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  #1  
Old 04-07-2002, 07:36 PM
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W126 pedal fade, what the $&$&????

After a road trip with the SD, my brakes started to squeak, so i went out to re-bead the pads. I did several medium stops from about 40mph, some a little slower some faster, and then ONE hard stop. After the one hard stop i noticed insane pedal fade. It's like my brakes were completely gone. I'm sure this isn't the way mercedes engineered their brakes to work under stress, so my opinion is that i have crap pads on the front of the car. I put OEM spec ones on the rear, so they shouldn't be a problem, but i can't remember what i put on the front. Could crap pads cause this much brake fade? By insane fade i'm saying that i could push the pedal till it stopped going down and the car still would not stop quickly-at all, it kind of rolled to a slow stop. After 10 minutes of sitting all is fine again. Opinions wanted please
thanks
Ryan
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  #2  
Old 04-08-2002, 01:34 AM
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Ryan,

From what I know about brakes, and pads in particular, that is indeed brake fade. With the front brakes providing the majority of your stopping power, I would agree that the front brakes are suspect.

I would guess that the pads that are installed are POS...OR possibly the front rotor(s) have become contaminated with something.

The brake fade comes is generally a result of the rotors/pads getting overly hot (sure you already knew that tho . At this point, stopping power is reduced...so another idea is that maybe one or both brakes' pads are dragging while the brakes are NOT being applied and therefore generating heat....so then when you go to actually use the brakes for real, they heat-up THAT much faster and you see the brake fade.

As far as the brake pedal application....was the pedal firm when you saw the brake fade? or did the pedal continue to go to the floor? ....just reaching here...maybe the brake fluid is bad? water? bad master cylinder?

In any case, I don't like to screw around with brakes and play guessing games. Is this was me, with my limited knowledge of brake systems, I'd have it in the shop pronto.

good luck
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1985 300SD - 'Grace' (198K mi.)
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  #3  
Old 04-08-2002, 12:18 PM
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Your symptoms are indicative of a bad master cylinder.
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  #4  
Old 04-08-2002, 04:13 PM
BlackE55
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I agree with goldenbear.
From my experiences with bad master-cylinders, after a short time the pedal should go all the way to the floor and the car becomes unsafe to drive.
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  #5  
Old 04-08-2002, 04:41 PM
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its' not the master cylinder. That was just replaced less then a year ago, and on top of that, the symptoms don't lead me to that. I must have had a hard time explaining what was happening. Let me try again. The brake pedal doesn't go all the way to the floor, it stops, but the car doesnt seem to want to. It's like the pads have oil on them, or after you ride your bike through a big puddle and try to stop-does that make it any more clearer?? I'm sure it's pedal fade i'm just trying to figure out how to get rid of it. Its the same brakes as the 420 sedan, and i can't imagine a powerful car like that having brakes that fade this bad. once again, the pedal IS NOT going all the way to the floor, been there done that, fixed that problem once. thanks again
Ryan
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  #6  
Old 04-08-2002, 05:45 PM
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Ryan,

Jep...does, again, sound like brake fade.

I guess the first thing I'd try is bleeding the brakes and wiping the rotors down with solvent to make sure they are contaminant free. While you're under there, take a peek at the pads and see if there's anything unusual looking about them.

If it still behaves the same after that, I'd change the pads or bring it some a tech.
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1985 300SD - 'Grace' (198K mi.)
2010 Honda Fit Sport
2013 Honda Accord Sport
1996 Lexus LS400 (Retired)
1995 Ford Contour SE (Retired)
1976 Porsche 914 (Sold)
1972 Datsun 240Z (RIP)
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  #7  
Old 04-09-2002, 12:36 AM
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Ryan..is your brake pedal hard or soft during your brake failure? if you use repetely you could be losing you vac assist for a bit until it builds up again. I've noticed this a lot after changing brake pads when pumping them up several times the vac assist cannot keep up until you back off for a few. try pumping you brakes and turn your key off and I'll bet your car will keep running.maybe vac pump is week or the booster has a leakdown..just a thought...paul
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  #8  
Old 04-09-2002, 12:39 AM
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thanks for your input paul. I do not believe that is the problem, it feels like i still have power assist. My booster went out at the same time as the master cylinder and I replaced them both at the same time under a year ago. Car shut off just fine as well, and the main factor was that i had to repeatidly accelerate back up to 40mph or so to be able to medium brake again, thus easily restoring any lost vacuum. Thanks for your input though, good idea
Ryan
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2002 330i.........current.
2004 highlander limited....current.
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  #9  
Old 04-09-2002, 12:57 AM
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ryan....yea...you may want just try changing the pads to a nice soft oe brand(textar) I get alot of glazed rotors that come in the shop with those s---ty hard after markets,but I've never noticed a stopping problem,just squeaky brakes. I'm going to make a note on this and try the quick stop on my next rotor change that are already glazed and see if I can duplicate your symptoms..good luck..paul.
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