RK55 HST slipping probelm

[oldnslo]

Based on the random slipping or surging I would check the charge pressure while this is occurring. The HST is a closed loop system where the work ports of the pump are connected directly to the work ports on the motor. The charge is to keep this loop full and under some preset minimum pressure. Loss of charge pressure would allow oil to escape this loop from leakage and allow the tractor to stop moving or move erratically but I would also expect some cavitation noise if this is happening.

Very rare that a system relief would randomly change pressures and they would only affect one direction of travel not both while charge have equal affect on both directions.

 

[TractorGuy]

My first thought is you should never drive any 4WD, HST tractor up a hill in anything other than 4WD low. Doing so has probably damaged something.

If it's still under warranty you might sweet talk them into running the necessary pressure tests to diagnose the problem and fix it. If you tell them you went up a hill in 2WD medium they will probably flag it as user error.

 

[5030]

One sustaining issue with the RK tractors is, Rural King outlets are ill equipped to troubleshoot any issues except minor ones. Why I'd never consider one.

 

[oldnslo]

My first thought is you should never drive any 4WD, HST tractor up a hill in anything other than 4WD low. Doing so has probably damaged something.

If it's still under warranty you might sweet talk them into running the necessary pressure tests to diagnose the problem and fix it. If you tell them you went up a hill in 2WD medium they will probably flag it as user error.

Would you care to explain why you must be in 4WD and low range and what would be damaged if you do not do this. This inquiring mind would like to know...

 

[TractorGuy]

Would you care to explain why you must be in 4WD and low range and what would be damaged if you do not do this. This inquiring mind would like to know...

Just common sense. Low range is for operating under heavy loads such as driving up a hill with a backhoe fitted. 4WD increases traction. 4WD will be most valuable coming back down the hill.

It may go up a hill in mid range but doing so will place more stress on the components. If that were not the case the tractor would not be fitted with 3 ranges to begin with.

Slope instructions from the manual:

4WD Use

 

[Sportsman762]

Tractorguy, that is for starting off on a steep slope. If you use a higher range the tractor will not move as the transmission bypasses. Unless you just sit there with the hydro not moving and the pedal mashed your most likely not going to mess much up. I learned how to use differential braking due to the front on tractors being too light to steer when going up the hills were I grew up.
Steep Hill has a different connotation depending on where you live. Steep in FL is different than OH, and much different than MT.

I am really curious what the OP finds out about their tractor. Seems really odd to have this problem with as low of hours as they have. I would be very suprised if they damaged the tractor. Due to the age I am guessing factory defect.

 

[Littlegrey20]

Tractorguy, that is for starting off on a steep slope. If you use a higher range the tractor will not move as the transmission bypasses. Unless you just sit there with the hydro not moving and the pedal mashed your most likely not going to mess much up. I learned how to use differential braking due to the front on tractors being too light to steer when going up the hills were I grew up.
Steep Hill has a different connotation depending on where you live. Steep in FL is different than OH, and much different than MT.

I am really curious what the OP finds out about their tractor. Seems really odd to have this problem with as low of hours as they have. I would be very suprised if they damaged the tractor. Due to the age I am guessing factory defect.

That's what I'm assuming as well. I've babied this thing since I bought it brand new.
Also, I've heard of starting on a hill in low range but not keeping it in low range for any incline. The engine doesn't bog when going up the hills when it's not slipping.
I spoke with the mechanic at RK and he feels there's a problem in the hydrostatic pump. I assumed a seal bypassing, picking up air since I have checked the fluid and it would have more air bubbles than it should have after an episode of jerking.

 

[Littlegrey20]

Just to confirm . . . You say that it does this in Low RANGE and Medium RANGE too? Your RANGE selection doesn't change anything?

It will do it in all ranges. Does it worse in low than medium and high though. Assuming this is due to engine rpm vs speed of the tractor.

 

[5030]

I still think it's the fluid pressure in the transmission. Pressure controls clutch pack clamping pressure.

 

[ptsg]

I still think it's the fluid pressure in the transmission. Pressure controls clutch pack clamping pressure.

What clutch pack? It's an hydrostatic transmission.