Hello Folks. I'm trying to get some new ideas on how to replace that felt/fiber friction washer that places a drag on the take-up reel. I do not favor this type of clutch vs. the magnetic ones on some of the other Sony's. I had purchased a WM-150 that I started working on. I'm waiting on a replacement gear from China at the moment (no one else sells them) and trying to figure out how to remedy the slipping clutch. I initially cleaned the felt washer with 99% isopropyl alcohol and then took a tiny pick to sort of lift the nap. I did replace a cracked clutch gear and slightly stretched the metal spring. All this did absolutely nothing, the clutch still slips too easily, that felt washer is pretty much shot. How are you folks making this repair? Seems no one is selling this need material, essentially a 0.5mm non-woven compressed felt sheet. Cheers. -Norm
What's the symptom, very low takeup torque ? Note the reel gears are also failing in WM-150-type mechanisms and need to be glued or replaced. How have you figured out the clutch felt pad is the problem ? It's not something I've seen on this mechanism and restored many of them. An alternative solution is to remove the felt entirely (assuming it is indeed the problem) and put very high viscosity grease there instead. However this is a compromise solutiuon because the takeup torque will become highly dependent on temperature. Quantity of grease also has to be fine tuned to obtain the correct torque. You say extending the spring did absolutely nothing and clutch slips too easily. When rotating the 2 parts by hand, is there any resistance at all ?
Hi Valentin. Thank you for your reply. The symptom is very low take-up torque, not enough to pull the tape causing it to wrap around the capstan. The forward reel gear was indeed cracked, a replacement is on the way. The reverse reel gear is in tact and the tape did try to play in REV play mode but at some point the take-up reel begins to slip too much causing the tape to wind around the capstan. I'm guessing at this point, the felt pad and perhaps the plastic clutch disc has compressed and/or glazed too much? I will try to take a 3000 grit sponge to ever-so-lightly rough the plastic disc. I've read that someone tried applying rosin [the kind that you put on violin strings] to increase the friction but an AI search recommended against it. When rotating the two parts by hand, there is little friction. One small caveat, and I should have mentioned it earlier, the clutch spring was from a Panasonic RQ-SX70F. The WM-150 was bought as a parts unit and didn't have a spring. The Panasonic spring was the same size and fit right in. I just don't know if the gauge of the springs are the same. I may also try to make a new spring from a guitar B-string to increase the friction. Cheers!
The clue with the spring is important. I wouldn't focus on the felt pad or plastic disc surface, don't think the problem is there. The stiffness of the actual spring is by far the biggest factor determining friction in the clutch assembly. The friction coefficient of that surafce cannot be modified significantly by sanding it to make the surface rough or by adding rosin. The headroom is little, you can't increase it 5x by doing this. Rather what I think happens is the spring is simply too light and even elongated it just doesn't apply enough pressure. RQ-SX spring is much lighter, as the clutch itself spins much faster. This is another variable: stiffness of the clutch and clutch speed are inverse proportional. To increase the takeup torque one can either add more clamping force (stiffer spring) or make the assembly rotate faster by changing gear ratios. I think only fix is to either find the correct spring or make one with correct wire diameter (which is thicker than the RQ-SX one).
Thank you, Valentin, for pointing me in the correct direction. I will focus on the spring. I will attempt to remanufacture from a guitar high E or B string. I have successfully made one in the past for another parts unit that was missing one. I got lazy this time and grabbed an available RQ-SX spring that I had laying around, clearly not a good choice. Cheers. -Norm
Let us know how it goes. This clutch should have some resistance when rotated by hand, that should be the target. Like not hard to turn, but a fair amount of resistance.
