RTV X900 HST Repair

[jhuggans]

Bought a broken 2018 X900. Was told the transmission was bad as it would only barely move forward or backward. After reading other stories I assumed it had to be the HST. My first move was to add hydraulic fluid to the reservoir, which was about two gallons low. No change. Pulled off the HST today and found this. Seems pretty straightforward with what is causing the lack of movement but my question is two parts; I see zero appreciable damage anywhere other than the two plungers so would that mean everything is fine after replacement and secondly, how could this happen to just two?

I bought the machine for $3k so putting some money into this is worth it to me. Just want to make sure I prevent this from happening again.

 

[OlFerguson]

Any wear on the swash plate

 

[jhuggans]

Any wear on the swash plate

Need to get a better picture. The line seen on that bearing surface is perfectly smooth.. No lip.. Can't even feel it with a fingernail. The bearing surface on the other side is immaculate, zero wear. I can get a better picture tomorrow.

 

[Nicksacco]

Nice job of diagnosing and repair.

What do you think happened?

It appears that the piston shown was "hammered".

I wonder if lack of hydraulic oil and/or water in the system would cause the system to "hammer" as it starved for oil under a significant load?

Is that a "groove" worn in the swashplate from the damaged pistons?

What does the other piston look like? same?
Any big chunks of metal to be seen?

I'd be curious what the 3 filters in the system caught.

Check the unloader and associated linkage too. If the linkage gets out of adjustment it makes shifting difficult - a possible contributing factor.

 

[TECH101]

Bought a broken 2018 X900. Was told the transmission was bad as it would only barely move forward or backward. After reading other stories I assumed it had to be the HST. My first move was to add hydraulic fluid to the reservoir, which was about two gallons low. No change. Pulled off the HST today and found this. Seems pretty straightforward with what is causing the lack of movement but my question is two parts; I see zero appreciable damage anywhere other than the two plungers so would that mean everything is fine after replacement and secondly, how could this happen to just two?

I bought the machine for $3k so putting some money into this is worth it to me. Just want to make sure I prevent this from happening again.
View attachment 133186 View attachment 133187

Most models have a tank located underneath the passenger seat, it that is empty or low the machine will not drive forward or reverse

 

[jhuggans]

Most models have a tank located underneath the passenger seat, it that is empty or low the machine will not drive forward or reverse

Yeah, when I bought it that tank was basically empty. I added 2 gallons but I think it was just too late. Damage done.

 

[jhuggans]

Nice job of diagnosing and repair.

What do you think happened?

It appears that the piston shown was "hammered".

I wonder if lack of hydraulic oil and/or water in the system would cause the system to "hammer" as it starved for oil under a significant load?

Is that a "groove" worn in the swashplate from the damaged pistons?

What does the other piston look like? same?
Any big chunks of metal to be seen?

I'd be curious what the 3 filters in the system caught.

Check the unloader and associated linkage too. If the linkage gets out of adjustment it makes shifting difficult - a possible contributing factor.

I have to believe it was simply ran low on hydraulic fluid. How it only destroyed those two pistons I haven't a clue.

This is the upper swash plate:

There is an obvious mark but man I cant feel anything with a fingernail. The back of the larger swashplate is perfect. Zero marks.

Now here is the lower bearing surface:

This has certainly seen better days. The shiny surface is completely worn from those pistons being pressed against it. I need a snap ring plier to pull the lower plate off, but I'm assuming there is some damage.


So far my shopping list is this:
K7591-14112, the lower cylinder block with all the pistons, $650
K7591-14244, lower swash plate, $85
6C300-11740, lower swash bearing cradles x2, $50
K7591-14720, lower thrust bearing, $330
K7591-11140, o-ring seals x2, $40
K7591-14250, gasket, $30
K7591-14210, upper thrust bearing, $100 (why the larger one is 1/3 the price of the smaller one makes no sense)

I'm at roughly $1500 in repairs. If I could find a used HST for somewhere in that range I'd really like to go down that path.

I did check the unloader and it was extremely loose. Pushing the brake barely moved it at all. Adjusted the cable to closer to spec.

 

[Nicksacco]

Well good for you for digging in.
I think we're past any more guesses and time to think about making it work and the costs - yeah.

Assuming the frame and such are all in good shape and you want to restore it to working order $1500 is reasonable. Add 5 or so gallons of UDT and another 200 for oil, brake fluid, and filters and it sounds ok.

Have you gone thru checking lubrication/wear in all wheel hubs, CV joints, FWD case, etc? Might be good to calculate total cost of repairs before you go further.

Here are some links that I hope will help you. I wish you best of luck and hope you continue posting.

Kubota RTV Aftermarket Accessories, Parts & Tools

Accessories, parts, gear, and more for the Kubota RTV 400, 500, 520, and 1140

www.everythingkubotartv.com

Used Kubota RTV Parts | Kubota RTV Parts for Sale

Find the used Kubota RTV parts you need at Sun Coast Cycle Sports! We carry quality Kubota RTV salvage parts like motors, frames, differentials, and more.

suncoastcyclesports.com

Kubota - Used Parts - Power Sports Nation: The Cheapest Used ATV and Side by Side Parts

PowerSportsNation is the largest used ATV and UTV parts warehouse in the nation.

www.powersportsnation.com

And of course, Ebay

Rtv900 Kubota Transmission for sale | eBay

Get the best deals for Rtv900 Kubota Transmission at eBay.com. We have a great online selection at the lowest prices with Fast & Free shipping on many items!

www.ebay.com

2007 KUBOTA RTV900 ENGINE MOTOR TRANSMISSION TRANNY GEARS | eBay

Removed From: 2007 Kubota RTV900.

www.ebay.com

Your most expensive transmission part fits the following - according to Messicks: K7591-14112

 

[jhuggans]

I have one last conundrum: Do I buy a used HST over replacing parts in my current HST?

eBay ($2000 2015 HST 4500hrs): https://www.ebay.com/itm/156311930624
Kubota Parts: ~$1500 in parts

The eBay route does have a 30 day return if there are problems with it. I feel like I *could* be in a better position with the eBay option.

 

[ruger1980]

Before ordering parts or making your decision you need to inspect both valve plates and the motor rotating group surfaces. You will have to replace the valve plate for the pump anyway. Inspect the charge pump as well.

I would be less concerned about the thrust bearing for the motor and the cradle bearings as long as the do not show significant wear or contamination.

The area marked below of the port block looks like it could be damaged.

All of this will drive your decision, but a used part is just that and it is a gamble.

 

[Nicksacco]

I think @ruger1980 has great points.

I'll add a couple more thoughts. In the end it's not always about one thing.
Since I don't know the condition of the rest of the unit here goes:

1) Check out the front brakes/hubs and see if there's oil in them and the overall condition. If not, a rebuild will probably be necessary due to bad seals/brakes.

2) Servicing the unit will take about another $300 in filters, and UDT.

3) Tire and wheel condition. CV Joints and Tie Rods.

4) Rust, leaks and general wear on things like frame and controls.

5) Do we know where pieces of that motor are? In the filters?

You make your best guess and move forward. Personally I like working on machines but I'm also retired and have lots of time!

Another thought is that asking people on ebay to accept an offer is acceptable. Sometimes there is a "Make Offer" button. Either way it never hurts to ask.

 

[hagrid]

The valve plate is fooked hard. The whole system needs dismantled and surveyed.