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Old 11-25-2005, 09:28 AM
Registered User
Join Date: May 2005
Location: Salisbury,NC
Posts: 46
Hard Brakes

My wifes 300 2.5 brakes are not working correctly. Some mornings. not often She will have a hard brake pedal and little brake. After warming or you can actually press on the brake pedal and after it compresses then you have good brakes. What is the issue. Could a fluid change fix this.

Joseph Blackwell
1985 300SD
1990 300 2.5 Turbo
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Old 11-25-2005, 09:56 AM
Join Date: Aug 2000
Location: Holland, MI
Posts: 1,316
"Power" brakes use vacuum to provide an assist to produce a lot of pad pressure from very little foot pressure.

If the vacuum source is interrupted, the brakes lose this assist and require more foot pressure to provide the disc pad clamping pressure.

You need to check for vacuum at the source and at the brake booster when the pedal feels hard. If there is high vacuum at the source, but low at the booster, there is a leak. If there is high vacuum at the source and the booster, there could be an internal problem in the booster itself.

If there is low vacuum at the source, it could be a 'balky' vacuum pump.

Have a look and get us more information about the nature of this problem.
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Old 12-03-2005, 02:01 AM
unkl300d's Avatar
Registered User
Join Date: Jul 1999
Location: San Francisco, Ca
Posts: 2,442
vacuum issues: hard brakes, no shutoff

check this link.

let us know what you find. The bug is going around.
1979 300D 220 K miles
1995 C280 109 K miles
1992 Cadillac Eldorado Touring Coupe 57K miles SOLD
1979 240D 140Kmiles (bought for parents) *SOLD.
1989 300SE 148 K miles *SOLD
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Old 12-03-2005, 12:22 PM
Registered User
Join Date: Jun 1999
Location: Albuquerque, NM USA
Posts: 1,946
Since it's a diesel, a vacuum pump is required. That's the "source."

Kent Christensen
'07 GL320CDI, '06 SLK350
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