Serial number 8HR00272. Gray market machine. right side track runs slow. Been chasing this around half the summer. Thought we had a pump flow issue. Cat went through the pumps and it didn’t fix anything. I’ve got 500+ pilot pressure. Both pumps build 5000 psi and I’m getting 5k out of the main control valve on the track pressure lines. Negative pump pressure is at 500 when I start the engine and drops to 100 when I activate a function. Points to a track motor right? If I swap the pressure lines coming out of the mcv, the issue immediately switches sides. If I swap pilot lines on the mcv, the pedals run backwards but issue stays on the right side. If I track the machine and hit a joystick function the machine will straighten out. Cat installed a mulching head and had to add a diverter valve to make it work. We have also bypassed that but the problem persists. I’m at a loss and the cat tech support is also at a loss. They are usually excellent help and he finally suggested that we get a cat tech on site who has access to a hydraulic guru. That idea disgusts me. Any ideas? Did I miss something?
I think I would be looking at the swivel
I considered that but the symptoms switch when I swap the hoses at the mcv and wouldn’t I get a creeping track on the opposite side when I dead head the tracks to check pump pressure?
I think I would put the drain hose off the swivel in a bucket and hit the travel note I would watch for a bath if it’s bad
If you suspect a motor, pull the case drain hose off the motor and cap it. Put a short hose on the case drain and run it into a bucket. Block the sprocket from turning and operate the motor at high idle over relief. Good motor will barely ooze any oil. Bad motor might blow the hose out of the bucket if you don't hold it there. It's also possible for a swivel packing be blown between the lands and dropping pressure back to a return in the main valve. If I suspected that, it was easier to pull the swivel apart to find it.
I don’t believe it’s a motor because I can swap hoses at the mcv and make the issue switch sides. It very well could be the swivel though.
If there is no record of anyone having been in the swivel that’s the first place I’d be looking, after the case drain line test that JohnC mentioned. Amazing that the dealer people never mentioned it.
So I unhooked the case drain at the swivel. No case drain oil comes out of the slow side and we get a bunch of oil from the faster side. Not much oil from the swivel itself. Cat sis says 5 gpm is acceptable case drain on a travel motor. 6 is not.
Just pinned both tracks. Case drain is almost equal and nothing leaking from the swivel
You are making me think first if the motor was leaking at port plate or pistons it should cause high case drain if something is bypassing in head on motor you would not see high case drain it I remember right there are seals and back up rings in there
If I swap pressure hoses coming out of the mcv, I can make the issue go to the left side. That leads me to believe that it can’t be a track motor.
Could you tee into pilot line on slow side and see what happens to the pressure when you use the joy stick
Ain't that a 2 pump machine? If so, while tracking, lightly curl and hold the bucket in carry. Actually, operating any upper function will do the same thing. This will change the travel flow from one pump to each track to one pump on both tracks. If it tracks straight on one hyd pump, the issue is in whichever pump drives the lazy side.
I thought both pumps were joined when you did multiple operations while traveling. It was mentioned that the machine would straighten out when a joy stick function was operated. Just to be clear, the hoses from one track motor were swapped to the other track motor and the problem went along with the swap. I don't remember for sure but I recall someone telling me those pumps were positive control and not negative control like the smaller Cat excavators. Either way there are a couple of hoses attached to the main control valve that also connects somewhere on the hydraulic pumps. Somewhere close to where those hoses attach to the main control valve there should be a couple of cartridges. I would be tempted to swap those cartridges and see if the problem changed sides.
Oops I'm thinking of the wrong machine model. The 311B is a two pump machine and is negative control. There are two hoses coming from the valve to their own pumps and they signal each pump to come on stroke. As I recall they were either on or off meaning that they were not load sensing. You might swap those two hoses and see if the problem switches sides. That would be a clue we could work with. I don't have a book for that machine so don't have a schematic I could research and share with you.
Here's the schematic for an 8GR which is the World equivalent of the 8HR.
I left the machine before I did this but yesterday we swapped the pilot lines on the valve and the machine still was slow on the right, the only thing that changed were the pedals.
We did swap those 2 signal hoses over. Cat ran them through a small valve that they added when they put the diverter valve in.with those hoses swapped as soon as we hit any function it tried to stall the machine. The cat tech support guy called those the negative pressure hoses. At an idle they each had 500 psi and dropped to 100 when a function was activated. He said that was fine.
I mean installing a gage on pilot line and see the pressure at travel and then travel and implement
OK, then the next usual step is to install a flow meter and do tests on each pump and travel circuit. It is entirely possible that the pumps are not matched for flow rates. When it is mentioned that the Cat dealer went through the pumps, what does that mean. Most of the time it's bearings and seals and leave the governor controls alone because they don't have a dyno to bench test with.
Pumps just got returned from cat where they disassembled them, inspected, resealed, ran them on an dyno, and charged me $4000 to do it. We actually sent them to New Hampshire where they had a dyno because I originally thought I had a flow problem.
Out of interest did they supply the dyno reports when the pumps were returned.? @John C. Attached the Hydraulic SysOp just in case it's any use. Use anything that says 8GR it will also apply to the 8HR machine.
I had a similar issue with slow swing and one slow track, ended up being the governer in the pump was sticking. If I moved multiple functions I could get it to speed up as well. It was a 315BL
Thanks Nige for the attachment. I'm still reading through it and trying to resolve in my mind how it says the system is supposed to work and ways in which it is actually working presently. Mike L, have you done any cycle times on the boom up and stick out functions. It would also help if you have cycle times for track rotations.
Here is a dumb thought are the plungers on travel pilot valve worn ???
Alright. I spaced out for a few days but got back to it today. unhooked the diverter valve going to the mulching head so I could run it stock. It tracked 98% straight. I plumbed the valve back in and it still tracks straight. It slightly tracks to the right but it’s good enough for a machine that looks like it’s been through a demolition derby. Now I can’t get it to act up. I dunno. Maybe I flushed something out when I was messing around. I’ll let the owner run it and see what happens. Thanks for all the help.