Kubota BX1880, BX2380, BX2680 HST Neutral Spring Adjustment

BX1880 / BX2380 / BX2680 Owner Service Guide

When you take your foot off the speed control pedal, the HST neutral spring pulls the transmission's trunnion arm back to neutral, and the tractor slows and stops on its own. This is called dynamic braking. The spring weakens with use, so Kubota calls for checking and adjusting it every 100 hours. A weak spring lets the pedal return slowly and lets the tractor roll farther before it stops.

How the linkage works

The speed control pedal connects through the HST pedal link and the speed change rod to the trunnion arm on the hydrostatic transmission. Pressing the front of the pedal turns the trunnion arm and the swash plate for forward travel; pressing the rear turns them for reverse. When the pedal is released, the neutral arm and the tension of the neutral spring return the trunnion arm and swash plate to neutral. A damper on the pedal link slows the linkage so it cannot move abruptly.

The neutral spring is on the right side of the transmission, under the front of the right fender.

Checking dynamic braking

Do this test on level concrete or pavement with a clear area ahead of the tractor.

1. Start the engine and run it at full throttle.
2. Shift the range gear shift lever to high.
3. Press the speed control pedal forward and get the tractor moving.
4. Take your foot off the pedal and note where you released it.
5. Measure the distance from the release point to where the tractor stopped.

If the tractor rolls farther than 3 m (10 ft), the neutral spring tension needs to be increased. If the tractor creeps forward or backward with the pedal released and the engine running, the problem is the HST neutral position, not the spring. That is a separate adjustment made with the rear wheels off the ground; schedule service and do not use the tractor until it is corrected.

For more on using the speed control pedal, see our video:

Adjusting the neutral spring

Kubota recommends having a dealer make this adjustment. The procedure below is for technicians and experienced owners.

1. Park on level ground, set the parking brake, stop the engine and remove the key.
2. Remove the step.
3. Loosen the lock nut on the adjusting rod.
4. Turn the adjusting nut one half turn to pull the neutral spring tighter.
5. Tighten the lock nut.
6. Reinstall the step and repeat the dynamic braking test.
7. If the tractor still does not stop within 3 m (10 ft), repeat the adjustment a half turn at a time.

From the factory, the adjusting rod extends 10 mm (0.39 in.) from the stay, shown as dimension M below.

Damper arm

The feel of dynamic braking, meaning how quickly the tractor slows once the pedal is released, can also be changed by moving the damper to a different position on the arm. The damper position changes how much force the damper applies to the pedal linkage.

Parts

Parts catalogs: BX1880, BX2380, BX2680.

Related

• Engine start system check
• Brake pedal adjustment
• HST oil filter replacement
• BX Owner Service Guide

To have the adjustment done at Messick's, schedule service.