David brown 990

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Db990jesse
Posts: 1
Joined: Thu Jan 10, 2019 6:14 pm
Location: The Netherlands

David brown 990

Post by Db990jesse » Thu Jun 20, 2019 3:32 pm

Hello everybody,

I'm new to this forum and also not from the UK so it may be that I'm using the wrong terms to refer to certain parts. I have a 990 which has a problem whith the lift. It will lower in TCU but lowers very very slowly in the other positions. I have cleaned the bypass and hold valves but this doesn't seem to help. I have fitted a shaft for the lowering speed control but after opening this fully it fell in the chest. When fitting the quadrant box again I lost one of the rings fitted between the lever and the spring and between the lever and the nut. After reassembling the box without one of the rings, the lift started lifting after moving the lever a bit and continues lifting untill it can't go any further. I think this is caused by the missing part. Now my questions: which valve causes the problem with the lift? How can I remove the valve chest? And if I remove the valve chest will I be able to reach the shaft? And if i reassamble everything again with both of the rings will the range of the lever be normal again?
Thanks in advance,
Jesse

User avatar
ollek
Posts: 3743
Joined: Tue Apr 10, 2012 1:20 pm
Location: South West Finland

Re: David brown 990

Post by ollek » Fri Jun 21, 2019 5:05 am

All parts must be present and assembled in the correct order and all adjustments must be made correctly for the 3-point hitch to work. First, fit all parts in the correct palace and the perform the group 3 adjustments correctly. The adjustments can be found in the following link https://dbtc.co.uk/index.php/informatio ... lic-system There ere also an explanation about how the Selectamatic system works and some fault finding tips before and after the settings instructions. For lift, you need to have the spool valve fully down, by-pass and hold valves closed and the non return valve open. For hold you lift the spool valve about 1 mm and this will open the by- pass valve and the non return valve will now close. The hold valve is still closed. For lower you lift the spool valve fully up (full movement about 2,5 mm). Both the by-pass valve and the hold valve are now open and the non return valve is closed. The oil from the pump escapes via a open by-pass valve and flows to the transmission lubrication circuit, the oil from the lift cylinder escapes trough a open hold valve and flows to the lowering speed valve and from there back into tank. As you can see, there are many valves used for the different functions and the only valve moved by the operator (hydraulic lever) is the spool valve. Some valves are opening and closing depending on the position of the spool valve and on some on the pressure acting on the valve.

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