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so yesterday I found a dime sized brake fluid spot under my '13 E350 4matic, brake reservoir was down almost to low mark, so I filled it, then removed all three lower panels, to look, saw nothing leaking. I checked all the lines from the master to the anti-lock and from there to the wheels, nothing, nothing wet under the dash and looking under the hood I can't see any wet spots, but the drip is coming from the front left plastic fender well at the back, this morning it left a quarter sized spot, same place, any thoughts? It's gotta be the master cylinder right? I can't see any leak under the hood either, Thanks in advance for your comments,
Pierre, do you have a case of rusted brake lines with a tiny pinhole?
Rusted steel line from the outside or from the inside... It's not going to be easy to spot because brake fluid is transparent and runs thin unlike engine oil leaks.
Try to chase the leak back up towards source... not easy to do 🤞
Pierre, do you have a case of rusted brake lines with a tiny pinhole?
Rusted steel line from the outside or from the inside... It's not going to be easy to spot because brake fluid is transparent and runs thin unlike engine oil leaks.
Try to chase the leak back up towards source... not easy to do 🤞
Yes, up on a lift, pulled three underbody panels, rear brake lines are rusty but dry, no loss in braking, boosting or lowered pedal. no leaks can be seen, but brake fluid is hard to see, I see the whole lines from the antilock block to the back, no leaks, I see the lines from master to anti, no leaks, so Im guessing the master cylinder but was hoping someone could confirm before I order MC and reservoir. I cleaned the brake booster which was mildly dusty, but still can't confirm brake fluid is running down the front like one would usually see with a master cylinder leak.The drip is left front inner fender well right beneath the master cylinder.
Last edited by pierrejoliat; 08-29-2022 at 09:49 AM.
Yes, up on a lift, pulled three underbody panels, rear brake lines are rusty but dry, no loss in braking, boosting or lowered pedal. no leaks can be seen, but brake fluid is hard to see, I see the whole lines from the antilock block to the back, no leaks, I see the lines from master to anti, no leaks, so Im guessing the master cylinder but was hoping someone could confirm before I order MC and reservoir. I cleaned the brake booster which was mildly dusty, but still can't confirm brake fluid is running down the front like one would usually see with a master cylinder leak.The drip is left front inner fender well right beneath the master cylinder.
You need to see the source of the leak with your eyes and touch it with your hands/fingers before ordering parts.
Bright LED flashlight and remove the bulkhead/doubler surrounding the booster and reservoir.
I’m sure you wiped your finger along the threads of the brake lines at the MC. There is a line with a crimped flex connection as part of it coming from the MC. Try wiping your finger at either end of the crimps for a leak.
knowing you, you already did this, but I needed to type it anyway. Lol
I’m sure you wiped your finger along the threads of the brake lines at the MC. There is a line with a crimped flex connection as part of it coming from the MC. Try wiping your finger at either end of the crimps for a leak.
knowing you, you already did this, but I needed to type it anyway. Lol
Does wifey use "brake hold" often ?
Is there a chance she actually mushes the brake pedal as if it was pkg brake pedal... sometimes sensing for HOLD can be unresponsive, other times it's very touchy.
Hmm, I never thought about dye, I have some old stuff I used for a A/C leak on my daughters car. Hmm... No, she doesn't use the hold feature, I do however and have had it in my last two cars so I can activate it pretty softly. I suppose I could pull the wheel and wheel well liner like Chassis suggests and the cowling above the vacuum booster, the wipers and washer nozzle hoses come through that and there's a body stiffener bracket right across the top of the brake booster that needs to move as well. I do appreciate the help!
Yes and thanks Surya! it's leaking out a foot further to the rear I believe, but will check again tonight, looks like I'm pulling the wheel and inner fender liner, wonderful!!!
I trust you will find where it's coming from . Local mechanics had used dye method to source the problem with my dad's car A/C related issue as well. I have not seen it's been used to check thebrake lines either but it makes sense .It may be as simple as seals or gaskets
Looking at these 2 videos, I think you can use hand pump, vacuum and/or pressure type like mightyVac to find the potential BRAKE FLUID leak point in MC or Brake Booster.
On my Brake Booster there is a service/sensing port which now I use to attached a vacuum sensor. That is 4mm OD pipe.
However, you need to plug off the bigger hose , so that no vacuum or pressurized air do not run to the engine's vacuum pump.
I think 3-5 psi pressure is enough, you check for pressure decay.
If you use vacuum, perhaps you can see oil level sinking down from MC and it may leak into brake booster. Also vacuum decay to look for.
Did someone maybe add brake fluid and spill it and not clean up or notice?
No, I found the spot, then opened the hood to check the reservoir, which was low, I filled without spilling to the max line and a few days [now] later it is down an inch again. with a quarter size spot now each morning in the garage.But I did wonder, but the last time anyone else was under the hood was a March oil change,
Surya: I will vacuum test the vacuum booster tonight, thanks! boy, sure hope I don't need a booster too! I have had no change in pedal height, pressure necessary or braking ability, without the spot, I wouldn't know anything was wrong. Thank you for the videos!
Last edited by pierrejoliat; 08-30-2022 at 08:56 AM.
OK, so I pulled the wheel and wheel liner to check left front brake line, it's dry, I also vacuum tested the brake booster, held vacuum for three hours, reservoir stayed at max fill, I'm at a loss, can't find the leak! This is frustrating. Wheel liner was wet at bottom, but no sign from where, gotta be the master cylinder right? I put a piece of white paper under MC as best I could, no stain, came out dry. So maybe the MC is leaking into the brake booster then out the bottom, if so, how can it still hold vacuum? is there a liner in the BB?
Last edited by pierrejoliat; 09-01-2022 at 08:53 AM.
Use cable tie as wet sensor or boroscope method if brake booster holding brake fluid is the suspect.
Your leak could be from MC but when pressurized only and into brake booster.
If say really brake booster is now has lots of brake fluid, a vacuum can possibly be maintained, pressure maybe the better test tool.
1st video
Owner of video doesn't allow a link. Go to Utube and search this :
Brake Booster Full of Brake Fluid - Where'd it all come from?
I own a 2010 E350 4Matic and I found a Leak and had to replace about 3 1/2 ft of brake line on the driver's right rear. the line comes in from the Master cylinder along the rocker panel up in front of the left rear wheel arch and up parallel to the left wheel assembly. Goes to the center of a junction block right in the middle of the frame and splits for the right rear and left rear wheel cylinders. My Leak was right after it came up and above almost above the wheel axle. It rusted through and a pinhole spraying fluid up against body pan near the trunk corner. I cut it back about 15" to where it drops down to the rocker panel and double-flared the old line installing a union and put the new line up and over to the junction block, double-flared the end and installed. Inspecting the right rear line it was pretty crusty with rust so I bent the line for new one there installing new fittings and double-flare each end. Looking at how Mercedes-Benz doesn't use soft stainless brake lines is Beside Me? i also bought some under body rust preventative spray and covered all the lines I replace and all the other lines I could see! It helped I was a Plumber for 41 years and have 1/4" & 5/16" tubing benders and Flaring tools made the job easy for me. Having bend miles of copper and stainless tubing the FIX was simple and easy. More work getting the car up in the air to crawl under and bleeding ALL the lines. Starting with right rear, left rear, front right, and left front last. I did it 2X and went through a BIG bottle of DOT-4 brake fluid.
Yes, my rear brake lines don't look happy, but their not leaking yet, Living in the snow belt of CLE helped with the rust I'm sure. If I still keep the car a few years, I will be replacing both rear lines from the Junction block too. Well, since I still can't find the leak, I will replace the Master Cylinder later this week, I got it for 240.00 delivered with reservoir, from AutohausAZ, genuine Mercedes parts as I was afraid of aftermarket and the OEM was not available.
So I finally received the new master cylinder and reservoir for my '13 E350 4Matic, looks like a big project, would some kind soul be able to post the WIS procedure for changing this out? It would be awfully helpful, Thanks in advance, much appreciated!
08-29-2022, 09:02 AM
Thanks in advance for your comments,
