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Reply to "ZF Synchro Repair Discussion"

I have been having "follow-up" discussions on my second gear cone replacement with a couple members.

I want to try and make things clear in my discussion.


This thread below goes into excruciating detail on the gear / cone relationship. It really was helpful to me to understand things.

Minimum Synchro Clearance etc. etc.

Trying to boil it down to the basics (as I see it...):

  • The cone and the syncro ring have mating surfaces.

  • One (or both) wear

  • As they wear, the syncro ring rides lower and lower on the cone. This is a secondary effect, but the measurement between the bottom of the synchro ring and the face of the gear is what you use to measure the ring / cone interface. Once one (or the other) wears, the braking action of the synchro on the gear is lost. Once the braking action is lost, the shift (up or down) grinds.

  • In my case (and in most ZFs) – the cone wears before the ring. My clearance between the synchro ring bottom and gear face was .000”. New it's .050", and a good used set is about .035".

  • I fixed my 2nd gear grind by having a new cone machined and attached to my gear. Now I am back to .050” clearance when the synchro ring is set on top of the cone.


    The cone and synchro ring are just a brake… There is really not “synchronization” going on – the synchro stops everything from spinning at a different rate than the gear, so parts don’t grind when you jam it into gear.

    Is that helpful?

    Rocky

    Cone (upper grey part with grooves) and Synchro Ring - disassembled. The ring is upside down.



    Gear and ring in mounted orientation, showing the gap between the bottom of the ring, and the top of the gear face. The gap is due to the interference between the cone and the ring angled faces.

    Sorry this is out of focus.

  • Last edited by rocky
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