My L70D is dropping slowly ,nothing strange. When I go to lift it first drops a little and when I stop lifting it drops about 4 inches straight away . If I pull the lift lever a small amount only it will drop from top to bottom in about 10 seconds with no attachment fitted . I pulled the load holding valve and the peg valve from the lift side of the valve block . The load holding valve did have a bit of wear where it seats so I switched with the one from the tilt out section . All the O rings and backup rings looked O K but I changed them anyway (always keep a set) . The tilt out would not hold any pressure but I doubt it is connected . My problem is still the some . Its like the holding valve is opening prematurely or something . Anyone got any ideas ?
If your problem is only related with boom down issue, I will check the BSS solenoid valve, if installed. Did you check the shock valve?
Thanks for that Steve but no BBS on this machine . The shock valve from my understanding is part of and behind the load holding valve . If so I had it in my hand and it looked O K . Is there an easy way to check it in situe ?
Bad cylinder piston seal. What you describe is classic "displacement cylinder" syndrome, the rod packing is actually holding the load until you shift the spool and open the rod end up to tank. My guess.
It took a couple of minutes to get my head round that but it makes sense . Never heard of it before . If I get a guage on the rod side of the system or let the oil off it will confirm . Thanks Iantraxco
Volvomad, you got it faster than I did the first time You are exactly right, pressure guage on the rod port will show pressure multiplication, bleeding oil off the rod side, if the piston seals are bypassing of course it will drift badly.
Thanks lantraxco very much for that .A month late . Only got the seals yesterday ,didn't want to rip the cylinder encase I needed the machine . Nothing and I mean nothing left only the guide bush . I have done both rams as the other one had been weeping for atleast a year . Must try it out tomorrow and then change oil and filter . I have been using 10W engine oil with the last number of years . I am tempted to go back to hydraulic oil ISO 46 . I had pump cradle bearing problems before on hydraulic oil more than once . They broke the locating tabs off . Was it luck, coincidence or oil? Anyone ? My ambient temperature rarly goes below freezing or above 30 C . With in that range Volvo will allow almost anythingshort of butter.
Thanks lantraxco very much for that .A month late . Only got the seals yesterday ,didn't want to rip the cylinder encase I needed the machine . Nothing and I mean nothing left only the guide bush . I have done both rams as the other one had been weeping for atleast a year . Must try it out tomorrow and then change oil and filter . I have been using 10W engine oil with the last number of years . I am tempted to go back to hydraulic oil ISO 46 . I had pump cradle bearing problems before on hydraulic oil more than once . They broke the locating tabs off . Was it luck, coincidence or oil? Anyone ? My ambient temperature rarly goes below freezing or above 30 C . With in that range Volvo will allow almost anythingshort of butter.
Well done, let us know how she goes! I always lean toward the AW46 myself, but nothing wrong with 10W really. The cradle bearing issue could be something to do with oscillation in the system, or possibly pressure spikes? I'm just guessing there though, I'm no pump tech, lol. Hey, after you drain the oil, if you can on that machine you may want to have a look around the hydraulic tank? Those seals have to have landed somewhere?
The pressure spikes may have come from the operator . He is very good , does not abuse the machine (smooth direction changes and hydraulic operation )but he always kept the oversized bucket overfull and drove the machine to its limit and then some . All the seal should be in the filter by now but when it is out I can see most of the tank . What beats me is the same seal went about 10K hours ago and I dropped like a lead baloon
The load holding valve may have been bypassing as well the first time around, or had a piece of seal stuck in it for a while? These machines get more and more complicated, so they do funny things that are hard to diagnose, and then we add electronics to the mix, computers and sensors oh my!