JD 448 backhoe problem

[TraderMark]

I'm not a JD guy either, but I do have a lot of experience with hydraulics.
I looked up the 448 backhoe at the JD parts site and the parts manual shows that the dipperstick valve section does have an individual port relief for one port. This port relief acts independently and seperately from the main relief. The port relief only relieves its particular port and is therefore set lower than the main relief which regulates the pressure to all the ports.

It sounds to me like you have a bad port relief. You can test to see if it's the port relief in several ways. One of those ways is by swapping the port relief from the stick section with the port relief from the boom section. If the port relief is bad, the problem will follow it to the boom section.

Please use standard safety practices and make sure nothing can fall on you or others because when you remove the port relief there is nothing left to hold the oil flow back and if the boom is up and not supported it will come down. INSTANTLY!!!


Hope you get this sorted out soon!

Mark

 

[doppler46]

Okay Tradermark I now see what you were saying. I found a link that shows the valve broken down. The difference between the dipper and the boom relief valves are that the relief valve is mounted on top of the dipper valve. The boom relief valve is located on the bottom of the boom valve. The part numbers are the same so I will swap them tomorrow after work or Saturday, time permitting. Either way I will post a response. I hope it will be a postive one. Thanks!

 

[doppler46]

Finally fixed. I removed the pressure relief valves from the boom and the dipper control valves. The dipper relief valve was stuck and would not move. I took it apart and there was a piece of looked like rubber wedged between the rubber piston rings. I cleaned it up oiled it and reassembled it. Works like new. Cost of repair zero dollars and I like that! he pressure relief valve from the dealer is 290.83. Dug two trenches this morning with it. I have had the backhoe for 3 years and it sure does come in handy. Thanks for all the help!!

 

[TraderMark]

Glad you got that problem licked!

Mark