315c Cat

Iam working on this machine 12,500 hrs I had the hyd pump rebuilt because it was worn installed the pump and run pressures and I cant get more than 3000 psi on any single pump function bucket, swing and travel when worked one at a time so I know its not in the pump because the negtive control line works fine and when I use both tracks pressure is ok I have checked circuit reliefs they are fine so somewhere in the main control valve it is bypassing you can hear it and it only has one main relief that works also any one ever run into this And I have gone into the monitor and changed the modes so that is not it either

One of my customers had a 315 CAT, can't remember wether it was a B or C, and I had a similar problem with it after having the pump rebuilt about 8 years ago. Basically it would travel/counter rotate like it should when both travel peddles were used at the same time but still had no power to each individual track for turns, etc. Too, the functions would work individually but had no real power unless another function was operated at the same time, so that both pumps were having to work at the same time.

I spent several days troubleshooting and re-troubleshooting, and could find nothing glaringly wrong.... all of the function worked, but at the same time they didn't.

I wound up getting the customer to let me get a second opinion from a dealership guy. Between he and I we spent a large part of yet another day testing and going over the same things I had already done several times myself, with the same results. Eventually we decided to do a test with both tracks blocked so I ran home to get another piece of round stock so we could block both tracks at the same time. The dealership guy stayed with the machine and simply began reading the manual, again.

When I got back he said he was pretty sure he had found the problem and showed me part of the schematic that included the passages inside the pump. Turns out there was a passage common to the pressure side of both pumps. Thing is the ports into each side are supposed to have orifices in them, and the orifices were missing.

With no orifice it caused each individual pump to bypass x amount of oil which resulted in the low pressure output. Basically each function would still operate but with no real power. When both pumps were stroked together, the pressure from each side deadheaded into each other allowing the system, as a whole, to reach full pressure, so the functions all worked as they should.

What I found out was that my pump shop had bought out another shop several months before. My customer needed the machine running ASAP so instead of rebuilding his pump we had done a swap for a pump they had on the shelf. Unfortunately the pump I got had been built by the shop they had bought out. My guys had stand tested it and it appeared to be OK. Problem is when they tested pumps they always did it with both pumps stroked to maximum at the same time so they knew that the combined output matched factory pressure and flow specs.

Nobody could ever figure out why the orifices had been taken out of the pump I had, nor why there didn"t even appear to be any threads left where the orifices were supposed to be threaded in. In the end my pump guys simply rebuilt the old pump and we were back in business.

Standing on the ground looking in at the end of the pump there were two plugs in the housing just below where each of the main pressure lines hooked up. With the plugs out you could stick a small, straight screwdriver or scribe into the hole until it bottomed out. I cantt give exact measurements but you could tell that the probe should stop at a certain place, but was extending on into the pressure ports.

There's no other reason I can think of, off the top of my head, that would cause the problem your describing other than this, and it seems to match to a T if I'm understanding things right.

Hope this helps, and please keep us updated. Wayne

The restrictors were missing I installed some and it works fine now

Glad to hear you got it figured out. When it comes to hydraulic problems, especially with the newer excavators, there are so many small things that can cause BIG problems...and are all but impossible to find.