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990 tranny rear end/axle vent Location


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#1 1oldbuzz OFFLINE  

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Posted April 08, 2015 - 03:56 AM

Need a little help

MTD 990 rear axle/tranny vent location

where is the vent on these units

I can't seem to find one

is there one

Since I have the tractor torn down

I want to be sure the vent is clear/clean and doing

what its supposed to do before reassembly

Thanks


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#2 Cat385B ONLINE  

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Posted April 08, 2015 - 04:45 AM

If it does have one, which most don't, it will be through the head of the dipstick.



#3 JDBrian OFFLINE  

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Posted April 08, 2015 - 10:25 AM

I think all hydrostatic drives need to have a vent somewhere. If not, heat causes pressure to build up inside the case. This eventually causes seals to leak. I had this happen on a JD314. Someone had replaced the fuel filter/vent with a standard filter that didn't have a vent hole. The axle seals were leaking and the fluid shot out the fill hole about 6" when I opened it. I think many have the vent built into the fill port or at some other point high on the hydro unit where there is little fluid to make it's way out. I think the service manual is in the manuals section and could give you the info. you need. 


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#4 Canawler OFFLINE  

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Posted April 08, 2015 - 10:57 AM

The service manuals show no vent on these and they definitely could use one as they build up quite a bit of pressure when the fluid heats up.  I know I've made a mess when checking the level when it's warm. :smilewink:   I don't know if anyone makes a dipstick/vent combo but that would be the ideal setup. 


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#5 Sawdust OFFLINE  

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Posted April 08, 2015 - 12:25 PM

I've wondered about this myself since I have the version that just has the threaded fill plug. I know the other version has a dip stick tube in the same hole but does it screw in or pressed in. This would be a good conversion if it just screws in. Cutting a hole in the edge of the frame & a hole in the tool box wouldn't be a problem.  :tapping_fingers:



#6 1oldbuzz OFFLINE  

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Posted April 08, 2015 - 02:54 PM

I did look in the manuals this morning
Dead end for a vent.
However it did show to fill to a plug located lower down
on the back side.
Now the fill plug has a dip stick that does not reach down
that far,so why have the dip stick?
I will be reinventing the wheel to come up with a vent.
Even automatic transmissions in vehicles have a vent.

Thanks for the replies

#7 JDBrian OFFLINE  

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Posted April 10, 2015 - 10:08 AM

The way the vent works on the JD314/317 is that there is a port on the bottom of the fill tube where a piece of transparent plastic tubing (Tygon) is attached. This acts as a fluid level indicator. This is routed horizontally in front of a viewing slot in the frame back plate. The tubing goes up over the rear end to a conventional plastic gasoline fuel filter. That has a 1/16" hole drilled in the outside casing as a vent. It doesn't take much of a hole to do the job. The filter traps any mist that may be in the oil and the other end of it goes to a port on top of the rear end. I guess the idea is that any fluid building up in the filter would drain back into the base. You can get vent/filter/caps for hydraulic tanks like those used to make wood splitters. You may be able to adapt something like that to work. 






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