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Allison Transmission Parts

Troubleshooting Charts For Allison Transmissions AT / MT (B) / HT / V
The troubleshooting information contained in the following charts outlines the possible causes of transmission conditions and their remedies. Several possible causes are indicated; numbered items indicate suggested remedies for the causes. For Sales and Service Call America's #1 Supplier of OEM Allison Transmission Parts and Authorized Allison Dealer;
TransDiesel Transmission Call us: 1-407-295-1221

R - RETARDER NOT FUNCTIONING PROPERLY (Models With Output Retarder)
Condition Probable Causes Suggested Remedies
Excessive Retarder Response Time 1. Priority valve sticking. 1. Clean valve.
2. Pressure regulator valve sticking. 2. Clean valve.
3. Charging valve sticking. 3. Clean valve.
4. Air lines leaking or incorrect size. 4. Replace air line.
5. Clutch piston seals leaking. 5. Replace seals.
6. Accumulator piston seals leaking. 6. Replace seals.
No Retarder Operation at Low Speed 7. No air supply. 7. Check and repair air supply.
8. Regulator charging valve sticking. 8. Clean or replace valve.
9. Pressure regulator valve sticking. 9. Clean valve.
10. Charging valve sticking. 10. Clean valve.
11. Check valve malfunctioning, omitted, or installed backwards. 11. Replace or install check valve correctly.
12. Clutch piston seals leaking. 12. Replace seals.
13. Retarder clutch worn. 13. Replace clutch.
No Retarder Operation at High Speed 14. Air supply too low. 14. Check air supply, correct as necessary.
15. Air line to retarder control valve ruptured. 15. Replace air line.
16. Air control defective. 16. Repair or replace control.
17. Retarder control valve sticking. 17. Clean or replace valve.
Low Main and/or Retarder Pressure 18. Charging valve sticking. 18. Clean or replace valve.
19. Pressure regulator valve sticking. 19. Clean or replace valve.
20. Rotor hub seals leaking. 20. Replace seals.
21. Accumulator piston seals leaking. 21. Replace seals.
22. Clutch piston seals leaking. 22. Replace seals.
No Retarder Output 23. Throttle (fuel) interlock/wiring defective. 23. Repair interlock/wiring. (Refer to vehicle service manual.)
24. Master switch malfunction. 24. Repair master switch. (Refer to vehicle service manual.)
25. Air actuator piston sealrings damaged. 25. Repair air actuator piston sealrings, retarder valve body.
26. Retarder valve sticking. 26. Repair retarder valve body.
Harsh Retarder Apply 27. Plug valve installed incorrectly. 27. Install valve so that dimple on valve is toward springs.
28. Pressure regulator valve spring incorrect of broken. 28. Replace spring.
Retarder Will Not Release 29. Brake pedal assembly or manual apply valve malfunctioning. 29. Repair brake pedal assembly or manual apply valve. (Refer to vehicle service manual.)
30. Air actuator piston sealrings damaged. 30. Repair air actuator piston sealrings retarder valve body.
31. Retarder valve sticking. 31. Repair retarder valve body.