TheSamba.com :: View topic - transaxle: synchro cones with 3 sets of 3 wider teeth, why?

Mon May 02, 2016 12:08 pm

What was the original purpose of having three sets of three wider teeth on the synchro cones? Weddle is selling used 3rd/4th synchro cones with a note saying 3 sets of 3 teeth may have been removed. I didn't understand the reason for this so I asked someone about it and he explained that the stock part has three sets of three teeth that are wider than the rest, and only those nine teeth engage the slider and drive the gear. He said those nine teeth are removed so that the other (21?) teeth make contact which makes it stronger. Looking at some used stock cones I can clearly identify the wider teeth and see that they carry all of the load. They are also worn heavily on the flanks of those teeth making them unusable. Removing those teeth and allowing the "new" narrower teeth to make contact would make the part usable again. I believe that's the main reason for removing them, the extra strength is just an added benefit. But what is lost by not having them? They must serve a purpose or else VW would have just made all the teeth the same size. I also have some cones that have 3 sets of 5 wide teeth. I'm just trying to decide which ones to use in my trans.

Mon May 02, 2016 12:21 pm

The theory was as the 9 teeth wore it would start engaging the rest, problem was it caused it to kick out of gear before this happened.

Mon May 02, 2016 1:31 pm

So if you were building a performance box with new cones, you would grind off the wide teeth or install them as is?

Mon May 02, 2016 3:05 pm

Many variables

Mon May 02, 2016 9:48 pm

The story I heard from one of the German mechanics that got his training in Wolfsburg in the 60s was that originally all of the teeth were the same width so all of them took the load.
Then VW started receiving complaints from owners that sometimes it was difficult to pull the trans out of gear. By reducing the number of teeth in contact, they eliminated this problem.

If you have low mileage or new cones, I would not grind off the perfectly good synchro teeth. The 3x3 wide teeth are capable of taking almost anything you can put into them.

Mon May 02, 2016 10:04 pm

It might make more sense if you saw the machine they used to make the part. Good chance, it was less work to machine away only the minimum amount of material necessary, and doing so leave behind "spare" teeth.

Tue May 03, 2016 9:30 am

VW experimented with different configurations before settling on the 3x5 (or 3x3) groupings. One iteration had all drive flanks equal, with every other coast flank "short". I don't recall if 3rd & 4th gear had "reversed" configurations, but I imagine they did.

It's interesting to see equal teeth used by VW in later years. We did the same when we had them made. All teeth were equal, which allowed the "slick shift" mod (in which every other tooth was knocked off both slider and cone).

Tue May 03, 2016 11:40 am

Bruce, I think you've got it right.

Pablo, your post prompted me to take a closer look at my parts. I have two '69-72 IRS boxes apart currently, an early AH with coarse gears and a late AH with fine gears, plus an AT ('73+) with fine gears and brazed hubs. They had no sign of being opened before, but who knows. The early one has the 3x3 tooth arrangement on 3rd and 4th, the later AH and AT have 3x5. All of them are on both the drive and coast flanks, meaning they are interchangeable between 3rd and 4th.

The early first gear has 3x5 on the drive flanks and 3x3 on the coast flanks. The later firsts are 3x3 drive and coast. All of the second gears are 3x3 on the coast side only, with all of the drive side teeth being equal and fully engaging the slider.

Tue May 03, 2016 11:54 am

By "early" I mean splitcase transaxles, not early tunnel transaxles. Studying the early Borg Warner parts shows the many changes made over the years. I appreciated the way early gears ran on bronze bushings, rather than needle bearings, too ..

Tue May 03, 2016 2:53 pm

I assumed that's what you meant. I just used the terms early and late to differentiate between two late transaxles that are not more than a couple years apart. Even with such a small sample from near the end of production it's easy to see they were still refining things.

Tue May 03, 2016 4:40 pm

The continuing refinements seen in VW transaxles over the years put even the Porsche engineers to shame, IMO ..