This is just an information post for those who own equipment with Twin-Disk transmissions such as the dreaded Case 4994 and this may be useful if and when the original controller dies. I've had our controller sent out to be repaired twice and unless there is some way to improve them they seem to be doomed to fail again. Good luck fixing it. It is claimed that the original is engineered for exact overlap and that is great as long as the transmission is in new condition. BUT there is NO feedback into the controller to compensate for wear and altering the shift parameters (as is found in automotive applications) . FYI, after I installed a decelerater pedal, it never shifted so smooth.

This transmission is really quite simple in its operation and shifting. The original solid state controller supplied by case had quite a few complexities involving shift timing and clutch engagement overlapping as well a low engine oil pressure disengagement and more.

This controller, which can be made to replace the original when it will no longer work, is actually fairly simple.

To understand how the controller works, you need to know how the transmission works. This “Twin Disk” tranny works similar to (but not the same) as an 18 speed truck tranny . R, 1, 2 & 3 are all in a group. So you can start out 1,2,3 then it shifts into the next range and uses those three clutches again so you get 4,5,6. Then in another part of the transmission it goes into high range and starts over again. Shifting from 3 to 4 is a double shift so is going from 9 to 10. Going from 6 to 7 is a triple shift (see chart).

Basically the controller has to engage three different clutch packs to get a gear engagement. If you use a 3 pole rotary switch you can do just that. I have found and created a list of some of the major parts needed to build one. Why? Because some people have asked for this info and I hope this helps.

I have built a few controllers so far, one for myself and some for other owners. Mine is the prototype and is very complex compared to the ones that can be made with the parts listed here. The rotary switch http://www.electro-nc.com/rotaryus/d8.pdf is heavy enough to take the 1 amp load of each solenoid it controls. Also you can search eBay "Switch, Rotary, Ceramic, Open, 4P, 17 Pos." I've used 3 of them. The enclosure should be big enough to contain all the relays and the switch with room left over. To plug into the tractor’s existing plug that goes to the transmission is also listed and available online. It is the smaller plug that goes into the original controller. The only thing that still needs to be connected to the original controller from the original plug is the output speed sensor and that is only useful for the speedometer on the dash if it still works. Otherwise you don’t even need that. The rear steering will not be affected by this controller, but if the original controller fails in that area I would suggest using a steering controller from a 4890 to run it.

The wiring diagram really isn’t that complicated once you follow the individual circuits. The worst part is understanding the relays in the diagram. Here's how they work: The second one down is labeled "hold relay" once it is initiated by pushing the button, it feeds power back into itself until the power supply is interrupted. It stays live while in operation holding pole 2 engaged. It can be interrupted (stopping the tractor) by either putting in the clutch thus interrupting the power from coming through the hold disable relay. OR when going into neural and the hold disable relay is energized. (this is so that if you turn the selector switch from forward and accidentally pass neutral, it will not engage into reverse until the initiate button is pushed again, safety feature) Note that this relay uses the 87a circuit of the relay. The bottom relay just controls the power to pole 2. If you build one, make sure you bench test it to see that it works (using a test light on the connector plug pins). Follow the circuit numbers and run the wires into the appropriate locations on the connector as listed in the chart. You will also need to get a fused power source (probably 10amp is ok) as well as a ground.

For best results use a pencil type soldering gun and fine solder. Please don’t be insulted but you may want to practice on something less expensive than the rotary switch before starting.

For an optional gear selection indicator, you can buy the 4 pole switch listed and use the extra layer for indicator lights showing which gear you are in.

The parts list shows part numbers and where to order them from. You can get some of the stuff such as relay sockets and wire at many auto parts stores. I would recommend about 20 gauge wire.

I mounted my initiate switch remotely on the side of the throttle lever. Put it wherever you want though.

The solenoid chart shows which solenoids are engaged in which gear. You have to click on the attachment below labeled 4994 chart

The rotary switch contacts go “open” between selections so you may have to get used to switching it from gear to gear without going into neutral as well as skipping a few gears.

Once in operation, you can start in 1,2, or 3 with the foot clutch. But if you try start in 4,5, or 6 it will just slam into gear when the clutch is released an inch or two. Foot clutch only works with circuit T54.

The initiate button (normally open intermittent switch) makes it so you can turn the selector from N to 1 without the tractor taking off. Push the clutch in, turn the switch to the desired gear push the initiate button. When you start to release the pedal part way, and you get partial engagement the initiate button can be released. Release the clutch pedal and you can shift as normal. To stop, push the clutch pedal in all the way and release. Be sure to install a master switch and turn it off if you leave the cab with the engine running!!

If you build one please let me know how it goes, or if you need help let me know too. Before building or using this please assume all responsibility for its operation. E-mail is [email protected]

To see the chart click on the attachment labeled "4994 Transmission Chart" it is in microsoft word format

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(controller 1.jpg)

(controller 2.jpg)

(controller 3.jpg)

(4994 newer version.jpg)

y 4994 transmission chart.doc (85KB - 1679 downloads)

4994.jpg (70KB - 1172 downloads)

controller 1.jpg (144KB - 1074 downloads)

controller 2.jpg (106KB - 1016 downloads)

controller 3.jpg (102KB - 1056 downloads)

4994 newer version.jpg (99KB - 1024 downloads)