[T3] Auto shift issue

[Jim Adney]

On 9 Sep 2015 at 9:28, Tim Keohane wrote:

> My T3 is shifting (automatic) from 2nd to 3rd at 55 mph. It seems like it was at 45 mph in april. It has been sitting for 3 months and upon re-introduction to the road it just started this. The shift from 1st to 2nd is at 20-22 mph. The shift is very positive (solid engagement) and that we must run it up to 55 to get it to shift into 3rd. It will stay/cruse in 3rd unless/until the speed drops to 45 mph, then it down shifts to 2nd. It seem like it's about 10 mph to high. 
> Bently suggestions are the next step: checking pressure 
> 							        verifying that the vacuum modulator/canister is the proper one. 
> Does anyone know the thread size for the test ports. ( I will make 2 pressure testers)

The shift points vary depending on how much throttle it's given. 
That's what the vacuum modulator does (varies the shift point 
depending on intake manifold vacuum.) So if you're doing this test 
with full throttle, shifting at 55 is probably correct.

If this actually changed recently, the first thing to do would be to 
pull the vacuum hose off the VM and see if the hose is full of ATF 
(red.) If it is, you need a new VM. A little bit of black oil is just 
condensation from the intake, so that can be ignored. The correct 
'72-3 VM is different from the early one, and is very hard to find.  

The AT pressure test points are M10 x 1 threads, but a brass 1/8" NPT 
fitting will work there for temporary testing. The pressure specs 
given in the Bentley are correct for the '68-71 ATs, but not for the 
'72-3 ATs. Unless the diaphram in your VM has broken (ATF in vac 
hose) it's very unlikely that you will find that the VM is to blame 
for this change, so I would not expect it to need re-adjustment. The 
VM adjustment is a set once and forget thing.

It's possible that something in the valve body has just gotten sticky 
and needs to be "exercised" to free up. It may just need to be driven 
and warmed up a few times.

> I have changed the fluids and cleaned the screen.

Always a good move.

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