Hydraulics Diagnosis

[Hydraman]

Don't know about the CUT's-- but on my 3020 the hydraulic pump is mounted in front of the engine, and has two 3/4" lines going to it from the rear of the tractor. In order for the pump to get oil there is another pump inside the tranny/hydraulic reservoir to move the fluid to the front of the tractor/hydraulic pump. If this "charging pump" goes bad, it could react the way you described. But, I would definately check the screen and filter first! On my 3020, when the filters are changed, I only lose the amount of oil to refill filter case while doing it. But, when cleaning screen, ALL the fluid drains out. So, make sure to have drain pan large enough to hold all the fluid when checking screen. On my 3020, when I clean the screen, I attach a shop vac to the filler and turn it on; then, when I pull the screen-- the vac keeps the fluid from draining out!!! Don't know if this little trick will work for you, or not. Good luck! Don

 

[Anonymous Poster]

symptom #3 definitely indicates air in the cylinders, and when combined with the other symptoms, indicates a lot of air in the cylinders.
You may also have a lo flow situation or lo pressure, but I'd bet on air being the major problem.

 

[Estif]

Just came in from draining the fluid, taking off all the filters, and then taking off all the suction line between the reservoir/transmission and the pump.

1. The screen does have some odd, small globs on it. Like maybe some bits of dirt fell in when I was checking the dipstick.
2. O-rings are all in good shape, and everything was tight. I'll be replacing the o-rings anyway, long as I'm in there.
3. I didn't start the tractor up at all, but there were still bubbles in the drained fluid. Guess this is just from making the drop from the transmission into the bucket.
4. The filter - not the screen, this one looks like an oversize oil filter - screws onto a mounting, of course, that is inline with the suction line. The suction line is rigid. The connections at the mount are compression fittings. May just be my lifelong loathing for compression fittings, but that's the only part of the line that makes me even a little suspicious. But there's no sign of a leak, even there.

So, now what? Put everything back together, new filters, new fluid, and see if it works? Should the air that's going to be in there as a result of opening all this up just work its way out? Likewise, should the air that's probably still trapped in the cylinders just work it's way out if everything's sealed up where it should be? That's my understanding of how it's supposed to work in an open system like this, that it doesn't need bleeding like on automotive brakes?

Steve

 

[kubmech]

O.k. Steve, looks like everything checks out as far as the delivery system is concerned. Now the next step would be to flow test the pump. However, most guys don't usually have a flow meter laying around the garage so......You have a couple of options. Put it all back together and give it a try (yes running all your hyd functions against relief should bleed out all the air) Listen to the pump while you are operating the hyd's. Is it making any noise, does it get hot to the touch real fast? Do the hyd's even build enough power to open the relief valve and bog the engine? Should get about a 300-500 rpm drop off when hitting relief (say bucket curled all the way back and hold it there) if you are not getting that then I would have to say the pump is the problem. That's about the best way to tell if the pump is the problem. The other option is to remove the pump and dissasemble it carefully. Look at the aluminum housing (the gears will most likely look good) is it erroded wear the gears ride? if you can click your nail on the ridge then that would confirm the bad pump. Another option (if the spin on filter is on the return side, can't remember on the 950) you can cut that open and check for aluminum particles. That is also a good sign of pump failure. You can even check for that by draining the trans at the lowest point, depending on wear the filter is in the system. And see if any aluminum particles collect in the drain pan. They will be very fine. At this point, I would suspect the hyd pump.

 

[Estif]

Found the problem, I believe. Tuesday night I didn't have all the fluid and filters needed to reassemble and try it out, so I decided to go for pulling the pump off. First, though, I did cut the spin on filter open and found very small amount of aluminum filing. So, took the pump off and found it has a coupling on the shaft that mates with something inside the engine. The service manual said "remove the nut and washers on the end of the shaft and remove the coupling." Sounds good, except the coupling wouldn't budge. While prying and beating, I managed to break the shaft off the pump, leaving it stuck in the coupling. Thought, well, whether the pump was dead before or not, it surely is now. This morning I took the coupling and showed it to a mechanic at the JD dealer. He knocked the shaft out and we found that the key had sheared, allowing the coupling to spin on the shaft, giving intermittent pumping, apparently. That is, it spun under torque from the engine. To hand pressure, it was like a press fit.

I do appreciate all your assistance here, all of you. I have a pump on order and will post when I get things put back together.

Steve

 

[kubmech]

Glad to see you found the problem. I am curious what the inside of the pump looks like, so if you get a chance?/w3tcompact/icons/wink.gif?

 

[bgott]

If it doesn't fit, force it! If it breaks, it needed replacing anyway!/w3tcompact/icons/grin.gif Glad you found your problem. Sometimes, in spite of using any and all diagnostic procedures, you just have to take stuff apart and look at it to find the problem.

 

[Estif]

No problem. I'm posting a picture of the disassembled pump. Or at least trying to. Insides look pretty normal. Gears are pristine, bushings look fine. Very fine ridge in just a couple spots around the holes where the gear shafts or bushings contact the aluminum cover. May be a little ridge in the wall of the body where two of the bushings are - at least I can't get them out. The gear with the longer shaft is the one that I broke off...it was a couple inches longer still.

Just got the pump back on tonight, but the plumbing's still all over the floor. Christmas is ten days away, I've been making presents at a fairly frantic pace.

Oops, it says my picture's too big, and I can't figure out how to make it smaller. Sorry.
Thanks,

Steve

 

[Estif]

Rejoice, I have good tidings of great joy! Well, besides the much greater tidings of much greater joy announced by the angels...

Last workday of the year for me was yesterday, so today I finally put all the hydraulics back together - and it works! Faster and smoother than I can remember! There will be some seat time catching up with things after I get back from the family gatherings!

Thanks again,

Steve