David Brown 880 Selectamatic hydraulic issue

[dgs]

Hi I have a David Brown 880 Selectamatic tractor 66/67 model.
The 3 point linkage (hydraulics) will not lift if the tractor is pointing downhill, even on the slightest slope. It’s fine if tractor is uphill or on level ground. Both filters are new and oil level is correct. If I raise the 3 point linkage on level ground and then back the tractor slightly up an incline or drive it downhill, so tractor is pointing downhill. While on that incline I can lower the 3 point linkage but it will not raise again while on the downhill. It does not appear to be starving of oil, because it makes no noise. I have tried overfilling about 3 litres and it made no difference. If I have to dismantle it, I would first like to have some idea what I should be looking for. Has anyone experienced this issue and or have some constructive input on this? Cheers DGS

[essexpete]

How does the pump suction work on the little DB?

[Jeremy Rowland]

Hi David and welcome some problem you have there, I can make a few suggestions, think I would measure the hydraulic oil pressure first to give some idea if there could be a sticking valve of worn pump or other restriction, as Pete says it could be the suction pump or even a hydraulic hose that is collapsing on the inside? Very odd that it does this on a slope and not at any other time, is it worse when the machine is hot?

Jeremy

[dgs]

Thanks Jeremy... It's the same hot or cold and as said, it's only on a down hill slope.
I haven't yet checked the pressure and because all else works so well I would imagine it's ok. Plus I don't have a pressure gauge, though correct, it could be worthwhile to eliminate the pump and values.
However, thinking about it nothing's different or changes other than the slope which makes me think that perhaps it could well be an oil line issue (split or crack) that only becomes exposed on the downhill. Have you ever heard of an issue like this? I think all the lines are hard fixed internally. Cheers David

[essexpete]

I have asked on the farming forum for you.
https://thefarmingforum.co.uk/index.php ... ic.338094/
Seems odd when you have the oil levels up. It seems to me that air must be being drawn into the system quite high up with in the back end to come out of the oil. The other thing, and I have absolutely no idea, is there a one way non return valve in the suction line that would prevent loss of prime in the pump when not being used? Just thinking that it might, if not working, be causing a problem when the nrv is out of the oil level. Presumably the oil pickup must be well to the rear of the backend housing?

[dgs]

Hi Pete
Thank you for putting it on the farming forum, much appreciated. It'll be interesting to see what comes from it.
I agree with you, I think air must be entering the system quite high up perhaps a small line crack or o ring.
Yes there is a one way non return valve in the system, though I feel if it were the issue it would be playing up all the time.
Yes the oil pickup i think sits roughly just passed half way back in the transmission housing.
I'm hoping I have proven our air leak theory correct. Haven't pulled it apart yet, though today, according to the dipstick I overfilled the transmission by approximately 7.5 to 8 litres. The manual I just got says it should take 24 quarts, I guess that means imperial quarts which in litres is 27.2765 litres or in US quarts 22.71 litres. I don't know why but with the oil to the dipstick full mark it only had 19 to 20 litres of oil in it. So it was low be it US or imperial quarts.
Guess what? No it hasn't fixed it but it's heaps better, it now works on most downhill slopes unless it's a very steep slope.
So it's now running around 28 litres of oil which is what the manual states. However it's still not 100% right, so the question remains... Does it have an air leak? I tend to think perhaps it does have a small leak somewhere but for now it's heaps better.
Thank you kindly for your help.
Cheers David

[FOWLER MAN]

Hi David,
I used to run David Browns back in the 60's but the memory fades over the years.
As i expect you are aware the hydraulic pump is housed in the P T O housing at the back of the tractor.
It is fed either from a suction strainer or a full flow filter, depending on the age of the tractor. This is housed under the gearbox and connected to the pump by a bronze colored metal suction pipe.
The strainer end of the suction line will be immersed in oil at all times but I think the pump end of this pipe could be out of the oil when the tractor faces down hill, allowing it to suck air if there is a leak in the pipe or at the joint ???
You would have to remove the P T O housing, ( and maybe the cross shaft ? ), to access it, (quite a bit of work). Get more advice before tackling it.
The " David Brown Tractor Club" would be a good place to start, you'll find them on line.

Fred

[dgs]

Hi Fred... Thank you kindly for your help. They say age will not weary them. I think you're actually spot on.
Cheers David

[essexpete]

David out of interest how/when did the symptoms start?

[dgs]

Pete I haven't had it all that long and it was doing it when I first got it.
Cheers