Noble mmt6 gEARBOX tRANSMISSION Service and Upgrade

Jun 14

The Getrag-Ford 6-speed manual gearbox with Quaife Automatic Torque-Biasing (ATB) limited slip differential, also known as the MMT6 transmission were installed in the Noble M12 & M400. The gearbox came from a Ford Mondeo ST220 that was produced in Europe during the early 2000s. We are going through a complete engine rebuild on a Noble and we decided to go through the gearbox since it is getting old. The gearbox was first opened in 2010 to receive upgraded shift forks. It was known in the Noble community the plastic pads on the shift forks would break off when the horsepower is raised. Two of the four shift forks have been modified. The owner provided us the invoice to give an idea on the costs for this modification.

The gearbox was opened, and we immediately noticed that it was filled with water at one point. We spoke with the owner about this, and it is suspected that the gearbox sat out in the rain or water was flushed through the gearbox while at the mechanic shop. This is a no-no and is unacceptable. The milky brown oil along with rust indicates that it has been like this for a while.

Reported damages:

Synchros – 3rd and 4th had rust on them due to water.
One of the modified shift fork pads that had brass or bronze blocks fabricated onto it, fell off.
Another modified shift fork pad was loose.

Stock and Modified Shift Fork Comparison.jpg

All the bearings, synchros and seals on the three shafts and Quaife ATB limited slip differential were replaced with new ones. The gears, the three shafts, hubs, sliders, and ring gear were surface treated.  The surface treatment improves fatigue strength, reduces friction as well, strengthen the shafts even around the splines and improves gear surface life.  Also leaves a hard, smooth polished surface on the gears.  This aids the synchros, helping them grip better, thus smoothing and can increase speed shifting. — All the bearings, synchros and seals on the three shafts and Quaife ATB limited slip differential were replaced with new ones. The gears, the three shafts, hubs, sliders, and ring gear were surface treated. The surface treatment improves fatigue strength, reduces friction as well, strengthen the shafts even around the splines and improves gear surface life. *Also leaves a hard, smooth polished surface on the gears. This aids the synchros, helping them grip better, thus smoothing and can increase speed shifting.*

The gearboxes have been around for decades, and they are getting old and being affected by rust. We decided to have the gearbox casing vapor blasted to give it a lustrous finish.