There has been a lot of people mailing me about F55s (and F55 - slower lower geared version of the same chair) concerning the "clunking noise" that the gearboxes produce when turning left/right/left as the free play in the motor & gearbox is slammed back and forth. Most peoples start doing this a little as the gears and bearings become "run in" or "bedded in" during the first two weeks use or so. But this is normal and slight.

This should be how things stay but after around 2 months (in my extreme case - I really hammer mine!) or more typically 6 to 8 months the clunking and level of free play and backlash in the system seems to start to get worse. The wear/damage/noise/fault actually can be one of three things. Or all of them if you are unlucky!  I have had them all! But my chair is "tuned" and has a bigger power control unit etc, and I wheelie & bang up and down kerbs etc. all the time so its expected in my case...

But it seems to happen to all the chairs judging by the people I speak to.

There are three causes...

1. The wheel or shaft keyway becomes worn - new complete gearbox/motor assembly needed. EMD who make these offer NO replacement parts! So there is little choice. You may need wheels, keys, and motor assemblies! Also make sure the shaft that the wheel fits on is greased with copper grease or similar as a few months later after getting wet you will possible NEVER remove it if not. Be warned...

2. The rubber "cush drive" becomes worn, this is the USUAL fault after a few months. These too are really simple to replace, but as usual you cannot buy parts! Good job a rubber Hoover belt cut into four short pieces fits perfectly then!

3. Thrust bearings, bearings, shims in the gearbox become worn. I abuse mine and these bits are all as good as new so this is very unlikely. The gears themselves don't seem to wear at all. Bearings, shims etc are easy to replace anyway..

  First thing to check for and the easiest, is the wheel where it fits onto the shaft. It uses (incorrectly! Ask any engineer!) a square "dowel" or key to transfer power from shaft to wheel. This can and does become worn, and the wheel retaining bolt does nothing to help here. Although tightening it up really tight "disguises the sound, so it can make it quiet for a while.

   A picture of a stock new motor/gearbox from sunrise medical waiting to be fitted. They are handed (left and right! And come in two "speeds" - one slow for F55 and one fast for F55s - The difference is simply the gear ratio. Then I can repair and rebuild the old ones! So they will be faster yet, (due to some rewinding with less turns, and some taller phosphor bronze gearing from Rebel Replicas*)

  Another picture... These gearboxes use a large nylon gear for quietness, driven by a single worm gear on the motor shaft input. They are actually riveted together so these need drilling out and replacing with normal nuts/bolts if taken apart.

  Unscrewing motor to gearbox bolts. Easy, and no mess. This seperates the motor and gearbox. This is how you get to the rubber cush drive.

  Separated with the (new in this case) rubber cush or "shock absorber". This rubber bit is what drives your chair! It removes shock, vibration from the driveline making the chair smoother and quieter. Shame its crap then...

  The rubber bit put back into the motor side... You can use four bits of round Hoover (OK vacuum cleaner then!) If yours are ruined...

  Gearbox with rubber cush removed.

  Close up of the part that fails and causes all the clunking... The middle bit is only needed to hold everything in place when you put it back together.

Only the four round bits do anything. So any four bits of rubber that are the same size work ok. (Vacuum cleaner belt... and a sharp hobby knife)

Mine has four harder "nylon" based material (unknown name) now. So they don't fail any longer.

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