Knuckleboom: Back to Work: Test, then Disassembly!

November 15-17, 2013. So when I last left this project in July 2013, I had some issues to sort out, and the following posts after that I had some time to think and come up with a solution.  Now it was time to work to see if I could fix it.

Before I jumped in taking pieces apart, I decided to do a quick test to see if my previous theories were correct.  First I got a ruler and split it down so it would fit down the filler neck, and measured the fluid level in the primary tank and the secondary tank.  Both of them were about half full.  I popped a battery into the truck (I keep all batteries on maintainers so they’re always ready for action) got some fresh gas and poured it down the carb for a quick prime, and after pulling the choke, it fired right up!  I engaged the PTO, and moved the crane for a couple of mins until it wasn’t moving very quickly anymore.  Then I shut down the truck, and grabbed my ruler to check the tank levels.  Sure enough, the primary tank was empty!!!! And the secondary tank was almost full!!!

So that proved my theory that the drain-back hose was restricting the flow and starving the pump of fluid, thereby pumping air into the system.  Whew, it was a relief to know I was on the right track with my solution set.

Now for some real work, first up, removing the secondary tank since it was already full of hydraulic fluid.  I disconnected the hoses and spliced them together so I could get it out with all of the hydraulic fluid in it.  Then it was time to remove the primary tank.  I wasn’t looking forward to it, as the last time I removed it was not a fun task.  The last time I was unable to disconnect the PTO shaft from the pump, so I pulled the pump from the tank under the truck, left the pump sitting and pulled out the tank.  That reassembly task was not much fun.  This time I was determined to get the PTO shaft out too, and leave the pump in the tank.  After testing the connections, I found that it was removeable at the joint to the PTO drive on the transmission, so that was perfect!

Now that the tanks were out, I could mock them up with the 3rd tank and all of the fittings to see if I was missing anything.


I had the majority of fittings, but I was missing a ¾” plug, and an 1½” all-thread close fitting.  Not too bad considering I had bought some of them back in July, and some of the others online from, like the 1½” drain hose, barb fittings and a few others.

Now it was time to cut some big holes and prepare to weld on some more bungs.  After some measuring and marking, I got out my Dewalt ½” drill and 2” hole saw.  I would have preferred using the vertical mill, but the time and hassle of getting it clamped just wasn’t worth it, I’d just have to be careful.  The problem with hole saws and metal is that they like to grab, and really twist the drill.  The trick is to apply just enough pressure to cut but not so much that it can grab.  Once it breaks through, then you swivel it so it enlarges the cut through area in a counter-clockwise fashion, so that the hole saw teeth can’t grab!  Here are the two tanks with their holes cut and cleaned up with a flapper disc in the grinder.

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With the holes cut, now I could weld on the bungs on each tank.  One of the tank’s was brand new, so welding that one on had no risk, the other one was the primary tank, and there was some residual oil in it.  It smoked a bit, but otherwise was ok.  If this had been a gas tank, I would never have welded on it, but since it was oil there was a much lower risk. (NOTE: there is a safety concern with welding on a tank that’s had petroleum product in it, so do this at your own risk, I am not responsible for your actions!!!!)

Here’s the tanks with their additional bungs welded on:

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At this point, I knew what additional parts I needed, and I needed to work on a few other tasks before the weekend was over.  There will be more updates next weekend!