Terex HR12 jerky whilst tracking

[Digrivs]

Hi to everyone. I have recently joined this excellent looking forum following some internet research in to a problem I have with my mini digger.
The machine is a 2004 Terex HR12. I purchased the machine to do a self build and have owned it 2 years. The problem started to occur about a year ago and is gradually worsening. The symptoms I have are as follows. When tracking if I just move the levers very slightly a nice steady and even slow track will occur. If I move levers to fullest extent I also get a very smooth track at full speed. However if i attempt to track with the levers anywhere other than slight movement or full movement a bucking/jerking occurs which will build to the point where I have to release the levers and wait for the machine to stop before I attempt to track again. The same jerkiness is also now starting to occur whilst operating the boom. I have all the workshop manuals and have ordered a hydraulic pressure gusts set. Whilst I am a fully trained car mechanic hydraulics is very new to me.
Just to add. I have fully serviced the machine including flush and refill of hydraulic oil and replacement hydraulic oil filter using genuine terex parts. I have also renewed the tank breather and all flexible hydraulic pipes. The fault was present prior to this work being carried out. The machine has done 2000 hrs and I would say that is genuine as the rest of the machine reflects this
I am hoping someone may be able to guide me towards a solution. Any help gratefully received

[digger-man-dumper]

Hi to everyone. I have recently joined this excellent looking forum following some internet research in to a problem I have with my mini digger.
The machine is a 2004 Terex HR12. I purchased the machine to do a self build and have owned it 2 years. The problem started to occur about a year ago and is gradually worsening. The symptoms I have are as follows. When tracking if I just move the levers very slightly a nice steady and even slow track will occur. If I move levers to fullest extent I also get a very smooth track at full speed. However if i attempt to track with the levers anywhere other than slight movement or full movement a bucking/jerking occurs which will build to the point where I have to release the levers and wait for the machine to stop before I attempt to track again. The same jerkiness is also now starting to occur whilst operating the boom. I have all the workshop manuals and have ordered a hydraulic pressure gusts set. Whilst I am a fully trained car mechanic hydraulics is very new to me.
Just to add. I have fully serviced the machine including flush and refill of hydraulic oil and replacement hydraulic oil filter using genuine terex parts. I have also renewed the tank breather and all flexible hydraulic pipes. The fault was present prior to this work being carried out. The machine has done 2000 hrs and I would say that is genuine as the rest of the machine reflects this
I am hoping someone may be able to guide me towards a solution. Any help gratefully received

I have driven machines with like sounding symtoms, If the track levers are responsive by been short when trying to acheive medium speed the levers are going to be very jerky, If I was you I would ( for a test ) be working something out that allows me to rest my wrist or arm on some sort of tempory support or lock my hands / wrists against my knees to work out if the motion of moving / swaying is causing the levers to rock, Is the problem better with lower engine rev's ? / ( red ) Neuson use to have this same problem due to short travel levers on the 1st batch of 1404 excavators brought to the uk 7 or 8 years ago, The later machines & machines from Wacker Neuson have longer levers & this has fixed the problem. Hope this helps you sort your problem.

[Digrivs]

Thank you for a swift reply. I haven't driven the machine for a few weeks but from what I recall engine revs make no difference. I see what you are saying about locking wrists. I will certainly try that. However this is a problem that wasn't always there and is a problem that is worsenenjng. I will try your suggestions and report back. In the mean time if anyone else has suggestions please feel free to add.
Thank you

[Muz]

Welcome Digrivs .. this could be a whole range of issues, but sounds like you have a pump/oil problem ... anyway.... can you see into the hydraulic tank and see if it has froth and bubbles in it ? Hydraulic oil is not compressible but air is, and if there is any contaminants in the system or air yet to be expelled it will mix and compromise its performance, and give the results you describe

[Digrivs]

Hi muz. Thank you for the welcome and your reply. There should be no contaminants in the hydraulic oil as the system was thoroughly flushed and refilled with correct viscosity hydraulic oil. I will check the sight glass for air bubbles this weekend. I will also have my pressure gauge kit by the weekend so will be able to test pressures as required. Unfortunately as a novice to hydraulic systems I'm unsure what pressures to expect. I should add I changed the hydraulic accumulator sphere also in an attempt to resolve this issue

[Muz]

Hi muz. Thank you for the welcome and your reply. There should be no contaminants in the hydraulic oil as the system was thoroughly flushed and refilled with correct viscosity hydraulic oil. I will check the sight glass for air bubbles this weekend. I will also have my pressure gauge kit by the weekend so will be able to test pressures as required. Unfortunately as a novice to hydraulic systems I'm unsure what pressures to expect. I should add I changed the hydraulic accumulator sphere also in an attempt to resolve this issue

The tank is only 2/3 of the system though ... the rest is in the rams and pipes, that said, it should remove most of the contaminants(if it was that) if youve done that..... which leaves us with pump,servos and block problems, next stage is to do a pressure test and find out what the pump is doing, and if its consistent, or variable whilst under constant load

[Muz]

I appreciate your automotive experience, but what led you to change the accumulator ? (just trying to get a handle on your thinking?)

[Digrivs]

I appreciate your automotive experience, but what led you to change the accumulator ? (just trying to get a handle on your thinking?)

I have a complete lack of hydraulic knowledge. I won't pretend I'm anything other than a beginner. However I assumed, probably wrongly, that accumulator sphere may have some damping effect. As I was suffering jerky operation and the hydraulics were completely drained whilst renewing all the hoses I felt it good practice to replace while I was there. Nothing overly educated in my decision. Purely a chance it may help resolve the issues I had.
once again thank you for input.

[Locofitter]

Track tensioner and idler wheels ok?
Final drives ok?

Probably a very silly suggestion but have you tried putting new tracks on? I found this a while back, rubber tracks were half way worn so I put new ones on and problem went. Never boughr cheapo tracks again.

[Digrivs]

Thanks to all for reading and replying. A little further information. I have been operating the machine today and trying to take notice of what's occurring. It was noted that if I track with levers fully pressed forwards (so that no jerking occurs) and crowd the bucket round it is noted that the digger will turn to the right. I can assume the bucket ram and right hand side track motor are fed on the same hydraulic circuit and that this wouldn't be normal?