F40 Gearbox Clutch

The F40 gearbox is found in many GM vehicles, including the Astra J VXR. This gearbox suffers from a few issues, starting with poor gear selections into 2nd, especially when changing from 1st gear. This will eventually lead to popping out of 2nd gear, which is when the gear is selected and clutch released with throttle (load) applied, the gear ‘pops’ out and the gearstick returns to neutral. Once this starts to happen, the only resolution is to have the gearbox repaired.
The first image below shows worn/burred engagement teeth on the synchro hub ring, and on the next image the engagement slots on the gear itself, which the synchro hub ring locks onto. This excessive wear affects the gearboxes ability to synchronise the gear speeds prior to full engagement, which in turn stops the smooth meshing of these two parts. Replacing these worn parts with a new gear will allow for correct gear speed synchronisation and meshing of the synchro ring when selecting this gear.

Repair kit includes: new 2nd gear; new synchromesh hub with 1st and 2nd triple ring synchros; a new set of bolts, and a new selector fork for 1st /2nd and 5th /6th gears.

Once the gearbox is removed, it is stripped, cleaned and meticulously inspected for any other issues, before replacing the faulty components with our repair kit.

Full gearbox removal is required for the repair, and we highly recommend that whilst the gearbox is out an uprated clutch is fitted at the same time.

Once rebuilt the gearbox is refilled with 2.5 litres of Fuchs Titan Race SRG gearbox oil. Typically we find that the manufactures do not put enough oil in the gearbox from the factory, so we refill with the correct amount, and it is important to add this to your service schedule and replace the oil annually, refilling with 2.2 Liters (0.3 will remain in the gearbox when drained)  following the rebuild. Annually changing the gearbox oil using Fuchs Titan Race SRG, along with the addition of a short shifter, has led to very positive feedback from customers regarding improved overall feel and reliability of the gearbox.

Although the manufactures quote 295lbft, we often see standard cars putting out around 320-340lbft. The quick spooling twin scroll turbo producing higher than expected torque and long gearing often lead to clutch slip in higher gears.

‘What is Clutch slip?’ Clutch slip is when the torque output of the engine is not being fully transferred across to the transmission via the clutch friction plate, resulting in engine RPM rising without a corresponding rise in vehicle speed. This is most often noticed by the rev counter needle shooting up and ‘hanging’ whilst the wheel speed catches up with the engine. This often occurs at peak torque between 2500-3500rpm, and is more likely to happen in higher gears and on inclines due to the increased torque ‘moment’ that occurs in these scenarios.
This is caused by the clutch cover being unable to retain sufficient clamping force between the clutch friction plate and flywheel.

Fix

We have teamed up with clutch experts Helix Autosport, who have exclusively produced our heavy-duty clutch covers, which resolve any slip issues by increasing the clamping force onto the flywheel. There are 3 options, first being an uprated Cover and plate to suit the stock dual mass flywheel (DMF). For those going even further with power, there is also a sprung uprated organic friction plate available and 6 paddle options which pairs to a solid mass flywheel (SMF) for the ultimate setup when chasing maximum engine output. Click here for prices