3rd and 4th Synchro rings

[Bruce2]

I've got a few gaps in my knowledge of 3rd and 4th gear synchros so I am hoping everyone can help complete the list.

The first synchros for 3rd and 4th are easy. The split case gearbox from 53 to 60 used synchro rings 113 309 295. AFAIK, this is the only part number used for the entire run of that gearbox.
Here's a pic of a couple of these synchros. Note how thin it appears compared to a later synchro.


When the tunnel type full synchro gearbox appeared in Aug 60 for the 61 model year, it used synchros with part number 113 311 295. This synchro has a large chamfer on the OD end opposite of the dog teeth. It needs this chamfer so it can fit in the recess of the 3-4 clutch gear. In Nov 61 (axle number 4 371 905) the inside of the clutch gear was opened up so that this chamfer was not needed. In Mar 62, a new synchro without this chamfer appeared, 113 311 295A. This change was done so that the clutch gear can better center the synchro ring. The new 295A synchros cannot be installed with the earlier 3-4 clutch gear.
Here's a back-to-back comparison pic of a 295 on the left and a 295A on the right.


We are all familiar with the currently available synchros, 113 311 295D. These have the 4 large notches grouped together to provide an imbalance that according to VW reduced howling when the gearbox was cold. They also have 3 small notches in their OD to indicate the angle of the tops of the dog teeth, 120°.

Here is what Long Enterprises has to say about the change from 110° to 120°:

Tech Tip #2 Synchros: 110° vs 120° Face Angles

Question: What is the difference between synchros with the 3 notches on the side (113 311 295D) and the ones without (113 311 295A)?

Answer: The 113 311 295D synchros with three notches on the sides have 120° face angles and the 113 311 295A (no notches) have 110° face angles.

The 113 311 295D have synchronizer teeth with 120° degree face angles. When these synchros were first introduced the face angles on the engagement teeth of the sliders were also changed to 120°. The additional 10° more gradual angle provided improved shifting. The first 3-4 slider with 120° face angles on the engagement teeth was introduced at the same time (late 1971) and can be identified by two annular grooves, one on either side of the shift fork slot. This 3-4 slider requires a 113 311 295D synchro (120°) on both 3rd and 4th gears. The 002 311 315 3-4 slider (72-75, 5mm shift fork) uses the 113 311 295D synchro on 3rd and 4th also.

Notice how they skip from a 295A to a 295D.

In the orange Bentley manual on page 35 of the transmission section, it states:

Beginning in 1972, grooves were machined into one part of the 3rd and 4th gear synchronizer rings. This gives the ring an imbalance that, in conjunction with centrifugal force, keeps the ring in continual contact with the gear wheel. This helps prevent 4th gear howling, which sometimes resulted from a cold transmission. See fig 9-37.

Fig 9-37 has an arrow pointing to the 4 large notches grouped together that we've all seen.
Then they go on to say:

Midway through the 1972 model year, a second kind of redesigned synchronizer ring was introduced in production. This ring resembles the one that was previously shown in fig 9-37, but is for use with 4th gear only. Subsequently, a redesigned 3rd gear synchronizer ring made its appearance. The new 3rd gear ring was introduced gradually and, therefore, may not be found except in transmissions manufactured later in the 1972 model year. However, both of these redesigned synchronizer rings can be used as replacement parts in earlier transmissions.
Note---
The latest-type synchronizer rings should always be used for 4th gear repairs. The earlier-type 3rd gear rings, however, are adequate as replacement parts if the latest-type rings are not available.

I've read this Bentley quote over several times and I understand it to say there are 3 different synchros that all appeared within a few months of each other. So far we've got two changes: the 4 large notches and the 120° dog teeth. What is the third change? What are all the part numbers?

In my inventory of synchro rings, I have:
113 311 295
113 311 295A
113 311 295C
113 311 295D

Here's a 295C and a 295D. Both have the imbalance notches, and the 120° indicator notches. Given that, what is the difference between them?

Is there a 295B? What's it's design change?

[Pablo2]

I suspect that both the rings shown are 295D, as according to VW, the 295C was the old 110* (so didn't have the 3 small notches).

I'll have a dig in my old inventory, and search for a 295C in a box. (You may have used ones from a '70 transaxle?)

[dangerous]

Hmmmm.
Good post!

I will have a dig through my synchros.
I seem to recall some differences with the number of teeth and oil grooves in the bore,
and perhaps the dog slot width.
I only recall these differences from earlier ones, and first gear,
but will have a look at the later/ 3rd & 4th ones too from now on.

I would also like to confirm that those two were from unopened VW boxes?
(just to be sure, since the parts do appear identical)

[Bruce2]

The synchros on the left came from the box above it. That's why I said they were 295C. However, I'm buying Paul's suggestion.

[dangerous]

I just went through some of my old synchros and
all the late ones, with the 4 imbalance notches are the same.
...or at least it appears thus.

While this first one is actually a 1960 bus, second gear synchro,
it does have the same angle taper in the bore, but smaller,
so will not work on 3rd and 4th, because it sits too high
when compared with all the other third/fourth synchros.

Apparently VW DID increase the diameter of the taper by .05mm early on,
so this may be why this synchro sits a little high on later 3rds and 4ths.

It is obviously different, (so should be a different part number)
but being that the first run of tunnel trans, which Long Ent. says used the same part number for 2nd thru 4th,
it was worth a mention.
Likely it is the same part number as the 3rd and 4th in a split case trans. (?)

I found it in this trans:
http://www.shoptalkforums.com/viewtopic ... 0&t=113189



I have put these in an order that I think is the correct progression of changes.

This is the first of what I believe to be the 113 311 295:
It has similar oil grooves in the bore like that odd one above.


This one is still an early style that has the larger chamfer,
but has less grooves in the bore. I think we can safely call this one the same: 113 311 295.


This one is the first of the later style hub, ie it has a smaller out chamfer,
but has the same number of teeth and grooves in the bore. Perhaps we can call this 113 311 295A


This one is the same as above, but has less grooves in the bore.
Of interest the Genuine Brazil VW replacement parts most recently available
is the same as this in tooth count and bore grooves, and the box says: 113 311 295-1,
but being that it is the same as the 113 311 295A except for its internal grooves,
we can call the original German version 113 311 295B until we know more..


This one has the same grooves in the bore as the one above,
but only has three sets of 6 teeth.(like later ones). I think this is the 113 311 295C.


And of course, this last one that is the same except the imbalance notches. 113 311 295D

[Bruce2]

Your first ring from the 1960 Bus is curious. It looks exactly the same as the split case 3rd-4th ring. But the split case ring does not fit the 61 and later 3rd-4th gears. It rides too high with a gap of over 3mm, so it will not work. It would be interesting to know if the one you have will fit later 3rd-4th gears, or does the 1960 use a smaller synchro?

I had a look at the used synchros I have and all of the ones with the imbalance notches also have the 120º notches indicating they are 113 311 295D. I've never seen one with the imbalance and without the 120º notches. Nor have I seen earlier ones with the 120º notches.

I think the one in your 3rd pic is a 113 311 295 due to the large chamfer that is required to fit the 3-4 clutch gear that was made up to Nov of 61.

All the other differences are curious. I have many that are exactly the same as the others, but they all can't be unique part numbers because there aren't enough letters between A and D to count them all. Some of the machining differences must be irrelevant to part number changes. Maybe the internal grooves, or the number of external dog teeth???

[dangerous]

Good catch, on that early 2nd gear ring.
While mine is well used, it still has about 0.75 to 1mm gap,
it is true that the taper is smaller and would sit too proud,
if fitted to a 3rd or 4th gear gap is about 1.5mm.
I will edit my note to mention that it is a different diameter taper.

I will also make a note on one photo above, of which synchro matches the new Genuine VW Brazil synchros.

I did find a note in one of my old Bentley manuals,
that says they increased the diameter of that cone on the gears, by .05mm,
but this was merely to open up the gap, the part numbers of the synchros did not change.

[Casting Timmy]

At first the "D" come without the imbalance notches, they added the notches without changing the rev on the part. I found this in a factory manual and actually opened a box with them not too long ago. The factory also noted to use the non-notch versions on 3rd and the new notched version on 4th to use up old inventory.

[Casting Timmy]

I'll have to check the factory maual again, but it's biggest and most common note about the C was that it was obsolete, very short lived. I can try and get the date range for it again.

[Pablo2]

C was replaced by D in Jan '71

[Bruce2]

I saw a seller on the Samba with pages of the parts manual as his background, so I asked for copies.
Here's the use of 3 & 4th synchros up to 68. It appears that 295C was used from Jan 68 to Jan 71.



And for his generousity in sharing his parts book, if anyone needs any NOS 247B 1st gear synchros, here they are:
http://www.thesamba.com/vw/classifieds/ ... id=1618364

[TJSVFGUY]

Does anyone know the purpose of the "imbalance notches" on 113-311-295D?

[Pablo2]

Doing so eliminated a noise

[madman4]

Hi
Looking for a pair of 3rd/4th syncroring 113 309 295 for a 51 splitcase.
Where to find them ?? ....
Thanks a lot
Pat