Hydraulic control issues

[Bounce]

Been a while since I’ve been on here but hope someone might point me in the right direction with some issues on my Dextas hydraulics.

Symptoms are:
When in position control and the control lever is raised slowly, the linkage jumps up quickly a few inches at a time rather than a nice steady lift. I can move the control lever up a couple of inches, nothing will happen, then move it a tiny bit more and the linkage rapidly lifts 4-5 inches.
The flow control makes no difference to the rate the linkage lifts.
When in qualitrol it won’t lift the linkage, but I can lift in position control, flick it back to qualitrol and it holds the linkage in that position.
When using an attachment that puts pressure on the draft control spring (eg plough) it rapidly lifts the attachment out of the ground in both position control and qualitrol before slowly dropping it back into the ground.

Hope that makes sense. Thanks in advance.

[Hair Bear]

Assuming the oil level is correct then I'd go for the oil pickup/strainer blocked.

[Billy26F5]

Here's the manual: http://www.smallholderservices.co.uk/si ... hydraulics Page 25 shows what Ford considered, but definitely check the oil and filter first. Try lifting something and pulling out the external service valve to isolate the cylinder and see how quickly it drops if at all. If it holds well don't disturb the cylinder or asociated parts of the circuit. If it doesn't replace all seals in the cylinder and asociated parts of the circuit while the top cover is off. I would do a full overhaul of the hydraulics but see what you consider as this is a job that will take a while to finish. There should be no effect from the top link in position control.
Sandy

[Bounce]

Thanks for that. The hydraulics were resealed and cleaned out last year, and plenty oil in it. Looks like I’ll be having to strip the top cover again over the winter…

[dewaltdisney]

Hi Bounce, I have a used Dexta hydraulic pump if you find you need one. Here is a link to my advert https://www.preloved.co.uk/adverts/show ... 2019950337

Thought I would put it to you in case.

Cheers

DWD

[ianpdexta]

late reply!
Just wondering if you have air in the system? not moving then moving fast once the friction has been overcome would fit your description. I'm not sure how the system is bled since the main cylinder is the highest point, if it has piston rings rather than rubber seals then minor leakage would bleed the air out automatically but much better with some weight on the arms.

Regards
Ian

[Billy26F5]

I see what you mean but it doesn't seem to be an issue in these hydraulic systems as you can have the top cover off many times and it will recover in only a few seconds every time.
Sandy

[Bounce]

Thanks for your replies.

I’m just getting round to looking into this, I took the top cover off yesterday and removed the suction filter. The oil was clean but there was a bit of debris in the filter, not sure if enough to cause the symptoms described earlier.

I am going to go through the top cover again and check the valves, and check all adjustments on the linkages. I’m seeing in the manual that to properly adjust the linkages you are supposed to have a special tool (T.8512/a) to hold the lift arms in a certain position, does anyone have any tips or tricks as to get the lift arms locked in this position without the tool?

[Billy26F5]

There are three details that require a special tool according to the Ford manual, but this can be done without them. The arms should be 1/2" above the lowest position, they can be locked by tightening the mounting bolts for the adjustment (remember to loosen them to the correct torque before assembling the top cover). The qualitrol gap is 0.396" while the position control one is 0.449".
Sandy

[Old Hywel]

I can’t comment about the operation of the draft control in the original post. However, the description of the linkage in position control doesn’t seem unusual. Slowly raising the hand lever will cause the arms to lift in a series of small jumps or steps. Wear on the internals may well affect precise movement. Indeed, on my 4000, there are only three or four stops between full up, and down.
This is in contrast to the Fergy arrangement, which provides controlled incremental lift. Something to do with limiting the pump feed, rather than output.

[Bounce]

Thanks again for your replies. Getting it back together now, haven’t found anything obvious that would cause the erratic action of the lift arms, like you say may just be one of these things I have to get used to.

Only thing I did find was I hadn’t previously correctly adjusted the position control linkage. I’ve just got the flow control valve to go through but as far as I can see from the manual there is not a lot in there that could cause any real problems.

[Bounce]

Just a quick update on this one, everything back together and seems to be working exactly as it should be, qualitrol and position control doing exactly as the manual saying it should with a nice smooth lift while raising the control lever, with the flow control adjusting the speed as it should.

3 things I found while going through the system:
- suction filter and return filter slightly dirty, cleaned the suction filter, replaced the return
- position control linkage quite a bit out of adjustment (thanks again Sandy for the correct measurements)
- flow control valve was sticking, removed and cleaned, fitted new O rings etc.

Hopefully this might help anyone else who has similar problems with their hydraulics.

[Billy26F5]

Glad it's sorted.
Sandy