I've got a B&D CMM 1200 (2009) cordless electric mower. This season it has developed a low rumbling noise, clearly some sort of vibration that is amplified by the whole mower body. It comes and goes, unpredictably, sometimes affected by moving/turning/tilting the mower and other times just coming and going even as the mower is held still over concrete driveway. I opened it up and ran it with the body top removed; no difference. I didn't find anything loose (I had replaced the battery myself so I was concerned that soemthing may have gotten loose) but lightly tightened the three bolts holding the motor housing on to the mower body; no difference. Running it again it looked to me as though the motor shaft seemed to wobble/oscillate slightly and even spark a tiny bit and that seemed to coincide with the noise, but it also looks like the brushes or whatever they are called seemed designed to have a little give so I don't know if some wobble is normal. I've had the mower for five years, and have had almost no problems. Last year the mower's performance suffered and it seemed a little noisier but the B&D service guys said that was due to an improperly balanced/sharpened blade; balancing the blade fixed the problem. This is a different noise that comes and goes. Anyone know/suspect what is going on?
rumbling noise in Black & Decker CMM 1200 cordless mower
- Thread starter jad11050
- Start date
When the blade became out of balance, it may have placed an uneven wear on the motor. If that's what happened you may need to have it repaired by a qualified technician. As for the brushes having some "give", that's normal as they are held against the armature of the motor by spring tension. There should be a "fan" underneath the deck. Check to make sure none of the fins on it have broken off. If some have broken, this could be the source of the vibration. Replace if necessary.There is also a blade "insulator" and a bushing (which looks like a metal plate), which will wear down over time. Make sure both are in good shape. The "bushing" usually doesn't wear down, but it can.
Thanks for your insight. The bushing and insulator looked fine when I replaced the blade. I guess I was wondering if it makes sense that the spring tension of the brushes could be the problem; could they wear out, get loose somehow? In other words, since the wobble seems to coincide with the noise, does that mean it is wobbling too much / more than normal, or is something else wrong and an otherwise normal wobble is bumping into whatever else is wrong?
I'm not sure I understand where this fan is. "Underneath the deck" suggests to me access from below where the blade is, but that doesn't seem right. Any help?
I'm not sure I understand where this fan is. "Underneath the deck" suggests to me access from below where the blade is, but that doesn't seem right. Any help?
The "fan" (at least that's the name I know it by 
), is located under the deck, but above the blade. The blade actually fastens up against the bottom of the fan. (I'm not always that great at explaining things, so here is a Youtube link that may help. https://www.youtube.com/watch?v=fSYyU-_UNUQ )
As for the brushes being held against the armature via spring tension (compression), that is done so the magnets will maintain a constant amount of pressure to ensure good contact against the armature, as they will eventually wear down over time.
), is located under the deck, but above the blade. The blade actually fastens up against the bottom of the fan. (I'm not always that great at explaining things, so here is a Youtube link that may help. https://www.youtube.com/watch?v=fSYyU-_UNUQ ) As for the brushes being held against the armature via spring tension (compression), that is done so the magnets will maintain a constant amount of pressure to ensure good contact against the armature, as they will eventually wear down over time.
Thanks. The video is great, and my first thought was, "wow, how did I never notice the fan before? It looks like an obvious culprit and an easy fix." However, I went to look at my mower and I discovered why I'd never noticed the fan - it doesn't have one. Maybe that is on an earlier 1200 (mine is type 2 from 2009 I think) or on the CMM 1000? Someone else suggested that the ball bearings can get worn/dented, but replacing them sounds like something easy to screw up. Alas, I think I'm going to have to take it to a service center.
The one we used to have didn't have a fan on it either. Evidently this was added some time after the one you have was built. I wasn't sure when they added them, and after reading your post this sounded like it may have been the problem. One other thing you may want to do is, with the motor unplugged, slowly turn the blade and gently move it back and forth as you turn it. (I;e Try to move it back and forth, turn it about an 1/8th of a turn, and repeat.) Do this until you have turned the blade at least one complete turn. Watch for any "play" in the shaft. If it moves back and forth, it will need some bearings. If it is bearings, it may be cheaper to replace the motor. Even though bearings are relatively inexpensive, labor sure isn't. You also may want to remove the housing and check for any debris that may have managed to find it's way inside.