vibrating car between 2000 and 2500 rpm

[Peter]

Recently my 280SL 1969 vibrates between 2000 and 2500 rpm. This is speed and gear (automatic) independent. This also happens in Neutral. Above and below these rpms the car drives fine.

My conclusion is that it must be the engine or torque converter.
Adjustments such as valves, ignition, CO at idle are all checked and correct.

Any idea what these could be?

Thanks for help, Peter

[gcw206]

Check your flex disc and all the fasteners.

[Nicolas Aristodemou]

If your car has emissions control system it could be a malfunctioning vacuum solenoid valve located next to the relay boxes.

[Peter]

I don’t suspect the flex disc as they are  behind the transmission.

I have a early 69 emission control with only the system to cut off below the 1100 rpm, but I will test if it’s out of control, but it’s a long shot.

[Peter]

I tested the emissions control system today, it works fine so I haven't found a reason for the vibration problem yet.

Peter

[Nicolas Aristodemou]

Peter the 2 way valve which alters the timing by about 17 deg operates between 2400 and 2200 rpm which is where you say you feel the vibration. Check the valve operation by touching it and feeling it vibrating slightly at about 2400 rpm and again at 2200rpm. That is a simple way to check its correct operation.

I had a similar problem and that valve was the issue. Of course when I installed a Bluetooth 123 ignition, there was no longer any need for the function of this valve, but I still kept it operating although I programmed the ignition to ignore the 2 way  valve controlled vacuum.

I hope you resolve your vibration issues.

Nicolas

[Peter]

Tanks Nicolas,

You have the 1970 emission control system, mine is the 1968/69 which closes gasoline supply on the FIP below 1100 rpm in 2, 3 and 4th gear. This system works fine. No other systems are connected to it.

I have a 123 ignition with vacuum which is changing the ignition timing, but this is of course a different issue.

Or am I missing something?

Peter

[Nicolas Aristodemou]

Peter, if you do have the electromagnetic  vacuum valve connected between the vacuum pickup point on the intake manifold and the distributor it could be that, like was in my case. If you don't then there is something else that is causing the vibration.

Have you tired enriching the mixture screw on the fuel injection pump? Not the idle mixture screw,  but the rack position adjusting screw that is accessed by removing an allen screw (5mm allen key) and turning the adjusting screw with a fine bladed screwdriver by say 1/2 a turn. You can find this illustrated in the technical manual.

It is not difficult to do and easily reversible if it doesn't improve matters.

As you mentioned in your post the engine vibrates even in neutral  which means the issue is not transmission related. That is all I can suggest.

Nicolas

[Peter]

Thanks Nicolas,

I'm going to look at this also.

I will also check the v-belts and pulleys again.
My feeling is that it is a mechanical problem, because when I drive above 3000 rpm and releases the throttle, so no fuel supply, the car also shakes between 2000 and 2500.

Peter

[Peter]

I found the issue.

The bulky bracket for the air-conditioner compressor and  alternator has two broken bolt and a specific part for extra stability is missing. Due to this the alternator start to vibrate between 2000 and 2500 rpm.

Peter