Hallo,my treadmill is jerking on slow speed and I feel vibration on high speed and it stops after some time ,what could be the problem,I have installed new deck belt and bearings

Warped brake rotor usually cause high vibration at high speeds. But you can also feel it at lower speeds. But bad ball joints and tie rod end will cause vibration at high speeds. Ball joints will pop at pot holes, sometimes. Tie rods can be felt in the steering wheel at a stop. Move the wheel slightly to the left and right, you can feel/hear a tap as you turn it.

You probably have a wheel balancing problem. You hit a curb one time or another, or your spokes (if you have any) aren't adjusted equally.
The rule of thumb is the faster one goes the vibration multiplies. Hence you can't feel the same vibration at slow speeds. Also listen your engine, your engine mounts could be shot or too loose, it expounds engine vibration the faster the engine runs, and you feel it in your overall driving. Check to see if everything is tight, the fork, the shocks, the brakes. I wish I'd still my bike, it was beautiful, but got broadsided by a car. Glad I wore my helmet at the time.

tes the speed sensor. RUN the software calibration for troubleshooting and fix it. God bless you
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The Steps for Newer Style Console Calibration

1. Locate the calibration area on the rear or underside of the console (a hole, near the console's center, that goes through to the electronics board. (This hole should not have a screw in it.)
   

2. Insert a pencil (eraser end), into the hole and feel around for the cal button (will click when pressed).
   

3. Press the button 2 times (with the pencil eraser). The first click should show CL11 in the console, the second click should show CL21.
   

4. If the process was done correctly, and CL21 appears in the console, you are in "calibration mode." The next few steps consists of pressing buttons on the console and observing settings. This will not require any other tools.
   

5. Press ENTER. CL22 should display in the TIME window and (??) in the SPEED window.
   

6. Press ENTER. CL23 should display in the TIME window and (??) in the SPEED window.
   

7. Press ENTER. CL24 should display in the TIME window and (??) in the SPEED window.
   

8. Press ENTER. CL25 should display in the TIME window and (??) in the SPEED window.
   

9. Press ENTER. CL26 should display in the TIME window. You should then see the letter "E."
   

10. Press ENTER. You should see "SS" or "55" in the console.
    

11. Push the STOP/START button. For safety, at this point, you should step off, or be off, the treadmill.
    

12. Push the ENTER button. The walking belt should start to move, accelerate to maximum speed, then stop on its own.
    

13. When the belt stops, the incline should self test by raising to its highest incline position, then lowering back down to its lowest position.
    

14. Once the incline test is complete, push the POWER button 2 times. The unit should shut off and the console should go completely blank. If this happens, the treadmill is done calibrating and is ready for use.
    

15. If the letter "F" appears in the SPEED or INCLINE window when the power button is pressed 2 times, the treadmill is indicating a failure somewhere either in the SPEED or INCLINE (depending on the window the "F" appeared in). Troubleshooting the failure would be the next step.
    

Sounds like a transmission problem.

could be tires need balancing or front end alinement

Check / replace the high tension leads.
I had a problem with hessitation / jerking also at very slow speed in stop start traffice. I was the EGR ( exhaust gas recirculation )valve. Car is now like new.

When running or walking on my Ironman Triad Treadmill it jerks like it is going to stop every once in a while not all the time. Do you have any idea what makes it do this. I have had this Treadmill for 5 years and never had a problem before.

Have you changed the trasmission fluid and filter in your jeep lately, if not do so and that just might stop the jerking in your jeep, and if that does not do the trick you will need to have your trasmission checked out by a trasmission shop.

Check both belts to be sure they are adjusted and not slipping.Check the underside of the walk belt to see if it feels frayed in the center as compared to the edges, the center always wears more than the edges a really worn belt must be replaced. if it is nor worn there is a wax lubricant for proform treadmills that can be purchased at retail stores that sell treadmills.Sears, dicks sporting goods and also treadmilldoctor.com are good places to buy it.

Check the drive belt. It probably has chunks missing or at least has flat spots (narrow spots) that cause the belt to jump every time it goes around a pulley. That will set up a heck of a vibration. Also check the pulleys for free movement. The drive belt is above the blade drive belt....