I've had aircooled trannies both last and break using them on an AAZ 1.9TD Westy. Difference is in how gently you shift. Letting some people inexperienced with manuals drive Westy quickly broke the 3/4 slider on the first tranny.

Now being more selective about who can drive the Westy (mostly myself), the second tranny has lasted 12 years.

Some pros/cons of the aircooled tranny:
Pros:

They are cheap and relatively plentiful used in north america.

4.57 final puts 60mph cruise right at 3000rpm. The AAZ TD is happy and very fuel efficient around that rpm range.
The TD still has enough torque to climb hills without downshifting (better than a 1.9l gas Vanagon or even the 2.5l Eurovan Westy I had fr a while)
Downshifting to 3rd allows passing at up to 70mph.

Cons:
Big gap between 4th and 3rd. On hills too steep for 4th, I'm hesitant to run the Diesel at high revs for extended time.
High 1st means more clutch work starting up steep hills. (but compared to a gas engine the Diesel has lots more torque even right from idle so it is not too bad)
Weak 3/4 gear slider and unlike the later trannys I don't think there is an upgraded partnumber to put in.

(Bt.w. I have a rebuildable tranny in the garage (needs said 3/4 slider exchanged) if anyone in western Canada wants one. Also have the right bellhousing to fit it on a VW inline 4 engine (Diesel or gas))

Martin

________________________________
 From: Dennis Haynes <d23haynes57@HOTMAIL.COM>
To: vanagon@GERRY.VANAGON.COM
Sent: Tuesday, August 14, 2012 10:38:16 PM
Subject: Re: Transmission upgrade

I often forget the early diesels can use the earlier trannies. Yes the air
cooled has more HP. Diesels are harder on trannies due to the "pulsing" they
produce. Add a turbo Diesel and you get a lot more torque to add to the
problem. Go for a later tranny and just swap the rear shift rod.

Dennis

From: ralph meyermann [mailto:ralphmeyermann@gmail.com]
Sent: Tuesday, August 14, 2012 8:32 AM
To: Dennis Haynes
Cc: vanagon@gerry.vanagon.com
Subject: Re: RE: Transmission upgrade

Doesn't the gasser have more than 49 hp,it should being able to use the
faster gear ratios and get to speed. Just wanting to keep the same shifter
assembly I already have

Velma 82diesel 1.6 na westy

On Aug 13, 2012 11:01 PM, "Dennis Haynes" <d23haynes57@hotmail.com> wrote:

While it sounds impressive to drop 1,000 rpm the Diesel is geared low for
good reason. You need the RPM to get the horsepower. Also the air cooled
tranny is a weaker box overall. A number of parts are smaller and thus
weaker. A turbo engine especially a turbo diesel should have no problem
tearing up the air cooled tranny.

Dennis

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