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Thread: MF168: sudden linkage hydraulics failure

  1. #1
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    MF168: sudden linkage hydraulics failure

    Calling the BFF brains trust.

    Was removing old fence posts, lifting them with a chain on the lift arms. Some were resisting almost to the limit of the system. There was a quiet "bang" & the lift arms went instantly to the ground. With the engine at idle, there is a very unpleasant sounding, quiet "thump, thump, thump" at about engine speed coming from the nether regions. :-(.

    P.t.o. still turns.

    Auxilliary pump still pumps oil (thru an open port, at zero pressure).

    Tractor still moves.

    Thus: gearbox is ok; p.t.o. (& linkage pump) shaft is not broken.

    An internal hydraulic fitting may have blown - but why the thumping, which does not sound like the relief valve.

    Q. 1. Is it safe to drive 500m home or should I get it towed (thinking of bits of metal moving to unwanted places here) ?

    Q.2. Any guesses about what might have failed?

    All suggestions welcomed.

    JV

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    Re: MF168: sudden linkage hydraulics failure

    I will GUESS that it is the connecting rod that joins the ram in the top cover to the upper lift arms, either broken or more likely just popped out. and sit on the crown wheel.
    I would not advise anyone to drive it as it could do way more damage, but if it was mine I probably would end up chancing it and cursing my bad luck when it only made it 3/4 of the way.

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    Re: MF168: sudden linkage hydraulics failure

    Quote Originally Posted by gone View Post
    I will GUESS that it is the connecting rod that joins the ram in the top cover to the upper lift arms, either broken or more likely just popped out. and sit on the crown wheel.
    I would not advise anyone to drive it as it could do way more damage, but if it was mine I probably would end up chancing it and cursing my bad luck when it only made it 3/4 of the way.
    Maybe, but the thumping is there when the tractor is stationary, engine running and both hydraulic levers down.

    On reflection, I'm guessing one of the pump locating dowels has broken. If I remember p.t.o. shaft rotation correctly, the load reaction will try to force the pump down on the right hand side, & if so, the standpipe could have disconnected from the pump. This would explain the sudden and total loss of lift on the arms. The thumping could be the now unrestrained pump moving against the transmission housing.

    Easy enough to check tomorrow: remove the locating dowels. I'm hoping that is the problem, coz with any luck the lift cover might not have to come off.

    JV

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    Senior Member Cowabunga's Avatar
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    Re: MF168: sudden linkage hydraulics failure

    My guess is that the lift cylinder holding studs have sheared off underneath the lift cover.
    The Duck 2015

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    Re: MF168: sudden linkage hydraulics failure

    Update: My theory of sheared locating dowels was not correct - but I wasn't far wrong!

    A circlip over one of the cylinders (holding a cover on a valve chamber?) has failed; gone somewhere!

    Need to remove the pump to determine what need replacing.

    Do I need to split the tractor to get the lift pump/aux. pump assembly out, or is it simply a matter of removing the p.t.o. shaft?

    JV

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    Senior Member MF-ANDY's Avatar
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    Re: MF168: sudden linkage hydraulics failure

    got to split it again i'm afraid john

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    Re: MF168: sudden linkage hydraulics failure

    Quote Originally Posted by MF-ANDY View Post
    got to split it again i'm afraid john
    Yeah, thanks Already come to that conclusion and made a start today! Bugger! Still, I'll install the drive shaft shear tube correctly this time

    Wonder why the circlip came out? ( It's the one closest to the stand pipe which delivers oil to the top cover. ) The rebuild done about 100hrs ago was by an experienced (now retired) MF bloke, so I should put it down to Murphy's Law #232 I spose.

    JV

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    Re: MF168: sudden linkage hydraulics failure

    Quote Originally Posted by john maddock View Post
    Yeah, thanks Already come to that conclusion and made a start today! Bugger! Still, I'll install the drive shaft shear tube correctly this time

    Wonder why the circlip came out? ( It's the one closest to the stand pipe which delivers oil to the top cover. ) The rebuild done about 100hrs ago was by an experienced (now retired) MF bloke, so I should put it down to Murphy's Law #232 I spose.

    JV
    shouldn't come out unless something is worn. make sure you pull the cap back with a 1/4" unc bolt after inserting the clip. the clip will then be partially covered and held in place.

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    Re: MF168: sudden linkage hydraulics failure

    Update, for those following the thread:

    Pump is out. Discovered the missing valve head jammed between the front yoke and the valve body on the side where it once lived, and the valve shaft jammed between the rear yoke & the valve body on the same side. Both yokes broken in 2 places as a consequence, with the 2 pistons on that side jammed in their cylinders. Worse, one of the 4 studs holding the pump together has been bent as a result of the jammed parts so I can't get that valve body off.

    Given up for the moment & will sleep on how to proceed. At the mo, I'm thinking to hacksaw the stud through between the yokes, remove the yokes & weld a nut on the remains of the stud to remove it, shielding the pump body from spatter. Repair kits do not include studs, so it will be a case of buying a suitable bolt & cutting a new thread on one end.

    On t'other hand, I haven't discounted the idea of a new pump, in case there are unseen problems in the existing, after repair, to trap the novice
    Life's too short to be pulling things apart yet again as a result of another failure!

    JV

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    Re: MF168: sudden linkage hydraulics failure

    Jeez! Four and a half years have passed since that little episode! To finalise, a new pump was installed.

    Now to the current problem which I hope the Brains Trust can help with.

    I have a small backhoe (JD8A) on the linkage almost permanently, the top link of the hoe is connected to the dead pin, not the tractor top link connection.

    A few days ago, on startup from cold, the linkage failed to lift. Moving the control levers though their arcs did nothing. After about 30 seconds, the links began to lift in jerks.

    The loader, driven by the auxiliary pump worked normally, so I presume the oil inlet strainer is not blocked, and since the top link is not connected, the control valve linkage from that is not out of adjustment.

    After a few minutes of work (warmed oil?) the linkage worked normally.

    No problems in recent days, but today the same problem appeared, even when the oil was warm. If I used the 'hoe boom was used to raise the links, they stayed up. If I moved the Position Control lever down, the links went down (as they should) but would rise only part way under their own power.

    Some years ago, a similar problem was diagnosed as a leaking O ring on the Pressure Control valve, and replacing it (but as I remember not with the correct size) seemed to fix that problem.

    Also worth consideration: as reported on another thread, I had the local dealers re-adjust the control levers, and the result was not satisfactory. I've been careful to not use Pressure Control since. At the time, I asked if anyone knew of a source for the Special Service Tools so I could re-adjust the levers. It appears they are not available.

    I'm assuming that it will be necessary to take off the lift cover to sleuth this problem. My question is, is it likely to be something I can fix -and what should I look for to decide that - or should the almost-certainly-expensive serviceman (most likely a young bloke with limited experience of old stuff, like last time) be called?

    JV
    Agtronix - the home of the Weedswiper

  11. #11
    Senior Member Footsfitter's Avatar
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    Re: MF168: sudden linkage hydraulics failure

    Hi John,

    Still over here and just woke up after a lay-in!

    What little I've done with old masseys was way ago, but thinking through your symptoms sounds like the hydraulic pump is struggling to get oil flowing and then the jerking is it pumping as best it can with an issue effecting the output? Possibly a suction issue- perhaps not a blocked strainer given you had it apart a few years ago- put still possible, how about the pick-up pipe being cracked or the gasket/seal for it sucking air (or is it submerged?) then how about the check valves those scotch yoke pumps employ? something wrong with one of them could produce the fault of no oil at startup and jerking when it does prime/pump eventually?

    sounds like the cover is going to come off?


    best rgds

    ff
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    Re: MF168: sudden linkage hydraulics failure

    Quote Originally Posted by Footsfitter View Post
    Hi John,

    Still over here and just woke up after a lay-in!

    What little I've done with old masseys was way ago, but thinking through your symptoms sounds like the hydraulic pump is struggling to get oil flowing and then the jerking is it pumping as best it can with an issue effecting the output? Possibly a suction issue- perhaps not a blocked strainer given you had it apart a few years ago- put still possible, how about the pick-up pipe being cracked or the gasket/seal for it sucking air (or is it submerged?) then how about the check valves those scotch yoke pumps employ? something wrong with one of them could produce the fault of no oil at startup and jerking when it does prime/pump eventually?

    sounds like the cover is going to come off?


    best rgds

    ff
    Good evening ff. I had wondered if you were still soaking up some Australian vitamin D. Truth is, vitamin D produced by Tasmanian sunshine is far superior than that in W.A.

    Re my recalcitrant MF168, the loader & 'hoe, powered by the auxiliary pump are ok, and as I understand it, the aux.pump gets it's oil via the same screen as the lift pump, so I don't believe a blocked screen is the problem - but could be wrong. I haven't yet had a chance to look at the workshop manual, but I agree, it's probably a lift cover-off job; not looking forward to that, having done it numerous times over the years.

    JV
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    Re: MF168: sudden linkage hydraulics failure

    To continue the story: I'd discounted ff's proposition that the inlet screen (for both the lift and auxiliary pumps) was blocked, coz the loader supplied by the aux. pump worked as normal. Instead, I assumed the problem was isolated to the lift system, especially considering the problem emerged suddenly.

    However, this a.m., with the coldest day of the year so far (around 10C.) the aux. pump growled considerably on start up. Feathering the clutch reduced it, and in addition the linkage lifted slightly. After a few minutes of this, the linkage system became normal, suggesting ff was correct all along and the pump was cavitating until the screen cleared - for what ever reason.

    In a vain hope to be able to get to the inlet screen I took off the Response Control cover on the transmission. Couldn't even see the screen (of course!) but I found some grey jelly-like goo inside the cover. Not the usual buttery goo from water in the oil, but more like the jelly I've found in diesel tanks on occasions. (A biological connection?)

    I've taken enough lift covers of 100 series MFs to know that I will do that only as a last resort; the control arm roller can be a real bugger to get back into place - not to mention the delivery pipe from the lift pump - so I'm wondering if flushing the transmission by running it for a few minutes with diesel will dissolve and dislodge the goo.

    More to the point, how much of a risk is doing that to the pumps, especially the aux. pump which has two sets of gears in an aluminium housing?

    Brains trust?

    JV
    Agtronix - the home of the Weedswiper

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