Skool Me On Synchro Function?

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Duggie

Duggie

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So 1st and 2nd gear was grinding in the little 64 Dart I brought home. I bought "THE transmission book" and sequentially scattered the tranny all over the work bench. All the synchro stop rings have nice, pointy teeth. A buddy says,"Synchros are weird. Look on the inside for wear on the groves." I look and the grooves on the inside that look worn are not on 1st and 2nd. The only gear that looked slightly worn was the points on 1st gear.

Would someone please explain (in small words) how a synchro functions? I'd really like to know! :D
 
IIRC it provides a 'friction' surface (more of a sliding interlock) to allow the spinning gear to match the rotation speed of the next gear.
 
The insides of the synchros not on the outside with the points but the inside has little ribs on it and those are the ones that feel closer and closer on the cone of the gear and get tighter and tighter and stop the gear..
If you put the synchro on his gear with some oil you can spend it on their lightly but if you push it down on there it will stop. It's kind of a pressure activated kind of deal. So if those ribs are worn out they won't have any bite and will not slow down the gear to synchronize..
 
Say you are driving in 1st gear, then shift to second.

To get it to go into 2nd, 2nd gear needs to be spinning at the same speed as the gear it is trying to engage to.

So the Brass Synchro is the ring that rubs up against the gear to bring it up to speed. Once up to speed the shift collar wiil slide over the brass points on the synchro and continue to slide over the points of the gear to lock it into 2nd gear.

All 4 gears have synchros that do the same thing for each gear.

The synchros can look perfect but there can be enough wear inside the brass cone that it bottoms out on the gear, not being able to grab the gear with the inside of the brass cone, not speeding it up when pressed together.

Not being able to speed up the gear, they will not mesh together smoothly, so they grind until the grinding force brings it up to speed then they will slip together and go into gear.

Best thing on your trans rebuild is to replace all the brass synchros with new, even though the others may look OK, but they are not.
 
Learn something new every day. I knew what the synchros did but I thought they worked more like an automatics clutches.

So cool to learn about the cone aspect.
 
Thank you guys! That's what I needed to know. I hate doing monkey -see, monkey - do steps without knowing what's going on.

Now, I'm armed and dangerous!:elmer:
 
Duggie said:
Thank you guys! That's what I needed to know. I hate doing monkey -see, monkey - do steps without knowing what's going on.

Now, I'm armed and dangerous!:elmer:
Click to expand...
I'm not sure but I bought my rebuild kit from Brewers and I want to say they were fifty bucks for the set I hope! LOL and not 50 bucks each but while I had it apart...
 
One other thing besides the synchro and the obvious new bearings and seals rebuild kit I got new 1st 2nd 3rd 4th shifter arms with new shifter ears to connect to them on the outside of the case. I just wanted those connections to be new.. the less slop you can get in that stuff the tighter the shifting...
 
This one here shows some good detail of the strut keys in operation.

 
Great stuff everyone! I got the lesson before my ADHD kicked in and i go to apply it to my transmission. I pressed the synchro on each gear as hard as I could. 1st and 2nd that ground before, I could spin on the gear, though not easily. 3rd and 4th, that did not grind, I could not spin at all.

I haven't had this much fun since the hogs tried t eat my brother. :thumbsup:
 
j par said:
I'm not sure but I bought my rebuild kit from Brewers and I want to say they were fifty bucks for the set I hope! LOL and not 50 bucks each but while I had it apart...
Click to expand...

Yep, ordered the trans bearing and gasket kit from Brewers along with new synchros, 3 of the "dog ears" and a few factory linkage clips to replace the odd ball stuff that was holding it all together. The shift forks showed what looked like minimal wear to my untrained eye. It all shows up tomorrow. Just in time to get my little shop bench back for the engine pull to replace the rear main and inspect the bottom end.

Hang on summer, we're coming!
trans layout.JPG
 
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