Hello all. I'm new here and not a pro, so please bear with me. I am working on a Cat 312 B L with about 3,000 hours on it. This machine is not used much, as it resides at a hunting camp, rather than a construction site, farm, etc. Over the course of about a month, all of the hydraulic fluid leaked out of the machine at the right hand drive motor on the tracks. I removed the cover and ultimately removed all four hydraulic hoses attached to the motor. I have found that the only hose damaged is the small (about 1/4 inch i.d.) hose, due to it rubbing against the framework of the machine. I don't know what purpose this line serves unless it bleeds off any internal leakage in the drive motor. As a sidenote, I'm quite confident the leak was not from the motor itself, as all the mud and sediment around it was not disturbed. The oil was running out of the framework of the machine. Also the hub under the center of the machine where all the hoses attache is all dry. No leaks there. Here's the part that raises a question in my mind. I took the cover off to access the left hand drive motor just to clean out all the mud and sediment. The same small line was worn nearly half into, but no oil leaks from this side. It was all dry. Why would the right hand side leak but not the left? Think there is a problem with the RH travel motor? The RH is a little weaker than the left. Thanks in advance for any thoughts.
There are 4 hydraulic hoses and the small one comes out of the bottom or side of the motor, correct ..? At least 2 of the other 3 are the same diameter. What you have are 2 identical hoses to drive the travel motor, a 3rd to release the brakes, and the small hose is the case drain for the travel motor. All piston-type motors will leak a bit of oil into the case so this line returns the leakage to the hydraulic tank. That's most likely why it has drained your tank when it failed. Obviously the hose from the other side has not worn quite through the outer casing to allow it to leak. Install 2 new hoses - unfortunately the Part Number varies depending on what Serial Number prefix of machine you have. Check the existing hoses, you might be lucky & one of them might just have an aluminium tag on it with the Part Number marked on it. The hose goes from the travel motor to the centre swivel as you have already found. After replacing the hoses fill the tank and you should be good to go. Maybe you could try routing the hoses on both sides of the machine a bit better so that they don't chafe so much on the frame. Zip ties are your friend.
Yes, the small line comes out of the bottom of the RH motor and the top of the LH motor (same motor just flipped to use on RH or LH, I guess). The case drain function makes sense. No tags or part numbers on the damaged lines, but believe it or not the local autoparts store had the correct fittings to make up new hoses. Thanks for the insight.
The small one is the brake release line.
Thanks ih100, but that raises a question. If the small line is the brake release, it would obviously release only when pressurized. The same line on the left side of the machine is worn nearly half into, which would leak catastrophically when pressurized, but it doesn't leak (my leak is on the right side). Any thoughts?
Sorry that's not correct, and neither was what I posted above ...... The travel brakes are released by the flow of oil in the 2 large hoses connected to a valve (brake valve) mounted on the travel motor itself. Applying hydraulic pressure to one or other of those lines (the other one becomes the oil return line to tank) releases the brake at the same time as it starts the motor turning in one direction or another. Releasing the hydraulic pressure stops the motor and internal springs apply the brake. The 3rd line is the signal line for the changeover of Low/High speed travel at the travel motor. The 4th line is the travel motor case drain. In the photo below which is of the LH side of your machine the 2 main motor hoses are marked 8 & 9, the smaller size hose connected into the top of the motor is the case drain, & the smallest hose of all connected to the bottom of the motor is the 2-speed travel signal line. For the RH side of the machine the positions of the last 2 lines will be reversed, i.e. the case drain line will be connected to the bottom of the motor & the 2-speed signal line connected to the top. Apologies again for confusing you earlier.
Thanks, I'm going to replace the lines, refill the hydraulic tank, bleed the pump as the owners manual says, and see what happens.
Sorry, hadn't got brain in gear - I was relying on memory!
No worries. I was also relying on memory when I made my first post ........ Definitely bleed the feed line to the pump before you start the engine if the hydraulic tank has been drained for whatever reason. It's always good practice.
I've been on the cat service info system and had a look at this. It isn't clear but it looks like one of the lines is connected into the brake valve, so that when the brake is applied, the oil released from the brake is ported into the return line. So it is linked to the brakes, even though not releasing them.
Thanks to all for the input. I put the machine back together and all seems well with the hydraulics, but I now have a new problem. I'll post a new thread. Thanks again and have a Merry Christmas.