091 Synchro Dilemma

[Dougy Dee]

I just finished rebuilding an 091 and I may have screwed up.

I bought several sets of new 091 synchros and I mistakenly installed a first gear one on second gear as well...
Of course I didn't catch this until it was all buttoned up and I was cleaning up.. The way I caught this is I now have too many 2-3-4 synchros and not enough 1st gear synchros remaining.

Although, it did fit good.

I remember looking at the two styles when they came in and other than more teeth missing from the perimeter there didn't appear to be any other difference.

I guess my question is Should I be concerned?

What problems will this create?

[Pablo2]

How frustrating .. after all that work. It's been awhile, but I believe if you measure one of the 3 slots on each of the two different synchros, you'll find those on 1st to be narrower (at least true with the earlier models). This could cause gear clash when downshifting from 3rd to 2nd. I happen to be going through my storage lockers today .. let me see if I can find both of these to compare.

[Dougy Dee]

This is the 4th or 5th 091 I've done since January. I must have been sleeping assembling this one...
I decided to take it apart.
The only difference I can see and measure is the extra missing teeth on the 1st gear synchro.
The taper and slots both measure identically. Mind you the new 2-3-4 synchros are German. The 1st is Brazilian.
It's now back together. Another 5.5 hours towards my education.
Thanks for your help...

[Pablo2]

Lucky you did. I now remember the difference .. 1st gear cone taper is 110*, while 2nd gear taper is 120*. (It's almost impossible to see it visually.) That synchro would have performed poorly, and worn out quickly.

[Steve Arndt]

This post should be saved for reference.

[dangerous]

The VW book says that for replacement synchro
use part number 091 311 295A for ALL gears.
It has teeth all around the perimeter.

I beleive the taper is the same for all the gears.

One of my suppliers told me this so I would only need to order one type of synchro,
and my workshop manual also confirms the comment.

...but while stocks are still around of Genuine VW synchros,
I like to keep the 1st gear one of the original type, 091 311 247B
and the other three the other type. 091 311 295A

Around the mid 1960s, on 113 style gears,
the face angles of the synchronizer teeth was increased from 110 degrees to 120.

The narrow slot synchros were also from the early trans'
and is the one that can only be fitted to first gear.

While this is not anything to do with the 091,
it interesting history all the same.

[Pablo2]

You're right .. it was the synchro tooth angle change, not the taper. So the incorrect synchro probably would have worked OK.

When VW went to the slightly larger diameter 1st/2nd cones (1964?), 1st & 2nd then used the same synchro (64-70).

Around 1970 VW made another change, and 1st & 2nd gears then had a 10* difference in tooth angles. Synchros with 120* tooth angles were identified with 3 small notches (on both 2nd and 3rd/4th). But late 3rd/4th synchros were often used on earlier gears without issue.

Did 1st gear tooth angle ever change to 120*? I'll search for that '70s bulletin that covers the changes. I think it was 2nd-4th gears.

[Henryhoehandle]

You're right .. it was the synchro tooth angle change, not the taper. So the incorrect synchro probably would have worked OK.

When VW went to the slightly larger diameter 1st/2nd cones (1964?), 1st & 2nd then used the same synchro (64-70).

Around 1970 VW made another change, and 1st & 2nd gears then had a 10* difference in tooth angles. Synchros with 120* tooth angles were identified with 3 small notches (on both 2nd and 3rd/4th). But late 3rd/4th synchros were often used on earlier gears without issue.

Did 1st gear tooth angle ever change to 120*? I'll search for that '70s bulletin that covers the changes. I think it was 2nd-4th gears.

You are correct... I have been there. Some time ago I made this same mistake but it worked fine....I am not sure about longevity as this was in a woods buggy, but it worked fine.

[Marc]

http://longenterprises.com/technical_in ... 20Tip%20#2