Flexplate clamp. Porsche 928 1978-95  ❭  922421255CL

Porsche 928 Flexplate Clamp Upgrade - Permanent Solution to the 928 Flexplate Problem

Protect Your V8 Engine from Catastrophic Failure

The Porsche 928 V8 engine is known for its performance and engineering excellence, but it also has a well-documented weakness known as the flexplate problem. If left unaddressed, this issue can lead to severe internal engine damage and complete engine failure.

Fits:

• Porsche 928 4.5L 1978-82
• Porsche 928S 4.7L 1981-83
• Porsche 928S2 4.7L 1984-86
• Porsche 928S4 5.0L 1987-92
• Porsche 928GT 5.0L 1989-91
• Porsche 928GTS 5.4L 1992-95

Diagram Ref No 25

This upgraded flexplate clamp is engineered as a functional and permanent solution to prevent crankshaft end float movement and protect the axial thrust bearings.

What the Flexplate Problem Is

In the Porsche 928 automatic transmission setup, the flexplate connects the crankshaft to the torque tube driveshaft. If the clamping system fails or loosens, the crankshaft can be forced forward under load.

When this happens:

• The axial crankshaft thrust bearings wear rapidly
• Excessive crankshaft end float develops
• The crankshaft moves forward into the engine block
• The lower block can be permanently damaged

It only takes 3 to 5 mm of forward crank movement for catastrophic damage to occur. Once the crankshaft bores into the block, the engine is effectively written off.

What This Upgraded Flexplate Clamp Does

This redesigned clamp secures the original flexplate clutch sleeve correctly and evenly, preventing forward crankshaft movement.

Unlike other aftermarket solutions, this clamp design focuses purely on mechanical integrity and correct force distribution.

Key design improvements include:

• Three precision-machined circular segments that fit perfectly around the original flexplate sleeve
• Even clamping force across all segments
• Three high-strength M8 12.9 grade socket head bolts
• Torque specification of 60Nm for secure fastening
• Compact, lightweight design to reduce centripetal forces

Why Other Designs Can Fail

Many flexplate clamp designs use two-piece clamping systems around a three-segment shaft. Basic vector force analysis shows that this design cannot distribute compression force evenly across all segments.

Uneven force distribution leads to:

• Inconsistent clamping pressure
• Potential loosening over time
• Continued crankshaft movement risk

Even Porsche’s original clamp used a simpler two-segment design with a single bolt.

This upgraded clamp eliminates uneven load distribution by using a three-part circular design with equalised clamping forces.

Why You Should Upgrade

You should strongly consider installing this flexplate clamp if:

• You own a Porsche 928 with automatic transmission
• Your engine has never had the flexplate fix performed
• You are rebuilding or restoring a 928 V8
• You want preventative protection against thrust bearing failure
• You are experiencing signs of crankshaft end float

Symptoms of flexplate issues may include:

• Unusual engine noises
• Difficulty maintaining correct crankshaft end play
• Thrust bearing wear during engine rebuild
• Visible crankshaft forward movement

Installing this upgraded clamp holds the driveshaft securely as originally intended and eliminates the flexplate problem completely when correctly fitted.

Engineering Focused on Functionality

This clamp was developed with one goal: to solve the mechanical weakness permanently.

• Stronger materials than factory design
• Reduced mass to minimise centrifugal stress
• Balanced clamping across all segments
• Designed for durability under high rotational loads

It provides a long-term preventative solution that protects one of the most valuable components of your 928 — the engine block itself.

Key Benefits at a Glance

• Permanent solution to the Porsche 928 flexplate problem
• Prevents crankshaft forward movement
• Protects thrust bearings and engine block
• Even three-point clamping design
• High-strength 12.9 grade bolts
• Lightweight and mechanically balanced
• Designed for long-term engine protection