Our large inventory of OEM Allison Transmission Parts includes a large line of new and rebuilt Allison automatic transmissions, and Allison Automatic transmission cores. All transmission parts can be shipped the same day in most cases. Call our Sales and Service Departments at 407-295-1221 or Email.

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

A - ABNORMAL SHIFTS ALL MODELS
Condition Probable Causes Suggested Remedies
Shifts Occur at Too High Speed 1. Governor valve malfunctioning (stuck). 1. Clean or replace governor screen and/or governor.
2. Vacuum modulator vacuum hose to engine kinked or leaking - light throttle shifting delayed. 2. Replace hose. Be sure vacuum line is free from kinks or bends and not close to exhaust components.
3. Modulation delayed (vacuum). 3. Replace vacuum modulator. Be sure that O-ring is installed.
4. Mechanical actuator cable kinked, broken or not properly adjusted. 4. Replace, adjust, or repair cable. Full actuator control cable travel must correspond with full throttle.
5. Mechanical actuator malfunctioning. 5. Replace actuator.
6. Shift signal valve adjustment too high. 6. Adjust shift speeds. Refer to transmission service manual.
7. Valves sticking. 7. Replace or rebuild control valve assembly.
8. Improper Modulator. 8. Inspect and replace, if necessary, modulator valve and modulator body.
Shifts Occur at Too Low Speed - Full Throttle 9. Governor spring weak or missing. 9. Replace governor.
10. Mechanical actuator kinked, broken, or not properly adjusted. 10. Replace, adjust, or repair cable. Full actuator control cable travel must correspond with full throttle.
11. Shift signal valve spring adjustment too loose. 11. Tighten spring adjusting ring to specification.
12. Modulator valve stuck open. 12. Check spring adjustment. Clean or replace modulator valve.
Rough Shifts 13. Governor valve malfunctioning. 13. Clean or replace governor screen and/or governor.
14. Vacuum modulator valve hose kinked or leaking. 14. Replace hose, check spring adjustment.
15. Mechanical actuator cable kinked, broken, or not properly adjusted. 15. Replace, adjust, or repair cable. Full actuator control cable travel must correspond with full throttle.
16. Mechanical actuator malfunctioning. 16. Replace actuator.
17. Vacuum modulator failed. 17. Replace vacuum modulator. Be sure that O-ring is installed.
18. Trimmer valves sticking (broken spring). 18. Replace or rebuild control valve body assembly.
19. Control valves sticking. 19. Replace or rebuild control valve body assembly.
20. Modulator valve sticking. 20. Clean valve. Check vacuum modulator.
21. Vacuum modulator valve spring not adjusted properly. 21. Adjust spring.
22. Engine idle speed too fast (N (Neutral [ or P (Park), if applicable] to D (Drive)). 22. Adjust engine idle screw. (Refer to vehicle service manual.)
23. Selector linkage out of adjustment. 23. Adjust linkage.
No Specific Shift; i.e.., 1-2, 2-3, 3-4, 4-5 (Up or Down) 24. Governor valve malfunctioning. 24. Clean or replace governor screen and/or governor.
25. Specific range valves malfunctioning (sticking). 25. Replace or rebuild valve body assembly.
Excessive Engine Flare 26. Refer to Chart G. 26. Refer to Chart G.
Our large inventory of OEM Allison transmission parts includes a large line of new and rebuilt Allison automatic transmissions, and Allison Automatic transmission cores. All transmission parts can be shipped the same day in most cases. Call our Sales and Service Departments at 407-295-1221 or Email.