Sometimes when I first start the car the brake pedal is very hard. When this happens I have to press on the pedal very hard to get any braking. It is like the motor is turned off. After about 30 seconds the brake pedal starts functioning properly. It is beginning to happen more frequently. The fluid level in the master cylinder is at the proper level. Is my problem the brake booster? Is this something that can be replaced by a home mechanic. Any hepl would be greatly appreciated.

Thanks, dtimmester

Could also be a tired vacuum pump or a vacuum leak. Cap the small line at the vacuum pump and see if that helps anything. Then cap as well the small line from the big brake booster vacuum tube and see if that helps anything. You won't be able to shut off the engine with the key while the small line from the big brake booster vacuum tube is disconnected. If nothing changes after those tests, I don't know how to tell whether the problem is a bad vacuum pump or a bad brake booster.

Sixto
95 S420
87 300SDL

VAc pump should generate 17" of vac in a few minutes, measured in the main line, not the accessory line.

Sounds to me as if the check valve on the main vac line to the booster is bad, and sometimes leaks down. Easy to replace, I think (although you may have to replace the whole line).

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Only because no one mentioned it...

Another item that might cause this problem is the diaphragm in the power booster could have become faulty...

Just trying to help...

Just out of curiosity when is the last time you had the brake fluid flushed and replaced?

Regards,

Alon

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'92 300CE - Sold
2004 C240 - 744 - C7 Wheels - Android Radio
2002 C320 - 816 - Sport Wagon

Less than 2 years.