Ok, so this is a website dedicated to Photoshop, but after 2 hours plus of searching the internet on how to fix this stroke issue in Illustrator along with a couple of forum posts with few replies, I thought I’d share the fix so perhaps others will be able to find it a bit quicker than me 
The problem I had was scaling a logo that I’d created which had a stroke applied to part of the lettering. I used the stroke effect normally, which was fine for initial logos and concepts but not when I needed to create the print setup version.
When you add a stroke in Illustrator – a 6pt stroke for example. When you scale the logo down or up the stroke remains at 6pt when you actually need the stroke to scale in proportion to the type or object.
By default, Illustrator does not scale strokes and effects at the same proportion as the object, it will keep the settings originally applied. There is a very simple fix to this issue, all you have to do is:
On a mac go to Illustrator > Preferences > General and check Scale & Stroke Effects.
On a PC go to Edit > Preferences > General and check Scale & Stroke Effects
The stroke should now scale at the same rate as the object. The only problem with this solution is that when you change this in the preferences it’s only changing the preferences on your machine, IT DOESN’T MAKE THE CHANGE DOCUMENT WIDE. This can obviously cause problems if someone other than you is going to use the file, as you can’t guarantee that they will have this option checked. A way around this problem is to expand the stroke lines instead of changing the setting in the preferences.
Excellent tip, thanks a lot. I’ve been trying to figure this out for a long time!
Glad you found it useful
You are an art saver. I always used Freehand, which I think is a better, more intuitive program, until I upgraded my Mac and now of course it’s unsupported and outdated. So I’ve been forced by Adobe to use Illustrator. Arrgh!
If not for you I might have ended up in the Self Inflicted Wounds column of the local paper…lol
Glad I could help
Thank you so much for posting this tip!! I was nearly pulling my hair out trying to solve this exact problem. The file I have was created by someone else, and had about 100 layers, so it was not logical to change the stroke on each layer. I have to scale down this file, and every time I would scale it down, I would get larger then normal stroke, and when I saved the document as a PNG, I would lose resolution, and the illustration would become pixelated. So glad I found this tip.
Once again, thanks so so so so much for postin this tip.
Excellent tip, thanks a lot. I’ve been trying to figure this out for a long time!
You’re welcome
Glad you found it useful.
I could kiss you right now