brake pedal drop usual suspects - PeachParts Mercedes-Benz Forum

lutzTD · #1 12-12-2007, 06:48 PM

i have been driving the beast again for about a week. i started smelling something like tranny or brake fluid a couple days ago when pulling away from a stop light, maybe burning smell maybe not, smelled more like raw fluid. today on the way home my pedal suddenly went to the floor. I limped home pumping the pedal figuring a busted line. I parked and let it cool off. Then I popped the hood and still plenty of fluid, I started it and held the brakes as hard as I could, after a minute or two it would settle to the floor. I was pushing very hard. I inspected around the calipers and master cylinder and I cant find any fluid. Is there something Im missing? Is there a usual suspect? could it be leaking into the vacuum system or something? I know these dont pull the vacuum into the engine and burn it. waas up.......

fdanielson · #2 12-12-2007, 07:07 PM

Classic bad master cylinder. It's no longer sealing to the bore internally and won't hold pressure, it may or may not be leaking. If it is leaking the fluid can be accumulating inside the power brake booster which will eventually make the booster fail. Get a replacement master cylinder, bench bleed it, and mop out as much fluid as you can from inside the booster.

I'm also in Lutz so if you want to get together and gawk at it shoot me a private message and let me know.

kerry · #3 12-12-2007, 07:07 PM

I believe symptoms are indicative of a bad master cylinder.

vstech · #4 12-12-2007, 07:09 PM

all the symptoms except the smell of fluid are classic MC failure. it's possible that you are leaking small amounts of fluid around the oring of the plunger, and it's leaking down the bottom of the MC into the firewall of the car, and you are smelling that.

JimFreeh · #5 12-12-2007, 07:30 PM

Pull the two fasteners that hold the master cylinder to the booster and check for fluid in the booster.

Brake fluid will ruin a booster, so if you find some, flush it out asap!

Jim

lutzTD · #6 12-12-2007, 09:04 PM

ok, thanx guys is the master cylinder a autozone part or a mercedesShop part? recommendations? ATE or TRW?

fdanielson · #7 12-12-2007, 10:23 PM

Autozone is going to charge you $150.00 for a Beck Arnley master cylinder with a 3 month warranty and it needs to be special ordered. Discount Auto Parts will order you a new Cardone cylinder for $65 with a lifetime warranty. Or you could simply click on the 'Buy Parts' link at the top of the page and have one sent to you from someone who specializes in Mercedes parts. Personally I'm more than a bit wary of the quality of parts you get at chain stores but I've installed many Cardone rebuilt components over the years and have had very good success with their products. If someone wants to sell you a private label Supr-Delux Quality Rebuilt unit then run away.

Don't neglect bleeding _all_ of the old fluid out of the system when you do this in order to avoid problems in the future.

lutzTD · #8 12-12-2007, 11:03 PM

i bought the TRW from mercedesshop. got pads to quiet the squealer on the front pass side while Im at it. hopefully the booster is not toast.....

turbobenz · #9 12-12-2007, 11:24 PM

if the booster is toast, Ill sell you one. I have a parts car. The brakes worked great on it, and when the engine is turned on the pedal sinks some (good booster).

lutzTD · #10 01-07-2008, 06:57 PM

well new booster in place, vacuum bleed all around with Dot4 until clear. Today I was driving home in traffic and on about my 5th emergency stop (Tampa norm) and my pedal went away again only this time I got a huge puff of smoke too. I got off at the next exit and had to pump 3 or 4 times to get any pedal. I limped into a lot and popped the hood. My brake reservior was overflowing and fluid all around was causing the smoke. I wiped everything down and used towels to get the reservior back down to the max line. The fluid was really hot. Does this seem like maybe there is water in the fluid and it is boiling and causing steam in the line? I was able to drive home normally after about 15 minutes.

Whats the trick to getting a complete fluid change? I think that is what I must need. Everything seems to work just fine cold....

nhdoc · #11 01-07-2008, 07:08 PM

I believe you have a caliper that is dragging causing the fluid to boil. Jack up one corner at a time, apply the brakes and release, spin the wheel and you will find the one which it is. It also can be caused by the flex hoses so if they are older than 10 years change them too.

lutzTD · #12 01-08-2008, 12:26 PM

Quote:

Originally Posted by nhdoc

I believe you have a caliper that is dragging causing the fluid to boil. Jack up one corner at a time, apply the brakes and release, spin the wheel and you will find the one which it is. It also can be caused by the flex hoses so if they are older than 10 years change them too.

can the caliper be rebuilt? I am through puttin money in this thing. its costing me about $100/day to drive it. literally.....

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