Pedals wobble and click under load

Question

I've been maintaining my own bike for a while now, the one thing I haven't been able to fix is the pedals wobbling. This is a little hard to describe but hopefully it's understandable, and I've attached some pictures. The pedals wobble perpendicular to the crank arm, i.e. they move vertically. When I am riding, I hear a clicking noise especially when I'm pedalling hard, which I think is the pedal wobbling in the same way, but under more load. I've done a lot of googling and all I've found is either steps on removing the pedal (which I don't think is the issue as it seems tightly attached to the crank arm) or steps on fixing the crank arm itself, which I also don't think is the problem. Again having said all that, I'm very much new to this, so any corrections or advice would be massively appreciated. I did have a mechanic address this problem about a year ago, he mentioned it was difficult to adjust my pedals specifically but he was able to fix it, although I didn't ask him at the time exactly what he did. My concern is that if I don't fix this, it may cause damage elsewhere and lead to more expensive replacements.

The bike is a Trek FX 7.4, I haven't replaced any of the pedal or crank components but I also am not sure specifically what model the pedals are, although I can probably try to dig this up if it's helpful!

Answer 1

Examine the pedal and crank arm.

(Note that the above diagram is not exactly like your pedal, but the basic construction is the same.)

Note that there is a shaft that runs inside the pedal, from crank arm to the end of the pedal. The pedal bearings (inside the central housing of the pedal) ride on the pedal shaft. Likely the bearings have gotten loose and the pedal is rattling around on the shaft. If this is the case you should go ahead and replace the pedals.

But carefully examine the shaft as you move the pedal up and down. Where the shaft mates with the crank arm you will be able to see 10-15mm of the shaft, and you should not see ANY motion between this shaft and the crank arm. If you see any motion there (while you move the pedal up and down) it means that the pedal is unscrewing from the crank arm and the crank arm will be very quickly damaged (if it isn't already).

Further, grasp the crank arm and move it in and out, checking for any flex between the arm and the crank shaft inside the bottom-bracket. Any motion here must be corrected immediately (tighten the crank nut) or the crank arm and possibly crank shaft will be damaged.

Answer 2

Is the pedal spindle moving in the crank arm? If so stop using the bike immediately. Loose steel pedal spindles wallow out the threads in softer aluminum cranks. Sometimes this can be fixed with a helicoil in the crank but often it's a ruined crank.

As you say the pedal clicks it's more likely that the pedal bearings are destroyed. If the pedal body is moving on the spindle this is the case. As Carel said in a comment unless you have high end pedals with serviceable or replaceable bearings just get new pedals.

Many pedals have a 6mm hex head in the end of the spindle for easier installation.