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Old 09-12-2013, 06:56 PM   #15
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I do not believe the dealer has given you an accurate description of how the system works. On our Sprinters I believe there is a still a direct hydraulic path from the master cylinder piston to the brake caliper, albeit one intersected by the ABS pump like on any modern vehicle, not truly fly by wire like all modern throttle controls are. All the various nanny systems actuate the brakes via the ABS pump. Brake by wire is coming for all vehicles and I believe may be the technology that is in hybrids today, but not on the Sprinter at this point. Yes the ABS pump does effect pedal feel, but that should NOT impart spongy-ness that is present on the first pump but not the second. That is still a symptom of air in the lines (and "wet" brake fluid becomes air as soon as the brake calipers get hot).
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Old 09-13-2013, 07:15 AM   #16
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Yes the ABS pump does effect pedal feel, but that should NOT impart spongy-ness that is present on the first pump but not the second. That is still a symptom of air in the lines (and "wet" brake fluid becomes air as soon as the brake calipers get hot).
It's kind of like the difference between a computer keyboard and a touchscreen. True fly-by-wire is all-electronic, as you say (like a touchscreen). But with five different computer programs driving that second pump to provide differential braking under different conditions (including braking the rear wheels only during acceleration— when you're not pressing the brake at all— to prevent spinning the wheels and losing traction) the end result is very similar to fly-by-wire even though the user interface is still mechanical (like a keyboard).

In any event, thanks for pointing out my error. I really meant to say LIKE fly-by-wire. Yeah. That's the ticket. Nice save, me!

The Sprinter Operators Manual specifically states (on p159) to use DOT4 or higher with a wet boiling point of at least 356°F. Some formulations of DOT4, DOT5, and DOT5.1 brake fluid are compressible even when "dry" (no water in the system) and can lead to a spongy feel, without adversely affecting the brakes' ability to stop the vehicle.

Just don't use a silicone-based mil-spec brake fluid. They don't form an emulsion when water is added, and you'll just have a high-boiling point brake fluid with low-boiling-point water bubbles in it. That's bad news.
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Old 09-13-2013, 10:12 AM   #17
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I wish I could remember who posted this. I believe it came off of the Sprinter Forum. In any case, I too thought I had spongy brakes. I asked the dealer, and they checked out OK. However I was still skeptical. I did the 'check' listed below and was satisfied that my brakes were OK. The process references the 02-06 Sprinter, but it made sense to me for my 2012. The Sprinter brakes have a different feel than my car, but they definitely work. Note that I am not claiming that the 02-06 Sprinter braking systems are the same as later models. The procedure below just helped me think thru what was going on.

FWIW, I do a lot of mountain driving, and have never had any brake issues (other than the odd feel of them compared to a car).

-------------

"I receive a lot of mail and phone calls on the subject of ('02-'06) Sprinter brake pedal feel, especially a perceived "abnormal sinking pedal".

Many first time Sprinter owners or those who drive other vehicles (more often than their Sprinters) are alarmed by a brake pedal feel that they are convinced is abnormal.

Here's how to tell if your Sprinter brake pedal action is "normal" OR in need of immediate service attention:

Engine running, push lightly on the brake pedal. Mushy and sinking seemingly endlessly toward floor? This may be NORMAL.

Engage Park and handbrake. Shut off the engine and then step on brake pedal 4 or 5 times. This releases the vacuum from the booster servo and reservoir-you should hear a loud hiss when pressing pedal each time until the vacuum is expended.

Engine still OFF, ALL vacuum expended, now step on brake pedal and exert a steady force. Pedal should move a relatively short distance (compared to before) and stop hard without further sinking- REGARDLESS of how long you exert foot pressure. This is the TRUE test of the brake master cylinder. If pedal slowly sinks to floor during this test- you have a problem.

Now step on pedal again and exert steady pressure while starting engine. With engine now running- the pedal should begin sinking steadily toward floor. This is NORMAL and indicates the engine's vacuum pump and the brake servo are working properly.

Take foot off the brake pedal and run the engine for a few seconds at 1500 rpm to build vacuum. Go back to idle speed, step on the brake pedal slowly-see the difference and the much greater sink distance compared to engine "off" and vacuum released?

Still convinced it's excessive pedal travel? Try this test-Engine running, move Sprinter to a downward sloping driveway, place in neutral and SLOWLY creep down hill. Gently apply brake pedal pressure and note how little pedal travel is needed to stop and hold the vehicle-now push harder-see how much pedal travel remains?

This long, soft, pedal travel is a normal characteristic of the Sprinters vacuum booster design when engine is running."

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Old 09-13-2013, 10:20 PM   #18
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Every time I get in my 06 after not driving it I think there is a brake pedal problem. I am going to try this procedure first thing tomorrow. On the flip side, if I just drove the Airstream more I would adjust and wouldn't think about it being a problem. Humm...
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Old 09-14-2013, 01:11 AM   #19
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Just don't use a silicone-based mil-spec brake fluid. They don't form an emulsion when water is added, and you'll just have a high-boiling point brake fluid with low-boiling-point water bubbles in it. That's bad news.
But silicone brake fluid is not hygroscopic so it's not as likely to have moisture in it in the first place. And it doesn't remove paint.
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Old 09-14-2013, 07:57 AM   #20
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But silicone brake fluid is not hygroscopic so it's not as likely to have moisture in it in the first place. And it doesn't remove paint.
Moisture ALWAYS gets in eventually, because a seal that keeps brake fluid in will not necessarily keep water out.

Living in New Orleans, where street drainage is a perennial problem and one has to drive through standing water to get anywhere, the issue of water in brake lines is also a perennial problem.

I've seen that statement about silicone brake fluid not removing paint before, but I have to wonder, why does that matter? I'm not in the habit of spilling brake fluid, and on the rare occasion I do spill a drop or two, I clean it up right away.

That said, if you really like the silicone brake fluid, you don't need to change to another type on my account. What a boring Forum this would be if we all agreed on everything. It would be like a Rush Limbaugh radio show. Fatuous comment by narcissistic radio host, then one caller after another saying "Ditto." "Ditto." "Ditto…" Where's the fun in that?
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Old 09-14-2013, 09:41 PM   #21
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Didn't say it wouldn't ever get in but glycol based brake fluids are like a sponge.

Trust me, not removing paint was a financial life saver in my one experience.

No comment on last paragraph.
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Old 10-08-2013, 10:04 PM   #22
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After nearly a month I can report back on the brake pedal situation. The closest Mercedes dealership that will service the Sprinter is Mercedes Benz of Northwest Arkansas. They bled the brake lines and that seems to have solved the problem. I'm not sure if Airstream would have rerouted or opened the lines for any reason but never the less problem solved in my case.

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Old 10-09-2013, 11:10 AM   #23
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Jeff64, great to hear on bleeding rectifying the feel to your satisfaction. When it comes to bleeding, the method used also can have an impact on how they feel.

I prefer the pressure bleed method, followed by pumping the pedal and lastly gravity or vacuum.

In general I found the brakes on every Mercedes that I have driven (e350 Convertible, e350 Sedan, Vito Van) to feel a bit spongy. Honestly I hated the feel. For the record my reference feel are BMW brakes and BMW's equipped with full out racing brakes. Direct and firm.

The brake feel on the Sprinter threw me for a loop. I love it. However, knowing myself, I will not be able to leave them alone. When the time comes for pads and fluids Im going with what I know - stuff made by the companies I use on track.

Fluid - Mercedes probably uses ATE or private labelled ATE. I plan to switch to Motul 660 race fluid. Higher boiling point with less water absorption.

Pads - Performance friction carbon metallic.
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Old 10-09-2013, 12:07 PM   #24
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After nearly a month I can report back on the brake pedal situation. The closest Mercedes dealership that will service the Sprinter is Mercedes Benz of Northwest Arkansas. They bled the brake lines and that seems to have solved the problem. I'm not sure if Airstream would have rerouted or opened the lines for any reason but never the less problem solved in my case.

Jeff
Did you happen to inquire whether they used the "official" brake bleed method that involves the use of the MB diagnostic computer?
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Old 10-09-2013, 04:32 PM   #25
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Did you happen to inquire whether they used the "official" brake bleed method that involves the use of the MB diagnostic computer?
No but thr service rep there (Tyler) is great to work with, I will shoot him an email and ask.
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Old 10-09-2013, 06:11 PM   #26
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Did you happen to inquire whether they used the "official" brake bleed method that involves the use of the MB diagnostic computer?
I asked your question and already received the answer posted below. If anyone finds themselves in need of service of a mercedes of any kind in North west Arkansas (Bentonville) I would highly recommend Mercedes of North west Arkansas, very professionl operation.

Hey Mr. Boyce,


I just checked with John- we did use the computer when bleeding the brakes. We do this especially when there is a known issue with the brakes, and because it is the proper procedure. If you want more details, I can have John pull the data he printed while hooked up to your sprinter. Thanks for the kind words about us out there on the forums!!!


Tyler Black
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