Cat E-120B travel problem

Our cat E-120B excavator travels fine when it first starts, turns good, pulls good, quiet..everything seems great, after its run a while it seems like the brakes are dragging, can't turn, every bump stops it.. sometimes you have to rock it back and forward a little to get it to move, and it seems to make a screeching sound when it moves..when it does travel it will suddenly break free and travel real fast then down shift to low range ( its always in low range on the switch) then it seems to bind up again.. HELP.. ANY IDEAS?? cat dealer was no help..they say its a grey iron machine, not ment to be sold in north america..BULL.. this is same dealer that sold the machine!! seems like it is shifting between high-low-and brakes slightly set is this possible?

It's possible that the brakes drag, just have to figure out whats causing them to do so. Not familiar with this machine but you may want to check to make sure that the brake release holds pressure. Up under machine there should be a bunch of lines, on ones I've seen the main drive lines, two or more go to a brake valve then to the travel motor. There should be a smaller line coming from this brake valve, try pumping this line going to motor up to 5-6 hundred psi with a port a power and see if it holds pressure at all. Have you checked the oil in your finals? I'm sure someone else will chime in with more info on specifics.

thanks for the info.

Thanks for the info, there is a small plastic hydrualic line going to the drive motor, is that what your talking about?

roadrunner81 said:

It's possible that the brakes drag, just have to figure out whats causing them to do so. Not familiar with this machine but you may want to check to make sure that the brake release holds pressure. Up under machine there should be a bunch of lines, on ones I've seen the main drive lines, two or more go to a brake valve then to the travel motor. There should be a smaller line coming from this brake valve, try pumping this line going to motor up to 5-6 hundred psi with a port a power and see if it holds pressure at all. Have you checked the oil in your finals? I'm sure someone else will chime in with more info on specifics.

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what is your machine serial number, ngw?

The brakes are released by the pressure operating the motor. They can't drag unless the motor is completely shot. You got some kind of hydraulic supply problem such as the motors them selves, the swivel, main control valve or the pumps.

John C. said:

The brakes are released by the pressure operating the motor. They can't drag unless the motor is completely shot.

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I'm glad you confirmed this John C. I didn't know enough about the 120B to be certain, but I did suspect this was the case.

The S.N is 7NF02360... Is there any way of testing the drive motor pressure at the motor itself to isolate where the problem is, the parts manual show a travel brake valve mounted on the drive motor, could it have a relief valve in it? Also could the rotary manifold be going bad and letting the pressure fluctuate, in affect confusing the drive motor? The machine has just under 7000 hours..both the engine and the hydrualic pump have been replaced ( lost half the pump function..no noise no warning just stopped) Thanks for the input!

I had a similar problem with my E120B.
Poor travel performanace when hydo oil is warm.
This is what fixed it.
check the main relief and sub-system relief to see if they are at factory specification.
Mine were out of adjustment, from former owner.
My machines travel brake valve was ok but the relief pressures in the left and right crossover pressure reliefs were way out of specifacation.
Test the swivel pressures for the travel circuit, and this was my main problem.
Found the swivel seals were worn, replaced seals with new seal kit
The repair kit is part number 1R-7903 cost $41.27.
I had it done at the CAT dealer shop
that and some other stuff came to $2896.94. $2264.00 was labor figuring out what was wrong and fixing it. Works like new now. Beats a 120 grand for a new one that does the same thing.
Hope this helps you.

To check the motor you block the track with a pin in the sprocket, unhook the case drain hose from the motor and cap the hose. Hook a short hose up case drain on the motor and put it in a bucket. Now start the machine and run that motor over relief. A good motor will only put a few drops of oil in the bucket when over relief. A shot motor will put a half a gallon in the bucket in less than a minute.

Checking the swivel is a little more complicated so you should check the motor and then the pressures. The pressures are controlled by the main relief on each associated valve. The circuit reliefs are on the motors themselves. Remember a low pressure could also be cause by oil flow leaking off somewhere else such as the swivel.

Good Luck!

wow!! great Christmas gift guys!! As soon as the snow subsides I'll bring it in and start checking things out. I'll let you know how I make out. Thanks again for all the help!

I have a swing issue almost like the swing break is sticking. Wondering if im looking at a new swing motor. Once and a while i get a bang when starting to swing and it feels like its a little sticky before the bang. cat E120b it seems to be gettig worse. Does the swing motor get feed through the rotory union? It wouldn't make sence that it did just wishing it was easy and cheep. Please help

Dave, the swing motor is in the car body, it gets its hydraulic pressure right from the valve block, I would start by checking the turntable gear and the drive gear on the swing motor, look for broken teeth, look for lose mounting bolts on the motor also check for excessive turn table play..if all this looks good, there is a swing brake option on your machine ( according to the parts book ) you will need to check the pressures on this as well as the motor itself as well as the reliefs..it seems a lot of these type of problems are signal pressure issues and not the actual componant failing ...Basically the system is not telling the componant what to do. Its a lot cheaper to do some testing than start replacing expensive componants. good luck.

Ok I will do exactly that. I appreciate the advice. Ill post my findings once i get it apart thanks again.

Oh, one more piece of info once its been running for a while if I throttle down to an idle and try to turn sometimes it will continue to bang untill I throttle up.