Excavator blade drift - Rotary Joint

[PoginyHill]

I've been living with a worsening problem with my Cat E70B excavator: the blade would always drift down. It got worse over time. I came across a suggestion (I think the heavy equipment forum) that the problem might be the rotary joint (the thing that directs hydraulics from the rotating part to the stationary undercarriage). I saw a YouTube video of a similar machine where the joint was rebuilt without removing the entire thing from the machine. Since removing the 7 connections from underneath was a bear, I thought I'd give this a try. But I had interference with the frame for the boom to lift the upper part of the joint out. I chose to cut a piece out of the frame rather than tackle the underneath portion of the rotary joint.The repair itself (7 blue O-rings plus a dust seal and an O-ring for the cap) was easy. Cutting the frame not so easy as it was difficult to get to.


 

 

 

 

 

 

[Iwawoodwork]

Did that cure the blade drift?   I have a similar problem on my Hitachi ex50urg but also one of the travel motors on one of the tracks does not release correctly when starting in the AM and will kill the engine after a couple of feet of  travel, after 10-15 minutes I can travel but with some drag, blade having to be lifted every couple minutes, then after working the excavator for a couple hours the machine travel on one track gets so weak that it will barley move on flat ground. looking for ideas  of where to start.

[PoginyHill]

Yes it did. Guess I should have mentioned that in my post. Blade is rock solid now wherever I leave it. Did not drift at all overnight. I didn't have problems with my track motors, but they all go through the same rotary joint, so it is a good bet that worn seals in the joint are at least contributing to any track problems.

[Iwawoodwork]

Thanks for the answer, from what info I could find on the net and now your info I will see what it takes to get  to that circle on my Hitachi 50. It is a O tail swing so pretty compact.

[mike_belben]

 you could isolate this blade drift issue to pinpoint the culprit but its labor intensive and in the end would not have improved your machine as much as just changing the manifold seals as a way to cross that off the list AND know they are done.  Im not usually one to advise you throw parts at it but spending time and money at a test that is just as much effort as the swivel repack is kinda.. Ehh..  I will leave it up to you. 


If you have extra long hoses laying around and the time for it, you can plumb the top side of the manifold hoses to jumper hoses and just lay them over the carbody and connect direct to the blade hoses.  Prime out the air a dozen times and then park it with the blade up, maybe even with weight ontop to accelerate the drift.  Now youve bypassed the swivel.  If it still drops down youve got a valve issue or a cylinder issue. 


Keep it mind a cylinder will not drift all the way down even if the piston seal is MISSING.. Unless fluid is also escaping through the valve or out the rod seal.  We all blame the piston seal for drift but its often not the culprit.  If no other leaks, a bad piston seal with drift a little then stabilize once pressure equalizes on both sides of the piston face. 

[PoginyHill]

one of the travel motors on one of the tracks does not release correctly when starting in the AM

On this problem, I'm wondering if there is something causing your travel motor brake to not release. Still could be related to the rotary joint, but might be a travel motor issue also.

[Iwawoodwork]

I agree that it could be a travel motor issue so do plan to get a pressure test done on the motor before tearing things apart. I do not have a book or gauge and MikeB lives to far away so will have to hire a local person to test pressures .