RTV500 Throttle Adjustments

Stonehaller · Oct 25, 2009

I have posted bits and pieces of my thoughts on the RTV500 cable adjustments in various threads and though I would consolidate everything here. Some information has come from discussions with the dealer but most is just my figuring on the RTV500 transmission works. If you have doubts, talk to your dealer mechanic.

The throttle peddle operates both a servo valve on the transmission for controlling the transmission ratio and the throttle cable to the engine governor. The cables and peddle stop need to be adjusted so that when the peddle is pressed to the stop, the servo valve reaches its maximum travel and the engine throttle is pulled to the stop on the governor.

First, find the maximum travel of the transmission servo. Disconnect the peddle cable and throttle cables from their stays near the bell crank (see pictures for where). Move the bell crank by hand until it stops. Mark the servo valve housing with a fine line so that you can see where the full travel point is for the servo.

Reconnect the peddle cable. When you press the peddle to the stop, the servo valve should stop just short of the full travel point you found and marked. Adjust the bolt stop under the throttle peddle if necessary to get the correct position on the servo valve. You want the bolt to be the stop in the system not the valve so when you ram the peddle to floor the stop bolt is taking the force of your foot not the valve.

Now put the throttle cable back in the stay but leave the adjustment nuts loose. Have someone hold the peddle to the floor and adjust the throttle cable so that it just pulling against the stop on the governor.

There is an adjustable stop on the governor for the full throttle position. This stop will control the max engine speed that the governor will regulate. According the dealer, maximum unloaded RPM should be 3650 to 3875 RPM. I did not see where Kubota publishes a speed/power curve for this engine but that RPM range must be where the engine makes peak power. Since there is no tach on the vehicle, you would need a tach with a clamp on ignition probe to check the RPM. If you do adjust the throttle stop, then re-adjust your throttle cable.

I hope this helps you other owners that have questioned the performance verify that yours is setup correctly.

timswi · Oct 26, 2009

Thanks for the info Stonehaller...Looks like I'm maxed out on the servo based on your instructions. I think they checked that at the dealer when I complained about the lack of power. They did up the idle a bit at the time..Didn't do anything either.

Need to hook it up to my Sun machine to check the max RPM's yet, but I'm going to guess it's in spec too...Guess I'm getting all I can until someone comes up with a perfomance package for this. Maybe a computer flash, who knows.

Stonehaller · Oct 28, 2009

The only other thing I can suggest is to ask your dealer about checking the relief pressures in the transmission. The transmission should automatically change the ratio under load. Mine does. I do not know exactly how the RTV transmission works, but for the transmission to automatically change ratio (shift) there has to be a valve that reacts to the hydraulic pressure to sense the load on the transmission. As the load increases, the hydraulic pressure increases and this valve should channel oil to decrease the swash plate angle, in a sense shifting to a lower gear. If that valve is not adjusted correctly, then transmission will not 'shift' correctly.

timswi · Oct 28, 2009

Mine does not downshift under load on it's own. I have to let up on the gas to cause a down shift. If I have the pedal mashed it just keeps running out of RPMS.

The dealer tech says that is normal for all HST's, including the tractors. Makes no sense to me and seems like a massive design flaw. It could act like a CVT without this "feature".

The whole thing is counterintuitive and Kubota really doesn't care.

Don't get me wrong..I love everything about the 500, except for the lack of load power and the goofy letting up on the gas thing...Try explaining that process to a newbe driver of the 500, they look at you like you're crazy...Maybe I am. Anyway, for what this machine costs, we really shouldn't have to have these conversation...Although I really appreciate the help!!!

Let's face it, this is underpowered for the transmission set up that they created. Never wanted a RZR level of speed, but general power isn't too much to expect. It get's kind of embarassing sometimes.

Oh well. Live and learn.

Stonehaller · Oct 29, 2009

I think there is something out of adjustment with your transmission and the dealer just does not want to investigate. The RTV transmission is different than a hydrostat in a tractor. Mine definitely 'downshifts' automatically on a hill.

Did you get a recall notice for water leaking into the timing chain cover? Since my RTV is 2.5 hours away at a cottage, the dealer agreed to show me what needed to be done so I would not have to trailer it back down. When I stop by, I am going to look into ordering a shop manual so I can do my own repairs/adustments if necessary in the future.

timswi · Oct 29, 2009

Didn't get that recall notice...Yet. Is it a tough fix?

Yeah, I thought that letting up on the pedal thing made no sense...You're saying that if you keep the pedal mashed, it downshifts? You don't have to let up?

Ricochet · Oct 30, 2009

Good info! This is basically the same process for the other RTV models as well.

Stonehaller · Nov 1, 2009

Timswi,

The fix for the recall for water leaking in the timing case looks fairly straight forward. There is a range of serial numbers so yours may or may not be affected. Ask your dealer about campaign PSB-2009-022.

My RTV will downshift with the peddle mashed to the floor. I got a quick look at the shop manual. The transmission has a pump and two motors. The pump swash plate is control by the servo that is connected to the peddle. So movement of the peddle, as we know, will change the ratio of the transmission.

There is one fixed displacement motor and one variable displacement motor. Both motors are mechanically tied together to drive the transmission output. The variable displacement motor is normally in a neutral position. This variable displacement motor gives the transmission its CVT properties. Increased hydraulic pressure in the transmission will angle the swash plate of the variable motor and 'shift' the transmission to a lower gear.

So when you step on the peddle, you angle the pump swash plate of the pump and create oil flow in the transmission. This rotates the fixed displacement motor and since accelerating the vehicle from a stop takes some power, the hydraulic pressure will raise and shift the swash plate of the variable motor lowering the ratio and increasing the torque output of the transmission. As the vehicle gets up to speed, it takes less power to keep it going so the hydraulic pressure drops and the variable speed motor shifts back toward the neutral position in effect shifting the transmission to a higher gear. At max. speed only the fixed displacement motor is powering the vehicle. If you start up a hill, the load on the transmission increases, raising the hydraulic pressure and shifts the variable motor to create a lower gear.

If your transmission does not shift automatically, then possibly the relief valve is set too low so the pressure never gets high enough to fully shift the variable motor or the swash plate in the variable motor may be stuck.

timswi · Nov 2, 2009

Stonehaller,

Thanks for the info...I think a call to the dealer is in order.

mstordahl · Nov 14, 2009

Exactly, the servo as you call it is what actually controls the pump swashplate angle of the hst, not your foot. It is what will back the hst off when coming into a heavy load, and speed up as the load decreases. It is not the relief valves job to do this. If your hst does not downshift, the servo needs adjusting.