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Old 04-07-2016, 07:25 PM   #1
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Airstream Interstate 2016 Ext- soft brake pedal

Anyone experience a soft brake pedal on their Interstates? Our Airstream Interstate 2016 Extended does.

It has been to two different Mercedes-Benz dealers in Northern California. Both say that is normal. I even offered to pay for the second brake bleed. The second visit the dealership said they bled the brake system.

It feels like the classic air in the brake lines. Soft pedal.

My concern is three-fold: 1). When applying the brakes, the brake pedal depends before making a "somewhat" firm resistance. 2). If I pump the pedal, even once while slowing down, the pedal feel improves. 3). While sitting still, engine running I can almost push the brake pedal to the floor.

This concerns me.

Yes, the coach does slow down, but in the instantaneous emergency stop I may not have enough time to pump the pedal.

Background- I am an auto enthusiast. I work on my own vehicles and years ago in my twenties, was a line mechanic. I have done some German sports car club racing. So I feel I have some pretty credible experience.

Anyone experience a soft brake pedal in their motor coaches?

Haasman
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Old 04-07-2016, 09:14 PM   #2
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I have an SOB Sprinter MH and on the Sprinter forum there is a detailed post on why the brake pedal seems soft. Mine is a 2013 and have had several occasions to make a panic stop (once with a trailer) and inspite of the soft pedal, it stopped the way it is supposed to stop! I've been building hot rods for 50 years, and I too was a bit nonplussed the first time I hit the Sprinter brake petal. As the kids say, "no worries". BTW, pumping the brakes on an Sprinter with anti-lock brakes is counter productive.
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Old 04-07-2016, 09:17 PM   #3
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I noticed mine seems like there's not much there for the first half inch of travel but then it's firm. And it does firm up if I release and reapply. Never felt like the brakes were weak tho. I've heard others w/ the same observation so apparently it's the nature of the beast.
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Old 04-07-2016, 09:59 PM   #4
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I haven't had any stopping issues in the 140,000 miles that I have on my 2011 Sprinter 2500 service van. It is always loaded close to the GVWR, so I travel heavy too.
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Old 04-07-2016, 11:23 PM   #5
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From my experience the Sprinter has what I would call a progressive brake pedal feel. If you press lightly it seems like a soft pedal, but if you hit it hard and fast it stops quickly. I think it is the design of the power brake assist. The faster you press the pedal the more boost you get.

I had the experience a few years ago to participate in a Mercedes USA Sprinter Tour event. I was able to drive two different Sprinters, one a 2500 cargo van and the other a 3500 box truck. They had a panic stop route setup and a Ford E350 cargo van to drive for direct comparison. The Sprinters stopped faster and with more stability than the Ford. These were full panic stops on dry pavement at about 30 mph, engaging full anti-skid. It was a fun and enlightening experience. They also had a modified test Sprinter that could disable the Electronic Stability Program. It was driven by professional drivers for the demo with participants strapped into full five-point harness seats in the second row. These vans also had large water tanks to add weight for the demo to cause the van to tip up on two wheels. The ESP uses the brake system to control the van in violent steering maneuvers. The first photo below is a sharp panic turn with ESP. The second photo below is without ESP, note the van is up on two wheels and has outriggers to prevent a tip over. I was strapped into the rear seat for one one these runs. What a wild ride.
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Old 04-07-2016, 11:53 PM   #6
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Quote:
Originally Posted by Haasman View Post
Anyone experience a soft brake pedal on their Interstates? Our Airstream Interstate 2016 Extended does.

It has been to two different Mercedes-Benz dealers in Northern California. Both say that is normal. I even offered to pay for the second brake bleed. The second visit the dealership said they bled the brake system.

It feels like the classic air in the brake lines. Soft pedal.

My concern is three-fold: 1). When applying the brakes, the brake pedal depends before making a "somewhat" firm resistance. 2). If I pump the pedal, even once while slowing down, the pedal feel improves. 3). While sitting still, engine running I can almost push the brake pedal to the floor.

This concerns me.

Yes, the coach does slow down, but in the instantaneous emergency stop I may not have enough time to pump the pedal.

Background- I am an auto enthusiast. I work on my own vehicles and years ago in my twenties, was a line mechanic. I have done some German sports car club racing. So I feel I have some pretty credible experience.

Anyone experience a soft brake pedal in their motor coaches?

Haasman
I have a 2014 Interstate Ext. You've described the brake pedal in my Sprinter exactly! I've taken it to the Mercedes dealer twice regarding this issue. They've bled the lines and checked it thoroughly and can find nothing wrong. Unfortunately this seems to be a common problem with the Sprinter.
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Old 04-08-2016, 05:09 AM   #7
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Quote:
Originally Posted by Haasman View Post
Anyone experience a soft brake pedal on their Interstates? Our Airstream Interstate 2016 Extended does.

It has been to two different Mercedes-Benz dealers in Northern California. Both say that is normal. I even offered to pay for the second brake bleed. The second visit the dealership said they bled the brake system.

This concerns me.
It takes some getting used to. But one thing to remember with your brakes: they aren't just hydraulic, not just power-hydraulic. They are computer-power-hydraulic thanks to traction control, anti-lock braking, and other devices that ALSO control braking force. Acceleration Skid Control in particular will apply the brakes to one wheel all by itself if that wheel starts to slip (i.e. spin faster than the others) without you touching the brake pedal at all.

It's not exactly drive-by-wire, but it's getting closer to it all the time with each new control device they add.

The brake pedal feels mushy compared to other vehicles, but it really IS perfectly normal for a Sprinter. Don't pump the brakes to try to increase the braking power, because it will have the opposite effect; pumping the pedal confuses the alphabet-soup braking sensors:
ABS Anti-lock Braking System
ASR Acceleration Skid Control
BAS Brake Assist System
EBD Electronic Brake-force Distribution
ESP Electronic Stability Program
The BAS and EBD in particular are responsible for the mushy-feeling pedal. Basically B ASmeasures how hard and how fast you press the pedal, and electronically applies additional braking force accordingly. EBD applies a different amount of braking force to each brake if necessary. So when you press the pedal, you're telling a computer chip how to apply the brakes, you're not doing it all by yourself as in other cars.

Like James Kirk said to Saavik in Star Trek II: The Wrath of Khan, "You have to learn why things work on a starship."
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Old 04-08-2016, 08:38 AM   #8
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Quote:
Originally Posted by Jeff64 View Post
I have a 2014 Interstate Ext. You've described the brake pedal in my Sprinter exactly! I've taken it to the Mercedes dealer twice regarding this issue. They've bled the lines and checked it thoroughly and can find nothing wrong. Unfortunately this seems to be a common problem with the Sprinter.
This is not a "problem"! Protagonist did a pretty good job explaining how the MB brakes work.
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Old 04-08-2016, 11:33 AM   #9
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Choked on my coffee when I read Protagonist's comment. My wife made the exact same quote to me when I was commenting on an operational question with my Sprinter chassis.......


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Old 04-08-2016, 11:38 AM   #10
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...

Like James Kirk said to Saavik in Star Trek II: The Wrath of Khan, "You have to learn why things work on a starship."
"Spock, where the hell is the power you promised me?!"

"One damn minute, Admiral."

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Old 04-08-2016, 12:32 PM   #11
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Not a Star Trek quote but remember, "In space, no one can hear you scream . . ."
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Old 04-08-2016, 01:42 PM   #12
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Airstream Interstate 2016 Ext- soft brake pedal

Or an even scarier quote, "I have no mouth, but I must scream..."


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Old 04-09-2016, 12:19 AM   #13
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This is not a "problem"! Protagonist did a pretty good job explaining how the MB brakes work.
Hmm. My BMW has all these latest and greatest safety features. Its pedal is firm and at the top. My 45 ft. Eagle weighed four times what the Sprinter does, its pedal was firm and at the top and felt much better in a hard braking situation. In fact out of all of my vehicles the Sprinter is the only one that feel uncomfortable in with a hard fast stop. I feel that is a problem.
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Old 04-09-2016, 05:48 AM   #14
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Hmm. My BMW has all these latest and greatest safety features. Its pedal is firm and at the top. My 45 ft. Eagle weighed four times what the Sprinter does, its pedal was firm and at the top and felt much better in a hard braking situation. In fact out of all of my vehicles the Sprinter is the only one that feel uncomfortable in with a hard fast stop. I feel that is a problem.
Well, we can't argue with that comparison of brake feel between your various vehicles. But brake pedal feel does not equate to brake effectiveness in this case, and in the four years and 27,000 miles that I've driven my Interstate, I've never once had reason to complain about the brake effectiveness, even in New Orleans rush-hour traffic. So you'll have to forgive me it I continue to insist that it's not a problem.

Please allow me to ask this question… Even with the mushy brake pedal feel, has your Interstate ever failed to stop when you needed it to stop? Not counting times when you might have pumped the brake pedal and interfered with the various brake-assist features, that is…
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