Brompton - front wheel with Shimano Dynamo hub - resistance/friction problem
 

Hello
I'm riding a Brompton (6-speed/Shimano Dynamo hub front wheel) and I have the following problem :
Suddenly my front wheel has a resistance though there is no visual friction. I rode to my office without any problem and when I set off to return home the problem was there (so it did not occur while riding).
The wheel hardly does one revolution when spun fairly hard and when riding you feel the friction that slows you down.
There also is a noise in the Shimano dyno-hub; sounds like a steamtrain (the faster you go the faster the noise (“chu-chu-chu”)). I removed the wheel in order to have a look at the bearings but I could not open the hub. I discovered a special key is necessary (Shimano TL-DH 20 Dynamo Hub Cap Assembly Tool – rather expensive).

I went to the shop and they told me they put in some grease (I wasn't able to see what they did). The problem was solved for four days and now it's back (again it did not occur while riding).

What in your opinion is the problem ?

Did anyone already open this Dynamo Hub ?

Thanks in advance for your thoughts.

Luc