Brake pedal travel

[Jeff64]

I have only had my Interstate a little over a couple weeks now with only around 1,000 miles on it, it seems to me that it has excessive brake pedal travel, it seems to go to within an inch or so of the floor, if I pump the pedal it does come up some, being a new unit I would expect the pedal to be near the top. I would like to hear from some other owners regarding your vehicles.

Thanks,

Jeff
2014 Extended lounge

[russ240]

Sounds like you have a serious brake issue (either air in the brake lines, a fluid leak or seriously low fluid ... though the later should turn on a warning light). I'd find a sprinter service center and have them take a look. If the pedal is really going that low before you stop I would not want to drive it. Not safe!

[UKDUDE]

Originally Posted by Jeff64

I have only had my Interstate a little over a couple weeks now with only around 1,000 miles on it, it seems to me that it has excessive brake pedal travel, it seems to go to within an inch or so of the floor, if I pump the pedal it does come up some, being a new unit I would expect the pedal to be near the top. I would like to hear from some other owners regarding your vehicles.

Thanks,

Jeff
2014 Extended lounge

(Sigh!) That's one of the countless things I had on my list after I bought mine earlier this year from a Mercedes dealer. Their service department told me they could find no problems with the brakes.

[joemikeb]

Originally Posted by Jeff64

I have only had my Interstate a little over a couple weeks now with only around 1,000 miles on it, it seems to me that it has excessive brake pedal travel, it seems to go to within an inch or so of the floor, if I pump the pedal it does come up some, being a new unit I would expect the pedal to be near the top. I would like to hear from some other owners regarding your vehicles.

Shortly after taking delivery on my 2013 AI earlier this year I took it to the dealer with the same complaint. I was told that was actually pretty normal, but that if I wanted them to, the service department had had some luck flushing and refilling the brake fluid, which they did free of charge. Apparently it helped because I did not notice or think about the condition since then — at least until last evening.

There was nothing on television I wanted to watch so I entertained myself reading the Mercedes Benz Sprinter manual — an effective soporific by the way — and came across the following on page 50 under the heading

BAS (Brake Assist System)

BAS operates in emergency braking situations. If you depress the brake pedal quickly, BAS automatically boosts the braking force, potentially reducing the stopping distance.

• Keep the brake pedal firmly depressed until the emergency situation is over. ABS prevents the wheels from locking.

The brakes will functions usual once you release the brake pedal. BAS is deactivated.

After reading that as well as the subsequent information on EBD, ASR, and ESP on the rest of pages 50 and 51 I decided to test it out. It was late and the traffic on nearby I30 was light at that time of day so I had a decent test site. I am now satisfied what I had previously experienced was the result of BAS kicking in. I am also convinced that since the dealer flushed and refilled the brake system the pedal does not go quite as low as it seemed before the drain and flush.

[ROBERT CROSS]

How "hard" is the pedal when the engine is not running? Feel normal? Is the ABS working?
If so the system is most likely working as designed.

The newer abs power brake systems add a LOT of assist which can bring the pedal way down.

Bob

[PSchw]

I had the same impression of the brake when I got mine in March. Got it to MB Sprinter and they told me it is normal. Now after 10k miles it really feels normal, and never had a brake problem.

[Jeff64]

The brakes actually work fine, I just dont like what I consider to be excessive brake pedal travel, most newer model vehicles that I have owned the pedal is hard and at the top, several inches of travel seems a bit to much. I'm going to take it to the MB service department and complain a little and see if i can get them to improve it any. I'll post the results.

Jeff
2014 Extended lounge
Springfield MO.

[Excella CM]

From a human factors POV the long pedal travel is not the best engineering solution, since in our experience with most vehicles, long pedal travel indicates a fault. Brakes should be designed to feel the same when they are working normally regardless of underlying technnology, I think.

[Protagonist]

Originally Posted by Excella CM

From a human factors POV the long pedal travel is not the best engineering solution, since in our experience with most vehicles, long pedal travel indicates a fault. Brakes should be designed to feel the same when they are working normally regardless of underlying technnology, I think.

Due to computer control the brakes are actually fly-by-wire to a large extent; brake pedal pressure doesn't necessarily directly translate to stopping power. How FAST you press the brake also has a lot to do with it. If you've got to stop in a hurry, STOMP on the brake and you'll stop. If you're easing up to a red light, press slowly.

[russ240]

My assessment is that the pedal moves from it's resting position just above the accelerator pedal to just below the accelerator when the brakes are on for most stops I make. Perhaps and inch or free travel, no different than any of my other vehicles.

[73shark]

My brake pedal is a little soft on initial application but firms up after release and reapplication and stays that way until the next time. But it's not what I'd consider excessive.

[russ240]

Originally Posted by 73shark

My brake pedal is a little soft on initial application but firms up after release and reapplication and stays that way until the next time.

That sounds like a classic case of air or old brake fluid that has soaked up too much moisture to me. I bet a complete flush of the brake system (with at least a few manual pumps at each wheel the old fashioned way with a guy stepping on the brake pedal to compress the fluid, not some fancy pump or vacuum doing the job) would make your pedal consistent every time. Of course getting that last bit of air out of a brake system can be aggravating and I've been frustrated before when I let someone else do it. This may sound backwards but a brake flush is one of the few jobs that I really don't trust to a professional, I'd rather do it myself.

[Protagonist]

Originally Posted by russ240

That sounds like a classic case of air or old brake fluid that has soaked up too much moisture to me.

Nope. When I had my Interstate at my local Sprinter dealer for its Schedule A 10,000-mile maintenance, I asked about the brake pedal travel, and after pulling the tires to check the brakes, bleeding the system, etc. the pedal had exactly the same feel.

There are no less than FIVE computer programs that affect the brakes:
1 - Anti-Lock Braking System (ABS)
2 - Brake Assist System (BAS)
3 - Acceleration Skid Reduction (ASR)
4 - Electronic Stability Program (ESP)
5 - Electronic Brake Force Distribution (EBD)

All described in pages 47-50 of the Sprinter Operators Manual. According to the dealer, when you press the brake pedal, you're not really applying the brakes. You're telling the computer to apply the brakes, and the computer decides how much braking force to apply to each corner.

As I said in my previous post on this thread, the brakes are "fly-by-wire."

By the way, the manual specifically say, on page 47:

Do not pump the brake pedal. Use firm, steady brake pressure instead. Pumping the brakes reduces the braking effect.

[masseyfarm]

Everyday I am reminded why most of my vehicles are 96 or older.

Dave

Originally Posted by Protagonist

Nope. When I had my Interstate at my local Sprinter dealer for its Schedule A 10,000-mile maintenance, I asked about the brake pedal travel, and after pulling the tires to check the brakes, bleeding the system, etc. the pedal had exactly the same feel.

There are no less than FIVE computer programs that affect the brakes:
1 - Anti-Lock Braking System (ABS)
2 - Brake Assist System (BAS)
3 - Acceleration Skid Reduction (ASR)
4 - Electronic Stability Program (ESP)
5 - Electronic Brake Force Distribution (EBD)

All described in pages 47-50 of the Sprinter Operators Manual. According to the dealer, when you press the brake pedal, you're not really applying the brakes. You're telling the computer to apply the brakes, and the computer decides how much braking force to apply to each corner.

As I said in my previous post on this thread, the brakes are "fly-by-wire."

By the way, the manual specifically say, on page 47:

[russ240]

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).

[Protagonist]

Originally Posted by russ240

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.

[kaylorsan]

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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[Sebtown]

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...

[73shark]

Originally Posted by Protagonist

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.

[Protagonist]

Originally Posted by 73shark

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?