Hold Valve 990

The place to discuss all matters relating to David Brown Tractors. You will need to register your user name before you can post. If you have already registered could you please make sure that your location details have been completed. Go to My Account in the Main Menu on the left, and then go into "Edit Your Information" and complete your location details. Give the Country (and State/Province if you wish) if outside the U.K. County if within the U.K. Location details helps other members if you need spares, technical advice, or the nearest practical help.

DISCLAIMER -

David Brown Tractor Club Ltd
Forum/website Disclaimer

1. This [forum/website/chat room] and the advice and opinions expressed herein is not a solution for mechanical, electrical, valuations, other problems, breakdowns or issues experienced in relation to the vehicles referenced.

2. If reliance is thought to be placed on any of the information guidance or input provided such information will be expressly confirmed as appropriate to be relied upon.

3. In the absence of any such confirmation no reliance should be suggested or inferred.

4. Members must not disclose information to 3rd parties in anticipation that reliance will be given by non-members.

5. Non-members must not purport to give advice on behalf of David Brown Tractor Club.

6. If you or someone you know is experiencing difficulties or repeated breakdowns you must seek assistance for an appropriately qualified expert who holds themselves out as such.

7. Any comments are free of charge and made or posted on an ex gratia basis. No member or non-member may advertise their professional services

Any user inactive for more than 3 months will automatically be deactivated, please contact admin@dbtc.co.uk if you would like to be reactivated.

Please be aware that your user name and entered location can be seen by all members. We only store information you have entered which is your email address and username, your IP is also stored, we have no access to private passwords.

If you do not agree with your information being stored, please do not register an account, If you wish to unsubscribe at any time please email admin@dbtc.co.uk giving your username.

Amended 27/10/18

Moderators: Segrie61, admin

Post Reply
dbdgc
Posts: 10
Joined: Mon Jan 28, 2019 1:24 am
Location: New Zealand

Hold Valve 990

Post by dbdgc » Mon Apr 08, 2019 5:38 am

Hi Couple of questions that a few wise men may be able to help me with please.

The Hold valve on my 1966 990a is very stiff when I tried to remove it and after reading a few different posts, some say to polish it with a 1500 grit paper or a brasso paste or similar, others say never use any emery paper on them. So what is the best approach to clean the valve and polish it so it fits freely?


Also the steel ball is missing and the retainer is one large hole instead of the three little holes. I am trying to source new ones of these now. What impact does this have with these missing?

User avatar
cobbadog
Posts: 770
Joined: Tue Oct 11, 2011 6:18 am
Location: beautiful Coopernook NSW. near Taree. NSW. Australia

Re: Hold Valve 990

Post by cobbadog » Mon Apr 08, 2019 5:43 am

I would try the least harmful way first, polish with Brasso or similar. the only thing I can think of by using 1500 wet n dry paper is that you must ensure it is clean of all carborundum grit as that would chew up your seals.
I too have read the posts about the ball bearing and some models seem to have it and others don't. You will have to wait for a definite answer on that. Did it work ok until your issues now? If so it doesn't need the ball bearing to my way of thinking.

User avatar
ollek
Posts: 3969
Joined: Tue Apr 10, 2012 1:20 pm
Location: South West Finland

Re: Hold Valve 990

Post by ollek » Mon Apr 08, 2019 7:34 am

The ball in the hold valve acts as a non return valve for the TCU pressure. All functions except for the control of the TCU pressure will work without the ball. Later 94-series tractors do not have a TCU function and therefor there is no ball in the hold valve on these tractors. The TCU function is used with agricultural implements that have a support wheel, to transfer some of the implement weight to the tractors rear wheels. And one more thing, there is no seals in the valve chest that can be damaged by by the carborundum grit. The grit will score the valve plunger and the boring, making the valve sticking and can also make the gap between the valve plunger and the boring t5oo large. Any excessive grit will end up in the bottom of the gear box, making no harm to the gear box.

philedge
Posts: 271
Joined: Sun Dec 03, 2006 11:27 am
Location: Chester UK

Re: Hold Valve 990

Post by philedge » Mon Apr 08, 2019 7:16 pm

ollek wrote:
Mon Apr 08, 2019 7:34 am
Any excessive grit will end up in the bottom of the gear box, making no harm to the gear box.
Really?? The couple of times ive changed the gearbox oil and cleaned the suction strainer theres been paste of magnetic bits stuck to the magnet. If small steel bits can get sucked through the strainer, then I for one would be absolutely certain that abrasive grit will get sucked up too. Only difference is the steel bits have a chance of getting caught by the magnet whereas the grit will just circulate through the whole gearbox/hydraulics.

Id be meticulous in cleaning out any abrasives used in or anywhere near anything that needs oil or grease to lubricate it.
'66 880 Selectamatic rat.

dbdgc
Posts: 10
Joined: Mon Jan 28, 2019 1:24 am
Location: New Zealand

Re: Hold Valve 990

Post by dbdgc » Mon Apr 08, 2019 9:15 pm

Thanks Ollek and cobbadog, I will try the brasso first then move up to 1550 grit if necessary.

The issue is when I lift my mower it will hold it at full lift with no issues but as I lower it. It will get to about half way then just drop, after that there is no or very weak lift. So I removed the hold valve cleaned and replaced then it lifts and holds, until I lower it and it drops and the issues return.

This is when I noticed that the valve is tight and difficult to remove and refit, also the ball was missing.

I use the tractor for mowing and hay rake, it has a loader as well. What mode do you recommend for these operations? Height control or Depth control.
With the ball missing from the hold valve i will not use TCU then.

dbdgc
Posts: 10
Joined: Mon Jan 28, 2019 1:24 am
Location: New Zealand

Re: Hold Valve 990

Post by dbdgc » Tue Apr 09, 2019 3:27 am

Ok as per my previous post I polished with brasso and cleaned it all up
Replaced the valve and it seems nice and free.
tested the unit by lifting my mower.
It held in the air at full lift.
I start to lower it and it drops to the ground and now no lift with any weight on it. If I switch to the Loader via the 3 way take off valve , the loader doesn't work either.


So dont think this is the cause of my issue after all, any ideas?

User avatar
ollek
Posts: 3969
Joined: Tue Apr 10, 2012 1:20 pm
Location: South West Finland

Re: Hold Valve 990

Post by ollek » Tue Apr 09, 2019 5:42 am

It sounds like you have dirt circulating in the say stem and now the by-pass valve is stuck open or the small restrictor in the valve plunger is blocked with dirt. Change the hydraulic filter, clean the suction screen and change the oil. Then clean the by-pass valve.
Last edited by ollek on Tue Apr 09, 2019 6:51 am, edited 1 time in total.

User avatar
ollek
Posts: 3969
Joined: Tue Apr 10, 2012 1:20 pm
Location: South West Finland

Re: Hold Valve 990

Post by ollek » Tue Apr 09, 2019 6:36 am

Use height control for any implements working above the ground. Use depth control for implements working in the ground an producing a draft force (ploughing). Use TCU/External for loader operation and any other external equipment (trailer tip). Keep the control lever fully back for lift and let the spring return the lever for hold for the loader or the trailer tip. Push the lever half way down in the quadrant for lowering of the loader or the trailer tip. No harm will be made if you try to use the TCU pressure by pushing the lever further to the front, but you can not control the TCU pressure in the lift cylinder if the ball is missing. The TCU pressure starts to build up (if the ball is present in the hold valve) when you push the lever to the front starting from about half ay on the quadrant. The TCU pressure is dependant of the lever position and the full TCU pressure is 50 bar when the lever is fully forward. Please note that the use of the Selectamatic hydraulic system is explained in the Operators Manual, and I do think you would benefit from getting one.

dbdgc
Posts: 10
Joined: Mon Jan 28, 2019 1:24 am
Location: New Zealand

Re: Hold Valve 990

Post by dbdgc » Tue Apr 09, 2019 11:29 pm

Thanks Ollek
Emptied and cleaned the magnet and gauze, this model has no filter, pretty clean as I did this back in February
Cleaned and flushed the valves.

And it lifts strong again. haven't had time to lift and lower the mower yet, try that in a few days.

Did find a few small pieces of clear plastic type material, about the size of a pin head in the Hold Valve port, that wouldn't of helped.

So Far looks good
Might have to do it a few times to flush all the crap out

Also managed to find a new ball and retainer for the hold valve :D

User avatar
ollek
Posts: 3969
Joined: Tue Apr 10, 2012 1:20 pm
Location: South West Finland

Re: Hold Valve 990

Post by ollek » Wed Apr 10, 2019 5:55 am

There should be a by pass filter in a bowl on top of the rear axle on the left hand side. The part number for the filter is K914441. Please see the following link for the correct filter. http://www.davidbrownparts.com/Filtration.html Scroll down and you will find "Hydraulic filtration". Please be aware that there is a lot of filters out on the web sites, that are of dubious quality.

dbdgc
Posts: 10
Joined: Mon Jan 28, 2019 1:24 am
Location: New Zealand

Re: Hold Valve 990

Post by dbdgc » Wed Apr 10, 2019 10:10 pm

Thanks Ollek
Replaced that back in February as well, with a case filter K914441
I have ordered another one and I will change it when it arrives

I replaced all the fluids and filters in Febuary and have been slowly tidying the old girl up.

After years of neglect I think its just going to take a while to flush all the dirt out. I will probaly have to drain oil and clean the filters very regulary.

Post Reply

Who is online

Users browsing this forum: ardiel, DRM, tomryall and 18 guests