Transmission & Overdrive Rebuild Services

Feb 2016: We are currently only rebuilding Triumph TR3A (four synchro) through TR6 transmissions and A and J type overdrives for Triumph TR transmissions.  We have been and continue to primarily be a Triumph shop, and currently our workshop is too busy to accommodate work for Austin Healey and MGs.

Wishbone Classics has experience with all original transmissions and Laycock overdrives found in popular British sports cars. Additionally, if you have a standard MGB or Triumph transmission we can also convert these to overdrive specification for you. Need a fast road or competition transmission and overdrive? No problem, we have special purpose custom parts in addition to extra preparation services that will transform your original British sports car transmission into one that can handle the rigors of weekend track events or full-on competition use.

  • All standard gearboxes built to better than factory specifications & tolerances
  • Fast Road & Competition transmissions and overdrives available
  • All units dynamically tested, insuring problem free use for you
Every gearbox rebuild begins with a complete tear down and inspection. We will not reuse any component that we don’t believe will service you for the future. Transmission cases receive a high pressure degreasing and are then cleaned on the interior and exterior with high pressure soda blasting. Soda blasting is a non-abrasive method of surface cleaning with the benefit that any remaining soda is dissolved during a final warm water rinse prior to unit assembly. Gears are treated similarly and for fast road and competition use the gears and shafts can be isotropic finished as a means of improving the components surface finish with a positive impact on reducing friction, heat and increasing the life of the gears. All transmission internals are mock assembled to check fit and clearances. Prior to final assembly, all internal transmission components are ultrasonically cleaned to insure maximum cleanliness. The final result is a gearbox that will outlast and outperform the one that was originally in your vehicle – and it’ll look stunning too!
We also rebuild Laycock overdrive assemblies – A, D, J and LH types. Cleanliness is of an even greater importance with overdrive units due to their complexity and myriad of internal passages. After initial degreasing of the overdrive cases, the cases receive two ultrasonic cleanings, again insuring no residues or debris are left in any nook or cranny. Depending on overdrive type the friction clutch surface is either renewed or replaced with new. For fast road and competition use, we use friction materials with higher coefficients of friction in order to increase their torque holding ability. Also for fast road and comp use, we have a few tricks that can be applied to the hydraulic systems to quicken overdrive engagement and also to allow overdrive use in lower gears for more real-world flexibility. 
All transmissions and overdrives are dynamically tested on our transmissions test stand. The stand is setup to test the gearboxes at approximately the equivalent road speeds of 25 and 50 mph. During the tests we are able to shift between gears, confirming proper synchronizer and shift linkage action. Overdrive operation can also be tested, and overdrive operating pressure can be verified. And of course we’ll be able to catch and correct any of those minor gasket or seal leaks before you get your transmission.
Transmission & Overdrive Assembly Gallery