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  #1  
Old 12-14-2003, 01:12 AM
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79 300SD starts in 2nd gear ???

I just got a nice low mile 79 300SD. Its transmission - (722120-02-009792) works well except that it starts in 2nd like a 240D automatic when either D or S is selected. Otherwise this transmission tests out well. It engages very quickly in both 1(or 2) and R from neutral, the shifting is firm and right on the correct shift points, it never slips and never slides into a shift. If I start out in L, and immediately select D, it works just like a 300SD should, starting out in 1 and shifting upward. My other W116 300SDs shift into 2 after about a 20 foot roll.

In summation, if I select D or S, it starts in 2. It wont kick down to 1 ever. It will manually shift down to 1 at low speeds and it will start in 1 when L is selected. It has new filter and fluid. The old filter and fluid were clear and fresh in appearance.


What would be keeping the transmission from going into 1 ??

Thanks,
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Last edited by jmfitzger; 12-17-2003 at 02:22 PM.
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  #2  
Old 12-17-2003, 02:31 PM
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W116 - Overload Protection System

After reviewing the electrical schematics for the W116 300SD, it appears that in order for the transmission to start in 1st gear when D or S is selected, a signal must be applied to the AT solenoid valve.

The AT solenoid can be activated either by the kickdown switch or the Overload Protection Device. There is no other source for activation signal.

Since the transmission does not downshift under any circumstances when the kickdown switch is activated, the AT solenoid must not be working.

I will appreciate it if someone with knowledge can verify this diagnosis.

Also, where is the AT solenoid valve? How do I get at it?

Thanks
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Old 12-17-2003, 03:54 PM
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Location: Evansville, Indiana
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Follow the wire from the kickdown to the transmission. Somewhere on the right front (I think, not sure) the wire connects to the solenoid. I THINK you can remove the solenoid without draining the tranny, but I don't know for sure. You may get a bath in tranny juice if you try!

Apply battery voltage to the solenoid when you find it. It must click when voltage is applied -- if not, it's stuck.

I don't know for sure if the W116 started off in 1st or had the "second gear sitter" situation -- meaning that it sits in 2nd while stopped and immediately kicks down to 1st when starting off. The W123 300D does, so does my 220D, but I'm not sure about the W116. If it is supposed to and doesn't, check the vaccum and bowden cable systems, something isn't working correctly.

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
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  #4  
Old 12-17-2003, 06:32 PM
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The 116 body 300SD had an electric kick down to first gear. It took place at the release of the brake pedal. It was controlled by a box behind the passengers side kick panel.

Because the device operated at every take-off the coil for the kick down solenoid was often open circuited. if kick down does work from the switch beneath the gas pedal then the problem is usually in the box and solder contacts are often the problem. The whole process is best described in the 1978 new product manual 300SD.
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  #5  
Old 12-18-2003, 04:59 PM
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Now that you mention it I hear a clicking sound coming from behind the passenger side panel. When it clicks the tach jumps. The tach is also wired up to the overload device, So I will check out the AT solenoid with 12v to be sure it is operating then, if it is I will dig out the overload protection device and reflow the joints.

Thank for the helpful insights,

Merry Christmas
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