i am having cruise control problems with my 84' 300cd. sometimes it works, but usually it doesn't. when i move the lever upward to set/accelerate it will accelerate the car but when i release the lever the cruise control does not engage.

Mark,
Do a search on here on cruise control - your problem sounds pretty typical. More than likely the amplifier.

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Jim

Your symptoms sound exactly like those on my 300cd. Replaced the amplifier and it works great.

Blocking the air recirculation valve on the turbo units have helped me get rid of the surges on my 300D turbo 1985. But I would like clear the fact that i did not have any problems with setting or engaging the cruise control. It was the surges that were driving me insane.

MVK

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One penny saved is three penny earned.

1985 300D Turbo 179,000miles

where is the amplifier located and how difficult is it to replace. i am mechanically inclined but the car is new to me. thanks for all the help

first think I always check, make sure you have german bulbs in the tail lights meaning they better have a silver bottom. Copper and brass, throw them away.

Then go from there.

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Current Stable:
1994 S500 v140, 210k miles, white with grey.

Former Mercedes in the Stable:
1983 300CD Turbo diesel 515k mi sold (rumor has it, that it has 750k miles on it now)
1984 300CD Turbo Diesel 150 k mi sold
1982 300D Turbo Diesel 225 sold
1987 300D Turbo Diesel 255k mi sold
1988 300 CE AMG Hammer 15k mi sold
1986 "300E" Amg Hammer 88k mi sold (it was really a 200, not even an E (124.020)
1992 500E 156k mi sold
etc.

Re: bulbs....http://www.gdl-online.com/bulb.html


Good Cruise reference:...http://www.gdl-online.com/begin1.html#contents

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The Golden Rule

1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)

the resistance of the bases are different.

Well when I change the bulbs to german ones it always works. You can read about it or do it. the choice is yours.

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Current Stable:
1994 S500 v140, 210k miles, white with grey.

Former Mercedes in the Stable:
1983 300CD Turbo diesel 515k mi sold (rumor has it, that it has 750k miles on it now)
1984 300CD Turbo Diesel 150 k mi sold
1982 300D Turbo Diesel 225 sold
1987 300D Turbo Diesel 255k mi sold
1988 300 CE AMG Hammer 15k mi sold
1986 "300E" Amg Hammer 88k mi sold (it was really a 200, not even an E (124.020)
1992 500E 156k mi sold
etc.

On my '81 300CD the amplifier is above the steering column near the firewall. It is silver in color and appr. 4" x 1" x 5". It is easiest to remove the "strap" from the car and then the strap from the amplifier. There is a ten wire connector attaching to the system. Yous may have more or fewer wires going to and from the amplifier.

The bulbs will affect the cruise control only when interupting when you brake. It is necessary to have European bulbs in the brake lights. They are available at the McParts stores.

I hope this is of some help. I have tried to be accurate in description, but it's been awhile since I've worked on this.