bran3b

I picked up an early 5-speed core yesterday. My plan was to tear it apart and replace parts as needed so that I can replace the trans with bad synchros in my '79. This is what I found when I opened the cover. The 1st and reverse synchros look good to me, can you tell from these pictures if I am right? If they are good, I may just put it in the car and rebuild the one in there now for a spare.

Thanks for your thoughts.

mark kibort

little worn... they look a little rounded at the peaks to me... not a big deal with the S4 , but the early cars need synchros to be in good shape to shift reasonably well

GregBBRD

No synchro in reverse, until 1985 model year.

It's very difficult to tell how a synchro is going to work, from a picture, since there are very tiny dimensional changes between one that works fine and one that grinds. Especially tough, since your pictures are of 4th and 5th gears, which get the least amount of wear.

Show me some pictures of the gears on the other end of the transmssion.....the bigger gears.

Those little "peaks" have nothing to do with how the synchro works....they are simply what engages the gear with the slider, when you shift. However, when the synchro quits working, those teeth are what you hear "grinding" when you shift.

It is possible to tell more, with the transmission together, but only if you understand completely how the synchro works....I'm not sure I can explain how to do this....let me think about how to do that.

Finding a 35 year old transmssion, with this style synchro in it, which shifts properly, is getting to be about the same as looking for the Holy Grail.

I think of them all as "rebuildable cores".

bran3b

Greg, thanks for pointing that out, here is 1st gear. I guess I got a little sloppy with my pictures.

GregBBRD

That synchro looks very nice....it has obviously been replaced, since it looks way better than either 4th or 5th. How it functions depends on how much wear there was on the slider and what the rebuilder did with that silder.

How about a picture of 2nd and 3rd gear syncros?

There's another thread going with almost the same exact questions. Let me figure out how to show you guys how to get an idea of how these syncros are going to function with the transmssion together/figure out what needs to be replace when it is apart.

mark kibort

I thought those peaks contacted to speed up the driveline and they created more friction when pointy. guess not.. so what exactly slows or speed up the driveline.. what contact point? and how do you determine wear. I just remember my menchanic at the time of my old '84, looking at the synchros and saying" its worn out, we need new ones"
I seemed to remembrer that it was the tops of the hub vs the inner diameter of the synchro ring that made contact via the slider and then the syncho teeth would engage ... f they didn't slow or speed up to match, the both synchro teeth would make that awful sound. so its those rings ID and OD that determine wear?

James Bailey

Mark try not to embarrass yourself......

bran3b

Here are the 2nd and 3rd gears. The lighting was tougher.

GregBBRD

Yes, indeed the lighting was bad. However, I claim I can do these things in the dark, so let me tell you what I see.

In that first picture, you can see how the "pointy" teeth on the gear itself have had the peaks flattened slightly. This is not terminal for the teeth, but indicates that the synchro itself isn't doing its job and the teeth are grinding against the teeth on the slider, when the two are shifted together. While this wear could be from a "prior" bad synchro, I doubt that is the case, looking at what I can see of the synchro surface.

In the second picture, pretty easy to see the chunks of moly that have been "ripped" off of the surface of the synchro. That's not good. Missing moly means "replace".

bran3b

Thanks for the sanity check. It is better than I expected when I bought it, but still needs a rebuild.

mark kibort

Jim.. dont be an ***. (or can you not help yourself?) why dont you just explain how they work.

James Bailey

The good part about an internet forum is anyone can post anything. The bad thing is anyone can post anything. Giving advice to someone when you do not know anything/much about the topic to me is irresponsible and your comments about pointy teeth and syncros is proof of that. It also makes it clear why you THINK early transmissions shift poorly compared to the Borg Warner 1985> boxes. Your experience was with worn transmissions and a half assed rebuild where it got new syncros put on with worn parts.....
For simplicity think about brake pads and rotors....if you only replace the pads sooner or later the rotors get worn down too. Wear occurs on BOTH !
The engaging teeth "dog teeth" are what gets worn ground down AFTER the syncro friction surface starts to fail or the trans is abused clutch is dragging. The noise which people call worn syncros is from those teeth grinding on the slider. But reality is syncros themselves make no noise.
If as you maintain you get the effect of double clutching by dragging the shift lever across neutral while reving the engine with the clutch only partially disengaged... that would reek havoc on the sliders and dog teeth...
Like I said you should try not to embarrass your self....

mark kibort

I dont believe i was giving anyone advice and i did admit i didnt really know how they worked. thanks for the description. i think it was similar to my following post about the ID and OD of the synchro and hubs that slow or sped up the drive line... the friction surface does that work and are even grooves that channel oil away to make more friction.

your right about the internet and being able to say anything jim. my rebuild, (again , if i can correct you) was a complete rebuild. synchros, sliders, etc , etc. everything was replaced but gears. and they still shift bad.

your analogy with brakes is a poor one, as new pads on old rotors will work fine, with no difference. but worn synchros and hubs will not work well if only one is changed.

and jim, your comment about dragging the shifter through neutral whil reving the engine , doesnt do anything much different than double clutching . you are embarrassing youself by not thinking of the situation and being a little rude.

i understand your confustion , as you think the sychro is doing all the work to bring the driveline up to speed, but thats what happens on a traditional blip, and down shift from redline.... the sychro theoretically takes all the abuse.. (right so far Jim? ) a double clutch removes this force by spinning up the driveline with the engine directly, but takes way to long to use effectively in racing. So, what am I talking about?.... if you are familiar with the slight drag of the intermediate plate, you know it doesnt take much of a distance for the clutch to drag on the driveline. so, when partially engaging the clutch, the transmission comes effortlessly out of gear, (that's a timing/ feel thing and you really dont need a clutch to do that at the equilibrium force point) through neutral where the blip actually spins up the driveline to a higher speed, by the same friction that the "partially engaged clutch provides" (near 90% engagement) and then the very small difference in speed, the synchros accomplish with very little wear and no fuss. this is FAR less wear than full 100% clutch engagement and a blip and shift where the synchro bears all the burdnen of spinning up the driveliine..... Right????

Jim, the proof is in the pudding here.. there is a reason my transmissions synchros las for 10 years of racing on top of their prior abusive life. there is a reason i can race and downshift a car with bad sychros WITH no grinding.
The reason is, it is a good way to shift, and save the transmission. if you dont think so, you havent thought about it very well and actually, and ironically, you are embarrassing yourself..

James Bailey

OK Mark was this NOT advice.... ??? he was asking about syncros being worn and you tell him how the dog teeth look ?

mark kibort

greg also said they looked worn as well. I also admitted and clarified i didnt have a lot of knowledge in the subject.. only what folks have told me.
So, i guess the little points just allow the sychro to engage smoothly, when the working part of the synchro has done its job... correct?