Lotus Omega Carlton C36GET – ZF S6-40 gearbox
The ZF S6-40 6-speed manual gearbox is the heavy-duty transmission found in the Lotus Carlton/Omega (C36GET). Originally designed to handle the massive torque of the 3.6L twin-turbo straight-six, it is famously shared with the Chevrolet Corvette ZR-1 (C4).
1. Technical Identity & Rarity
The ZF S6-40 (specifically the “Black Tag” variant in early high-output applications) was one of the few gearboxes in the early ’90s capable of handling over $560\text{ Nm}$ ($419\text{ lb-ft}$) of torque.
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Lotus Specifics: While the internal gear ratios are shared with the Corvette ZR-1, the Lotus version has a unique bellhousing and output shaft configuration to mate with the Opel-derived block and the Holden-sourced limited-slip differential.
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Part Numbers: * ZF Number: 1052 000 072
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Opel Number: 90393285
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Clutch: Uses a massive 9.5-inch (240mm) pull-type clutch. Converting to a more modern “push-type” setup is a common but complex modification.
2. Market Value & Availability (February 2026)
Because these units were only fitted to ~950 Lotus Carltons and a limited number of ZR-1 Corvettes, prices have soared as the cars become high-value collectors’ items.
| Item | Estimated Price | Notes |
| Used Gearbox (Untested) | $4,500 – $6,000 | Often sourced from Corvette breakers; requires Lotus-specific housing. |
| Refurbished Unit | $12,000 – $15,000 | Fully “regenerated” with new synchros and bearings. |
| Master Rebuild Kit | $600 – $950 | Includes bearings, seals, and gaskets. Synchros are extra. |
| OEM Shift Knob | $350 | Leather 6-speed knob (very rare). |
3. Common Issues & Maintenance
Despite its “bombproof” reputation, the S6-40 has specific quirks that owners must manage:
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“Diesel” Rattle at Idle: It is perfectly normal for these boxes to “clang” or rattle in neutral. This is often caused by the dual-mass flywheel losing its damping effect or switching to a single-mass flywheel. If the noise disappears when you press the clutch, it is likely harmless “gear clatter.”
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The Roll-Pin Issue: A small roll-pin in the shift mechanism can work loose, causing the car to “jump” out of 5th gear or making gear selection vague.
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Breather Clog: The breather on top of the box can get stuck. If it doesn’t “rattle” when shaken, it needs cleaning to prevent internal pressure from blowing out seals.
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Fluid Choice: Do not use standard gear oil. These units originally required specific GM/Castrol fluids (like Castrol TWS or BMW MTF-LT-2 equivalents). Using the wrong oil can destroy the carbon-fiber synchro linings.
4. Corvette ZR-1 Cross-Compatibility
If you cannot find a “Lotus” gearbox, you can use a Corvette ZR-1 ZF S6-40 as a donor for internal parts. However, the input shaft length and the bellhousing bolt pattern are different. You must retain your original Lotus casing and front plate to make a Corvette unit work in a Carlton.
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