The Tortoise & Hare (not Aesop's version)

[jinman]

Those of us with Class III HST Boomers (TC35D/40D/45D and derivatives) have a wonderful Rabbit-Turtle switch to electrically shift our HST transmissions. Those of us with FELs have a switch on the right fender and another one on the Joystick. Both switches are in parallel and do the same functions, but the fender switch also has lights to indicate whether the transmission is in Rabbit or Turtle mode.

Since becoming a member of TBN, I've noticed through the years that the functioning of the Rabbit-Turtle circuit is often mysterious to many and a point of frustration. Many/most of the malfunctions are related to broken or disconnected wires, but occasionally there have been malfunctions of switches and relays that control the switching in this circuit.

It's been cold the last couple of days in Texas. Since I don't have any snow to plow (lucky me ) and I'm a little bored, I've decided to try to dispel some of the mystery around the operation of the Rabbit-Turtle circuit. I guess if I have to have an excuse, I'd say that the years of being an instructional designer are driving me to do this thread even though I'm in retirement.

The attached five (5) illustrations are in order of when you turn the tractor on through switching to Rabbit and back to Turtle. I think the descriptive text and illustrations are self-explanatory, but I'll be happy to answer any questions. These are very simplified illustrations that do not have a bunch of details like schematics. I hope they help to explain the operation of the circuit for those who haven't taken the time to figure it out in detail. As always, feel free to challenge me or discuss your interpretations. Enjoy!

 

[RobertN]

Nice slides!

Do you know, from the transmission, how the tortoise/rabbit function works? Does an acuator shift ranges in the tranny or something?

I wonder of the compl;ication of having the range lever, then a secondary range with bunny/turtle.

 

[jinman]

Robert, the solenoid is attached to a hydraulic spool. When that spool is shifted, it uses pressure from the HST charge pump to shift the motor's swashplate between 15 degrees (turtle) and 9 degrees (rabbit). The lower motor angle (rabbit) provides higher speed with less torque. The HST pedal changes the pump's swashplate and the rabbit-turtle solenoid changes the motor's swashplate. I don't know of any other tractor manufacturer with this dual-mode type HST.:thumbsup:

 

[RADIUM]

Excellent as always I wish you did this about three years ago when I owned my 40, I always wondered how it worked I just remembered as always being a great feature that really works when you have a load of dirt and you didn't want to shift to a lower range. While we're on the topic of hydrostatic transmissions does anyone know why they don't offer a TC 55 or 4060 for that matter whatever they're calling today with HST transmissions? Check out my video snow blowing in the new video forms take care

 

[JC-jetro]

Right on Jim

I don't even have an HST but certainly will keep a copy for future and a good read for now.

JC,

 

[Jackfr]

Great Slides Jim Hope you don't mind that I copied them for later use.

What do you know about pedals getting sluggish at 2500 rpm. Sometimes I have to press the reverse pedal to get the tractor to slow and stop. This is new and appears to be gettting slowly worse on our TC45DA.

Jack

 

[jinman]

Jack, you can lubricate the roller on the "B" shaped plate and adjust the return spring. Some of the later models (TC45DAs) have a heavier return spring to ensure the pedals return to neutral. If you were at low rpm, I'd tell you to bump it up, but you asked about 2500 rpm and the return spring adjustment or larger spring is your best approach.

 

[Jackfr]

Thanks Jim

Jack

 

[ENTS]

Great info Jim, thanks.:thumbsup::thumbsup:

 

[jinman]

Thanks Jim

Jack

Jack look at this diagram. Item 16 is the spring and item 1 is the nut you adjust to make it tighter.