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#1
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Brake pedal drops when parked overnight
Hi all, I'm a new member to this forum from L.I., NY. I drive a '94 E320 w/90K on the clock. I do most of the work on the car myself as a hobby. My present problem with the brakes is this; when parked overnight or extended period of time, the brake pedal drops to to floor, one pump and the pedal pressure is fine. On extended highway drives, the pedal sometimes also drop very low when I step on it by a toll booth or exit ramp, one pump the pedal pressure returns to normal. This been happening several months. Master cyl seems fine, it holds pressure while stepping on it hard with engine off and with engine running. Brake booster seems fine, normal pressure needed to stop car. I bled the brakes a few months ago, pedal pressure fine a few weeks, then reoccurring problem. I then changed the front rotors, pads, rear pads, flushed brake fluid; pedal fine for a few weeks, now it's dropping again. Anybody got comments on this? It's driving me nuts. Can't figure out where's the problem.
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#2
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Master Cylinder. If there are no external leaks I can't see how anything else could be at fault. I believe the condition you are describing is typical when the internal seals are begining to fail. When cold the seals shrink a little allowing the fluid to pass around them, after you pump it a couple of times and some heat is generated the seals swell back to close. It's dangerous to drive it in my opinion and should be replaced, TODAY.
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Marty D. 2013 C300 4Matic 1984 BMW 733i 2013 Lincoln MKz |
#3
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absolutely the master cylinder is starting to fail.
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David S Poole European Performance Dallas, TX 4696880422 "Fortune favors the prepared mind" 1987 Mercedes Benz 420SEL 1988 Mercedes Benz 300TE (With new evaporator) 2000 Mercedes Benz C280 http://www.w108.org/gallery/albums/A...1159.thumb.jpg |
#4
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i wouldn't drive it... this happened to me before in another car.... that said.. i did drive it to a dealer..and they switched it out in under 30 minutes.
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1989 300ce 129k ( facelifted front,updated tail lights, lowered suspension,bilstein sports, lorinser front spoiler, MOMO steering wheel, remus exhaust,stainless steel brake lines). (Gone) 1997 s320 154k (what a ride). Sold with 179k miles. Replaced with Hyundai Equus 1994 e320 Cabriolet 108k 1972 280se 4.5 153k Owned for 12 yrs, sorry I sold it [/SIGPIC] |
#5
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My VW was really bad about that sort of thing, and it was always the master cylinder. For some reason, either it was a bad design, or the extreme weather changes through the seasons would cause the seals to prematurely fail.
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2009 ML350 (106K) - Family vehicle 2001 CLK430 Cabriolet (80K) - Wife's car 2005 BMW 645CI (138K) - My daily driver 2016 Mustang (32K) - Daughter's car |
#6
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low brake pedal pressure
There could be several reasons for this. a)s mall leaks in master cylinder, b) small leaks disc brake cylinder seals, c) inadequate bleeding brake lines. Does fluid level change in master cylinder change? Hope this is possible answer. Abe G
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#7
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Thanks guys, I'll r/r master cyl asap. There's no loss of fluid in system, no leaks from wheel cyl's, and good pedal pressure after one pump. I'll change the master cyl and report back any change in pedal drop. Anyone got a link to r/r'ing a master cyl?
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