990 selectamatic hydraulic oil filter

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Posts: 29
Joined: Sun Jul 15, 2018 12:47 pm
Location: Louisiana, USA

Re: 990 selectamatic hydraulic oil filter

Post by gwatts » Mon Nov 26, 2018 1:31 pm

Thanks for the input. The reason I believe that the plate that I replaced part number K920521with causes flow restrictions is because I have a 1210 and a 990 that I did this to and both have terribly slow hydraulics. My theory is the 'valve" is a check valve allowing unrestricted flow when high demand is required. When no demand is present the valve closes and forces all circulating fluid to be filtered. It was taking 12 seconds to move a 3 inch hydraulic ram 5 inches. After removing the filter it took 2.5 seconds for the same travel. Granted the old filter was more than dirty. I did test the system and found 2000 psi.

Clearly, you know this system better than I. Am I wrong about the check valve? Is my solid plate an acceptable replacement?

Btw, Thanks for all the posts on the Chest valve, I was able to rebuild mine and get it functioning again.

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Re: 990 selectamatic hydraulic oil filter

Post by ollek » Mon Nov 26, 2018 1:49 pm

The valve below the paper filter opens up when the paper filter is blocked. This allows oil to get to the pump trough the gauge. At this stage the filter light in the dash board will light up, telling that you have to change the paper filter. If you have fitted a plate in stead of the gauge, then the pump will not get any (or very little) oil when the paper filter is blocked. The oil will go trough the paper filter OR trough the gauge. The later only if the paper filter is blocked and no oil will go trough the gauge if the paper filter is OK. There is nothing that opens or closes based on demand, the pump needs a amount of oil that is based on the pump speed and nothing else. Are you sure that both the O-ring on the filter neck and the O-ring between the pump and the inlet channel are in place and not damaged. Faulty O-rings on the suction side of the pump will let air into the system.

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Re: 990 selectamatic hydraulic oil filter

Post by gwatts » Mon Nov 26, 2018 2:04 pm

Thanks for clearing that up for me. These tractors belonged to an old rice farmer that was real casual about maintenance!

I replaced the hydraulic pump last year and installed new o rings at that time. Given the drastic performance increase I noted after removing the old filter I believe that is where all the issues lie.


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Location: Chester UK

Re: 990 selectamatic hydraulic oil filter

Post by philedge » Mon Nov 26, 2018 2:43 pm

The 880 manual supplement I have says the paper filter was introduced from serial num 543157 so thats 13000ish 880's running on gauze and a magnet filtration! I guess theres a similar number of 780/990's so its no wonder hydraulic problems regularly pop up.
'66 880 Selectamatic rat.

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Re: 990 selectamatic hydraulic oil filter

Post by db2d » Mon Nov 26, 2018 5:56 pm

Try davidbrownparts.com They probably have the filter you require

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