Hi everyone. Been reading this forum a while and finally decided to see if anyone could suggest where to start on this. I have a CAT 277 (SN CNC00566), which I believe to be somewhere in the 2002-2004 vintage. I bought this machine for cheap about 6 months ago. PO seemingly never cleaned the tracks which of course resulted in the tensioner frames rotting out completely. I rebuilt those, swapped almost all the bearings in the undercarriage, and rebuilt both sprockets. The drive pilot valve was leaking pretty badly and I recently replaced that as well as changing out the hydraulic fluid and filter with HYDO 10w. This issue became apparent before I changed the fluid or the pilot valve. I figured those both were in need of changing, so lets swap them and see if anything changes. Nope. The issue is that the machine and hydraulics are strong when its cold, just started up or after shutting it down for an hour or two. After running for about an hour or so, hydraulic power drops off considerably. The fluid/lines are just warm to the touch, not anywhere near what I would consider a problem temperature. I notice it mostly in the drive and less in the work tool side of things, although its hard to tell as I can't really drive into piles and things like that to really pick up good bucket loads when its acting up. After the machine is warm, top speed is reduced by at least 1/2. Turning becomes a problem where I really need to work it back and forth in order to turn, and this is on soft ground/muddy. When the machine is cold, I can spin that bitch on pavement with no issue whatsoever. When its hot, I can barely get it to turn at all on pavement. You can hear the engine loading up as I would expect under a heavy load condition, albeit less so when its hot. Onto the things I have noticed that might be an issue and give an idea where to start. When pushing a heavy load (like a boulder) I notice an odd noise from what seems like the engine compartment and on the right side, but hard to tell. At first I thought it was the turbo, but I am thinking it might be cavitation? It almost sounds like a bad bearing but only heard under heavy load on the hydrostatic. This happens hot or cold, and it does not make this noise while using the work hydraulics. The other potential problem I noticed is the machine, even when cold, is almost useless unless it is at full throttle. Again, mostly noticed on the drive side of things. At low idle, the machine can just barely move forward/backward. Mid throttle, it will have a very hard time turning on any surface. It doesn't become really usable until 3/4 throttle, but only for moving it around. I dont have a ton of experience with newer/pilot machines (yes, 2002-04 is a newer machine to me haha) and no experience with MTL's so I don't know if this is normal behavior or not. Just doesn't seem right to me. I have the RH drive motor at the hydraulic shop now for them to check out, but is there anything else that would potentially be the issue? I read through all the service documents I have about operation of the vane pump and piston pumps as well as the charge system and hydraulics flow. After reading this info, I am guessing my issue is either internal leakage in one or both drives when warm, or an issue with low charge pressure when warm. I don't have gauges yet, but I do plan on ordering a set shortly.
Hi ,why do you have the RH drive motor out ? Leaking, Noise, steering one way? The drive speed and work tool hydraulics, is dependant on good pilot oil pressure. The speed control valve in the hydrostat regulates a reduced pilot pressure to the LH drive pilot joystick . This regulated pressure is sensitive to engine speed and the condition/adjustment of the speed sesing control valve. A worn or weak pilot oil pump can cause the problems you are having Some things to check Does the engine speed drop off? Oil level correct ? Check that suction hoses to pumps have not gone soft or collapsed Fan speed while operating controls Pilot oil pressure
Hi Mark. Thank you so much for the reply. The reason that I removed the RH drive is some previous damage from the PO to the mount that I had welded back together which broke again (I'll post pictures, its gruesome). The mount and the motor more or less broke off the frame and caused all kinds of mayhem. I believe this failure occurred due to a bad bearing that had seemingly been left or unnoticed for a substantial amount of time, which allowed the bracket holding the 'bucket' that the drive is mounted to to flex back and forth repeatedly. I am in the process of fabricating new brackets and thought this was a good time to have that motor checked out while it was out. I was thinking about this a little while ago and I remembered that the LH drive brake is non-functional. I didn't think much of it, thought maybe worn clutches and it really didn't make any difference to me using the machine mostly on flat ground. Is the brake released by pilot pressure or hydrostat pressure? The thought occurred to me that if it is in fact pilot operated brakes, that perhaps with low pilot pressure it isn't enough to fully release the brakes and it just so happened that the LH drive brake is completely burnt out from dragging whereas the RH drive brake still has some frictions left to hold. I had been getting significant power loss to the RH track, but I simply discounted this to mechanical issues of the brackets and dragging. Engine speed does not change with this issue. Sounds consistent and strong. I did not consider fan speed changes with controls operation, and that would make sense as that is run off the pilot pressure, correct? Oil level is correct I'll check the suction hoses as well as pilot pressure.
the park brake is released with pilot oil and if the brakes are worn enough the brake seals can pop and lose pilot pressure To check just block off the pilot hose at the brake manifold on the inside left frame rail and see if your pilot pressure improves
Turns out the hydraulic shop I dropped the motor off to can't actually do anything with it...too big. So I picked it up today and had a look inside the brake housing. I found no linings on the discs at all, grooved out housing where the frictions and steels sit, as well as plenty of metal from the discs. Pictures attached. It's obvious that either pilot pressure is low overall causing the brakes to hang up, or the park solenoid isn't functioning. The piston seal in the brake housing LOOKS alright, so I'll be checking the actual pressure as soon as I get this drive motor back in and the brake ports blocked off. Seeing as I can't find any parts for this motor other than seals and brake discs, I think I'll be disassembling it to clean it out as I'm sure there was plenty of metal flake moving through the motor. My plan here at this point being an old machine and mainly used around my own property is to reassemble without the brake discs/spring washer and placing a shim that matches the compressed thickness of the spring washer, then blocking off the pilot line to the motor. The parking brake housing is junk because of the grooved outer spline and the machine isn't operated or parked on any hills to speak of so a park brake isn't strictly necessary. The question now is what am I missing? Do you foresee any complications or unintended consequences with my plan above to disable the brake? Is there a recommended flush procedure for the machine, or am i looking at disassembly/cleanout of the pumps too? There was 1 chunk missing out of 2 discs, but I was able to recover those. The rest was fine metal dust. Nothing I would expect to bind anything up. A service manual for this drive motor would be extremely helpful, even a parts list. I have a bit of endplay on the brake shaft (maybe a 32nd but I haven't actually measured it), but have no way of knowing what the spec is. Sorry for the long post here.