Changing the coupler

The nylon coupling is either cracked or missing. A flat key extends from the motor shaft and locks into the extension like a paddle in order to move the blades. If you can not find the insert, this style of interlocking is common mechanical design. There are sometimes a spring clip the paddle interlocks with. The nylon insert locks into the blade rod mechanism. I suppose the nylon insert is designed as a replacement part rather than replace the entire blade extension

That part is being manufactured again. Search eBay for "Blade Drive Coupler for Viking Blender VBLG01"

i have a perfect answer! and own this very modle with the same issue. Plus i have done it myself.
Instructions:
*on the lower part of the hadle you will see two holes, with a small 6" school sized METAL ruler (no thicker than 3/4mm) gently insert it inbetween the two holes and push down. ((The handle has a clamp there) NOTE: you MUST start at the bottom of the handle or you will brake it!
*then while still inserted push the ruler away from the jar. this should releese the clamp that will allow you to remove the outer piece. REMEMBER your handle is plastic.
*now slowly lift upward and the side clamps will release. STOPpulling when you get to the at the top clamp.
*now you want to carefully hold your thumb down with slight pressure on the top of the handle (where you see the ingroved space that connects the hadle piece, it looks just the same as the bottom but without the holes) and lift up the handle slowly. this should release the outter part of the handle.
* now that the outside piece of the handle is off you can see the scews, unscrew with a phillips scewdriver and take handle fully off.
*Lastly the wire-like rings MUST be slipped off towards the bottom. do NOT try to prie off the wire-like ring from the little piece that is holding it together to create the ring, you will snap it.
*after you have taken off the rings, clean them with VIM (with bleach) by placing them FLAT on the sink edge to keep them from changing shape. Scrup away. Also scrub the plastic parts but DO NOT use the VIM on the outside of the plastic handle as it could scrub away the silver paint. only do this on the inside to remove the mold and grime.
NOTE: VIMis the only thing i found that will even remove rust build up. use an old toothbrush to scrub away the rust and grime. preferably dry with the vim, no need for water. water will dilute the VIM and cause it to be uneffective.
* you can take the little nub that conects the rings off by twisting them to the left or right, for cleaning, doesnt matter. I tried both ways but prefer to keep them on.
* now that you washed all parts let them DRY or you will end up with the same rust and grime issue. After the parts have dried you can now reasemble youir handle, and have peace of mind :)
* Try not to overdue the assable and reassambling of your handle, keeping in mind it is made of plastic and plastic wears easliy.

Hope that helps.

Sounds like the teeth are stripped underneath the blade. Make sure it's put together correctly before you do anything else.
Download Cuisinart CBT 500 Manual

This sounds like the black rubber coupler has broken. The teeth often get knocked off. Have a look at the part shown in hte pictures here:
http://kitchenaidblenders.co.uk/Home/tabid/36/p/Two-%282%29-KitchenAid-Blender-Coupler-%2b-WS-Fitting-Tool-9704230_2plusWS/ProductID/175/Default.aspx

The piece that you need is referred to as the coupler. The coupler is a breakway part that is designed to shear and/or wear down in the event that the blender is overloaded. This is to avoid damage to the motor.

The coupler may be purchased individually and is an easy repair that can be done at home. You may purchase the part and access step-by-step replacement instructions at the following link:

http://www.mendingshed.com/kacoupling.html

I did the same thing. Order parts at thegourmetdepotco.com -- This problem is caused when you put the rubber gasket underneath the blade instead of above it. This causes two problems: 1. It lifts the teeth on the jar away from the teeth on the drive gear, which can grind down and break off the teeth, and 2. If the drive gear contacts the rubber gasket, it will melt the rim of the drive gear. In the future, to reassemble the jar after cleaning, first put the rubber gasket on the jar, then the blade, lastly screw on the base ring.

Yes.

The coupler - the black cylindrical piece that juts up from the motor base, and it has 6 teeth protruding inward toward the center of it - is responsible for transferring motion from the motor into the blade assembly. You physically set your jar on top of it.

If you're needing a replacement coupler for your blender, you may order it and find repair instructions at the following link:

www.mendingshed.com/kacoupling.html

If it is 2 yrs old,Just call the customer service,they will give you the parts for blender for lesser price or else go for new one.