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Internal Project: 370z Gearbox Parts

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The Nissan 370Z. A car of great heritage and some good old fashioned rear-wheel driven, manual gearbox’d fun. Though, a common problem comes by way of gear synchromesh rings made of something only a little harder than toffee. This renders each change into one or more gears a haptic, audible misery. 

Mike knows this first hand when his 370Z developed a grind into fifth gear. Three months later and the car was back on the road after a series of part numbers and updated (hopefully improved) part revisions. 

Inspecting the parts to see what went wrong

But that left us thinking, to the eye, the parts don’t look worn but the engagement on to the sixth gear is clearly different.

Worn Synchro
Good Synchro

Working (left) and Failed (right)

The failed synchro is flat on the gear face meaning it will not function as intended. The gap on the other ‘good’ synchro is 0.65mm and on a brand new synchro, this gap is usually 1.5mm.

We scanned both synchros, the input shaft and sixth gear to get a better idea of the parts.

Using 3D scan inspection tools to analyse the defects

So what is the wear diameter difference between a failed synchro and a worn but working synchro? Once we had the scan of the good synchro and the worn synchro we were able to overlay the data and inspect the differences. In the first instance, a Heatmap was created to see very quickly if we picked up any trend in the part diameters.

And we did. Looking at the below illustration we see the synchro was only 0.07/0.08mm larger but this was enough to create a situation where the synchro was not doing its job.

Once confirmed by the colour map, we conducted a sectional analysis to visualise the difference in an alternative way. This allowed us to see the minute differences between the two synchros in 2D. Sectional analyses are particularly helpful when comparing multiple parts and overlaying multiple profiles to see the variations between many parts.

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