Auto trans shifting problem - Mercedes-Benz Forum

 
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post #1 of 10 (permalink) Old 10-25-2010, 02:12 PM Thread Starter
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Auto trans shifting problem

I have a 1971 280S. I am slowly working on this runt of the litter and am pleased with my amature restoration efforts. I have repaired many of the problems but the auto trans has me stumped. The car will not shift into fourth. I hear there is a vacume line and actuator. Is it worth my time to remove and clean all that, could the problem be that simple? Other gears shift smothly. Oh also there is no passing gear
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post #2 of 10 (permalink) Old 10-25-2010, 10:25 PM
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The passing gear should be a kick down switch under the gas pedal, when you press the accelerator down far enough to hit the button the transmission kicks down to the next lowest gear.

at least in my car, as always I could be wrong.

Last edited by tgikal; 10-25-2010 at 10:27 PM. Reason: nvm :/
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post #3 of 10 (permalink) Old 10-26-2010, 06:25 AM
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Most four-speed automatics start in 2, are you sure it isn't in fourth?
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post #4 of 10 (permalink) Old 10-26-2010, 07:03 AM Thread Starter
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280S Auto trans shifting

I was certain I had read it was a four speed. That does sound strange for an automatic. The reason I am concerned is that I count it shifting quite smoothly twice after starting. That would be third gear. Then at around 45 mph It starts winding out begging for another gear. I do not have a tach but I once pushed it up to 65 mph and I would have bet that was close to red line.
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post #5 of 10 (permalink) Old 10-26-2010, 07:07 AM
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The starting out in 2nd gear prevents heavy creeping when you stop. You can try if it starts in first or second gear by putting the selector in L (or 2) and after you shifted from 1 to 2 put the selector in S (or 3) and then D (or 4).
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post #6 of 10 (permalink) Old 10-26-2010, 10:26 PM
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The trans starts in 2nd. You can get it to start in 1st by setting the shift lever into the '2' position. It will then shift into 2 and stay there. then manually shift into 3 and then 4. Engine speed at 60 mph in 4th will be approx 3000 rpm, which is normal.

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post #7 of 10 (permalink) Old 10-27-2010, 06:35 AM
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So it is like mine, didn't want to speak up before reading the last post.

The last shift should happen 35-45mph (really varies with the running condition of the car, so I've found) and take it all the way to the top speed of 85mph there is no overdrive like newer cars so it might act like it's starving for another gear, but that's just how they are.

I've driven it at 75mph engine reved to hell (so it sounds) for hours. not a single thing wrong.

I forgot mine was a 4-speed until someone mentioned 1st gear is the passing gear, so you only have 3 regular drive gears.

These cars can honestly handle 5k rpms with no problem. even being 40 years old.
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post #8 of 10 (permalink) Old 11-04-2010, 06:44 AM
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Quote:
Originally Posted by dkeith12 View Post
It looks like an electrical problem. The PCM controls the transmission as well as the fuel injection system so there could be a number of causes. Road testing with the scan tool is the best way to find out what's going on.
That would be a great idea... if the car was made in the '90s...

I don't think the car has a pcm, so I doubt that would be the problem...
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post #9 of 10 (permalink) Old 11-04-2010, 07:22 AM Thread Starter
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71 280 S trans kick down button

Thanks for all the advice on my transmission shifting problem. I now know where all four gears are. I need to find out why the shift down button under the gas peddle is not working but I have wound her up to 75 and although the trans feels like it could certainly use an overdrive the engine rpms don’t go much over 3K at high speeds.
What does the shit button connect to? I am hoping its an actuator that I can get at, remove clean and perhaps replace an O ring.
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post #10 of 10 (permalink) Old 11-04-2010, 07:31 AM
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It is connected to a solenoid on the transmission. You can check the system with a multimeter. First check if you have 12V at the button, than if you have 12V at the solenoid. It might be fuse-protected, check the fuses too (certainly if you don't have 12V at the button).
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