446B Backhoe Loader Transmission (Autoshift) Caterpillar

Location of Pressure Taps

The following graphics show the location of the pressure taps that are used on the power shift transmission.

Illustration 1	g00809642
Location of pressure taps (1) Clutch pressure for the all wheel drive (If equipped) (2) Pressure for speed clutch 1 (3) Reverse clutch pressure (4) Forward low pressure (5) Forward high pressure (6) Lube pressure (7) Regulated pump pressure (8) Pressure for speed clutch 2 (9) Pressure for speed clutch 3

Illustration 2	g00830889
Remove the floorplate for access. (1) Regulated pump pressure tap

Illustration 3	g00818936
Remove the floorplate for access. (2) Forward high clutch pressure tap (3) Forward low clutch pressure tap

Illustration 4	g00760120
Access the pressure tap from below the machine. (4) Pressure tap for speed clutch 3

Illustration 5	g00760122
Access the pressure tap from below the machine. (5) Pressure tap for speed clutch 2

Illustration 6	g00760124
Access the pressure tap from below the machine. (6) Pressure tap for speed clutch 1

Illustration 7	g00760125
(7) Pressure tap for the all wheel drive (If equipped)

Illustration 8	g00818889
Remove the floorplate for access. (8) Lube pressure tap

Test for the Transmission Oil Pump Pressure

This test will show if the transmission oil pump is good.

Illustration 9	g00830889

1. Connect a hose group with a 4000 kPa (600 psi) pressure gauge to the fitting at the regulated pump pressure tap (1) .

2. Place the speed/direction control lever in NEUTRAL.

3. Engage the parking brake. Start the engine and run the engine at low idle. Allow the engine to reach normal operating temperature.

4. Keep the speed/direction control lever in NEUTRAL. Run the engine at high idle. The pressure on the gauge must be 1650 ± 140 kPa (240 ± 20 psi).

5. Reduce the engine speed to low idle. Place the speed/direction control lever in NEUTRAL. Engage the parking brake. Stop the engine and remove the test equipment.

Test for the Transmission Clutches

This test will show if the oil pressure to the following clutches is good: forward high clutch, forward low clutch, clutch 1, clutch 2, clutch 3 and reverse clutch. The test will also show if the oil pressure to the transmission lubrication circuit is good.

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Illustration 10	g00809843
Pressure tap locations (1) Speed clutch 1 (2) Reverse clutch (3) Forward low clutch (4) Forward high clutch (5) Lube (6) Speed clutch 2 (7) Speed clutch 3

1. Connect a hose group with a 4000 kPa (580 psi) pressure gauge to each of the following pressure taps: (1), (2), (3), (4), (6) and (7) .

2. Connect a hose group with a 400 kPa (58 psi) pressure gauge to the fitting at pressure tap (5) .

3. Place the speed/direction control lever in NEUTRAL and engage the parking brakes.

4. Start the engine and run the engine at low idle. Allow the engine to reach normal operating temperature.

5. Engage the service brakes and disengage the parking brakes.

6. Shift the speed/direction control lever to FIRST SPEED FORWARD. The pressure on the gauge for the forward low clutch must be 1310 ± 210 kPa (190 ± 30 psi). The pressure on the clutch 1 must be 1380 ± 210 kPa (200 ± 30 psi). The lubrication gauge must be 70 ± 35 kPa (10 ± 5 psi).

7. Shift the speed/direction control lever to SECOND SPEED FORWARD. The pressure on the gauge for the forward high clutch must be 1310 ± 210 kPa (190 ± 30 psi). The pressure on the speed clutch 1 must be 1380 ± 210 kPa (200 ± 30 psi).

8. Shift the speed/direction control lever to THIRD SPEED FORWARD. The pressure on the gauge for the forward high clutch must be 1310 ± 210 kPa (190 ± 30 psi). The pressure on the speed clutch 2 must be 1380 ± 210 kPa (200 ± 30 psi). The gauge for the reverse clutch must read 0 kPa (0 psi).

9. Shift the speed/direction control lever to THIRD SPEED REVERSE and engage the all wheel drive (if equipped). The reverse clutch pressure must be 1310 ± 210 kPa (190 ± 30 psi). The pressure on the speed clutch 3 must be 1480 ± 210 kPa (215 ± 30 psi). The all wheel drive pressure (if equipped) must be 1480 ± 210 kPa (215 ± 30 psi). The gauge for the forward clutch must read 0 kPa (0 psi).

10. When the test is complete, put the speed/direction control in NEUTRAL, and engage the parking brakes. Stop the engine and remove the test equipment.

Problem

All forward clutch pressures are too low.

Probable Cause

1. The spring to the system relief valve is weak.

2. The oil level is low.

3. The oil filter is plugged. Replace the dirty oil filter.

4. Oil pump failure.

5. The neutralizer button that is on the shift lever or the tilt control lever shorted. This caused the solenoid control valve to de-energize.

Problem

Either a forward clutch pressure or a reverse clutch pressure is too low.

Probable Cause

1. The solenoid is faulty.

2. The clutch piston seals are bad.

3. The seals are faulty or the seals are missing on the input shaft.