Kubota RTV 500

[MattJ]

Reading this thread is getting me fired up from my own fun with the Kubota "engineers." They are really good at coming up with reasons its not a design flaw. Excuse number 4 from them on my HST failure was I used it in a cold location (Upstate NY). Its like our politicians lately, come up with endless random distractions from the problem and hope one sticks.

As for the poster mentioning the "bombproof HST's" I think a few posters here have low hour smoked ones they'd be happy to sell you. On the other hand my neighbor's "failure prone" belt drive polaris 500 has now towed back my Kubota for the second time.

 

[Stonehaller]

Secondly, and HST is a fluid drive transmission, it can not "down shift" when it wants to, there is no such thing. The whole issues here is that on an RTV type vehicle with an HST, you can not simply step all the way down on the peddle to get full torque, it is the way it works..

The RTV hydrostatic transmission is different from the hydrostatic transmission used in a tractor. The RTV transmission has loading sensing and automatically varies the transmission ratio. There is no direct connection to the swash plate in transmission as there typically is with CUT tractors. The foot peddle controls both the engine throttle and a servo in the transmission. The servo controls the swash plate on the transmission pump and will vary the pump displacement depending on the load on the transmission. There are two motors in the transmission. One with fixed displacement and one with a variable swash plate that is load sensing. Do a search in the ATVs & Utility Vehicles forum on the RTV500. There are threads that discuss adjustment of the servo and throttle cables. Proper adjustment is critical for optimum performance and seems that many RTV500s are shipped with the servo misadjusted.

 

[timswi]

Reading this thread is getting me fired up from my own fun with the Kubota "engineers." They are really good at coming up with reasons its not a design flaw. Excuse number 4 from them on my HST failure was I used it in a cold location (Upstate NY). Its like our politicians lately, come up with endless random distractions from the problem and hope one sticks.

As for the poster mentioning the "bombproof HST's" I think a few posters here have low hour smoked ones they'd be happy to sell you. On the other hand my neighbor's "failure prone" belt drive polaris 500 has now towed back my Kubota for the second time.

Matt, don't sell the 500 short. Seems that the new owneers of the 500 are quite happy with it's performance. Seems that Kubota made the servo and max RPM adjustments that thoe of us that bought the first ones had to do. It does make a huge difference.

They won't climb a pine tree in high range, but generally they are fine. low range is unstoppable. These are work machines with some play ability.

 

[Texas Fella]

Stonehauler:

Your discription is "spot on" as to the design of the RTV transaxle (I have atttended several training sessions on this unit). However, even with the variable assist motor (VAM), you still must choose between speed or torque, there is not "shifting" in the transmission. As the load is increased, the angle of the VAM swash plate is changed, thus engaging the VAM, this will decrease the speed (same amount of fluid is now being used by 2 motor, not 1). The whole point of my post was the with an HST (of any type) you can not push all the way down on the pedal and expect to reach the peak torque of the HST. On the RTV500, it is critical that all the adjustments are correct. Your local Kubota dealer has access to on-line information from Kubota detailing these adjustments. Sorry if I was unclear, I was also in a foul mood when I wrote that post (had been listening to customer complain all day) and was most likely a little harsh in my wording. Sorry, I am human.

 

[Texas Fella]

By the way, the HST is what is refered to as a "servo control" (no mechanical link from the foot pedal to the pump swash plate). This is very common on utility tractors of higher hp. This type of control system is what you will find on L30 and L40 series tractors, althought the transmissions themselves are different that the RTVs.

 

[Stonehaller]

By the way, the HST is what is refered to as a "servo control" (no mechanical link from the foot pedal to the pump swash plate). This is very common on utility tractors of higher hp. This type of control system is what you will find on L30 and L40 series tractors, althought the transmissions themselves are different that the RTVs.

Thanks for the replies and clarifications. I did not realize you were a dealer.

As far as the 'servo control' on tractors, is not their main purpose for peddle effort? Generally on a tractor the ratio is based on peddle position and does not vary with load as with the RTV.

 

[Texas Fella]

Yes, genrally the servo is used on transmissions with higher volume and/or higher pressures. When you get into the larger transmissions, the average person can not press the pedal down on a non-servo unit, especially under a heavy load. All the pressure in the transmission is not only acting on the motors (axles, tires, etc.) but also on the pump swash plate. The servo allows the operator to move (and hold) the swash plate by simply operating a valve and letting charge pressure (generally) do all the work. In the RTV series, the transmission is small enough that it does not need a servo the be operated, but it was designed with on for convience. With a servo, the designers also have much more flexibility in transmission placement. On non-servo units, you pretty much have to have a direct link from the foot pedal to the HST swash plate (usually no cables, they tend to strech under such load). Imagine the adjustment nightmare it would be to adjust an RTV if there were rods and cams from the foot pedal to the HST in the rear! Again, sorry if I was snappy on the first post.

 

[Texas Fella]

I read your post again and may have mis-understood you the first time a little. The fact that the HST is servo control does not affect the general operating charactoristic (power, speed, etc.) of an HST. It is just another way to control the operation of the pump swash plate.

 

[ptplumer1]

I am having the same problem with an RTV500. The engine turns up seeming fine in neutral, but in gear it doesn't reach full speed in either high or low gear. It also dogs on hills and almost stops on hills it has previously walked right up. I have changed the plugs not 10 hours ago, gapped properly. The fuel was treated.

Good info previously on the servo control on the HST. Did not understand that previously.

 

[blakesgoat]

hi all! had my rtv500 for a couple of months now. think I've read all the post on this machine. I have the same issues as everyone else. low power, no ability to pull hills at all. it just seems the little motor isn't putting it's heart into it. have tried the servo adj and throttle adj. tried adjusting spring tension on the governor. seemed to help, but in my experience with golf carts, this is not the answer. something I'm overlooking?