For over 10 years now Garage-D has been maintaining and upgrading the S15 6 speed gearboxes. With the knowledge we’ve accumulated over the years we have discovered the various issues these gearboxes face and what can be done to fix and keep them reliable.

s15 gearbox 01

The first general sign of S15 gearbox troubles is 3rd and 4th gears becoming difficult to select, this is a result of the locating circlip on the layshaft coming away and allowing the gears to move when trying to select gear. As these move they cause damage which shortly leads to terminal failure, which renders the gearbox scrap.

Using a leading gearbox manufacturer, we modify the layshaft and upgrade the circlip to a locking collar type of location as generally would be used in other high performance gearboxes.

We have noticed that even on low mileage virgin cars that the 6 speed box may commonly suffer from a noisy input shaft, people have thought their gearbox was on its way out when they start to hear a slight whine when their foot is off the clutch pedal but disappears when the clutch pedal is pressed down. This doesn’t affect reliability as it generally is down to the fact that these boxes are designed for a lighter grade of oil and a dual mass flywheel which many people replace for a solid version.

It is worth noting that our S15 gearbox modification is more of a preventive modification rather than a strength upgrade. S15 gearboxes generally fail from a combination of mileage and gear shifts rather than overall power, however heading towards 400bhp (flywheel) it is the combination of torque and clutch choice that will lead to gear failure which again renders the gearbox scrap. From here we recommend the Garage-D bolt in Nissan Skyline RB25 gearbox conversion which we can also supply all parts for including adapter kit -

General lead time to carry out this modification to your S15 gearbox is 2-4 weeks. When being done, we fully inspect the complete gearbox so should you have any other issues (synchro etc), this can be addressed at the same time.

Alternatively, we do stock gearboxes with this modification already carried out, however we only do these on a supply and fit basis taking your old gearbox in exchange. This is to ensure the gearbox we are taking in exchange is in good order and that the replacement gearbox is fitted correctly.

Pricing starts from just £550 +vat. Contact us for more information.

As a fully equipped workshop, we offer a fitting service on all of these options, please enquire for further details.

We also carry in stock:

  • A wide range of clutch kits
  • Our recommended gearbox oil
  • Replacement / upgraded engine and gearbox mounts
  • 1000’s of other new and used Nissan Silvia parts