How to Stop Treadmill Belt from Slipping and Changing Speeds

So recently I started experiencing the belt on my (out of warranty 5 year +) Proform 995 SEL treadmill start to slip constantly.  At slow speeds of around 3 or 4 miles per hour it was really bad, but at around 6 mph it was managable to run on, while still having a noticable slip to it.

To remedy the situation, I had tried tightening the walking belt using an allen wrench provided with the treadmill, but that didn't seem to make much of a difference. After reading that my treadmills walking belt should be able to lift up 3 or 4 inches in the middle, I decided to loosen the belt back to where it had been.

I was back to the drawing board, so I tried using some treadmill lubricant to coat underneath the walking belt, thinking that the belt might be sticking to the surface of the treadmill.  While this did seem to make a tiny bit of a difference, it didn't fix the problem. So again I was stuck with a treadmill that continued to slip and was unsafe to run on.  (I read later, that for my treadmill, you don't actually need to use a lubricant underneath the walking belt.)

Finally, I decided I would take the treadmill motor cover off and tighten the motor drive belt.  After opening the cover up I noticed little black shards of plastic near the motor belt.  While the motor belt didn't seem to be that loose, I decided to retighten the motor drive belt as best as I could. 

After loosening the two bolts holding the motor in place and then pushing down and back on the motor itself, and retightening the motor down, the drive belt did seem to be a little bit tighter.  Well to make a long story short, after plugging in the treadmill and turning it on, and then eventually walking on it, the treadmill was back to working like new!  I've since been running and walking on the treadmill many times and I must say I'm pretty psyched that I didn't have to scrap the treadmill.  This simple fix saved me from having to buy a brand new treadmill, or some expensive parts to fix it.

Here are the steps to tighten up a treadmill motor drive belt in order to fix a treadmill that is constantly slipping when walking or running on it.

1. Turn off and unplug your treadmill from the wall.
2. Take the motor cover off by unscrewing any screws hold ing down (or unlashing).  In my case, I had to flip the treadmill on its side to be able to unscrew the cover.
3. Once the cover is off, look for any shards of black rubber plastic which will indicate that the motor drive belt is slipping or worn down.  If the motor drive belt is completely worn out you may need to get a new belt. (Note: a good place to find replacement parts and belts for your treadmill is at the Treadmill Doctor.)
4. Unloosen the bolts holding down the motor itself.  Either by your self or with the help of someone else, push the loosened motor down and back to tighten the motor drive belt.
5. Now tighten the motor down, making sure that the motor drive belt is tight.
6. Test out the newly tightened motor drive belt.  Plug in the treadmill and start the treadmill up slowly (without anyone on the treadmill itself) at 1 MPH, or 2 MPH and slowly increase the speed until about 6 MPH.  If everything appears to be working correctly, stop the treadmill and start it up again at around 3 MPH, this time you can begin walking on it. Continue testing at higher speeds to make sure the treadmill is working correctly.
7. That's it, hopefully after tightening the motor drive belt your treadmill will no longer be slipping!