Introduction & Request for help on 4911 hydraulic problems

[wannabewelder]

Hi
Just a few lines to introduce myself. I'm a semi-retired electrical engineer with an interest in things mechanical. I'm in partnership with another guy and we own 27 acres of woodland and arable, including a pond, which we try to manage for the benefit of wildlife.
To assist with this we have 1980 Zetor 4911 which we acquired some years ago. Considering its age, the tractor was in surprisingly good condition and has done (almost) everything asked of it. We use it mainly for grass cutting using a Bomford slasher and hedge trimming using a Bomford "Farmtrim" cutter. We're not a commercial operation so everything comes out of our pockets, consequently we try to do things as economically as possible.
Now the problem.
The 3 point linkage on the tractor has never worked, as I believe it should, ever since we've had it but the (relatively) recent acquisition of the hedge trimmer has brought matters to a head.
Symptoms are:
1. It is impossible to get the 3 point to lift when the selector is in the "P" (position control) position. It will only lift in the "M" (Mixed) position. (We've not tried in the "D" (Draft) position).
2. Having set the hedge trimmer to a cutting height sometimes the 3 point will, without warning, start to creep up; which is most annoying.
3. The 3 point position depends on engine revs. If you let the revs. fall off the 3 point sinks.
4. When trying to use the outer circuit to power the hedge trimmer position rams there is a rumbling sound from the hydraulics area and somebody with more knowledge than me has said this is cavitation.
We've cleaned the magnetic plug and the top filter, which was pretty dirty and also the filter near the pump which had a lot of Hylomar gasket compound in it. The tractor has fresh gearbox oil and the pressure at the external services connector at the back of the tractor is 2400 psi
We have the Operator's, Workshop and Parts Manuals for the tractor but, having been translated from Czech, they're not always easy to understand.
Can anybody give us some clues to what might be the problem? My suspicion is that it's the control linkages rather than the valving in the distributor but I could be completely wrong.

Help please

Wannabe

 

[wannabewelder]

Meant to add
Does anyone know if this is any good http://www.ebay.co.uk/itm/ZETOR -ZETORMATIC-Tractor-Hydraulic -system-manual -CD-Zetor-Matic-/110962202337
and also add apologies for the tediously long post!

Regards

Wannabe

 

[grumpy6711]

Meant to add
Does anyone know if this is any good http://www.ebay.co.uk/itm/ZETOR -ZETORMATIC-Tractor-Hydraulic -system-manual -CD-Zetor-Matic-/110962202337
and also add apologies for the tediously long post!

Regards

Wannabe

Yes it is - check your messages

 

[prestonpaul]

Just don't pay for it
Sounds like you are having similar issues to me with my 6245.
I have yet to get mine sorted out but have found a few other problems along the way. I'm at work now but I'll post some suggestions when I get home.

 

[hve]

Hmmmmmmmmm, based on the dirty filters and gasket gunk, and the fact that the revs change the position of the TPL i suspect the pump is badly worn, at higher revs it pumps more fluid and that makes up for the losses in the pump.

Test the hydraulic pressure at slow idle and at 2000rpm and see if it changes drastically.

During the test you should hear a screaming sound coming from the hydraulic pressure relief valve bypassing .... assuming you have enough pressure to open the valve, i cannot remember what the pressure setting is, but 2400psi sounds about right.

Could just as easily be the seal in the internal TPL lift ram, which will not effect the pressure reading unless actively lifting something on the TPL.
but if it is the ram seal the TPL will sink down as soon as you turn off the engine (assuming you have something heavy on it)

Also i believe there is some plumbing between the pump and the control valves that can leak.

Sounds like you may have to pull the top off, or at least pull the pump out and check the pump and the o-rings and hoses that connect it.

Good luck

 

[prestonpaul]

In my limited experience with my 6245, I have had the following issues:
There is a pipe that runs through the diff housing between the pump plate and the top housing, this is sealed with o rings, mine got old and brittle and failed causing a loss of pressure. My lift cylinder seals were damaged and leaking which I am sure didn't help . The biggest problem I found was the linkage between the inner circuit valve (position control valve) and the lever that operates it had come adrift due to a worn lever and pin.
I am still having problems which I think could possibly be due to some other worn linkages or possibly a valve installed backwards.
Good luck and let us know how you go.
Paul.

 

[wannabewelder]

Hi all
And thanks for the responses. I think prestonpaul may have hit the nail on the head with the comment about the linkage.
I'm convinced now that it's unlikely that the problem can be solved without taking the head off the hydraulic unit and I'm not sure whether that's one best left to the professionals.
I took the plunge and ordered the Zetormatic CD and I received it yesterday. I haven't managed to digest it all - there are 100 odd pages - but it's far more comprehensive than the manual . It doesn't cover the 4911 specifically, nor does it deal with the cabbed controls but the photos of the internals and the description of operation of the hydraulic unit are very helpful. I'm still trying to get to grips with "antislip" though. Does anyone know what it means?

Regards

John

 

[dave_peters]

I havn't seen the CD, but I would suspect they mean weight transfer to improve traction with 3 point implements, this is when the select lever is in draft, ie forewards, this causes the hydraulics to lift when the top link is pushed in and drop when pulled, sensititivity according to the position of the main lift lever.

 

[hve]

I havn't seen the CD, but I would suspect they mean weight transfer to improve traction with 3 point implements, this is when the select lever is in draft, ie forewards, this causes the hydraulics to lift when the top link is pushed in and drop when pulled, sensititivity according to the position of the main lift lever.

Also.... (assuming the same as my 6745 UR1)
When the internal circuit control leaver is pushed all the way forward. well past the "down" position (regardless of the Position or draft setting lever, and unrelated to load applied to the top link sensor) weight controlled lift (called anti slip) is applied to the implement (TPL arms) to shift more weight onto the rear tyres to prevent Slip...... very handy for big mowers on hilly terrain!
the amount of weight transferred is adjustable not by the position of the inner circuit control lever, but by the "reaction speed" lever under the seat ...... but i forget which end of the arrow is more and less in this mode.... i recall it was confusing when i was reading the "Zetormatic I" manual .

The Zetor Workshop and user manuals are almost impossible to fathom, however the Zetormatic manual was much easier to follow ...... at least for my brain

 

[dave_peters]

Well, its 38 years since I had a 6711, so memories are a bit faint about it, but its only 3 years since the 7245 left.and I think the hydraulics were very similar to the 6945 that replaced the 6711.
The flow control on our 7245 had very little effect on the draft control or lift speed, and did not affect the drop speed at all I believe it diverted oil from the inner control lever for spool valves to the outer lever for internal hydraulics and vice-versa.
The control lever, when the select lever was on draft, was up or down for the last (rear) 40mm of travel, with the amount of draft control reducing the further the lever went foreward.

 

[hve]

The Zetormatic manual i have a copy of, is for the Zetormatic I Hydraulics, and does not cover the Zetormatic II as used on the Cristal.
(Zetormatic II has the draft sensors on the lower links, rather in the top link, otherwise very similar)
I assume all UR1's are Zetormatic Type 1, and i think this includes the 9 series UR1, but not sure.

I can test the antislip function on my 6745 by standing on the rear arms (to add 80kg of weight and lifting them up, then dropping them right down with the control lever in the "down" or whatever they call it position, then if you push the control lever all the way forward the arms will lift you up about 6" and stop... this is the anti slip setting...... the lift capacity in antislip mode is variable from 250kg to 500kg...... being the load transferred from the implement to the back tyres (without actually lifting the implement at all........... unless it is less than 250kg
The weight it can lift or hold in this setting is adjusted by the flow control leaver, but the flow control lever ONLY effects the load capacity of the TPL in Antislip mode[/],
out of antislip mode it may give some control of lifting speed (if you are lucky), more importantly It also controls Draught depth ......
.... in draft mode, it sets the reaction speed, and depth of the draft to suit different implements, based on the load applied to the top link sensor (on UR1's)
I do not have a plow, or any crops, so have no use for draft mode and have not tested it on my Zetor .

 

[wannabewelder]

Thanks to all who've responded - I feel I have at least some idea of what Antislip is now!
I thought an update might be appropriate. The problem isn't cured but, after lifting the hydraulic head, at least one problem has been revealed.
The seals on the lift cylinder have failed. One was actually broken and the other severely damaged. New seals (and new "O" rings as in Prestonpaul's response) are on order and hopefully this will go some way to solving the problem.
The other thing that I noticed is that, when moving the inner circuit control, the whole internal control linkage deflects sideways as if someting that it pivots about is worn. It's difficult to see exactly what is happening "from the top" as it were so I'll try a dentist's mirror to see if I can see more.
Further updates to follow as we progress.

Regards and thanks once again for all help

Wannabe

 

[prestonpaul]

Mine does the same thing. I am on the verge of ordering replacement parts (inner circuit control linkage and the rod it pivots on) to see if that rectifies the problem.
keep us posted with how you go.
Paul.

 

[wannabewelder]

O.K. Not much to report at the moment. I have the new piston seals but which way do they go?
The seals are flat on one side - just like a washer and on the other side they are "cupped".
I was told that the "cup" side should face the pressure - that is be towards the crown of the hydraulic piston, and the manual , in its inimitable czechlish, sems to agree with this but the seals that were fitted were fitted with the flat side to the craown of the piston.
Of couse it could be that "someone" had fitted the previous seals incorrectly or I may be misreading the manual / have the wrong end of the stick.
Does anyone have any idea?

Regards

Wannabe

 

[askinner]

The cupped side (Lip as they are called), go to the pressure side. This is the same with any hyd or oil seal.

 

[wannabewelder]

Thanks Skin7245
It's nice to have it confirmed. I think the seals must have been fitted incorrectly before.

Regards

Wannabe