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Old 07-11-2011, 09:16 AM
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Brakes - occasionally not there

The 90 300D (250D Turbo) has begun to develop a brake issue. 99% of the time the brakes work fine, the other 1% you hit the brake pedal and it starts to go to the floor and the car does not slow forcing a couple panic 'pumps'. Ideas? I need to have this fixed as soon ad possible for safety's sake. Thanks.


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Old 07-11-2011, 01:06 PM
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Most likely the master cylinder is by passing fluid internally. My vote is to replace the master cylinder.
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Old 07-12-2011, 12:07 AM
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Since that is a diesel, you should probably post and search on the diesel forum. Diesel's don't make any vacuum so they have a vacuum pump I think. That could be the problem. They can probably answer better on the diesel forum.
1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
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Old 07-12-2011, 05:59 AM
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X 2

For Carnut's MC suggestion.

Also, unless replaced previously,your Brake Hoses MAY be approaching their useful Safe End-of-Lifespan.
'84 300SD sold
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Old 07-12-2011, 12:22 PM
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Location: Dallas Area
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Had this problem one. One of my calipers was frozen, causing a drag on the brakes and heating the fluid to boiling. Once the brake fluid boils, you have no brakes.

Possible causes:
  1. Frozen caliper - drag causes brake fluid to heat and boil
  2. Old brake hoses with blocked passages - will prevent oil from returning, which in turn will casue a drag on the brakes and eventually cause the fluild to boil

Check each caliper for frozen pistons and replace all rubber brake hoses.

Also, brake fluid should be replaced every two years. Brake fluid is hygroscopic and with time its boiling point drops. Also, the water in the fluid promotes corrosion/rust which will tend to freeze the piston in place. New brake fluid's boiling point is higher and you have a slightly higher margin of safety in case of a dragging brake.
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Old 07-12-2011, 09:16 PM
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first thoughts is master cylinder.. had a bad MC on a Isuzu Trooper once>> had to pump like a mofo to get it stopped ....

if it is a dragging caliper - you can tell by ascertaining how well the car coasts - put it in neutral coming up to a light - is there any drag? binding? bad noise?

Kim Langley
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