On a versamatic windsor how full can the bag get before you change it?

Probably from underneath

I own a few Windsors and I believe those pulleys are threaded on in reverse. Unfortunately there's nothing to grab hold of on the other end while turning the pulley with a pair of pliers. When servicing Hako machines I normally remove the armature from the motor and grab it with a towel while turning the pulley off. Give that a try, if no luck I'll get into one of my Windors and see how its configured.

it comes up from the back,it is probably plugged or the sensor is dirty

You most likely will need to change the Yoke assembly. There is a sensor built in that gets clogged with fine debris over time. This will take care of the problem.

Check the line going from the bottom of the vacuum to the bag, it may be clogged. A coat hanger can help you clear any jams, but be careful not to puncture the duct.

You likely have one of two problems. Your return spring is broken, or your axle is bent. If your axle is bent, carefully inspect your chassis to be sure that the bent axle has not cracked or otherwise damaged the chassis. I have included a parts list as well as some links to these parts for your reference. http://windsorvacuums.com/partslists/s12_PARTS.pdf 2010 Axle Spring 86146570 windsor allstar javelin 5053 Windsor Sensor Axle 86137990 allstar javelin

Your Sensor most likely has an internal heat sensor that is shutting off the motor. Some vacuums install an external heat sensor with a reset button that you must push to re-start the vacuum. If your model does not have an external reset button it is most likely a sensor inside the motor. If it is defective the motor must be replaced to solve the problem. But first make sure the overheating is not being caused by a blockage somewhere or the bag is too full. Air must pass completely through a vacuum starting at the floor where it picks up the dirt through all the canisters, filters, bags, etc. and then is exhausted from the vacuum. Any restrictions or blockage can cause the motor to over heat.
That Vac Guy

I have the same problem, maybe we can flip the belt over and let it run on the smooth side for a while. That's what the person before me did and it lasted a good 6 months.

Likely the wheels are frozen with thread and hair at the sides of the wheels. Check for free movement of each wheel and pick out the debris around any that are hard to turn. Long needles and tweezers are good tools for this.