1985 190E 150K miles excellent condition....Hello, I could not find a post with this problem. When I have hot outside ambient temperature (hence hot under the hood) my brake pedal gradually looses travel until the front brakes start to engage. They will engage so bad that the vehicle comes to a quick stop. My remedy to get traveling again is to use 9mm wrench to open the front bleeders and release a touch of fluid and then I can drive off. If I park the car and temeratures drop, the pedal travel returns and all is fine until ambient temperature gets above 95 at which time the process repeats itself. The last time it happened I'm afraid it warped the front rotors. Car is parked now, awaiting my DYI actions. Benz mechanic in Salt Lake said that the front hoses could be deteriorating and when get hot they swell causing the fluid to be forced out into the calipers. It seems to me that when everything gets hot and the fluid needs room to get back into the master cylinder it is being prevented from doing so by a faulty master cylinder. Any thoughts on this problem? Renew master cylinder? Renew hoses? Renew front calipers? Of course, renew fluid. What are mbenz fluid specs? The benz mechanic said I should use only benz fluid but I would think any top of line fluid would be good.

Thanks in advance to all technicians and DYI ers, this forum has been most helpful to me in the past.

It also sounds like a master cylinder to me. The MC should allow the heated fluid to escape back into the MC tank. I agree that driving it in this condition will damage the brakes and could be dangerous. Do a search in this forum, I know this issue has been discussed recently.

thanks craig, my thoughts as well, on another post by jaybird336 titled "hot brakes" describes my situation except my rear ones work. Unfotunately, when this last happened it was at the I-15 and I-80 speghetti interchange in Salt Lake at rush hour on Friday.........had to hammer the gas and force the car to keep going till I could find a safe way to make my exit.....by that time the steering wheel was wobbling bad from warping front rotors. They feel fine now when cool but i bet with some montain driving and just a bit more than casual braking the warp wil rapidly return.

Something may be preventing the master cylinder from mechanically returning far enough to unblock the port to the reservoir, when the pedal is released.

Steve

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'91 MB 190E 2.3
'08 RAV4 Ltd 3.5
'83 Lazy Daze m'home 5.7

I would have the front calipers as well as the rotors checked. That much heat can't be good for the calipers either.