressure bleeder should be used. this is ok for those that are used to working with the sbc system, but there are pitfalls! i would not recommend letting joe bloggs garage have a go - take it to a garage familiar with either w211 or w230 brake systems.

incidentally there is a way of deactivating sbc in order to work on the braking system that does not involve the star platform. wis document AR42.46-P-0005TX details the method which involves locking/unlocking sequences to be followed. this procedure is only allowed for brake pad/disc or shoes replacement, but can be effectively used to renew brake fluid with a proprietary pressure brake bleeder set to around 2bar.

BEWARE, THIS IS JUST OBSERVED FACT, AND NOT A RECOMMENDATION - ALWAYS HAVE WORK CARRIED OUT BY COMPETENT PERSONELLE.
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I have ceramic pads. The pressure values are no different. I have a W164 with ceramic pads. No difference in pedal pressure. Actually the feel when you use them aggressively is lower pedal pressure with higher breaking levels and a higher degree of feel when you use them at the level the car was designed for.

Albeit Ceramic pads can get dirty. If you don't use them judiciously(meaning if you don't get them warm/hot the dirt can build up on the surface of the rotor and the pads. Normally you could take the car out, use them aggressively enough to wear off the gunk caked on the pads and rotor but in OP's case it's not likely to effect owners percieved benefit.

I wish you luck
Hary

Just another note on the pads. I have Akebono pads on the SL55 and C32. Neither have dust issues, like the stock pads do in spades.

Both cars have no noticeable difference in brake pressure required since the change, but the C32 does squeak in reverse now, which is worth the price for no dust!

So, bleed your brakes with a Motive bleeder and let us know the outcome of your dilemma.

Based on my experience, I can live with the dust from the OEM pads in exchange for less noise and shorter stopping distances. The dust the OEM pad generates is easily washed off the wheels with most any car shampoo. The worst "dusting" pads I ever had were on a MY2006 BMW X3. The thing would stop on a dime (no, a penny!) but the brake dust was crazy - it actually pitted the rims permanently. MBZ pads may dust but it easily washes away.

I can't comment on whether or not your perception of excessive force on pedal during this test is indicative of a problem ... but

worth mentioning .... a cool trick for getting through this test is to lock your knee and use the seat (fore/aft) adjuster to modulate the brake pedal pressure (and more easily keep it in the target/green region).

I like the akebono pads (have them on all 3 of my AMGs)... but i think the no-dust does does come at a performance cost.

hope that helps,
Chris

I've been driving a few days now since installing the OEM Mercedes pads. The brakes are noticeably better with less pedal effort. The brakes seem to grab much better. I'd say about 25% better. The Akebono pads were great for no dust, but I'd rather deal with the brake dust if it gives me better braking.

Is it possible to bleed the system using SDS and vacuum bleeder? On the surface it seems that it shouldn't matter whether you push fluid through the system by pressurizing, or sucking it form the bleeder? Am I missing something? The reason I am asking is simple - I have a vacuum bleeder, but do not have Motiv.

No, you MUST use the proper bleeding procedure with SDS connected.