On this page I will detail the method I used to eliminate vibration induced noise (rattling) of the front drive shaft assembly on my Kubota RTV 900 utility vehicle.

Shortly after I purchased my RTV 900 I noticed a loud rattling noise emanating from the underside of the vehicle.  During idle or creeping along in 2wd; the drive shaft that delivers power from the hydrostatic transmission to the front differential would vibrate loudly.

The noise was coming from several loose fitting u-joint/yoke assemblies that make up the front drive shaft. These assemblies mate with each other via splined and pinned shafts. The machined tolerances between the drive shaft and u-joint/yokes are not close enough to create a tight fit between the two mating surfaces. This leaves play in the assemblies that allows them to vibrate loudly when not under load (when running in 2 wheel drive).

Here is a photo of one of the splined shafts. The u-joint/yoke is held in place by a pin that is in turn secured by a cotter pin. This one is actually the forward half of the drive shaft.

Over several months the noise progressively got worse (so bad that my nephew started calling my RTV 900 "the rattler" ). It would embarrass me to show friends or neighbors my awesome new utility vehicle.

I contacted the dealer that I bought the RTV 900 from and was told by a parts manager that he spoke with a visiting rep from Kubota about the problem. The Kubota rep new about the issue and told the parts manager that Kubota was developing a new part to resolve the issue. This new part would be in the form of a new u-joint/yoke that was supposedly machined to tighter tolerances and that this new part would correct the problem. The parts manager told me to wait about a month for the new part.

At that time, I also searched on the internet and found that other Kubota RTV 900 owners were experiencing the same issue.

Over a month passed when I got a call from my Kubota dealer that the new part was available. The dealer replaced the part and it seemed to help.

After several hours of use, the rattle appeared again. I also found that other RTV 900 owners were getting their u-joint/yoke assemblies replaced (some several times) only to have the rattle reappear.

The design of the drive shaft assemblies is fundamentally  flawed. The two mating surfaces do not fit tight enough to withstand the vibrations generated by the diesel engine in the RTV 900 and thus slowly wear down and begin to rattle.

Since Kubota Corp doesn't seem willing to redesign the u-joint/yoke assemblies to correct the problem and would rather keep replacing them, I decided I would try to fix the current design myself.

Please note, that performing the following modifications may void any manufacture warranties on your Kubota RTV 900. Also, any damages to the vehicle, property, or personal injury or death resulting from the modifications listed on this webpage/website are the responsibility of the owner (you) and not me or Kubota Corp.

First to start off, remove the entire drive shaft assembly from the RTV 900 by removing the mid skid plate and unbolting the center support bearing from the chassis.
Lowering the center support bearing allows the ends of the drive shaft assembly to slide off of the transmission and differential shafts.

Then separate the u-joint/yoke assemblies from the drive shafts in preparation for drilling and tapping threads into the pinned sections of the u-joints/yokes.
The u-joint/yokes already have holes drilled in them for the keeper pins that pass through the u-joint/yoke and the drive shaft.
These holes should be tapped with 5/16th-18 threads.  There are two holes; one on each side of the u-joint/yoke. Tap each side.

Here is a picture of the tapped hole and the 5/16th set screw that will be installed on each side apposing each other in order to apply pressure on the shaft equally and to provide redundancy.

Here you will see that the shafts that are pinned already have machined into them a countersunk area on each side of the shaft. I can only assume that they are machined that way at the factory to facilitate easier assembly.

These countersunk areas prove to be advantageous because they are perfectly matched to the set screws and make for easy realignment. They also provide a larger contact surface between the shaft and the set screw. This provides a better hold and is less likely to become loose. Also, the set screws do not come in contact with the splines machined into the shaft so no maring/gouging occurs to the splines. The drive shaft assembly can be disassembled again by removing the set screws and the splined shafts slide out easily.

This is the set screw installed in the u-joint/yoke.

 Here is a picture of the reassembled u-joint/yoke and shaft with new set screws instead of pins. Locktite brand blue thread locker was used on the set screw. I thought of using Locktite red but was afraid I would not be able remove the set screw later. If one of these set screws ever comes loose, I will try the Locktite red.

There are two u-joint/yokes that are assembled in this manner. This takes four set screws total.

The next step is to provide some preload pressure on the ends of the drive shaft assemblies that are just splined and not pinned to the shafts. One that connects to the output shaft of the hydrostatic transmission and the other that connects to the input shaft of the front differential. After much thought I came up with the following solution.

I took a 3/4 inch machine bushing and placed one over the output shaft of the transmission and one over the input shaft of the front differential.

The bushing is only a fraction too small to slip over the shafts. So I ground the inside just enough to allow a snug fit with no side clearance.

 The bushing should fit so as it is difficult to install by hand but easily installed with very light tapping of a deep socket or pipe over the shaft.

This is a bushing installed on the output shaft of the hydrostatic transmission. There is a shoulder at the base of the shaft that is diameter of the shaft prior to the machining of the splines. This shoulder provides a stop for the bushing.

Here is the input shaft of the front differential. This has no shoulder, but rather the inner race of the bearing provides a stop for the bushing.

Here is the same input shaft with a bushing installed.

This is a picture of the transmission output shaft showing the available clearance (after re-assembly) for a rubber bushing. This is a splined only fit and does not have pins from the factory. I did not drill or tap this side of the u-joint/yoke. It is meant to slide or give to prevent binding. None the less, the fact that is isn't pinned allows it to be a source of noise from vibrations.

 I used a section of rubber heater hose cut 1/4 inch longer that the clearance between the bushing and the u-joint/yoke. I applied a good amount of grease and installed the rubber bushing between the metal bushing and the u-joint/yoke. After re-assembly the rubber bushing is slightly compressed providing preload against the u-joint/yoke. This preload prevents the u-joint/yoke from rattling.

On the front differential, the input shaft the clearance between the metal bushing and the u-joint/yoke was only about 1/8th of an inch. I found that a rubber garden hose washer worked best here.

My results were excellent and the drive shaft assembly is as quiet as when running the RTV 900 without the front drive shaft.

My nephew no longer calls my RTV "the rattler" and I am no longer embarrassed to turn on or drive the vehicle when friends and neighbors are admiring it.

I really hoped that Kubota Corp would fix this problem, but couldn't wait any longer for them.

Again, if you attempt to perform these modifications on your own RTV 900, do so at your own risk.

-Eddie Cornejo