ToonArmy

I'm a little curious about the brake pedal feel and travel with the SBC, and what is "normal".

I realize that with the SBC, the pedal feedback is artificial, not back-pressure from the hydraulics.

On my 2003 SL500 (I've had the first SBC recall work done), if I push the pedal down hard with the car standing still, it feels fairly soft and spongy and travels down to the floorboards. Now on a normal(non-SBC) car, that would mean very bad things with the hydraulics. However, the braking performance seems fine (leaving aside the less-intuitive modulation to get a soft-stop), so I'm not concerned about the safety, just the feel.

So, I'm wondering, do all the brake pedals feel like this, or would mine benefit from adjustment?

doltmo

To quote your typical service technician, "they all do that". I believe the brake-by-wire (SBC) system on the new SL's uses some special hardware to simulate the traditional brake pedal feel. It will not give you the same feel that a direct mechanical connection to the master cylinder provides. There is a thread currently on this forum ("Anyone have squeaky brakes") that goes into more of the details.

My '04 SL500 and my current '05 SL55 behave exactly as you describe. If you push down on the pedal (while stopped) it gradually sinks to the floor.

ToonArmy

Thanks, doltmo.

I was reading the squeaky brakes thread, which partly prompted the question.

The description of the rubber cone and springs makes sense, I was just curious if they "all do that". Thanks for the confirmation.

blueSL

Mine is the same. Although the rubber bung is designed to get stiffer and stiffer as you press the pedal more and more, you don't get the solid end point that you do when connected to the hydraulic circuit. When on the move, it's the same, but your whole perception changes because the brakes are applied very strongly long before you even reach this point.

It's very interesting how we are conditioned to how the brakes should feel. I've written elsewhere about the bicycle with the back to front steering; a similar thing happens if you try to brake with your left foot. Unless you're practiced, we're not used to modulating the pedal pressure with our left foot, so you tend to over-brake and the car stands on its front wheels.

ToonArmy

Yes, the muscle meory and sensory feedback training is quite amazing. Another way to see this is to watch a beginning driver, and see how much trouble they have modulating the brakes, or clutch, initially.

And tying together clutch control and standing a car on its nose with left foot braking, picture me the first time I drove an automatic after 10 years of manual transmissions, and tried to make a rapid gearchange.

blueSL

Hah! yes, a good hefty push with the left foot on the big pedal is just what you need to disengage the non-existent clutch...

ToonArmy

And yet, strangely enough, the harder I pressed the, um, clutch, the more my brain sensed "engine braking", and the more urgent it became to disengage, so the harder I pressed...

blueSL

Ah yes, a positive feedback loop!

tiggerfink

My brakes felt like normal brakes on a non-sbc car until I got the SBC upgrade. After the upgrade the brake pedal would feel like it was slowly moving to the floor at a red light. 3 months later, the brake pedal started to feel like a non-sbc brake pedal. The pedal does not sink anymore toward the floor at red lights.

Now my brake pedal feels like a short brake pedal feel like on GMAC cars.