manual shift interlock in starting circuit? - PeachParts Mercedes-Benz Forum

janko · #1 05-15-2002, 10:10 AM

the car in question is an 83 240d. the question. did this car come from the factory with a switch that required the clutch to be depressed to allow starter engagement? i can, start this thing with the clutch pedal not depressed. thank you.

SW · #2 05-15-2002, 12:54 PM

I don't think there is such thing on these cars. In my experience, I've driven an 81, 82, and 83 240D (all stick shift) and all of them started without having to press the clutch pedal.

janko · #3 05-15-2002, 01:02 PM

thank you, sir.

gnolo · #4 05-16-2002, 03:42 PM

I know several W123 Diesel and I have never seen this switch. Maybe the last owner set up this system because he often forget to put the stick shift on the neutral when starting the engine ?

JimSmith · #5 05-16-2002, 04:02 PM

janko,

For the model year 1975 the US DOT required an interlock on manual transmission cars that prevented starting with the shift lever in gear. The switch was just like the one that turns on the reverse light when you engage reverse gear, only it detects when the lever is in neutral. The device never required the clutch be depressed. I think the ruling was eliminated shortly after it was enacted and even the 1976 models no longer had this feature. Jim

#6 05-16-2002, 04:38 PM

Of all the 240D's I've owned, all have been manual and none of them, either Euro OR US have had any neutral or clutch pedal interlock.

Have a great day,

dieseldaddy · #7 05-17-2002, 03:35 PM

Are you saying that I should be able to start the car (mine is an '83 240D) while in neutral without depressing the clutch, but should *NOT* be able to start the car without the clutch in any other gear?

Also, I noticed (by accident) that I can shift thru the gears when the engine is off WITHOUT the clutch. Is this correct behavior?

It has been a while since I have owned a manual transmission car...

gnolo · #8 05-17-2002, 04:51 PM

When the engine is off, it is possible to shift thru the gears without depress the clutch of every car I know with a manual garbox. It is harmless.

JimSmith · #9 05-17-2002, 05:05 PM

Dieseldaddy,

Your car has no interlocks what so ever. So you can start it in any gear or neutral with the clutch in or out. If you start it in gear, with the clutch pedal out (clutch engaged) the car will move when the engine turns over. I have used this feature to drive home when the hydraulic cylinder in the clutch actuation mechanism failed. You warm the car up good so it will start easily, then shut it off and put it into gear, and start it. Not the smoothest start, but better than my 16 year old son was doing his first couple of times (and mine too, but that was so long ago I cannot recall the details). It gets you started and then you shift "clutchless" which requires a little practice.

The point is, I believe there was one year, 1975, when the DOT required an interlock. It may have been on 1976 models as well. The feature was quickly abandoned, but for those of us that had a 1975 model year manual transmission equipped car (I don't think the DOT requirement applied only to MB) there was an interlock. MB elected to implement the feature by having a switch in the gear selector lever mechanism, under the little rubber booty, much like the device that turns the back up lights on the car when you put it in reverse. It was easily defeated if you really needed to, like starting with the car in gear when the clutch mechanism failed (did it on that car too).

I thought all automatics had such a feature as well, preventing you from starting the engine in Drive or Reverse. I guess that is not the case, but I am about as ignorant of the details of automatics as you feel you are about manual transmissions.

While you can shift through all the gears with the car sitting still, with or without the clutch, with engine not running, it is not recommended. First, it doesn't do anything positive, and second, the parts inside, while fairly robust, were not designed to operate without oil being slung about to cover the parts, or to be in rubbing contact without rotational motion. The gear meshes are not affected though, as they are always engaged. It is the rest of the parts that are potentially going to suffer. An occasional selection of a gear when not running will not hurt though, as long as you don't force anything. It is possible to have the gear ratio selection features not match up (geometrically), in which case the lever will not move all the way, unless you are moving. If this is the case and you want to put the car in gear to prevent rolling (like in the winter when you might not want to engage the parking brake), try another gear.

Hope that helps, Jim