I'm refreshing a Muncie 4-speed M19, and I want to know if my synchronizer rings are worn or not.

I thought I would measure the gap between the brass ring and the gear, like so:


My internet searches (and look over service manual) did not yield any specification for this gap on a Fiero transmission.

So, does anyone have this information?

If not, I am hypothesizing that this spec will be similar on any transmission with the same kind of classic brass synchronizer ring design.

This video link might answer some questions
https://www.youtube.com/watch?v=MXsRfbOiBhE

Hope this helps

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"Because in a split second, It's gone"
Ayrton Senna

It's a nice how-it-works video.

At 7:15 in the video they mention that a gap of 0.030" to 0.060" is acceptable. For a medium quality rebuild?

The following website says 0.020" wear limit.
http://vwts.ru/vw_doc/eva2/TM01/ch7.2.1.html

I think that means that at 0.020", the syncronizer will stop working correctly. Therefore, during an inspection, it would only be advised to reinstall the parts if the gap is somewhat greater than 0.020"; as a wear allowance in service.

Another data point:

quote Mazda MX-5 Miata 1.8 1993 to 1999: Enthuasiast Workshop Manual: Place each synchro ring on the relevant gear's boss, making sure it is evenly seated. Using a feeler gauge, measure the gap between the back of the synchro ring and the flank of the gear. Standard clearance is 1.5mm/0.059in and minimum clearance is 0.8mm/0.031in; the latter will mean a short service life and poorer quality gearchanges.

Found here:
https://books.google.ca/boo...eler%20gauge&f=false