Kubota RTV900 no forward or reverse

[boyler]

Looking for a little bit of help on Kubota RTV 900W I have.

Its a 2005 model year with approximately 1018 hours on it. It is used to groom cross country ski trails with a set of Camoplast tracks. I was not driving it at the time but it was apparently going along and then just started to lose momentum and then stop. It was in medium 4wd at the time. (wrong gear imo)

Here is what I know about the unit.
-engine starts and runs fine, I removed the shift linkage cover from the HST and can see the input shaft spinning while it is running. Both shift fork/synchronizers move freely and the linkage is adjusted per Kubota repair manual. I have even gone as far as to manually shift the synchros while it is running and there is no reaction.

I installed a gauge into a port from the charge pump on the back of the HST per the manual, spec is somewhere between 3300-3800 psi. I have ZERO! I tried this in 2wd high if I remember correctly. The manual had a different port for forward and reverse and specified different gear ranges as well. Neither showed any pressure while running.

I then removed both high pressure relief valves and inspected the o-rings, spring and bore for damage. None found. Manual continues on and says HST is not serviceable. New one is $7500 from local Kubota dealer.

Fluid is clean, free of debris, chunks, metallic pieces etc. Filter is oem, no issues noted. Approx 400 hours on current UDT fluid.

I can see that the use of tracks, a trailer groomer and high speed could have killed this transmission but I guess I'm looking for more physical evidence that something broke. I was reading through the parts and service manual and was thinking of tearing down the back of the transmission and removing the valve block to inspect the brass thrust plates for wear. That is about a $750 repair.

I have searched online and come up with very little which is part of the reason I joined today. Any advice or information is appreciated. Thanks

Rob

 

[mddorange]

:welcome:
To the forum from Alabama. My son lives in Northwest Indiana and work for a steel processing plant in East Chicago.

 

[timswi]

Welcome...Don't know what the problem is but there have been HST rebuilds done for some here. I'd check with a dealer, $7500 for a new replacement is downright obscene. Might as well buy a new one.

 

[texasjohn]

I don't actually know...but here are ideas that occurred to me...
maybe a blockage in hydraulic input has occurred...filter or other input clogged
there has to be a hydraulic pump there somewhere...hope it is not integral to transmission...
I reread your post...you have the parts manual and seem to know your way around stuff...I would look for why there is no hydraulic pressure.

 

[SpudHauler]

I'd bet the main pump is worn out. Remove the cover at the rear and inspect.

 

[rjglenn]

1080 hrs is way too few to have a worn out pump unless it is employee driven (abused). I would be looking at the differential or transfer case. There are also some relief valves that may have failed.

 

[kwbretired]

I've read where the axles turn in the wheel but doesn't turn the wheel. Sheer pin broke?

 

[buickanddeere]

Iirc ebay has companies listing rebuilt hydro stat units. As you noted somebody has been lugging the transmission. "Shifting gears" doesn't really shift gears but varies the amount of swash plate travel with relation to throttle .
We had a couple of 900 units at work. The relief valve in the transmission was factory set to lockup the wheels when the throttle was released. The reverse torque "chuck" was wearing the splines in the front drive shafts and the CVJ bearings.

 

[Greenorange]

I came across this post the other day when trying to find a solution to my problem. My symptoms are exactly the same as you described in your post. I see that you had this issue a few years ago and I did not notice any useful answers.
I am hoping that you have since resolved your issues and be kind enough to share what the problem was or how you fixed it.

 

[cchris81]

I came across this post the other day when trying to find a solution to my problem. My symptoms are exactly the same as you described in your post. I see that you had this issue a few years ago and I did not notice any useful answers.
I am hoping that you have since resolved your issues and be kind enough to share what the problem was or how you fixed it.

Did you get it fixed? I have run into this. If all of your linkages are all good then it is usually 1 of 2 things (I've had both happen to me) 1 The differential failed and 2 like has been said is the HST. I've taken the HST apart once before and replaced all the brass valve plates (some people call them swash plates but that is incorrect, swash plates adjust how much volume a variable displacement pump pumps). If i remember correctly there are 2 variable displacement pumps and one fixed displacement. When I took mine apart the second time (first time was due to differential) there was a failed bearing on one of the pumps, the ball bearing were all in the case, and the valve plates were pitted due to cavitation. I could not see the bearing on the back pump because something it was holding it on in the differential case which i did not take apart. about a week after doing this all the kubota stopped moving again when i was going up a hill.

I'm prepping the machine now for tear-down, maybe i'll take a bunch of photos and follow through with this. I would test all the pressures, I think there are 3, forward, reverse, and charge. Make sure you test the charge pressure, I don't have the exact spec on it right now but should be between 100-200.

if you have 0 pressure in the forward and reverse ports it is unlikely the diff.

 

[cchris81]

I have also heard some people with this problem have a clogged filters, I wasn't that lucky, but for a few people that was the case.

 

[Greenorange]

I wrote this on behalf of my dad, but I know he still has it apart. He changed the brass plates, and replaced the charge pump. The pressure is only reaching 50 PSI still, and like you said it should be around 100 PSI and more. Filters etc. Have been changed too but still same outcome.

 

[cchris81]

Wow, he changed the charge pump? That's in the differential section of the transmission and as far as i can tell you have to pull the transmission from the vehicle to do. I tore mine down a couple days ago. The bearing was smashed on the most external pump. Parts on the way. This thing only has 17 hrs on it since I last tore it down a year ago (yeah its been sitting for a long time) I tested my forward and charge pressure. Charge i get about 50psi at idle and about 100ish at full throttle which is what you test it at. Forward I have about 3300. Reverse I couldn't get a good reading because it kept stalling the motor. I found out my relief valve was out of spec though, so much that it can be adding 900 additional psi, so I'm hoping that's why it was smashing pump bearings. I did notice my 2 inner pumps have some valveplate wear with 17hrs, felt some tiny imperfections on the back of the pumps, but at 360 a pump i have to just send it. We just got 2 tracked pioneer 1000s, so the kubota isn't as important anymore.

 

[cchris81]

I wrote this on behalf of my dad, but I know he still has it apart. He changed the brass plates, and replaced the charge pump. The pressure is only reaching 50 PSI still, and like you said it should be around 100 PSI and more. Filters etc. Have been changed too but still same outcome.

I think the book says 73 to 105 at full throttle, I'll double check. Have you guys tried driving it with the diff lock on? If it moves with the diff lock or 4x4 on then its a drive train problem. What are the F and R pressures? should be between 3200 and 3800. Keep in mind forward and reverse don't mean the gear selector, they are in respect to the hydrostatic, it switches between forward and reverse while the vehicle is moving forward based on conditions. The reverse pressure is harder to test because you have to take a linkage off and manually stroke the pump backwards with a lever. If he changed all three valve plates, and the charge pump he would have seen if anything was broken inside like i'm dealing with. I would test F and R pressures, then try the diff lock and 4x4, check all linkages. If it slowly died while driving that's indication of some HST failure like i pictured. If it just stopped, that's more indication of a failure in the drivetrain. If it is all apart I would inspect the differential and everything around it. Sometimes a sheared shaft or spline is difficult to see untill you start spinning things and watch where it stops.