[T3] Transmisison fun

[Jim Adney]

I had the same questions that Tim had, but your picture cleared most 
of that up. There seem to be 2 parts to this interesting failure:

First, the stud connecting your 2 shafts must be too short. I don't 
think this can happen with the stock stud, but I'd have to check the 
parts list to see how long it should be. It's also possible that 
someone "cleaned up the threads" in the input shaft, enabling a stock 
length stud to fall (almost) entirely inside it. 

Second, there has to be clearance for the input shaft to slide into 
the gland nut and pilot bearing far enough for the reverse gear to 
disengage. The hole in the gland nut is clearly plenty deep for this, 
but I'm surprised that the clutch disk spline didn't stop the motion 
sooner. I guess the point is that it doesn't take much for the 
reverse gear to disengage.

Really interesting observation.

Jim

On 21 Sep 2018 at 18:25, Soren Jacobsen wrote:

> > On Sep 21, 2018, at 2:57 PM, Tim Shreve <type3tim at cox.net> wrote:
> > 
> > I'm thinking that the "reverse gear" you speak of is splined on the inside
> > and those splines connect the input shaft to the main shaft; and that is
> > what transfers/carries the load. I.E. the short stud doesn't carry the load.
> 
> Yeah, exactly.  The two shafts are splined and the reverse gear (one of the two reverse gears, anyway) joins the two.  As you say, the reverse gear takes the load, not the stud inside.  The stud's only job is to keep those two splines pulled together.
> 
> > What happened to your circlip(snap ring) that holds the "reverse gear" in
> > its proper place?
> 
> The circlip was still securely in place.  When I discovered that I had a detached input shaft and yanked it out through the seal, the clip was right there where it's supposed to be.  That clip only prevents the reverse gear from sliding rearward on the input shaft.  But if the stud connecting the input shaft to the main shaft gets turned all the way forward (i.e., into the front main shaft) allowing the input shaft to move rearward, the reverse gear can slide rearward too (just not past the clip, of course).  I suspect (though I didn't try) that a good forward shove of the input shaft would have moved the reverse gear back into place and it would've engaged properly.  Useless long-term, of course, because the input shaft would just work its way rearward again.
> 
> For anyone else who's curious about this problem, here's an annotated picture of all the parts in question: http://blef.org/vw/transmissionmainshafts.jpg
> 
> Soren
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Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
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