Vanagon Diesel AAZ/AHU TDI gearing Inquiry

[Brahtata]

I have a 1983 1.6 Diesel with the 5 speed trans. If I opt to swap to an AAZ or AHU, do I absolutely need to regear my trans or get a air cooled 4 speed? Or can I just play around with different tire sizes? Thanks

[Gnarlodious]

You probably don't NEED to regear since the TDi can run at a higher RPM than the stock engine. AAZ also, but lesser so. Even so, it would get tiresome and expensive to do it incrementally.

More likely is that the added power and heat will wear it out sooner than you think, and ruin parts while it happens. You would be better off with your transmission built from the start for improved pressure, oiling and heat management. Especially if your transmission is already old.

Tire sizes is going to change your speedometer accuracy, if that matters.
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Vanagon ’83 diesel AAZ w/Giles injection, 5spd 4.57R&P+TBD and a '78 diesel Rabbit

[MarkWard]

Probably 200 to 300 rpm change cruising speed available with shorter or taller tires. You can use your 5 speed and then see first hand if your driving habits will work. We spend a lot of time between 60 and 70 mph, so for us taller gearing worked.

Get your conversion done and reliable. The trans can be out later in a couple hours. We had a customer with an air cooled 2.0 that the trans had failed. Money was tight so I sold my original diesel 4 speed. Van never sees the highway and the owner was extremely happy with the diesel gearing with his tired 2.0.

There are others running the shorter final drive with tall tires and claim it’s the cats meow with a stock wbx. Point is, get some data points for yourself and then decide.