RTV HST Adjustments

My WSM dated May 2007 says

1350 rpm for the idle

3000 rpm max

2000-2400 rpm for max torgue

Perhaps someone has the book for the 900's and can check the specs.

Don't worry about muddying the water, it was already pretty muddy, perhaps collectively this will clear it up.


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The only mention of idle speed in my Work Shop Manual is during the procedure for "Checking Neutral" or creep. It states 1350 rpm.

The rated engine speed of 3200 rpm appears many times throughout the RTV900 manual, especially during the Traveling Speed test. I found it strange that my machine would have factory settings of WOT at 3100 rpm?????

My RTV900 manual claims the following HP and torque specs.
 

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@ me37250: I had the same idea about extending my throttle lever, let us know how the spring works.

My next adjustment is to tweek the Servo adjustment screw to improve my power to the wheels going up a steep grade. I've found some posts that say turning the screw in will increase the torque, others say turning it out will increase torque. I plan to turn mine in 1/16 turn increments and then test drive to see results. I don't want to over do it.

Questions: Does anyone know which way you turn the servo adjustment screw to increase torque ? Will adjusting servo screw change the neutral position of the servo HST level causing 'wheel creep' requiring an HST rod adjustment ?
 
Tribute100,

I pretty well said everything I know about the servo adjustment screw.

3 turns out from bottom is it's max range, anything more does nothing. I had mine apart and verified that some years ago and it' in another thread here with depth measurements. But the number of turns is dead accurate.

1 1/2 turns out is the mid point.

Get a good mark on it with a die grinder or paint and keep track of where it was.

If you screw it in to the bottom there is the risk it will stick there. I had to take mine apart and clean it up.

If it does stick I would adjust the screw out 1.5 turns and the take it for a quick 2 minute drive with the hope it will pop out. Very delicate touch on the screw should be able to detect if that is the case.

All that being said, my thoughts are that 1/2 turn from the mid point (1.5) either way would be the max.

No idea which way is the reverse side and which is the forward side.

This is great, we are slowly building some accurate information on tuning the HST.
 
Just another thought; My theory on this HST system is that Kubota uses the same design in some of it's lawnmowers but without the gears just the HST system. One pedal gives you Forward and Reverse by moving the HST Lever either way and it's geared for general speeds cutting lawns. Then they added a 3 speed transmission with reverse for the RTV machines, but stopped using the Reverse side of the HST Lever. The HST Lever and the Servo adjustment are best around their mid points because the other side is the reverse circuits for both and not used on the RTV. That being said, the HST Lever must be as close to neutral or the mid point to work properly, but the Servo adjustment can be adjusted off the mid point of 1.5 turns because it never uses the reverse circuit so no big issue. If a little adjustment improves performance great.

Here is a RTV these guys modified so using the HST Lever on the reverse side they now have 3 speeds in forward and reverse. They never use reverse gear. So they must adjust the HST Lever to true neutral and keep the Servo adjustment at it's mid point with possibly a little bias adjustment either way, whatever makes it work best.

[ame]http://www.youtube.com/watch?v=QaRuB4pYQqc[/ame]
 
Just finished adjusting the servo screw on my RTV 900. Look at my earlier posts in this thread for previous adjustments to my machine. I was attempting to increase the torque to the wheels on a steep driveway grade that I have to get more speed. Here's what I did:

First, I did not determine how many turns out was the factory setting and I did not disconnect the HST rod from the cam lever assembly.
Warmed up machine for about 15 minutes and did a few test runs. My average speed up the grade was 8mph in "M" gear. Loosened lock nut, mine is a 14mm, actual screw was easy to turn. Use a piece of cardboard or something next to the muffler to keep from burning you hand during adjustment. I first started turning servo screw in, CW, 1/16 turn at a time, up to 1/2 turn, with not much change in speed up the grade. Then, from the factory setting, started turning servo screw out, CCW. I turned out servo screw 1 full turn out, and found that 1/2 turn out gave me the best power, a speed of 10mph up the grade. I was afraid to adjust the servo screw much per warning from AdamsRepair and also I have not confirmed the neutral adjustment on the servo piston using 2 low pressure gauges on the forward and reverse ports.

Note that I continued to check the HST lever neutral position that I had marked earlier(no wheel creep) during the servo screw adjustment and there was no movement off the mark. During all changes to the servo screw my unit shifted well. Still waiting on a laser photo tachometer I ordered (Ebay-$13.87) to verify my engine rpm that I adjusted to get full travel out of the HST lever on the Servo.

Has anyone increased the tranny relief pressure setting (spec pressure setting of 2133-2276 psi) ? I've read some recommending to bump it up to 3500 psi and even 3800 psi.
 
Tribute,
Sorry if I've confused you, but yes the HST Rod is never disconnected when adjusting the servo screw.

I think the Neutral Screw needs adjusting first, then the HST Rod and lastly the Servo Screw.

You missed the Neutral Screw and so the rest could all be for not.

My book shows higher relief pressures, not sure what your figures are for and a Kubota mechanic told me he had set one RTV to 4,000 lbs pressure with no ill effects.

Great way to test the servo screw, go job!!!
 

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SpudHauler,
I'm not sure where I picked up those other pressures I posted earlier.
Just found the relief pressure spec description in my downloaded RTV 900 Service Manual that I paid $10 for on site http://kubota.servicemanualvault.com/

"The relief pressure is set in between 25.5 to 26.5 MPa (260 to 270 kgf/cm2, 3698 to 3840 psi) when shipped from the factory. But, for the purpose of after-sales services, as it is impossible to reset the pressure precisely as set in the factory, its setting range is defined as a slightly wider range between 22.6 to 26.5 MPa (230 to 270 kgf/cm2, 3271 to 3840 psi)."

So based on this, it looks like the factory is setting that relief pressure between 3698 and 3840 psi.

I didn't want to have to take my unit to the dealer to have my pressures checked because of the hassle. I've never had shifting problems, once in a while I'll have to press on the brake. So, based on that, and since I only have 65 hours on my 2010 RTV 900, I was assuming my neutral adjustment on the servo was OK. I have no way of knowing what my relief pressure is set at. I'd like to think if I had the right gauges, fitting and tools I could do check it myself, but the procedure sounds involved on the relief pressure adjustment. My experience with any kind of dealer service shops has not been satisfactory. I may just drop by my local Kubota dealer and chat with the service technician to get a feel for their experience.
 
Later this weekend, I will post my recent experience with DIY relief pressure checking and adjusting. I have some good photos, but my camera is not with me right now.
 
I have the digital manual as well. Like and ass I gave my factory manual to the new 900 owner. dah! and did that twice, 1100 owner. dah! dah! ha ha ha

The manuals from Japan in the 70's where terrible and these show signs of that as well. PSI listings for relief pressures vary depending on the page you look at. Confusing at best.

I adjusted my relief pressures without gauges. ME BAD.

Reference: The pressure changes by 213 psi per 0.10 mm (0.0039 in.) in distance A.

Factory distance of (38.60 - 38.70) gives (3840 - 3280) psi.

Shorter spring length (38.60) equals more psi (3840).

Factory pressure difference of 560 psi for 0.10 mm distance doesn't compute with their reference. Thus the reason for pressure gauges after to verify actual pressure. Springs can vary under load.

What I did was went with a safe calculation of using their shortest measurement of 38.60 mm and wanting a little more pressure, my goal of 4000 psi, went with 4000 - 3840 = 160 psi difference, so 0.05 should give me 106.5 psi, new length of 38.55 mm giving 3840 + 106.5 = 3946.5 psi.

Measured the length of both as carefully as possible and went with that.

Never verified pressure.

Once again ME BAD!!!

But remember, this is the HIGH pressure side, the Neutral Screw adjustment is the LOW pressure side, nothing to do with these relief valves.
 
I just finished the rpm test on my 2010 RTV 900 with the laser photo tachometer I bought on ebay for <$14. First I adjusted my WOT back to the factory setting to see what it was set at. I had increased the WOT earlier to get the cam lever assy to reach full open stop and the HST lever to reach the full forward position less .040".

I tried putting the tach reflective tape on the fan blade, but found I did not get an accurate reading. I lifted the seat and was able to put the tape on the front of the fan drive pulley to get an accurate reading. Had to stick my hand down through the hole to get a laser shot on the pulley. Here are the readings I got:

Engine idle no load: 1380 RPMs (Spec says 1300-1400)
Engine WOT no load: 3550 RPMs (Spec says 3200)

I was surprised with the WOT rpm and glad I turned it back down. So now I have the problem again of the cam lever assy and the HST lever not reaching their max. I may have the use me37250's solution by extending the engine throttle lever assy to get the full travel of the cam lever and HST lever or use a spring to connect the throttle cable to the engine throttle lever.

Anyone have any other ideas ?
 
I've been watching this thread with lots of anticipation and I am fascinated with your ability to work on these RTV's with such rigor and desire to improve them. Cheers BJ.
 
TRIBUTE100 said:
I just finished the rpm test on my 2010 RTV 900 with the laser photo tachometer I bought on ebay for <$14. First I adjusted my WOT back to the factory setting to see what it was set at. I had increased the WOT earlier to get the cam lever assy to reach full open stop and the HST lever to reach the full forward position less .040".

I tried putting the tach reflective tape on the fan blade, but found I did not get an accurate reading. I lifted the seat and was able to put the tape on the front of the fan drive pulley to get an accurate reading. Had to stick my hand down through the hole to get a laser shot on the pulley. Here are the readings I got:

Engine idle no load: 1380 RPMs (Spec says 1300-1400)
Engine WOT no load: 3550 RPMs (Spec says 3200)

I was surprised with the WOT rpm and glad I turned it back down. So now I have the problem again of the cam lever assy and the HST lever not reaching their max. I may have the use me37250's solution by extending the engine throttle lever assy to get the full travel of the cam lever and HST lever or use a spring to connect the throttle cable to the engine throttle lever.

Anyone have any other ideas ?
Click to expand...
When you unhook the throttle cable from the cam lever assy. will the foot feed make the cam lever go to the full stop? Can't you adjust the throttle cable to hit full throttle after the cam lever hits full stop? What is stopping the HST control rod from traveling to the stop? Sounds like the Throttle cable is to tight? When I say throttle cable, I mean the little short one from the cam lever assy. to the Gov. on the engine, not the foot feed cable. I just yesterday messed around with an 1140. it was not getting full throttle the bracket that holds the T cable was loose on the bell housing.
Check your cam lever mounting bolts and position also. If the foot feed cable has been run too tight for a long time it will bend the brackets and on 1140 trans even crack the case by the bell housing web near the bolts. that is why there is a foot feed stopper bolt that needs to be adjusted, to keep from standing on the pedal cable too hard. I adjust the cable from the foot feed first (Full cam lever stop), then adjust the stopper bolt so the cable is not overly tight, then check the HST control rod adjustment(.040"), then adjust the the throttle cable to the Gov. lever so it hits governor stop while you are at Full foot feed. Now if you have creep after all this, you will have to adjust the servo piston screw(On the right side above filter) to get a good neutral. I have done it with out gauges just to get by, until I could set it proper with gauges. And if you have no shifting problem after messing with it I would leave it. Or tweek it just little bits until you still have neutral and shifting gets better.
Hope I make sense.... Like I said B4 I'm hands on kind of guy.
 
Amazing that the throttle is off so much. Just goes to show how all the adjustments need to be in-sync.

Zoomie (BCZOOM) could you add the following not to post #50 at the top.

RTV 1100 2009 specs. Other models may be different check your manual before attempting any adjustments.
Proceed at your own risk!

Thanks Zoomie
 
AdamsRepair said:
When you unhook the throttle cable from the cam lever assy. will the foot feed make the cam lever go to the full stop? Can't you adjust the throttle cable to hit full throttle after the cam lever hits full stop? What is stopping the HST control rod from traveling to the stop? Sounds like the Throttle cable is to tight? When I say throttle cable, I mean the little short one from the cam lever assy. to the Gov. on the engine, not the foot feed cable. I just yesterday messed around with an 1140. it was not getting full throttle the bracket that holds the T cable was loose on the bell housing.
Check your cam lever mounting bolts and position also. If the foot feed cable has been run too tight for a long time it will bend the brackets and on 1140 trans even crack the case by the bell housing web near the bolts. that is why there is a foot feed stopper bolt that needs to be adjusted, to keep from standing on the pedal cable too hard. I adjust the cable from the foot feed first (Full cam lever stop), then adjust the stopper bolt so the cable is not overly tight, then check the HST control rod adjustment(.040"), then adjust the the throttle cable to the Gov. lever so it hits governor stop while you are at Full foot feed. Now if you have creep after all this, you will have to adjust the servo piston screw(On the right side above filter) to get a good neutral. I have done it with out gauges just to get by, until I could set it proper with gauges. And if you have no shifting problem after messing with it I would leave it. Or tweek it just little bits until you still have neutral and shifting gets better.
Hope I make sense.... Like I said B4 I'm hands on kind of guy.
Click to expand...
AdamsRepair,
Yes, I had found earlier that that the throttle cable to the engine Gov. lever was preventing the cam lever assy from hitting the full stop. Now I may have caused this originally when I took the slack out of the throttle cable to improve the vehicles initial acceleration from a stop. Before I did that my cam lever assy may have been going to full stop, but not my HST lever until I adjusted the HST rod. I will spend some time today and use your step by step procedure to set everything up correctly and report my findings.
Thanks for your help.
 
TRIBUTE100 said:
AdamsRepair,
Yes, I had found earlier that that the throttle cable to the engine Gov. lever was preventing the cam lever assy from hitting the full stop. Now I may have caused this originally when I took the slack out of the throttle cable to improve the vehicles initial acceleration from a stop. Before I did that my cam lever assy may have been going to full stop, but not my HST lever until I adjusted the HST rod. I will spend some time today and use your step by step procedure to set everything up correctly and report my findings.
Thanks for your help.
Click to expand...
Using AdamsRepairs instructions, I proceeded as follows:

*Disconnected the throttle cable by removing cotter pin and stud at the engine governor lever
* Used a plastic torque wrench case (2 x 4 will work) to between the pedal and seat edge to hold the accelerator pedal down
*loosened the lock nut (14mm) under the hood to the pedal travel stud that stops the pedal travel under the dash board
*Used an open end 14mm wrench to adjust the pedal stop nut.
Using a feeler gauge I adjusted the stop nut until the cam lever assy just made contact to the full stop on the bracket. I checked the HST lever and it was still at the full forward position less the .040". Re-tightened the lock nut under the hood.
*I loosened the throttle cable adjustment nuts (12mm?) nearest the engine throttle lever until I had enough play to reconnect the throttle cable to the outer most hole on the engine governor level using the stud, washer, and cotter pin. While the accelerator pedal was still fully depressed I adjusted the throttle cable until it would hold the governor lever at WOT. You have to get the cable tight to achieve this.
*Then I removed the brace that was holding the pedal down in the cab. I checked the HST lever and it had returned to the neutral position I had adjusted the other day. I used a steel scribe to scratch the neutral position (no wheel spin) and the full open position (less .040") on the ground surface just below the HST lever for reference
* The throttle cable to the engine governor lever was loose with accelerator pedal released. I jacked the rear wheels off the ground, warmed the engine up, placed in "H" gear. No wheel spin at idle. As I turned the cam lever assy by hand (same as pressing the pedal) the wheel started turning before the throttle cable increased engine speed from idle, which concerned me. At WOT the HST lever was at full open (less .040"), which was good.
*I took the unit for a test drive, thinking the initial acceleration from a stop would not be good. It turned out not to be a problem, the unit started moving just ahead of the engine coming off idle. I found this acceptable even though the unit wasn't as quick off the line as when I had the throttle cable tight at the idle position.
 
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TRIBUTE100: These are the same settings that I found on my RTV when I purchased it. When depressing the foot pedal, the HST lever started moving well before the throttle/governor moves. This is due to the excessive slack at the governor cable, yolk end. This bothers me because the HST lever tilts the swash plates and increases the pump angle BEFORE the engine (and pump shafts) build the needed rotational speed. This means that your engine is always behind the curve. An analogy might be that you are starting the pumps in high gear and then asking the engine to dig itself out of the mechanical disadvantage. I suspect this condition will make it more difficult to initiate movement on a hill climb or overcome vertical obstacles. If you were to exaggerate to the extreme, imagine the swash plate at full tilt (maximum piston stroke) before revving the engine. This does not seem like an efficient use of this engine/trans setup.

I think the engine speed and swash angles should be perfectly synchronized... from idle through WOT. Now it's just a matter of figuring out how to do that with our crazy setup.

I didn't get much time this weekend to work on mine. Hope to add some posts when I get a chance.

FWIW, I put my reflective tape on the thickened section of the outer vbelt groove on the crank pulley. After removing the plastic cover near the fuel filter, there was just enough room to shine the laser tach under the fuel filter and hit the tape.
 
To clarify my previous post, although for a forklift, I found this video helpful in explaining the concepts behind our variable swashplate hydrostatic transmission. The first 40 seconds are kinda silly.

Our HST lever is analogous to the black lever in this video. The video shows one variable swash pump and two fixed swash wheel motors. Our RTV only has one fixed swash wheel motor that drives the transmission output shaft. Yes our RTV has an assist pump, but let's ignore that for the time being. Notice that the pump swash plate angle drives the wheel motor speed. This means when the HST lever moves, the wheels are attempting to accelerate. It's difficult for them to accelerate it the engine is not climbing the power curve and increasing RPM to provide the additional fluid volume. Also, Kubota did not attempt to control the engine/trans system with a computer. It is a purely mechanical control setup with cables, servo pistons and preload springs.
http://youtu.be/MTeJWE_Ou0g

If you want to know more about he guts of axial piston pumps, the following animation is very good starting around 1min 25sec. It shows a fixed swash plate angle for these pumps, but it's not difficult to imagine the pump movements if the swash plate were adjustable as is the case in our RTVs.
http://youtu.be/_WLtj_fzPAg
 
me37250:
Just read your posts this morning and watched the videos which I found informative. After thinking about the adjustments I made yesterday, I have the same concerns that you have about the engine speed and HST synchronization. In my test run yesterday up my steep driveway, I didn't have a load on the RTV and didn't try to stop and start on the hill. So my testing scenario was not valid, especially in a stop/start situation.

Another problem with the slack in the governor cable is that I think it would accentuate engine braking when releasing the foot pedal, as the engine speed would drop ahead of the HST 'speed'.

I still like your modification using the governor lever extension. What is the measurement between the outer most hole on the governor lever and where you have your cable is connected to your extension ?

I'm going to fabricate a lever extension like yours and try to figure out how to adjust the position of where the cable is connected, either through multiple holes or a way to slide that connection point in or out.
At this point, I'm reluctant to use a spring, but it may come to that. Let us know how the spring works out if you try it.
 
Interesting read and informative...Will be using this info in the spring when I remove my snow blade and go through the annual maintenance....Just a note ....once all the adjustments are dead on, I find that my hand throttle does a good job of keeping the engine in its sweet spot and thus allows me to utilize the throttle pedal in the same manner as the HST pedal on my tractors....(unfortunately no reverse).
 
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