The rear end does not stay in contact with the pool bottom.

Try moving the float closest to backup valve slightly. This can help it stay flat on bottom. Mine was riding on its back wheel and kept climbing too high and getting tail stuck in skimmer...and now it is riding smooth across pool floor now.

need less weight on vacuum hose in different place

on the rear of the polaris the jet is a swivel, it propells the polaris set it a 11:00 o'clock and it should travel level.

It sounds like there might be water in the head of your automatic pool cleaner. Take the head off and shake it. If you hear water sloshing around, you will need to replace the head.

Make sure that you have enough hose to reach the entire pool. This sounds simple, but this is a common problem with these pool cleaners. Make sure all three thrust jets of water are working on the bottom of the pool, also.

If the cleaner is going too fast then it is likely that there is too much water flow at the drive turbine. Is there a pressure relief valve in the water supply line (at the edge of the pool)? If so then change the tension on the spring to allow less water to get to the cleaner's drive turbine.
The speed of the Polaris is probably the cause of the front wheel lifting as well, however if (after adjusting the water pressure) the front wheel still won't stay on the pool bottom, then perhaps adjust the little jet at the back of the casing. Mine points a little "down" towards the pool floor and this tends to raise the bac k wheel (or alternatively keeps the front wheel in contact with the pool bottom or wall).

By the way, if you want to see how the cleaner works, then search for eHow and lookm at the repair/overhaul of the Polaris 180............. the mechanism is similar.
Good luck.

I battled with the track falling off for over a season. The pool guys said they fixed it. Tried the previous solution to adjust middle wheel but no luck. My solution was to remove the left wheel and the tank (to get to the screws). The wheel mount allows for minor adjustment but it is also reversible. Turn the mount around and this will extend the wheel base much more. Mine ran for several hours after doing this and so far the track stays on.