SBC: The Ticking Time-Bomb

[Deleted member 55947]

Exactly that.

Even the ABR systems?

 

[clk208]

As a matter of interest when I use the hold function it displays "SBC hold" on the dash, what does yours state?

Mine just states "HOLD" in white text with black background.

 

[Dieselman]

Mine just states "HOLD" in a little white box with black background.

Is that a warning or an instruction?

 

[clk208]

Is that a warning or an instruction?

It's just to inform you that you have activated the hold function.

Tap the brake pedal twice when you come to a stop at lights and it holds the brakes on for you, just like SBC does.

Just hit the accelerator when you are ready to move off. Pretty handy feature that I use more than I expected I would. Potential for embarassment when you hop into another car without a hold feature though

 

[John]

If you are buying, is there any way to see what life is remaining?

No, apparently not. Just tells you when it's service life is over (which I understand is 300,000 presses from another post).

 

[steve333]

Mine just states "HOLD" in white text with black background.

As above,i bet the pre 2006 cls's say sbc hold when the feature is activated,it's a very useful feature that other manufacturers have added-even my work transit has it

 

[Dryce]

Is sbc likely to fail because of age or mileage first?

It's complicated because there is the lifetime failure where the number of pumpactivations expires. So that simply depends on how much the brakes are used - which is down to driving style and environment. So you get a message even thiough it's still functioning.

Then there's the actual performance monitoring. The system measures how the pump performs when recharging the reservoir. If it doesn't meet various parameters then it is deemed to be failing. So you get a message even though it's still functioning.

MB appear to have addressed the life issue by adjusting the expiry count and relaxing the performance parameters.

In addition to these 'soft fail' circmstances there is also the potential for actual failure.

 

[Dryce]

Who in their right minds thought of using an electric motor to power the brakes?

Same sort of people who like to put automation in aeroplanes and move from direct control linkages to FBW.

They're called engineers.

The only issue I have with SBC is that they didn't think about lifecycle costs. The pump and reservoir should be something that is a lot cheaper as a component and in terms of labour to switch.

 

[Dieselman]

I can't agree. An electric motor will always eventually fail, so it doesn't make sense to use it for a safety critical item.

It would have been better to use an engine driven pump.

 

[mersum1es]

'Hold' is still available in newer cars without SBC if not said above...

Counter can be reset via star diagnose (developer mode menu), I've instructions how to reset but not checked yet is there actually counter value shown. Lifetime expiration yes/no is of course shown in 'common' star, but it also triggers 'brake service - visit workshop' white warning in the instrument cluster.

Edit: MB could have designed motor to serviceable, could be opened, brushes changed, etc... much cheaper than whole unit which now must be changed in every malfunction end customers wouldn't buy cheap chinese reset tools...

 

[mejermy]

As another prefacelift W211 man I agree as well. It's complexity for complexity's sake. And as for aviation FBW; let's talk about AF447 with it's side sticks and inputs unknowable between P1 and P2. What about the early Airbus models; remember the uncommanded loops over Russia carried out by one? Safely recovered thankfully. For other examples - try the pprune site. Boeing have been more reticent, wisely. The (IMO) very minor and limited benefits of SBC are simply worthless when bought at the expense of reducing a margin of safety and reliability.

That apart wonderful car.

 

[Dryce]

I can't agree. An electric motor will always eventually fail, so it doesn't make sense to use it for a safety critical item.

It would have been better to use an engine driven pump.

And engine based pump sould still need a mechanism to switch it on (or control it). So a valve or a clutch mechanism ready to fail.

MB addressed the issue through the performance monitoring and lifecycle counter.

The failures we hear about are normally not failures but warnings associated with this.

So it looks like it's a pretty well engineered system as a whole.

The main complaint in fact is the replacement cost for what should be a service item (givemn that it has a defined life).

 

[Dieselman]

And engine based pump sould still need a mechanism to switch it on (or control it). So a valve or a clutch mechanism ready to fail.

It would be constantly driven and use a mechanical pressure regulator. These virtually never fail and have been running for a long time on other makes of car.

There have been complete SBC failures, but irrespective, a braking system with a 5-8 year life is pretty poor.

SBC has been the most costly recall of any Mercedes item, ever.

This isn't a dig about power brakes, I have other cars with power brakes and really like the feel they give.

 

[Dryce]

Boeing have been more reticent, wisely.

Really? Two 757s and at least one 737 dropped out of the sky because of air speed indication problems and pilot disorientation. A 747 recovered with severe structural damage after pilots stalled it at high altitude.

So you don't need a FBW system to do this.

And are Boeing more reticent? The 787 is probably as radical a step change as FBW under the skin in terms of aircraft systems and materials engineering.

 

[mejermy]

You're not wrong, and Boeing may be up there with Airbus now, but were less eager to rush to full FBW. Regarding the pilot disorientation issues following partial loss of instruments, what happened to limited panel training? It is said (pprune again) that training is reverting to spending more times 'hands on' with the artificial aids reduced.

 

[Dryce]

There have been complete SBC failures, but irrespective, a braking system with a 5-8 year life is pretty poor.

The vast majority of reports relate to the warnings - not actual failures.

The issue is economic life cycle. I don't consider it to be a problem if some improved system goes on the vehicle and it requires replacing on - say - a 5 year schedule - as long as the lifecycle costs of running the vehicle are reasonable vs the benefits provided.

Getting hit with an £1800 cost on older vehicle doesn't fit within my view of 'reasonable' even though I'm capable of thinking about it beign amortised over a given ownership period.

So my only whinge is about the economics - which are a design fail.

 

[SavMan]

The vast majority of reports relate to the warnings - not actual failures.

The issue is economic life cycle. I don't consider it to be a problem if some improved system goes on the vehicle and it requires replacing on - say - a 5 year schedule - as long as the lifecycle costs of running the vehicle are reasonable vs the benefits provided.

Getting hit with an £1800 cost on older vehicle doesn't fit within my view of 'reasonable' even though I'm capable of thinking about it beign amortised over a given ownership period.

So my only whinge is about the economics - which are a design fail.

Wait until we are all driving electric cars and need a new battery!

 

[Dryce]

You're not wrong, and Boeing may be up there with Airbus now, but were less eager to rush to full FBW.

Boeing were the incumbent with existing designs and a base of trained pilots.

They had very very little incentive to change anything unless pushed by competition.

Airbus OTOH had a blank sheet of paper with the A320 family and were starting from scratch.

Regarding the pilot disorientation issues following partial loss of instruments, what happened to limited panel training? It is said (pprune again) that training is reverting to spending more times 'hands on' with the artificial aids reduced.

Pilots are really systems managers - and the systems they manage are very reliable so that they can go a whole career without encountering a critical failure. When they go wrong - then things can be very complex. The pilots are still left managing the systems (which is non-trivial workload in itself when things are going wrong) as well as dealing with the actual problem.

As for PPrune. Look at what happens when supposed pilots contribute posts about how the aircraft systems work and interact. It's not as if they don't correct one another. Consider the implications of that when you have a couple of guys up front alone over the ocean in darkness trying to figure what's real and waht's not while the altitude is dropping and the aircraft is taking on unexpected attitudes.

 

[Dryce]

Wait until we are all driving electric cars and need a new battery!

Actually that's one of the reasons that not many of us are driving electric cars.

It's presumably one of the reasons that Renault require you lease the battery on their plug-ins - which is at least quite an honest and up front way of managing the battery costs as propoer running costs. (A cynic mught also suggest it allows them to hide it from the up front capital cost of the vehicle - but I'll give them the benefit).

 

[mejermy]

Look at what happens when supposed pilots contribute posts about how the aircraft systems work and interact. It's not as if they don't correct one another.

Not clear whether you mean the posts or the systems self correct. Nett nett, I think it' about whether a high level of computer driven automation has improved safety, convenience (operating minima) and the operating experience or not. In commercial aviation I would say it is clearly the case that it has.

In cars.....?