*UPDATED*

2008 ML550 4Matic Brake Pedal going to floor. Fluid issues, not sure where fluid is going yet, don’t have update.

I did some preliminary looking around I don’t see any fluid yet. Will try and update about this.

Does anyone know what could be the issue?

Also, rather recently I did have the pleasure of having to purchase new rear brakes. It did have fronts done a while back, so not sure why when they did brake job, nothing was apparent at that time.

 

A couple of scenarios are that your master cylinder has failed and is bypassing, you can test this by pressing on the brake pedal while stationary if it keeps going down, its screwed, replace and bleed
The master cylinder is leaking back into the booster, if this is the case you can pull the vacuum line off the booster and dip the booster with a thin stick, if wet this is your problem, you will have to change both the master and the booster as the booster will be contaminated.
Brake lines corroded, this you can tell as it will be damp and leaking where they have rusted through.
Calliper seal failing as the above you will see fluid stains inside the offending wheel.
If your car has rear brake drums it could be wheel cylinders failing, you need to pull the rear wheels off and remove the brake drums, you will be able to tell straight away as it will be wet.

 

Ok so, if I understand it, your saying if the master is bad then I would just push pedal to floor, and if it does go all the way down, it’s bad? Assuming this scenario, call it option 1. Cost of master and flush, would be what? Id even do it myself and look for some way to save money? Any ideas on that? If this scenario is to lead to a booster also, possibly bad, option 2. Cost? Parts and labor? Ways to save money?

and option 3. I won’t be able to check this nor do I think I understand the way it would be feasible for this to happen so fast and not already have had some braking issues before the brake pedal went to the floor. And yes, I can confirm that while stationary, in park, it goes to the floor. Car still brakes which is bizarre considering I’ve added fluid and it’s drained but I don’t have any warning lights or way of checking for sure?

no rear brake drums. 4 wheel disc brakes. Anti lock still working and no abs light.

any chance you might be able to pick me up on answering my ?’s with some general information and it’d be helpful to know if I can do this myself in a garage with minimal tools and where to find the stuff needed.

anything else I need? Forgot?

ps., it’s -10 and it’s not getting any warmer here anytime soon in Chicago land area.

tia - Steve

 

Seeing that you are in The US and im in Australia the price is very different, if the master cylinder is losing fluid from, lets say the rear, you should be able to push the pedal down, it wont go all the way to the floor, it will be close to the floor but your front brakes will be operating normal and holding pressure no matter how long you hold the pedal, this is a safeguard built into the master cylinder to stop total failure and the same goes for if the front fail the rear will work, but if your master cylinder is bypassing you will get to the bottom and while holding pressure it will bleed down to the floor and will fail from holding you stopped.
You need to find where the fluid is going, fill it up and while in the garage keep pumping the pedal until it needs refilling again, look to see if you get a nice little puddle underneath the car, if nothing coming out from under the car, I would check the booster for contamination.

If you have never worked on brakes in the past I suggest you leave it to the experts, one thing you dont scrimp out on is brakes, not just for your own safety but for others also.

 

Ok so I think the master cylinder is bypassing. Does this sound right, I go to apply braking, it has some initial pressure as normal braking would do but it does go straight to the floor while stationary and while driving down road.

this would suggest as you said, master cylinder is being bypassed - and that means what exactly? I need to look for the puddles of fluid still, or is that something to do when I check it here shortly before and after bed.

I will be here for a while checking updates to my post as I am working from home and it’s late here in the states right now.

does this mean the booster pump or booster bypass could be the cause or what were your thinking.

Cheers and thanks for the help of course.

 

]A couple of scenarios are that your master cylinder has failed and is bypassing, you can test this by pressing on the brake pedal while stationary if it keeps going down, its screwed, replace and bleed. CHEAPER TO BUY NEW OR REBUILD?
The master cylinder is leaking back into the booster, if this is the case you can pull the vacuum line off the booster and dip the booster with a thin stick, if wet this is your problem, you will have to change both the master and the booster as the booster will be contaminated. CAN THE BOOSTER ALSO BE REBUILT AND IS IT BEST TO GET IT DONE BY DEALER OR CAN AN ASE MECHANIC DO IT FOR A COST?
Brake lines corroded, this you can tell as it will be damp and leaking where they have rusted through.
Calliper seal failing as the above you will see fluid stains inside the offending wheel.
If your car has rear brake drums it could be wheel cylinders failing, you need to pull the rear wheels off and remove the brake drums, you will be able to tell straight away as it will be wet.[/QUOTE]
WHERE IS THE FLUID ESCAPING FROM USUALLY, and DID YOU SAY WHERE IT WAS I SHOULD LOOK?

 

In a master cylinder there are 2 stages one for the front and 1 for the rear, if 1 fails, seal wears out or tears, you have the other to stop you, if it bypasses the fluid seeps past the seal giving you a pedal fell like it is leaking and will slowly go to the floor.

Bypassing usually does not lose fluid, it just gives you the feeling that the pedal slowly creeps down, the fluid has to be going somewhere, you just have to determine where, once you determine this you can work out what the fix will be.

 

You should be able to get a aftermarket brake master cylinder, I dont know where from in the states, i would google your model number with the word master cylinder.

Booster can be rebuilt, most mechanics that specialise in brakes can do this.

Just look around under the car on the floor in the garage if its leaking from underneath

 

Yea, i will need to find these part numbers for sure. Do you know off hand, what they might be or quickly find them to order particular parts?

just one final thing, I still don’t understand fully if the booster is bad or both or just ones malfunctioning, which one obviously is causing this and why the fluid is draining from the tank where I filled it up to check if it was the fix. It wasn’t so maybe it would make sense to look for the leaking fluid. I would think if the cylinder or hydraulic pressure is being lost, fluid is escaping and where, I have no idea and why, it would or could if the cylinder is in at the firewall right? So that means it’s leaking out into booster maybe? How would booster hold all that fluid? Where’s the leaking coming from not found yet. And does not mean the booster is bad right?

 

"If" it leaks into the booster it would be sucked into the engine and burnt with the combustion, seeing its cold there at the moment you might not see the smoke that it would produce but you would notice the smell.

Like I said before the first thing to do is find where the fluid is going, if you can find the leak on the floor then the fault is not far from the leak, If you still cant find the leak then its going into something thats holding it, I suggest the booster as I have come across this before, the booster will hold a litre or so of fluid before it starts being sucked out of the booster and into the motor.

Now I am not there, I dont know what could be the problem, I am only guessing on what you are describing, I am just giving you scenarios of what to look for, it could be something I have not thought of, so before you start just changing parts over, you need to check where the fluid is going.

Good luck

 

After replacing pads, you must (with the eng. off) pump the brake pedal numerous times until the pedal raises up.

Read steps 16 & 17 in the PDF.

 

I thought that too at first but he is losing brake fluid, unless he has cracked a brake nipple to push pads back and not nipped it back up?

 

Three days ago, he replaced the front pads.

https://mbworld.org/forums/m-class-w...ds-rotors.html

Who knows what he did in the interim. Was he waiting for the rear pads to arrive?

 

Ok, OP you should save yourself the money you are going to waste trying to do the job yourself and get a professional to do the job properly, it really can turn into a bigger problem if you dont know what your doing, for the amount you think you might save doing them yourself it could end up costing you a lot more if your brakes fail and you kill someone.

Like I stated in a previous post
Brakes are not something for the novice to attempt, you could do your self harm or worse someone else if you dont get it right.

Plus the more you have a go at trying to fix them yourself, the more you may screw more things up, it will end up costing you double for a professional to sort back out.
Do yourself a favour and just pay to have them sorted.