dgeesaman

iTrader: (7)

I finally removed the 1-2 clutch hub, 2nd gear synchro, and 2nd gear. I expected to find a worn synchro, and hopefully no damage.

What I did find was a little interesting. I noticed that the 3-4 clutch hub has a lightly machined surface facing the inner cone of the 3rd synchro assembly. The 1-2 clutch hub does not have this machined surface - in fact, the black oxide finish is still intact. I studied the 2nd and 3rd synchros, clutch assemblies, and could not find any other differences.

Which brings up a couple questions:
1) does everyone's 2nd clutch hub have an unpolished finish? Should I have mine lathed to a better finish (careful to not really change its dimensions, of course)
2) could this be the cause of 2nd clunk? I have to wonder if the unfinished face on the hub grips the inner cone more than it should, and that this results in heavy shifting.

Transmission experts, please chime in.

Dave

1st-2nd Clutch Hub



3rd-4th Clutch Hub

dgeesaman

iTrader: (7)

Bump - if anyone has any info on this, or another 1-2 clutch hub to compare, I'd really appreciate it.

dgeesaman

iTrader: (7)

I think I've found a better answer.

Regarding the pictures above:
The 1-2 clutch hub with the unmachined face has the exact same clearance with the 2nd synchro inner ring as between the 3-4 hub and 3rd inner synchro ring, and it's not a tight fit - .015 or .030 or something. It does not look to be a wearing surface, so the reason for the machining on the 3-4 hub may have been to get that diameter reduced to the proper clearance. It has nothing to do with clunky shifting.

Regarding my new theory:
Upon closer inspection, the 2nd synchro that came out of my car has a different key slots in the outer (toothed) synchro ring. The new synchro has a narrower slot, which keeps the outer synchro teeth more closely aligned with the clutch sleeve teeth. This way, the outer synchro needs to rotate less (realign) as the shifter pushes the clutch sleeve over the synchro and onto the gear teeth. So this is probably what Mazda did to smooth the shift to 2nd.

What's strange is that the TSBs indicate a rough 2nd shift problem that was resolved before the build date of my FD (mid-year of 94 model year), and the TSB says to replace the 2nd synchro and 2nd clutch hub assembly with updated parts. I re-used my 2nd clutch hub assembly ($$ replacement parts) so hopefully my set is already the post-TSB version.

Dave

DaleClark

iTrader: (55)

Good info. I think the lack of responses is due to the fact that VERY few people know transmissions. That's still something that's on my list to tackle and learn . It's not hard per se, but it is pretty different.

Anyhow, thanks for sharing what you've found!

Dale