Cat 277B RH park brake not releasing

[zigblazer]

I've searched everywhere and can't find the information I need. You can skip story and go to the next paragraph if you don't care how it happened. I'm in the middle of installing the drain tile system around my wife's new building. I've prepped two sides, and started putting in the washed rock and pvc. I was gently dropping in washed rock to cover the pvc with the skid today and it started making a periodic squeaking, such as a rock hitting a rotating bolt when moving. Then with a full bucket, I turned to start dumping and I was stuck. The RH track wouldn't move. Figured there was a rock stuck, even though I looked it over 5 minutes before because of the squeak. Didn't find anything, but took a few minutes to clean out around the cage just in case. Had my 9 yo son get in and try to move it so I could see what was going on. At first I thought it was something on one of the end idlers catching a bolt, but after a bit more movement, I noticed it was not at the correct period, and it would stop the cage first and the track would slip a little over the cage. After a little thought I figured out it was the park brake not releasing on the RH side only, not something stopping the track.

The electronic portion of the park brake seems to be working properly. The LH track releases and moves freely. The RH only moves a couple inches. Released and applied I can feel and hear fluid movement in the small set of lines going to the drive motor. While on the LH side there is no evident fluid movement. My conclusion is that the seal inside the park brake piston has failed.

If the system is one application solenoid and T'd to the two separate park brake pistons, then it would need to be either a hose flow problem (damaged) which is unlikely, or internal to the park brake actuator/piston or whatever it is inside the drive motor that locks it. Now I can't find any actual information, so I can't confirm that. I can't even seem to find a parts diagram from Cat right now, which I thought I use to be able to access. I've had this 277B for 5 years now.

Here's my questions. Can anyone confirm that there is only one park brake solenoid, or that the lines are T'd from the control out to the drive motors instead of individual lines out? Does anyone know if the park brake portion is serviceable at all? Can it be disassembled and resealed, can you get seals for it?

I am/was a med/heavy truck tech. My specialties were electronics/computer controls and component rebuild. I would much rather rebuild an engine, than to remove it from the vehicle, but I've done both many times. I have no fear of disassembling a drive motor if I have the special tools to do so.

 

[Cmark]

Can confirm it's one solenoid valve supplying oil to both brakes. How is the oil in the final drive looking?

 

[zigblazer]

Thank you. As far as I know and can tell, there is no separate final drive fluid. It would be nearly impossible to check it. That diagram helps a lot, but gives me another idea I'll try to explain below. Could you post the rest of that diagram, or where the green dashed line goes to at least?

Being that the electronics respond as expected and the LH brake releases, I'm going to have to say there is something wrong inside the RH drive motor. Release piston seal completely gave way or shaft bent. Unless the fluid movement I hear/feel while parked is on that fourth line and it is somehow interfering with the park brake release. But without knowing that lines purpose and when it should have pressure/flow, I can't say. Looking at that diagram the forth line isn't for park brake application, that is spring actuated and hydraulic release, the forth line is something else. So there shouldn't be fluid movement while the park brake is applied. So why do I have definite fluid movement going to/from the RH motor, but no evidence of fluid movement to/from the LH motor? Could something have gone wrong internally allowing flow where there shouldn't be causing the park brake to not release? Or could something have failed elsewhere, maybe sending fluid to that forth line which is preventing the park brake release, such as that line being a drain that is somehow now pressurized? By that diagram it sure looks to be a case drain, and if so it could cause the failure to release, and that also would mean my problem is not internal to the drive motor ($3,500 cat reman part) but would be caused by a faulty valve that line goes to. I don't want to tear into an expensive motor and possibly screw it up when it isn't even the problem.

I drug it around the building and all the way down the driveway to the shop. I took it apart to the point of removing the drive motor, but did not remove any lines yet. I wanted to talk to Cat parts to see if there are any parts available to repair that park brake inside the motor. Hopefully someone there can give me more information too.

 

[Cmark]

As far as I know and can tell, there is no separate final drive fluid.

Yes my mistake. It's a B series. My mind was on the wrong machine.

I think the smart money would be on a final drive failure. If the park brake piston seal had failed, I think it would take the flow away from the other side as well and it would not release.

The green dotted line is indeed case drain/loop flushing return. If you can feel fluid going through the case drain line then that indicates large internal leakage allowing charge flow to return to tank.

Attached schematic.

 

[zigblazer]

Thank you very much. If I understand correctly, my problem is not simply a failed seal in the park brake portion of the motor. It is likely a larger failure inside the motor allowing the charge fluid to return through the case drain/flush line.

Does that mean I need a new drive motor? Can you get seal kits and are they rebuildable without special tools?

 

[zigblazer]

I have a lot of experience with component rebuild. Mostly automotive. There isn't much on a pickup I haven't rebuilt. I've rebuilt starters, alternators, turbos, steering gears, steering pumps, axles, transfer cases, transmissions, engines, truck transmissions, truck engines, truck axles, and many other items that I can't remember right now. I rebuild the main hydraulic pump on my deere 310d, which was super simple.

Is this drive motor something I could rebuild myself?

I don't have a business doing this stuff. I don't make money with it. We are stretched financially because we are building a new building for my wife's dog training business. I am doing all the ground work. Currently halted in the middle of installing the drain tile. We have had no rain for 7 days, which is the longest stretch we've had all summer. Look like it should stay dry for 5 more and I need to get this done before our clay turns to a sloppy mess. I don't think I can get the deere in to dump the washed rock. I need my skid steer if I'm going to finish this week, but I am not sure we can afford to just buy a $4,000 motor. And I know I'm not physically able to shovel the rock into place.

 

[Nige]

If I understand correctly, my problem is not simply a failed seal in the park brake portion of the motor. It is likely a larger failure inside the motor allowing the charge fluid to return through the case drain/flush line.

Your problem MAY be something more than a brake issue, at this point it is impossible for anyone to tell.

Is this drive motor something I could rebuild myself?

I can get the motor disassembly/assembly instructions but would need the either the machine Serial Number or a Part Number from the existing motor first. The reason for that is that there was one motor Part Number fitted on machines up to MDH01599 and a different P/N fitted to machines from MDH01600 onwards. The earlier motor is superceded by the later one so if a machine 1599 or lower failed a motor it would likely have been replaced by the later P/N.
If you can find a P/N tag on the existing motor that would be good but if not would have to go by machine S/N and for a machine 1599 or lower assume that the installed motor is what it was originally built with.

 

[zigblazer]

My serial # is MDH01949. I think the part number for the motor is 280-7864. What you said make sense. If there is fluid movement, which there definitely is, it could only be charge fluid flowing. If a seal inside the motor let loose and is causing some pressure to build in the drain circuit, it could counteract the park brake release pressure, it would then in effect keep the park brake applied. I think you are correct, if the park brake seal let loose, then there wouldn't be enough pressure built up to release the LH brake fully. But some pressure in the drain circuit fighting the park release pressure could cause only the RH brake to not release.

 

[Nige]

I think the part number for the motor is 280-7864.

That Part Number is the later one and ties up with your Serial Number. Here is the parts list which does include a seal kit. I will send you the disassemby/assembly instructions. Keep an eye on your PMs.

 

[zigblazer]

Thank you very much. I think I'll gove Ziegler a call in the morning, tried this morning, didn't work. But I'm glad I had to wait. I didn't see anything special so I'll give the rebuild a shot. Unless i find worn/broken parts, I expect it to work.

 

[zigblazer]

Took it apart today. Not going to work. A piston was stuck and broken in the bore. Ring was all scored. I'm guessing it would cost as much for the pieces as a motor. Put it back together and will call Monday to see about a replacement. Thanks for all the help.

 

[Nige]

Now your issues really start. The shrapnel from the failed motor will be everywhere right throughout the drive system and the implement hydraulics. Cleaning it all so that nothing can get stuck somewhere and cause another failure will present a significant challenge.

 

[zigblazer]

Do you have any suggestions as to how in depth I need to go for flushing? Is it a type of system and failure that needs the tank removed and cleaned, all lines disconnected and flushed, cylinders passively moved and flushed, etc? Or can I drain the tank and fill with diesel, run everything under no load to flush, drain, change filter, and refill with good oil? I guess with that method, I'd probably run everything again under no load, then change fluid again.

From the diagram, it looks like the cooler is on the return circuit for the motors only while the filter is part of the charge circuit but after the fan. And a screen on the inlet to the implement control valve. So at a minimum I would want to disconnect the cooler and back flush it separately. Pull that screen and clean it out. Drain and try to flush the tank if there is a drain that wouldn't route everything right through the drain manifold.

I've flushed a couple systems, but they were much simpler. I flushed my Deere 310D, but that only has three cylinders, a pump, and control valves. At the moment I'm thinking I'd start by draining the tank (and trying to flush), disconnecting and flushing the cooler, clean the control inlet screen. Then what? Install the new motor, when I get one, refill with 80/20 mix of oil/diesel. Or pull more apart and flush the lines?

What would be the best way to go about flushing?

 

[Nige]

I'd suggest first to drain the oil and see if it's full of "sparklies". If it is then I think you have a major cleaning job on your hands.
If it doesn't look too bad then the next step would probably be to cut the filter and see what's in the bottom of the pleats. I know this link is not a hydraulic filter but it will give you the idea of how to do the inspection.
Report back with what you find.

 

[Gary Layton]

That is a very good video....thanks for the link. Looks like a good channel.

 

[zigblazer]

I drained the oil into a clean tub, nothing sparkling. I haven't taken the filter off yet, but I think that is a good start. Hopefully there isn't a pile of shavings hiding in the bottom of the tank. Thank you again.

 

[zigblazer]

Broke the damn arm cylinder rod on my excavator. Not good timing for the amount of work left to do before winter or the amount of money we have left to spend on it. Luckily it has been raining the last few days. Have to call tomorrow to see how much it is going to cost to get that fixed.

 

[zigblazer]

In case anyone was interested. I got a new drive motor from TLP. Even has a CAT label and s/n on it. Took apart the filter, found maybe 10 flakes of metal total, so I did not completely disassemble and flush the system. Drained, flushed tank, flushed lines to motor. Filled with new fluid/filter and everything is working great.

Thank you for all the help.

 

[Nige]

As insurance it might pay you to run it a few hours, change the filter again and do the same inspection to see if it’s picked up any more debris.

 

[zigblazer]

Sounds like a good idea. I was actually thinking of just draining the fluid and changing the filter after a few hours, but it would make more sense to see what is in the filter. Thank you.