MP 40 vs. 3/4 glass

DmitryB

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So I bought an MP 40 from a user here and just tried installing it in my tank to start mixing water right in there (tank is bare) - and the MP 40 is not staying attached to the glass. This is IM 170, the glass is 19mm. This is supposed to work, right? I am not using any spacers. Any ideas what's up? I did a search and it seems to be some people have had this issue historically, but never clear what the solution was besides not using MP 40. 😕 🤷‍♂️ 😭
 
How old is it? Have you disassembled it to clean the gunk from the wetside magnet if its used? Have you regreased it? Does it attach together on the glass fine without the pump running? Does it just fall off once running?
 
The pumps were I guess a year or two old. There were actually two wet sides, one was totally clean so possibly unused. I can't get them to hold with the pumps off, so never even turned them on to try. The dry side just slides right down.

Painter19820, I wasn't using any spacers on it at all.
 
I have 2 mp40s on my wb 290, they hold, but barely. Almost any bump can knock them off. They are right on the edge for compatibility imo.
 
4 on 19mm glass here. They have to be aligned perfectly. Sometimes I'll hold the dry side and have my Gal power it on in case I need to align it a bit. Make sure there a rubber pad on the dry side. I've had them come off and the side will not attach.
 
Here are the backs of the dry and wet side. Anything missing?

20260721_154832_35E77F65-DE36-468E-B00F-AECB35A8ACDF.png
 
The rubber is missing from the dry side. It may be on one of the spacers. I don't want to take mine off but you can see how thin the rubber piece if you zoom in.
PXL_20260721_195001087.jpg


EDIT:The honey comb pattern on the wet side is different than any of mine. Maybe it's sometime newer ones come with.
 
The rubber is missing from the dry side. It may be on one of the spacers. I don't want to take mine off but you can see how thin the rubber piece if you zoom in.
PXL_20260721_195001087.jpg


EDIT:The honey comb pattern on the wet side is different than any of mine. Maybe it's sometime newer ones come with.
Huh interesting. There were no extra parts with the package I got. Just two spacers, two wet sides, one dry side. I hope they sell those rubbers!

The honey comb pattern matches the inside of the spacers, so I think it may just be imprinted from the spacers.
 
Here are the backs of the dry and wet side. Anything missing?

20260721_154832_35E77F65-DE36-468E-B00F-AECB35A8ACDF.png
The thin rubber spacer on the dry side missing. Not sure what’s on the wet side. That’s usually smooth spongy stuff. You do have to mount the dry side with the cord going up and use the cord holder zip tie to keep weight of dry side up.
 
I just used the thinnest spacer on the dry side and it is staying up. So that was the problem. Probably don't want to use the spacer in the long run though, will have to get a replacement part for the dry side. Thanks all!
 

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