RTV HST Adjustments

[TRIBUTE100]

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 ?

Or would the adjustment of the servo screw resolve neutral adjustment, get the HST lever travel closer to the .040" clearance, to give the transmission more power ?

Just read on another site per a Kubota/New Holland factory trained mechanic that he's had to adjust the servo screw out 5 or 6 turns to get it right.

 

[AdamsRepair]

I don't want to lead you astray.. I'm kind of a hands on type person. Let me get my book back out and do some research, before I lead you down the wrong path. But Yes if the lever is that far off the .040" mark you may not be getting full speed out of the unit.
I will get back to you..

Jim

 

[TRIBUTE100]

In reference to my previous post about HST adjustment, can the engine rpm's be bumped up ? Specs say 3200 rpms on the RTV900, but I've read on some forum you could go to 3600. Could that damage the engine ?

 

[AdamsRepair]

Or would the adjustment of the servo screw resolve neutral adjustment, get the HST lever travel closer to the .040" clearance, to give the transmission more power ?

Just read on another site per a Kubota/New Holland factory trained mechanic that he's had to adjust the servo screw out 5 or 6 turns to get it right.

There are many variables that can effect your proper adjustment.
Is your cam lever assy. going from stop to stop? If not Loosen the throttle cable and control rod so they won't effect anything, readjust the cable from the pedal so Cam lever assy. goes as far as it will toward the no throttle position. Now when you push the pedal to the floor, is the cam assy hitting the wide open stop? If not adjust the pedal stop screw under the dash until it does. Now it should have enough travel to go stop to stop. <Adjusting the servo screw will do nothing for lever travel or Neutral position> Now for your other question. Yes adjusting the the neutral position on the servo piston screw will change the position of the lever a little. But normally you will have enough adjustment on the rod to compensate for that. As for the 5-6 turns out I call Bull.. because there is only about 3 turns of effective travel on the screw. If it was screwed in all the way to the bottom. then screwed out 4 turns it would not be touching the plunger on the inside any more. at that point you could just take the screw out. Don't mess with the Servo adjusting screw until you are positive all other adjustments are correct, including the Neutral adjustment (servo piston) 2 low pressure gauges installed in the forward and reverse ports. The servo screw is a last ditch effort to tweek things, it was not meant to be used as an adjustment. It was only there to center the spool in the valve.

 

[AdamsRepair]

In reference to my previous post about HST adjustment, can the engine rpm's be bumped up ? Specs say 3200 rpms on the RTV900, but I've read on some forum you could go to 3600. Could that damage the engine ?

The generator sets with the 902 engine run at 3600 rpm all day(SAME ENGINE DIFFERENT GOV CONTROLS) You decide! I would bump it up a little.

 

[TRIBUTE100]

AdamsRepair: Thanks you for your response. I understand your instructions and hopefully in the next few days I can check it out. I will let you know the results.

 

[BaiJiu]

I am looking foreword to your results.

 

[me37250]

TRIBUTE100: I've been struggling with the same issue on my 2007 RTV900. The servo lever was 1/4" shy of full movement. It was being limited by the wide open throttle (WOT) stop screw. As a quick work around, I wanted to increase WOT, but was uncertain where these engines redline. Thanks AdamsRepair!

Just wanted to let you know I found a non-contact, digital laser tach online for $16. It works awesome for temporary rpm measurements. I put a piece of reflective tape on the crank pulley and point the laser at it. Voila, measure RPM accurate to +\- 1 rpm. At operating temperature my engine was idling at 1350rpm and WOT 3100rpm. I mounted the laser pointer on a tripod to minimize my wobbly hands from introducing error.

 

[SpudHauler]

Me37250,

That was one I hadn't thought of, max rpm.

Lots of little adjustments to be checked to get full potential out of these machines.

 

[me37250]

SpudHauler: I can't find a dyno curve for my exact D902-ES03 engine model, but this link shows the D902-E3B engine series gains another 3.2hp if it's properly setup for 3600 rpm.

http://www.kubotaengine.com/products/engines/kubota-engine-line-up

However, if you click on the brochure for those engines, you will see that the torque peak is back around 2400 rpm. Also, torque seems to be falling off at higher rpm, so there may not be much gained by increasing WOT rpm. The transmission input pump shaft may spin a little faster, but the engine won't have optimum torque to keep up when the trans gets loaded really hard. Not sure I'm going to change WOT stop screw.

 

[TWO GUNS]

A couple of years ago, read where two Rtv owners turned their engines up.
Both stated the same thing. The was not no speed difference to talk about.
And one person was traveling in the mountains, and ended up doing the turbo thing.

...... think the Rtv transmission is only going to only do so much as far as speed goes.

Also know that you are trying to get to 25 mph in high



Two Guns

 

[BaiJiu]

I don't think I'll be messing with mine, especially since it is under warranty.

 

[TWO GUNS]

I don't think I'll be messing with mine, especially since it is under warranty.

What is your doing, I must of missed it.

 

[BaiJiu]

Sorry Two Guns I was talking about messing with the RPM on my RTV. Under waranty I would definitely hold the line.

 

[TRIBUTE100]

OK, here are my results based on AdamsRepair recommendations:
(2010 RTV900, 60 Hrs, Super UDT2 and Rotella T6 full synthetic 5w-40)

I found that the throtte lever on the engine (WOT) was preventing the Cam lever assy from reaching full open stop which in turn prevent the HST lever on the servo from reaching the full forward position with a .040" clearance.

Here's what I did to get the full travel of the Cam lever assy:
My throttle cable was attached the engine throttle lever hole closest to the pivot point. I pulled the small cotter pin and washer and moved the cable 'end' to the outer hole on the engine throttle lever. This allowed the throttle cable to have more travel thus the Cam lever assy. was able to move closer to the full open stop, but not completely.

I decided to cut the tamper wire off on the engine throttle assy. ( not under warranty) to increase the WOT. I had to turn the WOT screw out 2 full turns to get the Cam lever assy to hit the full open stop. This allowed the assy to pull the HST lever on the servo to full open less a .040" clearance. I did have to turn the stop bolt in slightly on the throttle pedal in the cab to allow enough travel. You have to loosen the stop nut under the hood to do this.

With the rear wheels jacked off the ground, I started the engine, put it in "H" gear and let it idle for about 15 minutes to warm up. I don't have a tach that will work on a diesel, but plan to get one. I was not sure how high the rpm's would go at 2 turns out from the factory setting. Gradually I pressed down on the pedal to the max, wheels spinning. Not sure of the top rpm, but the speedometer went over 30 MPH. I will verify top rpm before I max it out again. Time for a test drive.

Driving down my long paved drive I noticed it reached 25 MPH in "M" gear. I got to the state road, put it in "H" gear and was able to speed up to over 30 MPH, but it is a slight downhill grade. I found a level place and was still able to get it up to over 30 MPH. (Note: I had about 350+ LBS of weight in the vehicle including me and have a full front windshield). My max speed before was about 25 MPH, as stated in the owner's manual.

Now for the uphill load test. (Note that my location is about 2500' in elevation) Part of my driveway has a steep grade where before I could usually maintain about 10 MPH in "M" gear. It may have improved just slightly on that speed. I did let off the pedal slightly to get more torque.

Conclusion: Achieved higher speed on flat ground but really no change in speed going up a steep grade. I would appreciate any comments.

 

[me37250]

TRIBUTE100: This sounds very promising for eeking out a little more performance on a non-warranty machine. FYI, when on jackstands, I think the wheel speed is double if you don't have the diff locked.

Someone "tampered" with a 2009 RTV900 that I've driven. The tamper wire wass gone and the WOT screw was freewheeling because the lock nut came loose. It was screwed far enough out that the HST lever was the limiting element. This machine has been running 3580 rpm at WOT periodically through the past year and has not grenaded yet. Unfortunately, I don't know how many hours we've put on it like this.

For peace of mind knowing how fast things are spinning, again I recommend the digital laser tach for these simple measurements. I couldn't justify spending $100 on a tinytach or fiddling with an alternator pole device considering that I only wanted to measure WOT one time.

 

[AdamsRepair]

Cool
Tribute100, how is your shifting? and was there any creep? I like your POST it lets people know that there are way more variables, and adjustments that can effect your performance.

 

[TWO GUNS]

This is a great POST !!!!

It's going to come in handy for some !!!


....... thanks for sharing the info,
....... two guns

 

[TRIBUTE100]

@ AdamsRepair: I did not have any creep. The set up I described allowed the Cam lever assy to go back to 'full closed stop' and the HST lever on servo to return to that 'neutral sweet spot' where there was no 'creep' with wheels off the ground. I really never had a shifting problem. On my unit, the VHT Pressure Relief is a 'poppet valve' located just under and just forward of the transmission suction oil filter, right side of transmission. The cable to it comes directly from the brake pedal lever. The cable adjustment was slightly loose, but I did not tighten it.

@ me37250: That's good to know about the rpms. I will get one of those laser tachs to verify my rpms.

Thanks to SpudHauler for his post on RTV HST Adjustments.

 

[me37250]

Hope I don't muddy the water with this crazy post, but just like TRIBUTE100 experienced, my machine would reach the WOT stop well before the HST lever achieved full motion. My machine shifts like a dream and has zero creep, so I didn't want to mess with the neutral adjustment or servo settings. I just needed a little more throttle range of motion, but I was too timid to cut my safety wire on throttle screws.

Just as TRIBUTE100 did, I first moved the throttle cable to the second/outer hole. Unfortunately, no adjustments seemed to eliminate the throttle cable slack at idle or the short range of motion at WOT. I simply needed more range of motion or "stroke" on the throttle cable, and the adjustments seemed to be just outside the available cable changes. I probably could have overcome this by changing the neutral position etc, but if it ain't broke...

As an experiment, I tried to gain more throttle cable "stroke" by extending the throttle lever arm. Below is a picture of my mocked-up experiment. I scabbed together a few pieces of flat bar to get far enough out. Eventually I was able to reach full HST lever movement, full throttle lever movement, and all below the factory WOT of 3100 rpm.

Don't get me wrong, this looks, and is ridiculous, but it was an experiment. Perhaps I should add a "don't try this at home" disclaimer. I just wanted to throw the idea out about getting lock to lock movements without exceeding the 3200 rpm engine rating.

A better solution would be a tension spring connecting the throttle cable to throttle lever. The spring would need to be strong enough to pull the lever without stretching, but weak enough to stretch once the lever reaches the WOT stop. This effectively gives you a cushion to continue moving the HST lever despite the throttle reaching WOT. I bought a few springs to try this, but haven't had time to try them.