[T3] 73 auto trans type 3 ARR ?

[Jim Adney]

A few more comments on our AARs.

There were two different versions: a mechanical one for '68-9 Type 3s as 
well as all later MT Type 3s, and an electrically heated one for '70-3 AT 
Type 3s. To the best of my knowledge, VW/Bosch introduced the electrically 
heated one to heat up faster to meet emission specs for AT cars.

The mechanical AAR has a bimetal spring, just like the one you used to have 
in your home thermostat. That bimetal spring sticks down into the engine 
case and gets splashed with engine oil, so it heats up with the engine. The 
bimetal springs do not wear out, but the housing is a zinc diecasting, which 
can distort with time, causing the shaft to stick. This is particularly likely if 
someone overtightens the two screws on the top. This pulls on the zinc in a 
way that will distort the housing and cause the AAR to stick in place.

I can lap the housing bore and reset the spring to open and close properly. 
It's not a hard job, but I had to make some special fixtures to do it easily and 
correctly. I Locktite the screws, so they don't have to be tight.

The electrical AAR is a crimped assembly, so it can't be taken apart without 
cutting and bending things. It pretty much amounts to something you CAN 
take apart, but it's not likely to go back together nicely afterwards. I've never 
done it. They also stick, but I'm not sure why. Sometimes they can be freed 
up by cleaning with some sort of solvent, but often this doesn't work. The 
only way to fix them is to replace with a working one.

Replacing an electrical AAR with a mechanical one should be fine. It might 
not heat up as fast, but this is unlikely to be noticable unless you're driving in 
extremely cold weather (think freezing or less.) Being able to fix the 
mechanical ones is a huge advantage.

There's one possible problem with this replacement: I've been told that some 
late AT cases do not have that hole drilled out, to let the MT bimetal spring 
AAR stick down into the case. I've never seen this, but I've heard others 
make this claim. If anyone comes across an AT case that does not have that 
drilling (the one for a carb type fuel pump pushrod) please take a picture and 
let me know.

Testing:

The ONLY reliable way to test whether your AAR is open or closed is to 
block off its air inlet with your thumb, with the engine running at idle. If the 
idle speed drops, the AAR is at least partly open. If the idle doesn't change, 
the AAR is closed.

It's important to understand that closed does not mean a complete shutoff of 
air. It's not a fully sealing valve. Some air will always pass thru, but if the 
valve is in its closed position, there will be too little air to alter the idle speed.

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Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
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