Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
1989 GMC Forward Control 5.7 K, Automatic, 3L80/M40FACTORY OEM SERVICE PROCEDURE
Axle Ratio Identification
ASTRO & SAFARI REAR AXLE RATIO IDENTIFICATION
| Application & Code | Ratio | |||
|---|---|---|---|---|
| 7.5" Ring Gear | ||||
| FAG, FAK (1) | 3.08:1 | |||
| FAS, FAT (1) | 3.23:1 | |||
| FAH, FAL (1) | 3.42:1 | |||
| FAM, FAN (1) | 3.73:1 | |||
| FAP, FAR (1) | 4.10:1 | |||
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"C" SERIES REAR AXLE RATIO IDENTIFICATION
| Application & Code | Ratio | |||
|---|---|---|---|---|
| 8.5" Ring Gear | ||||
| KZJ, KZN, KZT, KZY (1) | 2.73:1 | |||
| KZK, KZU, LAC, LAJ, KZP (1), KZZ (1), LAF (1), LAM (1) | 3.08:1 | |||
| KZL, KZW, LAD, LAK, KZR, LAA, LAG, LAN | 3.42:1 | |||
| KZM, KZX, KZS, LAB | 3.73:1 | |||
| 9.5" Ring Gear | ||||
| KGT, KGX, KHB (1), KHF (1) | 3.42:1 | |||
| KGU, KGY, KHC (1), KHG (1) | 3.73:1 | |||
| KGW, KGZ, KHD (1), KHH (1) | 4.10:1 | |||
| KHA, KHJ (1) | 4.56:1 | |||
| 10.5" Ring Gear | ||||
| KJB | 3.42:1 | |||
| KJC, LHA | 3.73:1 | |||
| KJD, LHB | 4.10:1 | |||
| LHC | 4.56:1 | |||
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"G" SERIES REAR AXLE RATIO IDENTIFICATION
| Application & Code | Ratio | |||
|---|---|---|---|---|
| 8.5" Ring Gear | ||||
| PSR, PTA, PFT (1), PSW (1) | 3.08:1 | |||
| PSS, PTB, PSX (1), PTG (1) | 3.42:1 | |||
| PST, PTC, PSY (1), PTH (1) | 3.73:1 | |||
| 9.5" Ring Gear | ||||
| HBG, KCT (1) | 3.23:1 | |||
| HBB, KCR (1) | 3.73:1 | |||
| HBD, KCS (1) | 4.10:1 | |||
| PBJ, KCU (1) | 4.56:1 | |||
| 9.75" Ring Gear (DANA) | ||||
| BJH, GWG | 4.10:1 | |||
| BKH, GWF | 4.56:1 | |||
| 10.5" Ring Gear (DANA) | ||||
| HNA | 3.42:1 | |||
| HNB, HNH | 3.73:1 | |||
| BJJ, HNC, HNJ | 4.10:1 | |||
| BKJ | 4.56:1 | |||
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"K" SERIES REAR AXLE RATIO IDENTIFICATION
| Application & Code | Ratio | |||
|---|---|---|---|---|
| 8.5" Ring Gear | ||||
| LAP, LAU, LBB, LGB, LAS (1), LAY (1), LBD (1), LBJ (1) | 3.42:1 | |||
| LAR. LAW, LBC, LBH, LAT (1), LAZ (1), LBF (1), LBK (1) | 3.73:1 | |||
| LAX, LAB (1) | 4.10:1 | |||
| 9.5" Ring Gear | ||||
| KHK, KHN, KHT (1), KHX (1) | 3.42:1 | |||
| KHL, KHP, KHU (1), KHY (1) | 3.73:1 | |||
| KHM, KHR, KHW (1), KHZ (1) | 4.10:1 | |||
| KHS, KJA (1) | 4.56:1 | |||
| 10.5" Ring Gear | ||||
| KJF | 3.42:1 | |||
| KJG | 3.73:1 | |||
| KJH | 4.10:1 | |||
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"K" SERIES FRONT AXLE RATIO IDENTIFICATION
| Code | Ratio |
|---|---|
| ZBK, ZGS, ZHW | 3.42:1 |
| ZBL, ZGT, ZHX | 3.73:1 |
| ZBM, ZGU, ZHY | 4.10:1 |
| ZHZ | 4.56:1 |
"P" SERIES REAR AXLE RATIO IDENTIFICATION
| Application & Code | Ratio | |||
|---|---|---|---|---|
| 9.5" Ring Gear | ||||
| GUC, GUL, KCX (1), KDA (1) | 3.73:1 | |||
| GUD, GUM | 4.10:1 | |||
| 10.5" Ring Gear | ||||
| HJN, HJU, HJS (1), HJY (1), KSS (1) | 3.73:1 | |||
| HJP, HJW, HKH | 4.10:1 | |||
| HJR, HJX, HKJ, HJT (1), HJZ (1), HKL (1) | 4.56:1 | |||
| HKK | 5.13:1 | |||
| 10.5" Ring Gear (DANA) | ||||
| LBL, PBP | 4.56:1 | |||
| PZU | 4.63:1 | |||
| LBM, PBR | 4.88:1 | |||
| LBN | 5.13:1 | |||
| 10.5" Ring Gear (ROCKWELL) PJS | 5.13:1 | |||
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"R" SERIES REAR AXLE RATIO IDENTIFICATION
| Application & Code | Ratio | |||
|---|---|---|---|---|
| 8.5" Ring Gear | ||||
| PAL, PAR (1) | 2.73:1 | |||
| PAM, PAS (1) | 3.08:1 | |||
| PAN, PAT (1) | 3.42:1 | |||
| PAP, PAU (1) | 3.73:1 | |||
| 9.5" Ring Gear | ||||
| GUK, KCZ (1) | 3.42:1 | |||
| GUL, KDA (1) | 3.73:1 | |||
| GUM, KDB (1) | 4.10:1 | |||
| GUN, KDC | 4.56:1 | |||
| 10.5" Ring Gear | ||||
| KBW, KBY, KMW, KBX (1), KBZ (1), KMX (1) | 3.42:1 | |||
| HKP, HBW, GDP, HFP, HFY, HKS (1), HBZ (1), HFT (1), HHL (1) | 3.73:1 | |||
| GDR, HFR, HFZ, HKR, HBX, HFL (1), HKT (1), HFU (1), HHM (1) | 4.10:1 | |||
| HBY, GDS, HFS, HDZ, HFM (1), HFW (1), HHN (1) | 4.56:1 | |||
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"S" & "T" SERIES REAR AXLE RATIO IDENTIFICATION
| Application & Code | Ratio | |||
|---|---|---|---|---|
| 7.5" Ring Gear | ||||
| GAJ, PML (1) | 3.42:1 | |||
| GAK, HKB, HZP (1) | 3.73:1 | |||
| HKC, GAL, HZR (1), HZU (1) | 4.11:1 | |||
| 7.625" Ring Gear | ||||
| KUK, KUN | 3.08:1 | |||
| PMM, KUR (1), KUS (1) | 3.42:1 | |||
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"T" SERIES FRONT AXLE RATIO IDENTIFICATION
| Code | Ratio |
|---|---|
| ZAH | 3.08 |
| ZAD | 3.42:1 |
| ZAL | 3.73:1 |
| ZAM | 4.11:1 |
"V" SERIES REAR AXLE RATIO IDENTIFICATION
| Application & Code | Ratio | |||
|---|---|---|---|---|
| 8.5" Ring Gear | ||||
| PAW, PZX (1) | 2.73:1 | |||
| PAY, PBH, PBB (1), PBL (1) | 3.08:1 | |||
| PAZ, PBT, PBC (1), PBM (1) | 3.42:1 | |||
| PBA, PBK, PBD (1), PBN (1) | 3.73:1 | |||
| 9.5" Ring Gear | ||||
| GZF, KDH (1) | 3.42:1 | |||
| GZG, KDJ (1) | 3.73:1 | |||
| GZH, KDK (1) | 4.10:1 | |||
| 10.5" Ring Gear | ||||
| GDP, HHP, HHX, HKU, HHT (1), HJK (1), HKW (1) | 3.73:1 | |||
| GDR, HHR, HHY, HHU (1), HJL (1) | 4.10:1 | |||
| GDS, HHS, HHZ, HKX, HHW (1), HJM (1), HKY (1) | 4.56:1 | |||
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"V" SERIES FRONT AXLE RATIO IDENTIFICATION
| Code | Ratio | ||
|---|---|---|---|
| ZGA, ZGB | 2.73:1 | ||
| ZGC, ZGD | 3.08:1 | ||
| ZGH, ZGJ, ZGF, ZGG | 3.42:1 | ||
| ZGM, ZGN, ZGK, ZGL, ZFR (1), ZFS (1) | 3.73:1 | ||
| ZGP, ZGR, ZFT (1), ZFU (1) | 4.10:1 | ||
| ZFW (1), ZFX (1) | 4.56:1 | ||
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Factory Service Tools
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- β’ You smell fuel, burning insulation, or see smoke.
- β’ Brakes feel soft, pull hard to one side, or make grinding noises.
- β’ The engine overheats, stalls repeatedly, or misfires under load.
- β’ You are missing required tools, torque specs, or safe lifting equipment.
- β’ You are not confident in the next step or safety outcome.
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