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Case Tractors Discussion Forum

DB 990/1 Hydraulic Issues

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10-20-2013 19:18:04

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First let me say thank you to all of the fine people on this board that have both asked and answered questions that have helped me get this far.

I will try to make this post short but include enough detail to get some help.

I have just acquired a David Brown 990/1 selectamatic Serial number 850726/s.

This tractor has sat for over 10 years and it has been 16 years to the date of the last oil change.

The tractor starts and runs strong but thatís about all that works. None of the lights or gauges work, etc. The clutch and PTO work great but the hydraulics are another story.

The 3 point would not do anything. So I turned to these forms and here is where I have been and where I ended up.

The transmission oil looked much like a mint milk shake. This was of course due to split shift boots. I changed them and drained the oil. When I dropped the sump all of the parts for the relief valve were torn off and left inside the filter. The top metal cap with the o-ring was bent up like it had been bouncing along the side of the road for some time. I repaired the relief valve ( spot welded it back to the lower screen and reassembled it) and replaced the filter. I filled the transmission with SAE 10W-30.

I had no oil on the right side of the tractor so I rebuilt the 3 way valve on the left side of the tractor. It was stuck and would not shift to the ďLĒ position.
I removed the Cessna valve on the right side of the tractor the center hose coming out of the tractor case into the bottom of the valve body was broke off. I did not want to tear apart the PTO, Valve chest etc. to see if I could make it work. So I tapped the end stuck in the tractor and the peace that was in the valve body. Of course I flushed the valve by running the tractor and then changed the oil once again. Then I threaded a Stainless steel bolt into the top piece tacked it in place and faced it in the lathe then drilled a port through it. I then threaded it back into the part still in the tractor and we now have flow of oil to both sides of the tractor. Both remote hoses on the Cessna valve now have about 2,000 psi.

The 3-point still did nothing so I removed the hold valve and removed what was there. I polished the valve with 1500 grit sandpaper and cleaned everything there was not a 1/8 ball in the bottom bellow the little plate with the 3 holes in it. I put it all back together including a new ball.

I removed the By-Pass valve and it was missing the Orifice plate so I trimmed down a stainless steel shaft drilled a .020Ē hole in it cut off a small slice of it to make a new orifice reducer. I made a new ball retainer for the top and dropped in a new 1/8-inch ball on top. Polished the valve body and reassembled it.

Now the 3-point only works in TCU and functions what I thought was backwards. I.E you move the quadrant forward and it lifts move it back and the arms drop if you have 100 lbs plus on them.

I adjusted the connecting rod nut under the slower/faster cover. I looked under the right rockshaft cover everything in there looks to be moving correctly as you cycle through each setting. The cam appears to drop in the indent when the arms are all the way up.

At this point I removed the by-pass valve and looked at the top of the spool valve. If I place a rod on top of the stud and smack it, it definitely springs down, I cannot push it down by hand and it does not move up and down when the quadrant moves in any position. If I place a socket around the stud I can push what ever I am contacting up and down an 1/8 inch or so but it doesnít move with the quadrant either.

So this is where I am at now. I am very hopeful someone here can point me in the right direction.

I thank you in advance for any advise you can give.

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10-28-2013 20:24:14

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 Re: DB 990/1 Hydraulic Issues in reply to fillco, 10-20-2013 19:18:04  
Once Again Thank You for your reply with out the help of the two forums I would not have a chance in making this old tractor work again. I really donít want to see it end up in the scrap yard.

If you do get a chance to get me a photo and dimensions of that plug I would be forever grateful.

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10-26-2013 14:23:18

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 Re: DB 990/1 Hydraulic Issues in reply to fillco, 10-20-2013 19:18:04  
You got some good advise on the DB forum. It might act erratically if there is some air in it. Not hard to bleed, would seem like the logical first step.

I have box that I collect selectamatic valves/parts in, but there are some pallets in the way of getting to them, and my tractor with forks is getting the transmission overhauled at the moment... If I get the crops harvested and the 1494 back together I will get back to you with a picture and dimensions.

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10-25-2013 07:10:13

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 Re: DB 990/1 Hydraulic Issues in reply to fillco, 10-20-2013 19:18:04  
Once again thank you for the reply.

I finally bit the bullet and removed the Valve chest.

Everything went well except I had some trouble separating the Valve chest from the rockshaft housing.

I reassembled everything and of course now I have more questions.

The 3-Point now works in all three settings. However the RPMís have to be fairly high (it wont lift at all in idle) It seamed to work great until I hooked up the lower arms and then it slowed down, it will not lift much weight at all.

I did not bleed the system if that matters.

One other thing I noticed. The plug under the by-pass valve that is held in with a C-clip, has some damage. The bottom of it is flat as it should be. The top of the plug has a mushroomed bunch of steel on it; from pounding on it I would guess (I used a small deep well socket to pound it out so I donít think I did it). In photos I noticed that this plug had a stem coming out of it that looked like the top of a screw head. If this is something that could affect the tractor I will change it. Do you have a drawing with the dimensions of this plug? Or one you could measure for me? If so I could make one real quick.

Thank you in advance for your advise.

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10-21-2013 19:25:48

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 Re: DB 990/1 Hydraulic Issues in reply to fillco, 10-20-2013 19:18:04  

Thank you for your reply.

The Valve chest has to come out. This is not something I look forward to.
Is this as difficult as it sounds in the manual? I guess I am worried that I may have trouble reassembling the valve chest or the mechanical linkage. If I bite the bullet and tear down the tractor to remove the valve chest is this something that is a one-time deal? I mean is this something that has to be done regularly or something that if you miss an adjustment you have to remove it tweak it some and reassemble again?
Once you remove the control lever housing can you access both the hydraulic supply line going to the valve chest and the line going to the 3-point ram?

Thanks again for your advice.

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10-22-2013 04:00:29

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 Re: DB 990/1 Hydraulic Issues in reply to fillco, 10-21-2013 19:25:48  
Quoting Removed, click Modern View to see

Not difficult, just lots of steps that need done in order. The control linkage will only go together one way(getting all the adjustments right can take some time). Figure on spending a whole day to get it out and back in your first time.
Aside from the spool valve all the adjustments are done with the valve in the chassis.
Removing the control lever housing will give you access to both the high pressure lines(2 bolts on an O-ringed flange). The lube line is clamped to the side of the valve by a bolt which screws in from the wheel side, kinda a weird set up, but it works.

Once you get everything cleaned and working, you should never have to touch it again, so long as you keep the oil clean, and a filter in place. I have brought many of these back to life that have sat for a long time, stuck valves in the selectamatic valve was a common issue to nearly all of them.

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10-21-2013 04:15:30

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 Re: DB 990/1 Hydraulic Issues in reply to fillco, 10-20-2013 19:18:04  
Sounds like a plugged passage in the valve body, most likely associated with the spool valve since you have cleaned the other important ones to lift working. The valve has to come out to clean it properly. You might find something else stuck as well. Lots of little valves that don't like dirty oil or sitting for years.

There is a number scribed on the bottom of the spool valve, make sure when reinstalling it to set the movement of the spool valve within .001" of this number.

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