Sounds like the Grande was laid on it's side at one time and oil from the Final Reduction Gear transmission ran into the brake drum. Someone tightened the brake cable as tight as possible trying to compensate for the oil spill.
You need to remove the rear wheel and use a flat thin 36 mm open end wrench to remove the free wheeling chain sprocket . You may have to pound the handle of the wrench with a hammer or stand on it to break the sprocket loose.
Once the sprocket is removed, use a rubber mallet or a piece of wood to tap the shaft out of the center hub. DON"T use a metal hammer or you will damage the threads on the end of the shaft. If the threads are damaged you will have a heck of a time getting the sprocket to screw back on.
Once the final reduction gear assembly is out of the hub you can access the brake drum and brake shoe. Use brake shoe spray cleaner to clean both the brake pad and inside of the drum.
Reassemble the wheel by putting the Final Reduction Gear assembly back in the hub and screw on the Free Wheeling sprocket and tighten. Keep the wheel upright and vertical or else you will leak oil back in where you just cleaned it out.
Before you remount the wheel rotate the center part of the hub using the brake lever arm where the brake cable attaches. Use a shop towel or rag and Pull the brake lever arm forward to see if the brake keeps the center part of the hub from turning. If it does stop the center hub from turning then you have successfully cleaned the brakes and can remount the wheel and reassemble everything.
Once you have the wheel remounted, check the Final Reduction Gear for oil by opening the access screw on the left side of the hub. If oil runs out it's OK, if not fill with 80-90 wt gear oil until it runs out the access/filler hole , then replace the screw.
The squeaky front brakes may be just dirt on the brake shoes. Try removing the two rubber inspection plugs on the left side of the front wheels and use an air compressor to blow out the drum area. Do this in an open area preferably outside as some of these old brake shoes may conatin asbestos.
You can get the thin 36 mm wrench at most bike shops.
If you need new brake pads, oil seals or any other parts for your Grande please email me at zippymoped @yahoo.com