E220 Brake Fade

[MercedesLou]

Hi Everyone. Driving to work yesterday morning, going down a slight gradient road, at the junction I applied my breaks (auto mode) and nothing happened. I pressed the brake to the floor but the car carried on driving. Thankfully, no cars were coming or I'd have probably been written off. I drove slowly to work leaving loads of braking distance between me and cars in front of me. I had no warning lights. The brake fluid is full and hasn't been recently empty or refilled for air to get into it. The car was cold and had driven 1/4 of a mile when it happened. Back and front pads/discs are fine and not long been replaced. As I left work to take the car to the mechanic, pulling off the driveway, it happened again but thankfully, its a quiet road with no traffic coming. My mechanic looked at it last night and drove it for a few miles and and can't see why this would be happened but I'm terrified to drive it now. Does anyone have a clue why this might be happening please? Cheers, Lou

 

[Bellow]

It isn't brake fade. Fade occurs when the brakes are overheating - not the case here.

Is there braking available before the pedal can go no further?

Back and front pads/discs are fine and not long been replaced.

That might be a clue.
If the fluid at the caliper isn't released at the bleed nipple when the caliper pistons are pushed in for the new pads, it is pushed back into the system towards the ABS unit where it can if it gets the chance interfere with the ABS valves and create all sorts of problems. It is also possible that the master cylinder has failed (again, possibly connected to pad and disc change if the system was bled and the pedal encountered a corroded part of the MC bore).
Whatever it is, you need to stop driving the car and get it checked out by someone with a solid understanding of the hydraulic system - which is where the problem probably lies unless there has been something catastrophic happened at a caliper (eg, pad gone missing, etc).

 

[MercedesLou]

The cars staying on my drive and is going to the garage for a serious investigation tomorrow morning. I can't drive it until this is resolved. Its a ticking time bomb I know.

The rear discs/pads were changed about 3 months ago. The brakes had been fine up until Weds morning but just didn't work at all when I came to the junction but started working perfectly again after that. When I pressed the brake pedal, it felt the same as if it was going to work... but I had to put my foot to the floor and nothing happened at all. I thought the mechanic at work could help me but he was equally as confused by it as my discs/pads and everything else look fine.

 

[st13phil]

When I pressed the brake pedal, it felt the same as if it was going to work... but I had to put my foot to the floor and nothing happened at all.

Sorry to be pedantic, but the pedal can't feel "the same as if it was going to work", i.e. firm, with normal travel, and also "I had to put my foot to the floor" which implies lack of pedal resistance and that the brake pedal travelled all the way to the carpet in the footwell.

In order to stand the best chance of anyone diagnosing an intermittent fault, it's imperative that they are given accurate information about what exactly happened. I know that when brake failure is happening it's a scary time, but try to remember as it's important and will point the investigation in different directions: Did the pedal feel normal, with normal travel, but the car was not slowing so you pressed harder and the pedal dropped further commensurate with the additional pressure but still felt firm, or did it just travel much further than normal until it hit the carpet?

 

[MercedesLou]

Sorry, perhaps I should have just said the pedal felt completely normal (neither hard or soft) but I had to press it completely to the floor and still nothing happened. Its just hard to describe a situation when I don't know the correct terminology to use.

 

[Bellow]

Sorry, perhaps I should have just said the pedal felt completely normal (neither hard or soft) but I had to press it completely to the floor and still nothing happened. Its just hard to describe a situation when I don't know the correct terminology to use.

Does this describe it?
It offered resistance but went to the floor relatively slowly, not in a rush as if it wasn't connected to anything. A viscous feeling - like dragging a spoon through syrup?

 

[st13phil]

but I had to press it completely to the floor

If I stood on a car brake pedal that felt normal with both feet and used enough force to risk breaking the seat backrest, I guarantee I couldn't get the pedal completely to the floor.

Good question from @Bellow, above.

Supplemental question: Or did you just add more and more pressure without the pedal moving much and it felt as though it had hit something solid?

 

[MercedesLou]

Wow... its ok guys. Its at the Mercedes garage now. Strange he understood exactly what I described and didn't try to humiliate me once. Enjoy your keyboards boys.

 

[markjay]

You need to scan the car for fault codes using STAR diagnostic.

Not all brake-related issues bring-up a warning on the dash.

On my car, the servo boost vacuum sensor failed, the only way to know it was by a fault code on STAR. No warning on the dash (though it didn't cause brake failure).

 

[ShaunB]

Wow... its ok guys. Its at the Mercedes garage now. Strange he understood exactly what I described and didn't try to humiliate me once. Enjoy your keyboards boys.

Please come back and tell us what is wrong.

 

[Bellow]

Wow... its ok guys. Its at the Mercedes garage now. Strange he understood exactly what I described and didn't try to humiliate me once. Enjoy your keyboards boys.

We were trying to help you you ingrate.

edited to remove expletive in the interest of forum decorum. OP can insert his own.

 

[st13phil]

Strange he understood exactly what I described and didn't try to humiliate me once.

There was no attempt to humiliate anyone, just a genuine attempt to understand what you're trying to describe. Glad to hear the tech at the dealer did.

Please let us know what the diagnosis is.

 

[tonysmb]

Wow... its ok guys. Its at the Mercedes garage now. Strange he understood exactly what I described and didn't try to humiliate me once. Enjoy your keyboards boys.

Nobody was trying to be funny or humiliate you; on the contrary, they were simply trying to understand the sequence of events with a view to possibly having a view on what might have caused the symptoms as it can very difficult trying to accurately diagnose possible problems, and thus advise, on a forum. You weren't one but some posters will say "My car's making a funny noise, any idea what's wrong with it?". Well, it could be anything, unless clarification is sought.

I hope you get it sorted. Faulty brakes can be quite frightening but, if you didn't think about it at the time, don't forget that you still have a parking brake as a back-up, not the most obvious thought nor the most user-friendly if it's a foot operated one, or even a button, and whilst not the most controlled mechanism, or helpful to traffic behind, it's better than nothing.

 

[DSM10000]

Wow... its ok guys. Its at the Mercedes garage now. Strange he understood exactly what I described and didn't try to humiliate me once. Enjoy your keyboards boys.

Your attitude is appaling.

You came here for advice and experienced members tried to help you.

What you should have done was to immediately arrange for the car to be recovered to an appropriate garage for investigation.

The difficulty in trying to understand your problem was due to the odd terminology you used. That is fine as not everyone has a detailed knowledge of mechanical systems which is why you were asked specific questions to help understand the problem.

Your nsults are completely uncalled for but I doubt we will see you back on the Forum, unless of course you have another problem you need help with.