Dremel MotoTool model 385 clutch

There is a coupling between the drive motor and the chuck. You will need to take the tool apart to replace it. E-bay has these.

You screw off the collar on the tool, remove the chuck and inner part. The chuck is replaced with a special chuck (no inner piece). The special chuck has a square opening in it's nose that accepts the square end of the flex shaft inner cable. Is is actually a speedometer drive cable, from yesteryear.
Then you pull the inner cable out slightly, if it will, and put the inner cable into the square opening of the special chuck on your dremel motor. once engauged, you carefully screw the outer shaft housing on to the end of your dremel motor.
What you want to avoid is damaging this area during flex shaft assembly. I have had success with turning the output side of the flex shaft, while tightening the outer flex shaft onto the dremel motor. Stop tightening if it starts binding...
Rotation seems to help with alignment of all parts.

Cheers,

Doc

This has to be worth a go:

0 3 3 4mm Mini Electric Grinder Keyless Drill Chuck 3 4mm Shank for Dremel...

You can use a drill that fits directly ( one size) or you can use a small chuck made for the Dremel. example: http://www.homedepot.com/p/Dremel-1-32-in-Multi-Pro-Tool-Chuck-4486/100531881

Broken pin, bad clutch or broken shaft. Most likely, a pin.

Try some W-D40 and gentle hits on the coupling to liberate the chuck 3 pin holders.If you got this type of chuck:

> Enlarge Image

4486 Dremel Chuck

The Dremel Chuck holds Dremel accessories without using a collet eliminating having to use the wrench and creating quick and e

The part that goes between the motor and the chuck is called the CLUTCH UNIT,
REF 2615294309 it is a splined rubberised sleeve, it also fits the 276 and 396.
The price is £3.69 (including vat at17.5%) and can be obtained from Jaymac (Derby) Ltd.
http://www.dremel-direct.com/acatalog/service.html

My 15 year old Dremel 395 had the same problem so I took it apart. There is a plastic spline between the motor and the output shaft to the chuck . My plastic spline was split and had many of its teeth sheared off. The shaft lock acts on the output shaft side of this spline, so it was ok. Otherwise everything looked great; bearings ran free & had little play free, brushes ok. To be fair, my Dremel had seen hard use & doesn't owe me anything. No luck so far finding replacement spline parts, which if available should be easy to install. To take apart your tool, just google "Dremel Disassembly". GOOD LUCK!

I would go direct to Dremel.com or call them at 1-800-437-3635 and get the schematic and parts you need, I just checked and they have a parts diagram online that you can view. go to the section about manuals/literature and type in your model number. Good luck