Re: [T3] Vacuum modulator questions

["Jim Adney" <jadney@vwtype3.org>]

On 30 Jun 2007 at 19:32, Daniel Baum wrote:

> Jim Adney wrote:

> > Put the car in N and start the engine. Pull the VM end of the hose off. 
> > The
> > engine should change and there should be VERY obvious suction on the end 
> > of the hose.

> I tried this, and it worked exactly as described. When I pulled the hose 
> off, the engine got slower, and I could feel and hear the suction. When I 
> put my finger over the hose, the engine speeded up again.
> 
> Does this mean the vacuum modulator is OK?

This means that the hose/vacuum source is okay.

> Here is a pic of my vacuum modulator on the tranny.
> 
> http://www.type34.info/temp/modulator.jpg

That looks right. If you look closely at the first shoulder under the 
vacuum port, there is a VW part # stamped there, which I can't read 
in your photo. The dual carb VM is 003 325 391. The brown stripe 
would seem to indicate a 003 325 391 C, which is the 72-3 FI VM. The 
early FI VM is the A version with a yellow stripe. My books don't 
mention a color for the dual carb VM, so I can't be sure if you've 
got the right one. It might be worth your while to check the suffix 
on yours and look around for a proper one if yours is not right.

> The inner part, which I assume is the adjuster, is protruding slightly, is 
> this usual? Could it need adjusting? If so, why did it work so well up to 
> now?

ISTR that the adjuster is usually slightly recessed, but it's 
possible that it's just the wrong one that was adjusted to this 
extreme to be right (until now.) Note that adjusting it outwards 
should LOWER the shift points, so this seems odd here. But if this is 
really the brown stripe 72-3 version, which was quite different, then 
anything's possible.  

Seems odd that this worked until now, but I wonder if it's possible 
that something in your AT froze up from sitting and just now worked 
itself loose, now that you've been exercising it.  

Russ is bound to have better insight into this, since he's actually 
done the rebuilds and seen a lot more of these thru their complaints 
and repairs.

I would suggest doing a couple of things:

Check the part number and look for a correct one if yours is wrong.

Get a pressure gauge and check the adjustment of the VM. If something 
just worked loose, you may find that an adjustment might fix you up 
fairly well.

I had to refresh my memory on the AT shift pattern, so now I see that 
D is right next to N, so we know that if you can get into any forward 
gear, you can get into D. This means that the problem can't be in the 
shift shaft weld.

The Bentley says that if you have drive in R and 1, but can't get out 
of 1 in 2 or D, then the problem is a dirty valve body or a governor 
problem. You mentioned earlier that you had repaired a governor
problem. What was wrong and what did you do to fix it?

You've got a Bentley manual, right?

-- 
*******************************
Jim Adney, jadney@vwtype3.org
Madison, Wisconsin, USA
*******************************

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