Bosch 3725 DEVS Sander backer plate coming loose

[Doug Garson]

Anyone else have this problem? I was using the sander and suddenly the backing pad came loose! I pulled off the sanding disc and the screw was very loose. Took the screw out and examined the back of the pad, the plastic was chewed up. Kinda dumb design as the backing plate has a metal plate with 3 holes and the drive part of the sander has 3 tabs but the tabs don't engage the steel plate as it is covered by plastic. Reassemble it and torqued the screw nice and tight (threads look good) but even with some blue threadlocker the screw came loose in minutes. Also tried another backer with no damage to the plastic, same result. It has been dropped a few times over the years (3ft onto concrete floor) and perhaps it is running a little rougher but not dramatically so.

Any suggestions? It's my go to sander.
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[Joe Hendershott]

I've had that model for several years and it has never happened- so far. I've changed pads a half dozen times as well. It would be quite annoying.

[Ben Grefe]

I have that same model and on mine the backing plate left-hand thread screw completely striped out. I tried buying that piece again, but it’s basically the only part you can’t buy new (I figured at the time they do this to drive sales of new units).

I resorted to drilling this piece out, cutting right hand threads but (to be expected) it keeps unscrewing during operation.

I finally gave up and bought a new Bosch sander. I figured the old one lasted long enough.

[Doug Garson]

That's odd, mine is right hand thread. I'm going to try and clean the threads with acetone and try the threadlocker again unless someone has a better solution.

[Doug Garson]

I think I understand what's going on now. My original observation that it is a poor design was almost true, it is poor quality control. I looked at the original pad which I stopped using because the Velcro wore out and the holes in the metal plate line up with the holes in the plastic so the indents in the driver can engage the holes in the metal plate and not just the plastic. In both the replacement pads the holes don't line up so the indents only engage the plastic so the bolt holding the pad on may bottom out. Both replacement pads, bought in July 2017 are OEM parts or at least came in Bosch packaging and have Bosch imprinted on them. So a warning to anyone buying replacement Bosch OEM pads to make sure the holes line up. I'll let you know how I make out. I contacted Bosch even though the warranty on the pads is over and I'll advise their response, they may have had a bad batch of pads sneak past QA.

[Doug Garson]

I may have spoken too soon. I drilled out the plastic on one of the pads in line with the 3 holes in the metal part. I cleaned out the threads with acetone and blew it out with air. When I installed the pad I noticed the tabs on the driver aren't long enough to engage the metal part of the pad. I applied some blue threadlocker, let it sit 1/2 hour (the instructions for the threadlocker say you can immediately use the tool but I waited just in case) it ran for about a minute before it came loose. Next I added a washer to make sure the bolt wasn't bottomed out again used the threadlocker and, hope I'm not speaking too soon again, ran it for several minutes and checked the bolt, still tight so maybe the problem was the bolt bottoming out all along but why was it OK for over a year (it did come loose once or twice but when I retightened it, it held for months not seconds).