TH125 automatic - Revision history

Cliff: /* Fluid capacity */

2026-07-19T00:01:27Z

Fluid capacity

← Older revision		Revision as of 00:01, 19 July 2026
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	== Fluid capacity ==		== Fluid capacity ==

	~~Typical Fiero~~ 125C ~~/ TH125C~~ automatic transaxle ~~service~~ capacities ~~are~~:		Factory 1988 service information lists the MD9 / 125C automatic transaxle capacities as:

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	~~These~~ figures are ~~suitable as general~~ Fiero 125C ~~service-~~reference values, ~~but~~ rebuilt transmissions, replacement units, dry-fill conditions, and non-original transmissions should still be checked against the correct ~~service~~ information for the actual transmission.		Because the TH125C / 125C automatic was used throughout Fiero production, these figures are useful Fiero 125C reference values. However, earlier model-year documentation, rebuilt transmissions, replacement units, dry-fill conditions, and non-original transmissions should still be checked against the correct information for the actual transmission.

	== Fluid and filter service ==		== Fluid and filter service ==

2026-07-19T00:00:26Z

Fluid capacity

← Older revision		Revision as of 00:00, 19 July 2026
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	== Fluid capacity ==		== Fluid capacity ==

	~~For 1988 Fieros, the MD9~~ / ~~125C~~ automatic transaxle capacities are:		Typical Fiero 125C / TH125C automatic transaxle service capacities are:

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	~~Earlier model years~~, rebuilt transmissions, replacement units, ~~and~~ dry-fill conditions should be checked against the correct service information for the actual transmission.		These figures are suitable as general Fiero 125C service-reference values, but rebuilt transmissions, replacement units, dry-fill conditions, and non-original transmissions should still be checked against the correct service information for the actual transmission.

	== Fluid and filter service ==		== Fluid and filter service ==

2026-07-18T23:49:42Z

2026-07-12T14:52:00Z

2026-07-12T14:50:53Z

← Older revision		Revision as of 14:50, 12 July 2026
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	Gear ratios, final-drive ratios, and transmission codes can vary by year and application. Because transmissions may have been replaced or rebuilt over time, the installed transmission should be verified when exact gearing matters.		Gear ratios, final-drive ratios, and transmission codes can vary by year and application. Because transmissions may have been replaced or rebuilt over time, the installed transmission should be verified when exact gearing matters.

			== Gear ratios and final drive ==

			The TH125C automatic has three forward gears and no overdrive.

			{\| class="wikitable"
			! Gear
			! Ratio
			\|-
			\| 1st
			\| 2.84
			\|-
			\| 2nd
			\| 1.60
			\|-
			\| 3rd
			\| 1.00
			\|-
			\| Reverse
			\| Commonly listed as approximately 2.07
			\|}

			Factory final-drive ratios varied by model year and transmission code.

			{\| class="wikitable"
			! Model year
			! Final drive
			! Code
			! RPO
			\|-
			\| 1984
			\| 3.18
			\| PF
			\| MD9
			\|-
			\| 1985
			\| 3.06
			\| CD
			\| MD9
			\|-
			\| 1985
			\| 3.18
			\| PF
			\| MD9
			\|-
			\| 1986
			\| 3.06
			\| 6CD
			\| MD9
			\|-
			\| 1986
			\| 3.18
			\| 6PF
			\| MD9
			\|-
			\| 1987
			\| 3.33
			\| 7CPC
			\| MD9
			\|-
			\| 1987
			\| 2.84
			\| 7PSC
			\| MD9
			\|-
			\| 1988
			\| 3.33
			\| 8CPC
			\| MD9
			\|-
			\| 1988
			\| 2.84
			\| 8PSC
			\| MD9
			\|}

			The final-drive ratio affects engine rpm, acceleration feel, and cruising behavior. A numerically higher ratio generally gives more mechanical advantage but higher engine rpm at a given road speed.

			Because Fieros are often modified or repaired with replacement transmissions, the actual transmission code should be checked when exact final-drive identification matters.

	== Operation ==		== Operation ==

2026-07-12T14:50:21Z

Specifications

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 | Torque converter clutch
 | Yes, on TH125C applications
 |-
 | Fiero model years
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 | Automatic-equipped 2.5L four-cylinder and 2.8L V6 models
 |}
 == Operation ==

2026-07-12T00:46:10Z

Specifications

2026-07-12T00:45:22Z

Naming

← Older revision		Revision as of 00:45, 12 July 2026
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	* Turbo-Hydramatic 125C		* Turbo-Hydramatic 125C
	* 3T40		* 3T40
			* MD9

	In Fiero owner discussions, “TH125” is commonly used as a shorthand name.		In Fiero owner discussions, “TH125” is commonly used as a shorthand name.

	The “C” designation ~~generally~~ refers to the torque converter clutch version.		The “C” designation refers to the torque converter clutch version. In later GM naming, the same basic transmission family was commonly called the 3T40.

			The Fiero automatic transmission is also associated with RPO code '''MD9'''.

	== General Motors background ==		== General Motors background ==

2026-07-12T00:45:13Z

← Older revision		Revision as of 00:45, 12 July 2026
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	The “C” designation generally refers to the torque converter clutch version.		The “C” designation generally refers to the torque converter clutch version.

			== General Motors background ==

			The TH125 was part of General Motors' family of transverse automatic transmissions.

			It was introduced for transverse-engine applications and was used in a wide range of GM front-wheel-drive vehicles. In later GM naming, the TH125/TH125C was commonly referred to as the 3T40.

			The Fiero used the TH125C automatic transaxle from 1984 through 1988.

			Although the Fiero is mid-engine rather than front-engine, the engine and transmission are still mounted transversely. This allowed GM to use a transverse automatic transaxle layout similar in concept to front-wheel-drive applications.

	== Fiero applications ==		== Fiero applications ==

2026-07-12T00:41:15Z

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 Diagnosis should include the brake switch, third-gear switch, TCC solenoid, wiring, connectors, ECM control circuit, and internal hydraulic operation before assuming the entire transmission has failed.
 == Fluid and cooling ==
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 # Check vacuum or control-related items if applicable.
 # Verify that the problem is not engine-related before condemning the transmission.
 == Mounts and cradle relationship ==
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 * [[Engine mounts]]
 * [[Transmission mounts]]
 == Relationship to engine swaps ==
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 * [[Automatic transmission]]
 * [[Manual transmission]]
 == Manual torque converter lockup caution ==