In this article we outline some of the manufacturing flaws in gearboxes from Mazda. The TL:DR is that new isn’t always better in these complex systems.
Having an experienced builder taking the time to hand build a transmission will almost always result in a higher quality product than the same transmission being produced on an assembly line in a factory.
From synchro spacing issues, to oil galleys being clogged from the factory, we address many issues that may show up in your transmission in every rebuild we do.
Here’s one we came across with literally a few hundred street miles and first gear is toast. Manufacture flaws that don’t get corrected can cause a box to be worn out very quickly.
Note the gap between the synchros and the engagement teeth. There should be an absolute minimum of .7mm of flank gap and there is zero on this gearbox.
For comparison, here is a transmission with the proper gap.
We like to see more than .9 in a race box. Most come 1.1 or 1.2mm
Here we see wear on the 5/6 slider and fork on an NC 6 speed.
This shows a failing input shaft bearing. The bearing is allowing angles of misalignment causing abnormal wear patterns of these parts.
Another factory build flaw. Clogged input for the factory oil pump, or oil scoop as Mazda likes to call it.
That clogged hole is the outlet for that trough (below).
The oil scoop pumps oil and pumps it through to the input pocket to cool 5th gear, and helps oil the 5/6 hub.
