Ok Guys - got a chance to really run and operate the CAT 235 this weekend that I've been trying to get into shape after buying it with a blown motor on an auction. A couple of weeks ago some of you guys helped me with questions regarding the hydraulic swivel. It was leaking out the top under the valve body and so we put all new seals in it and it still wanted to leak. I thought I'd try it out this weekend even despite it leaking and see how it worked. What I noticed is the driving it forward and backwards seems to be just fine. Drives a nice straight line both ways. If I want to turn however it has a tough time, sometimes worse than others. Sometimes it won't even want to turn as I move the steering stick one way or the other it'll just sit there and not do anything or it will be barely moving one track. If I just drive straight back or forward and try again then it might work OK but it's very un-reliable in moving around that way. Another thing I noticed was the warmer the machine and oil got the weaker the stick seemed to be. There were times digging that it wouldn't really even act like it was pulling and I'd have to curl the bucket or lift the boom up to fill the bucket up. Other times it wasn't bad but it seemed somewhat weak for the size of the machine I thought. Another thing that I noticed right toward the end of the day was that pulling the boom out of the hole with a full bucket would sometimes pull up nice and quick and you could hear the motor pulling down and then other times it was very slow to come up and the motor wouldln't be pulling down under load, if I let off the control lever and then pulled it back again sometimes it would take off lifting quickly and loading the motor, then other times doing this it would act better for a split second, motor would lug down then let off and it would raise slowly. I know this is a lot but I don't know what I've got going on, maybe one thing maybe a multitude of things. The machine itself has about 22,000 hours on it so I'm guessing things are quite worn. What I'd really like to do is sell it and pick up a newer smaller machine with a thumb and coupler but don't know that I'd get much out of this one in it's current condition and don't know how much a guy should put into it? Any help would be appreciate guys. Thanks very much. Chris
The fact that it sometimes works well and lugs the engine makes me think it's a pump control or pilot system problem rather then anything serious in the pumps. That machine uses an under speed valve sensing pilot flow to signal the pumps up and down. I would be checking the pilot pressure first and inspecting the pilot filter. They check the pilot pressure under the cab on a -12 jic fitting . I think you could test it on the pilot filter too but Cat recommends doing it at the cab . I think it should be around 325 psi but I'd have to look it up.
Have new filters coming. Hoping that's a lot of my problem. Is it obvious where the pressure check port is under the cab? Is there a good way of checking the main pump output pressure? The stick has always seemed a bit weak to me but am not familiar enough with excavators to know what I should expect.
The pilot test port is a capped jic fitting under the cab about in the middle I think. The main pump tests ports are on the outlet lines on the pumps They will either be a plug or a quick coupler.
As for the steering problem, Your machine works best if you pivot turn or counter rotate to aim the machine and then travel straight making small corrections in direction. It doesn't like to travel in an arc very well. The lifting out of the hole at end of shift sounds to me like you are getting intermittent two pump flow. The crossover valves are set at twice the pilot pressure as the main spools for smooth engagement. Implement spools start flowing oil at 60 psi crossovers 120 psi. Also the crossover will only give oil flow not being used by the other pump. Later Bob
Hey Bob, have you ever installed a hydraulic thumb on a 235c excavator?
Bob was last here more than 9 years ago. stick to one thread and did you post up your serial number there?
And unfortunately he passed away around that time. A very respected member of this forum. Still remembered.
Very sad to hear of his passing, he clearly had a very broad in-depth knowledge of machinery.