RTV HST Adjustments


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Thought I would start a new thread on this issue that may just help many with shifting problems on the RTV series machines.

We will see as you will be the testers of my conclusions. ha ha ha

I had 2 machines; 2008 RTV900 standard model that I added a plow and cab to and enjoyed lots of winter snow plowing for 2 years. Then traded it for RTV1100 which I eventually added a turbo to and of course had adapted the plow on for another 3 years of plowing fun. Neighbors loved me. ha ha ha

Ended up selling for health reasons and moved to new home, read no more snow plowing.

Anyway, with both models the shifting was never ideal, although it got better when over 100 hrs showed up on the hour meter and some tweaking on the adjustments helped even more.

But for the longest time I never had a good feel for what steps to take and in what order. Now I think I have a better understanding and will try to do my own testing but that may not happen either. I have availability to both my RTVs, as friends ended up with each but getting to them and when is another question.

I've been around mechanics since I was 15 so that's 45 years of playing, learning and fixing. Had a license for 8 years but then changed careers. Never lost the joy of tinkering. Now you know the rest of the story.

I'll break it down in several post so they don't get too long and people can chime in to add what they have learned. Hopefully this will help many.

It's a little harder on this forum as they don't allow us to edit our own posts after a day or so, so hopefully I don't make too many errors.

The negative and the positive always brings out the better solutions.

Big thanks to Adams Repair for Jim's input and help to clarify what is happening in the servo regulator.



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Throttle cable.

Remember this is not a fix for bad engines, transmissions or poorly maintained RTVs. Lots of thing effect how these operate and this is just some of the things to watch out for in the area of the HST.

First is the link between your foot and the engine/hst linkage. The large HST Linkage on the side of the transmission needs to reach max travel when your pedal reaches it's maximum travel. The manual describes all kinds of adjustments, but after look at mine, it was so robust that both machines were fine right up to the very last time I checked. But you do need to be sure it does as this is your overall range of speed for the machine. Sounds simple but probably overlooked on older units. Again just make sure you get full movement and with both reaching their stops at the same time you reduce strain on your cables at the same time getting full speed.

Why is this important? Because the HST and the engine are both hooked to this HST linkage and that controls everything else.

Helps to have a second person working the pedal while you watch the HST linkage.


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Engine Throttle.

Now that the accelerator pedal and HST linkage are in sync you need to check the throttle.

Again when the pedal reaches the floor or max travel, the fuel pump lever should just reach max travel. Just looking for full throttle.

So the HST Linage should come to its stop as the lever reaches wide open.

Best way to check is have your finger on the fuel lever and feel for wide open then have your helper slowly move the pedal.

Your helper would be good here to, feed them lots of coffee and keep them in the cab operating the pedals.

Try to avoid over tightening cables as this means extra strain on the small throttle cable with possible breakage.

You can move the HST linkage manually yourself but if you have a helper it's easier and you working the system the way it normally gets used.


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HST Lever.

The other side of the HST Linkage is hooked to the HST Lever. And to adjust it the manual says to unhook the HST rod from the lever, move the lever forward towards the cab until it stops. Mark the case, reconnect the HST rod onto the HST Lever, then step on the accelerator pedal and when at full throttle your lever should be just .040th shy of wide open. If not loosen the two lock nuts and adjust. Here you are looking for just a little slack and the reasons is they don't want tension on the internals of the servo internals.

Much like holding a standard transmission in gear causes it to wear the shift forks because of the constant pressure on the fork. So a little clearance does the trick.

So now you have just synced 4 pieces of the RTV. The accelerator pedal, the hst linkage, the fuel lever and the hst lever.

Very important. All these need simple adjustments to basically make sure you get full throttle and full hst engagement. And because the HST and engine reach max at the same time the engine delivers the right amount of power when needed and the HST will be in the proper range to match.


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Servo Adjusting Screw

This is the screw that originally had me thinking it was the neutral adjust because of another poster suggestions a few years ago. He left the forum shortly after and never came back. Leading a lot of us down the garden path in the meantime.

But with Adams Repair and more reading and learning I've think we have a better handle on it's use and how to adjust.

So, first thing to do is put a mark on the threads now before you do anything.

I would use your wife's white nail polish or something similar, to put a dot at the end on the top. Give it lots of time to dry and then continue.

Best thing to do now is slowly turn the screw in until it bottoms counting the turns. Do this carefully and accurately. It's you only chance to get the factory setting recorded. It normally doesn't take pressure to turn as you are pushing against a small spring. When at bottom it will be solid and easily felt.

Should be 1 1/2 turns approximately to reach bottom. The dot of white will help greatly with the count and make it easy to return to exactly the same spot if you keep count.

Tell us what your count was and easiest to talk in terms of; started at; white spot at 12:00 turned in 1 full turn and white spot ended at 6:00 = 1.5 turns.

If you don't want to adjust this now, no problem do it after.

This is more for those like me that adjusted it and lost the count. I will bottom it out, back it off 1 1/2 turns and continue with other adjustments.


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Neutral Screw.

This is the screw I found out about after losing my servo screw adjustment.

So don't do like I did. Either leave the servo screw at the factory setting or make sure you know what the factory setting was before you adjust.

Now for this adjustment, you need to go to your local Kubota dealer and have them use their pressure gauges for the best neutal adjustment. AdamsRepair reports that adjustment can be off by as much as 100 lb difference when you try doing it any other way. Manual says 0 to 3 lbs difference between P1 and P2. So have the mechanics do this unless you have access to two low pressure gauges and the proper adapters for you machine.

After they adjusted the neutral adjustment bolt, and before removing the gauges, I would have them re-connect the HST Rod and check that it is adjusted for the best 0 to 3 lbs difference as well.

The mechanics reported that my neutral adjustement was off by quite alot, but as far as I know now, they didn't re-connect the HST rod and check that it was in the best adjustment for neutral.

Otherwise if you like trying things yourself you could do the following after the mechanics have adjusted the neutral bolt;

Warm up the engine and transmission, have the transfer case in 2wd, transmission in H gear, back wheels off the ground, no brakes applied not even the emergency brake, hold the fuel lever wide open so engine is running at full song and watch for wheels rotating.

You can’t use the accelerator pedal at all. Use the fuel pump lever or the manual throttle, if you have one, to increase the engine speed.

You may have to adjust on the HST rod to get no wheel movement. Loosen both locking nuts and adjust the rod for best neutral by turning in both directions until you find the middle point between a little forward rotation and a little rearward rotation. Some report better results when it's a little bias to the rear.

Hopefully you have found neutral and it's time for a test drive.
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VHT Pressure Relief

Not mentioned very often is this relief system that is just below the servo adjust screw on the driver's side of the transmission above the axle shaft.

The black knob on the dash, the emergency brake and the brake pedal all operate some are all of this device.

It's meant to release the residue pressure off the HST when you use the knob, pedal or lever. So it's shifts easier.

That's why they shift better when stopped by jabbing on the brakes because at the same time you are opening this relief valve. And because the HST has allot of pressure internally you can't speed shift between H L M R without almost stopping if not stopping.

Manual has this adjustment covered, but basically you make sure the cables have slack so the device is off when not activated and cables are also tight enough that the small movement is there when you pull the knob or use the brakes.

If too tight you are constantly loosing pressure. Another reason for low power, poor performance.

I tried adjusting mine but it was so close it was a waste of time.

Older machines may need some adjusting.


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Yes there is one other big piece. The real gears and cogs transmission, High Medium Low and Reverse. You know that lever thing on the dash.

Everything so far was HST (Hydrostatic Transmission).

I adjusted mine here too by using the manual. It was a waste of time, but because I left no stone unturned, I wasted my time.

No magic here, just follow the manual for the older machines that might have and issue.

Kubota has some robust cables and you seldom hear problems with the actual shift mechanism.

Bent shift forks and shift forks jumping out of engagement are usually caused by problems with a HST not going into neutral and frustrated users trying to jamb the transmission in or out of gears.


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Servo Adjust Screw

Last step, all other things done. You have marked the screws location. Know the factory setting and that is where it is now. Right!

If it is mine, either the 9 or the 11, I messed up both, I will be readjusting to 1.5 turns out from bottom.

Taking it for a warm up run and then testing.

Remember each time you adjust. A little run will reset the location of the internals especially when adjusting out. The spring is not that heavy and it may be sticky. If you notice it never moves you may have to remove the 4 allen heads from the screw mounting cover and lubricate the area with transmission fluid to help lubricate and loosen the plunger. That's a whole other issue to be covered later if someone can't get any adjustment out of the servo.

For now assuming you did some trial runs between adjustments we'll assume its free and moving with each adjustment.

Servo Adjust Screw at 1 1/2 turns out from bottom.

Try moving the white dot, you have one right, by 1 hour as seen on a clock either way from 12:00 and test.

Don't go any further than 1/2 turn from the mid point that you start at, that being 1 1/2 turns. Thinking is any less than 1 turn out or any more that 2 turns out from bottom is no good. It should be somewhere between 1 and 2 turns out.

I can add as many screen shots of the manual for reference or assistance. Let me know.

Read all of this first, follow the order and hopefully you will have success.

Marking everything before will insure you can put things back.

Nothing is earth shattering here, just some fine tuning and step by step adjustments that most with some mechanical skills can accomplish.

Good luck and keep us update on any suggestions, progress or issues.
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Tater Driver - Nice write-up!!!

If you have any corrections, let me know and I'll edit them into your post(s).

I'm going to make this thread sticky.


Remember!!!! there are 3 different kinds of valve plates out there. Black steel rear section of tranny.

The first generation RTV's had no external means of relieving the pressure for shifting.

Second Gen.. has 2 spool valves on the left side, hooked to brake linkage, which relieves residual pressures to ease shifting.

Third Gen.. has a plunger(poppet) on the bottom right of the valve plate, hooked to brake linkage, which relieves residual pressures to ease shifting.

Adjusting Neutral will help all of these units. Then check your Linkage or cable adjustments. When having shifting problems.


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For those who have taken the time to read these post, I wanted to let you know that post #6 has some additions to it and will change slightly when bzoom applies the fix.

It's more detail on adjusting the neutral screw and making sure its done without the HST rod attached. And when done you may have to go back to the HST rod and re-adjust it to find the neutral sweet spot so the wheels stop turning in the test mode setup.

The other thing to note about all this is that the 'neutral screw adjustment/servo screw adjustment/HST rod adjustment' all are working on the same unit, so any changes to one will have some effect on the others. That is why multiple adjustments and testing may be required.

Confusing I know, but perhaps a little more knowledge will lessen the frustrations and will help get adjustments that make these units shift slicker.

And as AdamsRepair has posted, this is based on 08/09 models of the 900/1100 series.

This file is all of the posts in a txt document so it's easier to download and read. FILE UPDATED. SEE POST 19 OF THIS THREAD FOR NEW VERSION.
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For those who have taken the time to read these post, I wanted to let you know that post #6 has some additions to it and will change slightly when bzoom applies the fix.
Post #6 replaced with new text per request.


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I just registered here because I had to thank you for the help. I just picked up an 08 RTV1100 and it's a bear to shift from the L/R side to the H/M side. I'm ripping into it tomorrow and was excited to come across these posts to help me get things back the way they should be. I'll let you know how things go. I have a WSM, but it's for a 900. Hopefully I can find everything. :) Text downloaded.


The only differences between the 1100/1140 and the 900 trans. is the bellhousing bolt pattern. and the 1140 has more brake disc than the 900. There are some spring differences inside but that should not affect any adjustments you may make.

Hard shifting,, almost always the neutral adjustment, if off, helps.
Good Luck


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Good luck. Hope some of this helps.

Was hoping to have a crack at my old 2008 RTV900 but duck hunting season has the owner busy.

I'd suggest leaving the servo screw adjustment as is if no one has already tried to adjust it. Hard to know if the insides are moving freely when adjusting. At least leave it to the very last.

When I do try adjusting the one on the 900 I'll try an adjustment, take it for a quick short spin, then back out the adjuster 1/4 turn and then slowly turn it back in 1/4 turn and feel for when it reaches the valve body inside. That should tell me if it moved or not without having to take anything apart.
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AdamsRepair has done some testing and his findings show that the neutral screw requires the low pressure gauges to get an accurate adjustment.

Neutral pressures can be off by 50-100 lbs doing it by feel.

Seems there is no other method than going to the dealer for this one.

Unless you make a set of adapter plugs and get two gauges.

Not great news but not knowing is worse.

Having a dealer just adjust the neutral would allow you to do the rest and probably cost less.

I had originally see where a user had adjusted by feel and had good results. He may have just been extremely lucky and found the sweet spot.

Thanks to AdamsRepair for the heads up.


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Thanks Zoomie.

And here is the updated text file that goes with the step by step checks.

Please remove the one in post #12 and replace with this one.


Some call me Tater Driver


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My Unit: 2010 Kubota RTV 900 (60 hrs)

Using SpudHauler's Instructions Here is what I ran into:

Checked and adjusted throttle cable and engine throttle.

Disconnected the HST rod, marked HST lever at full wide open.
Before reconnecting HST rod, started engine with rear wheels off ground, to confirm that wheels did not turn when the HST lever was in a self centering position. Reconnected HST rod and adjusted so HST lever was .040" shy of wide open. (prior to adjustment, lever was over 1/4" from full wide open)

Did not adjust servo adjusting screw.

Neutral screw: Mine has a large cap nut(over 17mm) over it and I did not expose it. I don't have any major shifting problems, sometimes a little stiff, but no complaints if brakes are applied.

Now the problem: With HST lever adjusted to .040" shy of wide open, started engine (wheels off ground) but could not get into gear (slight grinding). The .040" clearance adjustment would not allow the HST lever back to that "self centering (neutral) position. Went back and adjusted the HST rod to the 'sweet spot' where the wheels would not turn. But, that put the HST lever back to over 1/4" off the full wide open position.

Question: Does that indicate the neutral adjustment is off and the pressure must be adjusted at the dealers ? Also, since the HST lever is not reaching it's maximum forward (less .040"), am I not reaching the maximum power of the transmission ?