RTV900XT loses drive etc when warm

V

valiant

New member
Hi all,
I've recently picked up a Kubota RTV 900XT with a blown engine, 4200hrs. I was able to pick up a low hour D902 out of another RTV that went straight in, and runs very well, 1200hrs. On testing it out, and making some adjustments (the 13 point Aurthuritis test), I have found out some things. When cold, it goes fine, but is weak in High range. When it is warmed up, it won't drive uphill in M any faster then L. And H is no faster [then L], but less torque. Coming up our relatively steep drive, it lost drive even in L, but when I put it in M then H and revved it up, I put it back in L and it drove up alright. When cold, in gear, it doesn't move, but when hot it creeps forward or reverse, depending on the gear selected. Also when it is cold, in L & M it locks up the wheels when the pedal is released, but it doesn't when warmed up. This morning I hooked it onto an immovable object (4 ton tractor), and in L it spun the wheels and 5-10 seconds later they quit turning, in L range. What might this appear to be? I have not changed the oil or filters yet (that is my next thing, then testing pressures) but it is a good level, and is very clean. I have not had an RTV before, only Mules, and bought this as our hills we run on are extremely steep. Any help or thoughts will be appreciated.
Thanks!
 
I'm not 100% sure about the XT models, but on the straight up 900, there's an aux pump that can be used to help with power (but at a loss of speed).
When more power is needed (e.g. when climbing up a hill), don't mash the go-pedal to the floor. If you do, the engine will start bogging down. When this happens, feather off the pedal to around half way. You'll know you hit the sweet spot of when the aux pump kicks in as you'll hear the engine revs go up and more power is available.
 
Yes, it's an older model with H M L, being the XT it has a sticker on the dash saying Plus 2 Variable HST. Will do and report back. Thanks
 
aurthuritis said:
If you have a high medium and low transmission then your machine is of the old designe. Change oil and filters with oem and super udt2 oil then report back. Change the oil in the tank under the seat also.
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This is good advice - I add that the suction filter in the hydraulic tank should be taken out and cleaned. Perhaps under load this filter is preventing oil flow. It is a very fine metal screen and is often not looked at. In fact the dealer from whom I purchased my first RTV did not know about this! At my first 50 hour oil change I could not remove the filter (way to tight) and I called to get advice about removing it, as it was still under warranty and I didn't want to damage it, and the service person had no idea what I was talking about! I eventually bit the bullet and used my burb gun and got is free. With regular oil changes it won't get clogged, but if your machine was in a mine and had minimal complete maintenance I wouldn't be surprise if that is your problem.
 
On the old models there is a rubber suction hose near the filters and the primary pump that can fail. Is can collapse and get flat or can also be completely internal blocking suction from the tank. Look for debris in tbe suction filter.
 
aurthuritis said:
On the old models there is a rubber suction hose near the filters and the primary pump that can fail. Is can collapse and get flat or can also be completely internal blocking suction from the tank. Look for debris in tbe suction filter.
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We live way back and don't get to town often, but will be picking up the oil and filters next week. The other day I pulled both filters off, and they looked good and clean. I pulled both short hoses, and they also looked good internally. Would it be worth replacing all oil lines? I also dropped the oil, and in an experiment, strained it and put it back, and there has been a noticeable improvement. But I think I am getting onto what is actually the problem - I'll try to describe it concisely. I had stated previously that when the oil was warm, it would not go into neutral - I think I know why. When hooked onto the tractor, I unhooked the HST lever on top of the tranny, and set it in low. I revved the engine some, then pushed the lever forwards. It spun fine, but when the oil was warm, when the lever returned to neutral, it still rotated, then when I moved it forward again, the wheels didn't move until I moved the lever backwards past neutral and forward again. Also when I pushed the lever back into reverse, it doesn't have enough power to drive it backwards, not pulling anything, towards the tractor! I believe that the servo piston is sticky, and when the oil is warm there is not enough pressure to move it completely. After the oil change, I think that is the first thing to work on. What do you think?
 
BiffNH said:
This is good advice - I add that the suction filter in the hydraulic tank should be taken out and cleaned. Perhaps under load this filter is preventing oil flow. It is a very fine metal screen and is often not looked at. In fact the dealer from whom I purchased my first RTV did not know about this! At my first 50 hour oil change I could not remove the filter (way to tight) and I called to get advice about removing it, as it was still under warranty and I didn't want to damage it, and the service person had no idea what I was talking about! I eventually bit the bullet and used my burb gun and got is free. With regular oil changes it won't get clogged, but if your machine was in a mine and had minimal complete maintenance I wouldn't be surprise if that is your problem.
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If I'm not mistaken, on the old models the tank under the seat is only for the steering, but could be wrong, I tracked the line as well to the pump behind the inj pump, and traced the oil lines from the tranny to the oil cooler. Mine was on the coast and we have found some seashells in the dirt, so likely had minimal use (and I don't know about its maintenance history) over several years. Thanks
 
The servo could be sticky. Probably the old oil had seen its limit of water absorption. Might check the pressure release poppet also. Let us know when you get the oil changed
 
Will do, thanks. It had been parked up for 18 months before I bought it (due to the blown engine) so that mightn't have helped anything...
 
How the Hell do you remove spin on filters …and look at them and decide ….”they looked good and clean”… ???

Did you cut them open and look at the media.. is THAT perhaps what you meant?
 
geohorn - I was simply stating that there was no noticeable grunge or anything inside them, and I have new filters on order, and only pulled them to see if there might be an obvious reason for the trans issues. I haven't opened them up yet.
 
valiant said:
geohorn - I was simply stating that there was no noticeable grunge or anything inside them, and I have new filters on order, and only pulled them to see if there might be an obvious reason for the trans issues. I haven't opened them up yet.
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I wasn’t intending to appear so “aggressive” in my prior post… I was only trying to point out that unless you cut that sheet-metal “can” from the screw-on-base…. then use an exacto-knife to cut the media from the stamped-sheet-metal end-pieces…unfold it and wash it in mineral spirits or solvent….and drag a magnet thru the residue to see if any of it is iron or steel….. and look at the media to see if anything is “grunge”.

Trust me…there WIll be “grunge”. Otherwise the filter isn’t doing it’s job.

The grunge will be mostly carbon. You’ll find all kinds of little black things that will look scarey. Place them on an anvil and hit them with a hammer…. if they shatter…they are merely carbon (a good thing.) If they flatten and spread-out….they are likely metal. (bad)

Any metal particles should be closely examined. A small bit of aluminum is common (piston and castings and mfr’g-process left-overs…
Brass and copper should only be experienced in very small amounts and very Early in an engine’s lifetime…from the break-in process.

Large amounts of brass/copper in an engine with more than a couple hundred hours on it is indicative of a failing bearing or bushing.

Chips of steel/iron (anything which can be picked up by a magnet) should be no larger than “dust” ..not “chunks” or splinters.

But removing a filter…and glancing at it without disassembling it…. is wasted time. Toss it in the trash and move on.

Hope this helps.
 
Appreciate all that, I've been far too busy to even get to it this week, I'll let you know how I get on when I get a bit of spare time for it. Will definitely open the filters up. I know what it's like to find bits inside - I once found a few broken pieces drained out of the rear end of a JD 3140 I was working on, and it was diagnosed as being broken synchromesh pieces etc - explained lack of 1st gear, lack of hydraulics etc...
 
I have replaced the oil and filters, and the sticky servo issue is gone, it works well, and overall it has improved. But there is still not a lot of torque to the wheels (far more torque then there was initially). I guess pressure testing comes next! I have opened the filters, and the yellow HST filter is clean, with no steel visible on close inspection unraveled, either side. The white initial oil filter does have some small steel filings, but nothing large or anything that could be identifiable. I will wash them both to see exactly what I've got. So hopefully it's not looking too bad on that side of things. Once pressures are verified I'll let you know. Will a low charge pressure affect torque? Thanks
 
Before you check pressure. Check the max no load rpm of the engine. Set it to 3800 rpm. Also check the peddle hst and rpm rationship to make sure that is in spec or all the rest may be for nothing.
 
aurthuritis said:
Before you check pressure. Check the max no load rpm of the engine. Set it to 3800 rpm. Also check the peddle hst and rpm rationship to make sure that is in spec or all the rest may be for nothing.
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So my tacho has finally arrived, and the idle rpm was 1500, and full rpm was 3500. So I have adjusted it to 3800, but not much noticeable increased performance with that. I have a reasonable understanding of hydraulic systems from working on tractors (HST is new to me, and I am welcoming this opportunity to learn about them firsthand), and have some gauges so I have some numbers for you -

Charge pressure hot - 100psi at idle, when lever slightly depressed drops to 90, then progressively up to 110 at full rpm, so good there.
Main pressure - not much impulse forward, hot stalled pressure 2500psi. Increased main relief valve 3 full turns, and it has noticeably increased the forward impulse, and put the overall pressure up by 300 or so psi, on slightly applying the pedal on high torque it give upwards of 3100psi but when fully depressed drops down to 2700-2800 or so. On a test drive it has definitely improved the torque at the wheels. Is it a bad idea to keep increasing the pressure and testing? Or should I open up the trans to see the condition of the plates etc? Is this the sort of thing that can improve with working it?

I have been running it around a bit for the last while and its performance has been improving. One thing I have noticed is that it easily goes full speed downhill, and sometimes seems to "overrun" itself, but always provides braking when I back it off, and since turning the pressure up the "engine" braking was a lot better.
 
Your pressure sounds ok. There are limits to how high you can go before cracking the case though. Have you done the peddle and hst speed lever adjustment? Did your engine hold 3800 at stall?
 
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