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Discussion Starter · #1 ·
My fisher MM1, when raised all the way, left and right is slow and jerky. It becomes “normal” after cycling left and right fully twice or so, but if it sits for a minute it’s back to stuttering and jerking.

This is only an issue when fully raised. Lower it a bit and it’s fine.

My first thought was low fluid. But I cycled it up/down/left/right, float, push down cylinder all the way, and add fluid. Did that probably 5 times, adding a little fluid each time with a turkey baster. Did that to the point when fluid would come out of the fill hole when unscrewing the plug after cycling. (Air in the system, or normal system pressure?)

I pulled and greased all the pins on the rams and pivot points.

It’s not a big deal to NOT raise the plow all the way to move it left/right, but if this is a symptom of something else I’d like to nip it in the bud.
 

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That sounds like either air in the system or aerated fluid. It could be that the filter is partially clogged as well. Short of doing a pressure test, which I'd advise, but folks rarely have the cabilibility or desire to do it; I would break it down, give it a full flush and clean/replace the filter, seal & oring on the bottom of the base, replace with new fluid and give it a whirl. You may need to purge the system afterwards, do so in short durations, and by the instructions (ask if you need them) to prevent airorating the fluid (again). It may not be a big deal, or inconvenience for you right now, but this will lead to premature failure of your pump ($300+).
 

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Discussion Starter · #5 ·
Yeah, I likely don’t have the means to pressure test.

My method of changing the fluid is this:
Move the blade all the way to the right, drop it in float and push down the lift ram. Drain fluid from the res. Disconnect the angle hoses at the pump put the right hose in a bucket of fluid and the left in an empty bucket. Move the plow manually to the left, pushing the fluid out of that cylinder and sucking fresh fluid into the right cylinder. Swap the buckets and push the blade the other way. Usually I’ll run through that twice. Probably overkill but whatever. Reconnect the hoses, refill the reservoir, and cycle the plow up/down/left/right a few times. Top off the res as needed. Repeat.


What are the instructions for purging?
 

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About the same, you have any bubbles coming out the level plug still?

When's the last time you looked inside the rez?
 

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Discussion Starter · #7 ·
Been a while since I peeked inside. If I can get the oring tomorrow I’ll give everything a good cleaning. Calling for snow on Tuesday. Finally

The last time I cracked the fill plug fluid came out but it was a little bubbly.
 

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Bubbles = air and aeration
 

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View attachment 190166 What should be replaced, this gasket and seal?
The gasket for sure. The filter could be cleaned, depending on how bad it is, I myself just replace them, cheap enough. The o-ring on the under side of the pump itself should be inspected, if it's lost it shape at all, or is cut, nicked or otherwise compromised, just replace it.

White Light Font Handwriting Line
 

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Discussion Starter · #11 ·
Thanks a lot guys, worked like a charm.

The only issue I had was getting a new o-ring. RepoMan, the one you circled they told me doesn't exist, and when I opened it up all I saw in that spot was an indentation that the shaft sits in.

The upper seal that I circled, they don't sell separately anymore. You can only get that if you buy a new lower motor flange (don't know what that's called.)

But everything works great now. Quick and smooth, just like it should be.
 

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Sweet, glad she's up and running!

That's the shaft seal that you circled.

That bottom o-ring may have only been on the old style pumps ("cast version"), most of the SEHP's had them, but you could replace them with the new style....it's been so long since I've worked on them to recall, but here is a picture of what it's supposed to look like.

Finger Auto part Engineering Machine Gas
 

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Discussion Starter · #13 ·
Ahh, I see. The bottom of mine didn’t look like that, but it also looked like I could’ve split the pump. Two bolts held the pump to the housing, then there were three more that looked like they held two halves of the pump together. I didn’t crack that open.
 

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Ahh, I see. The bottom of mine didn't look like that, but it also looked like I could've split the pump. Two bolts held the pump to the housing, then there were three more that looked like they held two halves of the pump together. I didn't crack that open.
Ah'yup, that's the new style, still used today in fact.
 
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