How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Fieldtech59 Your Own Question
Fieldtech59
Fieldtech59, Shop manager
Category: Construction and Road Equipment
Satisfied Customers: 111
Experience:  Construction equipment repair technician since 1986, JLG certified, Shop manager since 2006.
75637220
Type Your Construction and Road Equipment Question Here...
Fieldtech59 is online now
A new question is answered every 9 seconds

I have a 120 cat excavator (1992). Over the last year or so

Customer Question

i have a 120 B cat excavator (1992). Over the last year or so my final drives have been displaying less and less power. First I lost fast travel, but slow was still strong, but that has continued to decrease. Could it be the travel control level not actuating the valve fully, or should I look for a deeper cause?
Submitted: 1 year ago.
Category: Construction and Road Equipment
Expert:  Fieldtech59 replied 1 year ago.

Hello, yes, I've seen dirt/debris build up under the actuators for the drive control levers that restricts full movement and engagement of the drive controls, but if your machine suffers from slow/weak drive in both directions equally, it's likely not a control valve problem. Likewise, if both left and right drives seem equally weak, in other words, one side doesn't drive faster than the other, then it's likely not a drive motor problem. I only say that because the chances are slim that both drive motors crap out at the exact same time. It's not impossible, but improbable.

The best way to do a test of the drive motors is to remove the case drain line from the motor (be sure and cap the hose that you removed or it will leak oil from tank), then raise that track off the ground with the boom and operate that drive while you monitor leakage (flow) from the case drain port on the motor. If it leaks out more than a gallon of oil in a minute then the motor is suspect inside.

One other thing I can say about those machines is your problem can be in the rotary joint that delivers oil from the upper structure to the lower track frame. I've replace the rotary joint seals in several E70B and E120B Cat machines that was doing the same thing your machine is doing, weak drives, you could hardly get them to turn with the tracks. You might consider dropping that rotary joint and fitting new seals in it first. For someone who's mechanically inclined it's not a terribly difficult task, and even if it turns out to not be the problem, it's a major component that's been refreshed for not a lot of coin. Also, even if it's not the problem at present, it would be in the future because those seals will eventually fail on that vintage machine.

Related Construction and Road Equipment Questions