SBC: How difficult to stop car once it goes out? - PeachParts Mercedes-Benz Forum

shertex · #1 11-19-2015, 07:38 AM

I've already made the mental adjustment that replacing the SBC pump on my CDI is in my future...have no idea when....and that I'll shell out close to $1500 when that happens (unless it happens before July 31, in which case MB picks up the tab). I'm fine with that...really.

My concern is with the difficulty stopping the car once it goes out....especially if someone other than me is driving the car at the time. From what I've read, it can be very difficult to depress the pedal enough to get any really braking power. I should probably brief my wife and son on this, who, on rare occasions, may be driving the car. But I hate to make them paranoid.

FWIW....from MB's training materials regarding the backup hydraulic system: "This system meets the legally mandatory minimum deceleration of 0.3 g with a foot pressure of 500 N.(112lb/ft)."

Any thoughts as to how dangerous a situation it could actually be?

vstech · #2 11-19-2015, 08:44 AM

It depends on how you drive.
If proper following distance, and anticipated weak stopping are paramount on your mind, stopping would be startling but doable... Like normal, then panic stopping...

If you drive at the very limit of conservation, waiting till the last second to apply stopping force, then you'll likely have an accident.

engatwork · #3 11-19-2015, 09:14 AM

You have to mash on the brake pedal substantially harder. Disconnect SBC module if you want to give it a try.

Shortsguy1 · #4 11-19-2015, 09:19 AM

Those specs on the backup system are dismal. 0.3 g decel rate would feel very scary to most of us. A honda civic can stop from 60 mph to 0 mph in 130 feet or so. Your mercedes would take around 400 ft to slow from 60 mph to 0 mph. Or put it differently, very modest cars can slow at a rate of around 1 g (vs. the .3 g when your sbc goes out).

Regarding pedal force, 500 N is 112 lb of force (no ft needed in the units). I suspect for most of us, that is a pretty high pedal force. Our legs are very strong, but putting out that sort of force with 1 leg would require substantial effort, I believe.

I don't mean to be reactionary. I am just honestly surprised at how low the legal mandatory decel rate is.

shertex · #5 11-19-2015, 09:43 AM

I guess the real doomsday scenario is having the SBC go out at the very time you need to stop suddenly. Any other scenario you'd be able to allow for gradual braking and not get in a wreck. We'll see what happens when the time comes. In the meantime, I'll enjoy the best braking I've ever experienced.

mannys9130 · #6 11-19-2015, 10:07 AM

Both feet on the pedal, push like you're holding a boulder back from crushing you.

Keep in mind you take half a second to react. If I was driving a car that had imminent SBC failure, I'd be giving my self 5 seconds between cars so I could react and either slow or swerve.

Stretch · #7 11-19-2015, 10:18 AM

Sorry chaps - I had to google SBC and I've come up with some likely suspects but none so far have been automotive based!

My favourites so far are

Suicide By Cop

Small Bowel Cancer

Swiss Bank Corporation

and

Silly ***** ****...

shertex · #8 11-19-2015, 10:27 AM

Adding "Mercedes" to the search query should help....

Quote:

Originally Posted by Stretch

Sorry chaps - I had to google SBC and I've come up with some likely suspects but none so far have been automotive based!

My favourites so far are

Suicide By Cop

Small Bowel Cancer

Swiss Bank Corporation

and

Silly ***** ****...

leathermang · #9 11-19-2015, 10:30 AM

I do not know what SBC stands for either.... but assume from the results of not having it that it is the same as not having vacuum going to your master cylinder..
Manny's description is right on... and that was just to stop... not a fast stop... just to keep from rolling through a couple of stop signs...
I am not sure why you think it might go out relatively soon....but I would not be driving it myself or let anyone else drive it until that is fixed....
This ' maintaining proper distance'.... you can not do that with idiots operating the other vehicles on the road...

shertex · #10 11-19-2015, 10:33 AM

Sensotronic Brake Control

shertex · #11 11-19-2015, 10:40 AM

Quote:

Originally Posted by leathermang

I do not know what SBC stands for either.... but assume from the results of not having it that it is the same as not having vacuum going to your master cylinder..
Manny's description is right on... and that was just to stop... not a fast stop... just to keep from rolling through a couple of stop signs...
I am not sure why you think it might go out relatively soon....but I would not be driving it myself or let anyone else drive it until that is fixed....
This ' maintaining proper distance'.... you can not do that with idiots operating the other vehicles on the road...

It's not a matter of "fixing" something....it works perfectly fine, best braking MB I've ever driven. It may go out tomorrow....it may last another ten years. But I can't see dropping $1500 simply as preventive maintenance.

SBC is basically brake by wire.

leathermang · #12 11-19-2015, 10:50 AM

Why did you post ?
You claim to have made the mental adjustment to spend the $1500 ....
the reports are that if it does go out it is dangerous...
but then you say you do not see it as a good investment as preventative maintenance....
You are on both sides of the fence...
but of all the functions your car needs to be trustworthy on..... I put braking pretty much at the top of the list....

shertex · #13 11-19-2015, 11:02 AM

Quote:

Originally Posted by leathermang

Why did you post ?
You claim to have made the mental adjustment to spend the $1500 ....
the reports are that if it does go out it is dangerous...
but then you say you do not see it as a good investment as preventative maintenance....
You are on both sides of the fence...
but of all the functions your car needs to be trustworthy on..... I put braking pretty much at the top of the list....

To get a sense of the diminished braking capacity once it goes out.

shertex · #14 11-19-2015, 11:03 AM

I'd be very surprised if any CDI owners have preemptively replaced the pump....but perhaps some have.

dieselbenz1 · #15 11-19-2015, 11:06 AM

Well at least you will get the error message confirming you have no assisted brakes. The pump is only one component of the system, what about the wiring harnesses and SAM which can also have problems.

So once the error is annunciated it should be an immediate tow to the dealer! Lawyers may have a lot of fun discussing why someone knew his braking power was down significantly yet still chose to drive.