Hi I have a Caterpillar 303sr mini excavator that has presented a problem over the past 2 days .What happens is when the digger is cold its working fine all smooth then after a couple of hrs work the main boom hydraulic ram seemed to operate jerkily not smooth (on off operation) and even stopped once or twice ( controller dead) I turned off the machine and it operated fine again then would start jerkily operation again I stop machine for an hr had lunch and all good for the next 2 hrs till I went home. This was the same pattern for past 2 days. I seems like something is getting hot and failing. Pls Note All other hydraulic controls operate normally and smooth all day long (no problems) just the boom ram jerky. Hydraulic power is good through out the day just boom up and down jerky or non responsive. hydraulic oil seems not too hot I,m guessing can hold your hand on tank no problem for as long as you like and dash light not on. I notice there are 2 solenoids in the hydraulic bay one on top of the other the top one seems hot to touch but can hold hand on it the bottom one just slightly warm . I disconnected the top one and all my hydraulic left and right controllers went dead so I reconnected top solenoid again and then disconnected bottom solenoid had no effect all working controllers work fine bottom solenoid seems not to operate anything??? Some background 5 yrs ago when I brought the digger second hand it was set up for Japan and the controller were confusing the manual indicted there was a valve to turn to change the setting I could never find this valve( did not exist) and was told to just alter plumbing under set area I found these quick coupling hoses there and with abit of messing around got plumbing sorted so I'm used to ISO but the digger originally was set up for another arrangement ???. I mention this as I was mithed as to why the bottom solenoid seemed to be doing nothing and the top solenoid was working all the controller did I mess something up when I change the piping around 5 yrs back an now overloading top solenoid???. This digger does not see alot of work 5yrs 500hrs total 1500 hrs Another thing to mention the digger was a trenching digger and had these sensors on different areas on the boom and a control box in the cock pit it was all in Japanese and was a pain sometime and interfere with operations limiting the boom so I took the control arms off yesterday leaving the sensors in the parked position and the digger worked fine like this today in the morning and the afternoon I took these off as I thought they could be the problem but not the case. If anybody could help pls do so. I plan to fit a new hydraulic return filter next as I realize I have never done this before.
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