Ok, forget my previous answer.
You are right!!!!

2WD and 4WD ARE different.
So the half-speed 2WD speedo cable will quite sure be the reason.

Raimund

mark drillock schrieb:
> The recent VW parts list I saw listed different control units for a 90
> Syncro versus a 90 2wd.
>
> 90 Syncro 443 907 305
> 90 2wd    251 907 305
>
> Mark
>
>
> Raimund Feussner wrote:
>> Hmmm, that could be a reason, but:
>> All Vanagons use the same control unit, no matter if 2WD or syncro.
>> On the other hand, a unit that works with half the impulses will also
>> work in a syncro with standard impulses. So 4WD wouldn´t matter
>>
>> I used the 443 unit on a 2WD, but I can´t remember if it started working
>> at higher speeds only.
>>
>>
>> Regards
>> Raimund
>>
>>
>>
>> mark drillock schrieb:
>>> I wonder if the 2wd Vanagon uses a different control unit due to the
>>> speedo cable driven speed sensor only spinning at half the speed that
>>> it does in the VW cars. Syncro speed sensors turn at about the same
>>> speed as the cars. What type of Vanagon did you have?
>>>
>>> Mark
>>>
>>