Gr450 grinder variable speed has stopped woking, grinder goes to full speed when turned on with no affect from variable speed

It's possible that the variable speed control may be the issue with your Delta 23-197 grinder. However, before attempting to bypass it, there are a few other things you can check.
First, make sure that the grinder is properly plugged in and that the power outlet is functioning correctly. Check the power cord and make sure that there are no cuts or breaks in the cord.
Next, check the switch and make sure that it is properly engaged. If the switch is faulty, it may need to be replaced.
You can also check the brushes on the motor to see if they are worn out or damaged. If the brushes are worn out, they will need to be replaced.
If none of these troubleshooting steps resolve the issue, it may be possible to bypass the variable speed control. However, this is not recommended unless you have experience with electrical wiring and understand the risks involved.
If you do decide to bypass the variable speed control, you will need to identify the wiring that controls the speed control and connect the wires together to bypass the control. However, keep in mind that this will result in the grinder running at full speed all the time and may shorten the life of the motor. It's always best to have a qualified electrician or technician perform any electrical modifications to your tools.

that comes up as a craftsman brand by sears ( mass produced )
variable speed grinder

I cant find an exploded view or user manual
if you cant get the value information
think you will be up for an oscilloscope

This is an electric die grinder? Do a quick Google search for "Router speed control". That'll work fine for any electric die grinder.

Here's a link to download the pdf.
http://www.dewaltservicenet.com/documents/English/Instruction%20Manual/Delta/A15786.pdf

If it doesn't work, start here:
http://www.deltaportercable.com

You can check the online parts manual

however it doesn't give the size of the wheel, only the part number of which there are two

23269 and 23270

They are usually left handed threads so they will self tighten when running. Try turnung then the ither way.

GET A LOCK WASHER OR
USE THREAD LOCKER

The speed control is a small wheel located on the top of the grinder ahead of the trigger for easy operation with your thumb while the tool is runnig

http://www.searspartsdirect.com/partsdirect/index.action?sid=PSHx20080114x00001sj

The capacitor is easy to change and can be matched once you remove it by any electronics parts house.