My 1st Bob cat, owned it for 2 mo.s light work around the homestead, graveling drive, cleaning out an old collasped garage. about 15 hrs of use so far. I had a problem with my drives failing. Followed the 743 post about cleaning the large bronz filter in the center hose of the manifold did this. But still will not motivate. Was hauling crusher run fill to the old garage base filling it so I can pour a concrete slab, hauling material up a 15% grade, approx 200 feet travel distance, dumping and backing out with a 90 degree turn back down to the material pile. After 4 such excursions, activating the handles to back-up the the machine did not respond both handles went limp, and only the centering spring keep them in there rest position, no hydralic feel through the handles, after several attempts I got the machine backed out of the fill site, mostly it was the right side drive doing the moving, got machine back down to the flatts, and fiddled with the drive handles and occasionally I'd get a response, nothing indicitive of correct operation. Again I pulled the hose and large filter all looks pretty good to me. Last Sat. I spent the day trying to trouble shoot the problem, I don't have a manual so I may be off base with how the actual fluid flows, but I've deduced that the steel pipe from the drive pump adapter is the circulation from the pumps to the oil cooler ???, I was told the check shuttles above the drive out ports are pressure by-passes so I pulled the one above the right drive out, and all appears ok, than veiwing from the front of the machine, on the right side of the pump adapter, is another pressure relieve shuttle valve ??, I opened this up and there seemed to be a lot of built up pressure, so I'm thinking I might have a plumbing problem. Why because I hope so since both pumps seem to drop off-line symontianously, and when its working right plenty of drive power, I don't know what criteria is for condemning the drive pumps.
643 intermitten drive problem
- Thread starter Rob64
- Start date
It sounds like you aren't getting charge pressure, that's what the hose is from the oil cooler. Without it, the pumps will starve for oil.
You need to start by getting hold of a 200 PSI gague and install it into the oil pressure sender hole, you should have a sender screwed into the square block. Pull it out, install the gauge. Run the machine and see if it gives 90-120 PSI (or around that).
The bronze filter, did you clean or replace it?
Looking clean doesn't mean it is.... you can try running it without too, see if it changes.
You need to start by getting hold of a 200 PSI gague and install it into the oil pressure sender hole, you should have a sender screwed into the square block. Pull it out, install the gauge. Run the machine and see if it gives 90-120 PSI (or around that).
The bronze filter, did you clean or replace it?
Looking clean doesn't mean it is.... you can try running it without too, see if it changes.
Thank you for the input. I'd had an issue with the steel pipe which feeds the oil cooler, it came in Friday, so I got it installed this weekend. I had cleaned the bronze filter with brake parts cleaner, and compressed air from the inside to out. Installed pressue gauge per your instructions, at idle I got two PSI, at goverened output it went to four (4) PSI, I thought about removing the filter and seeing it that would improve it. When I picked up the new pipe, I asked one of the mechanics, and he explained the circulation thearoy to me, and said the hydralic pump has plastic vanes and they tend to fail over time. I had seen crumbly black particles on the filter outter surface, so I thought it might not be wise to remove this filter incase I have vane failure. If I understand correctly the hydralic pump maybe my ultimate issure?
The hydraulic pump should have steel vanes, not plastic...... Your lift and tilt still have lots of power?
It could also be something holding your charge relief open, 2-4psi is not enough, your pump is starving for oil, if you keep running it like that, you will cause pump damage.
I'm not sure where the relief is located on the pump, its behind a plug, but i can't tell you what one, no doubt its hard to get to....
I'm not using the machine, it's more the drive is sometimes available, but more trouble shooting till I have the problem solved. Since the fluid pressure goes from the pump to the hydralic control, is there some form of regulator in that case, that drops the fluid pressure before sending it back to the manifold?
![Pampers Sensitive Baby Wipes, Clinically Proven, Fragrance Free, Unscented, Water Based, Hypoallergenic, Multi-Use, Hand Wipes 336 Wipes Total (6X Flip-Top Packs) [Packaging May Vary]](https://m.media-amazon.com/images/I/41KLBHu9CAL._SL500_.jpg)
The way i understand the circuit is the fluid that goes to the oil cooler returns back via the pump that has a charge pressure relief. This restricts the flow so it reaches the correct pressure, the remainder goes back to the inlet of the hydraulic pump and reserve tank. The pressure is regulated by the main hydrostatic pump, there should be a relief screwed into the centre section somewhere.
When I was at the dealer Fri. he printed the plumbing parts and layout, 1 set for seriel # 14999 and below, an another set 15001 and above, my machine mimics the 14999 and below plan, higher seriel # appears to have the geared hyd. pump, an extra module to combine the oil flow from the drive motors, mine has a three hose arrangement drive motors with one line common from each motor feeding the oil cooler circuit, the line that is right of the bronze filter line, returns from the hydralic control box, it has a spring loaded shutle valve in it, and slots to keep it from completely closing off return oil, but I back off the line with it runnig, and there was very little oil coming back from the hydralic control box.
Not really sure where else to look. The older style had hoses everywhere and big port blocks...
