Bobcat 743 runs good for ten minutes then squeals like a stuck pig

[Joe Hall]

Hey guys. You guys helped me out before hope u can do it again. I bought a 743 has 2400 hrs. Decent machine. Runs great for ten minutes then it wont lift or tilt. And barely turns. Hydro oil overheating? Do these have oil coolers. If so where are they located. Im just hoping its not a bad hydro pump since it runs good at start up. I believe it is a 93 model. I Have seen some similar posts. And if it is the hydro pump is it a difficult job. Im mechanically inclined with cars but never worked on hydraulics

 

[Tones]

The 2 most common causes for hydraulics to squeal are 1, cavitation, oil not getting to the pumps, low oil level, sometimes jerky hydraulic movement. 2, a relief valve sticking part way open, pluged filters etc.
Changing the filters is a good place to start looking and cut the old filters open to see if there is any metal or rubber particles in them.

 

[Joe Hall]

Ok thanks. Are there only two hydraulic filters. Ive heard there are some hidden filter on these

 

[Bumpsteer]

One hydraulic filter above the battery, thats it. I use a Car Quest 85482, made by Baldwin

Older machines had a bronze in-line filter, long gone before your machine was built.

Oil cooler is under the radiator, looking into the engine compartment, acess door is in front of you, top of the fan housing. Look above the exhaust flex pipe, cover is held on by wingnuts.

Ed

 

[Joe Hall]

thanks ed appreciate it... im going to mess with it tomorrow. hopefully get something going.

 

[Joe Hall]

Okay put a new filter on with no change. Should i flush the system? Multiple flushes?pump or take a hose off to get the most fluid out of it? Also i was using iso 32 hydraulic fluid before so i bought some rotella 15 40 motor oil when i bought the filter because ive heard bobcat used to recommend it in the older machines.. Next step? How would i go about checking a relief valve... (Time to learn some hydraulics)

 

[crewchief888]

Do you have a strange "seat of the pants" vibration?

 

[seville009]

I assume you’ve made sure the hydraulic oil is full? I ask just because you don’t mention it.

 

[Vetech63]

You need to check the charge pressure on your drive pumps and make sure it's not dropping. Your implement pump is a gear pump on the back of your piston pumps and runs to your control valve. If your losing power in both, the only thing I remember them having in common is the hydraulic tank, and the pump drive on the flywheel. It sounds like you either have a suction leak, bad suction hose......causing cavitation in your hydra/hydraulic system. When this starts, check your hydraulic oil.......see if it looks foamy.

 

[Joe Hall]

Ok thanks for all the help. Havent been able to work on it the last few days. But i dont feel any strange vibration in the seat. The hydraulic was just filled when i replace the tilt cylinder seals. It was doing this before i changed the seals. Also I dont see any leaks from any lines. I havent ran it alot to see if im losing any hydraulic fluid. Ill try that hopefully tomorrow.

 

[crewchief888]

since you mentioned you resealed the tilt cyl...
was it doing this before you did the cyl?
if not, and you dont have a leak anywhere, try this,
engine running boom up and hold over relief for a few seconds, lower the boom and hold over relief.
then do the same thing with the tilt, both directions over relief.
older bobcats were notorious for trapping air in the system. it may take several attempts. also, the suction hose going to the pumps has a tendency to shrink to the point where the hose clamps arent tight. may want to check there as well.