Driving the Grossglockner road

It is very feasible as long as you do not plan to hike much at all, since I reckon about 6 hours for the drive without stops. The Großglockner road is a very winding drive, I can't think of many US roads that could compare.
It takes you quite a bit off the most direct way, though. I would also consider a more easterly route through the Salzkammergut, Sölkpass (hidden gem IMO), Klagenfurt and Loiblpass.

I think a night in Zell amSee is an excellent idea. First, because if the day you drive from Salzburg to Zell is rainy, driving the Grossglockner that day is pointless. A night in Zell am See gives you the option to drive the Grossglockner on the day you arrive, or the next day on your way to Slovenia.

Plus Zell am See is a very nice old town, the lake setting is beautiful, the tall peaks as a backdrop spectacular and what we did for an hour was we rented an electric boat and took in the sights from the lake. You can rent these along the lakeside promenade.

Another option, of the day you travel from Salzburg is nice weather, drive the Grossglockner and spend the night in Heiligenblut, at the southern terminus of the Grossglockner Road.

We stayed here in Zell am See:

https://www.pension-alpenrose.at/

And here just outside of Heiligenblut:

https://ederhof-heiligenblut.at/

This may be of interest also:

https://accidentallywesanderson.com/places/st-vincent-pilgrimage-church/

Paul

Thanks Paul, Zell am See does look very pretty. I am one of those who usually likes to make hotel reservations, though, for this trip in the first week or two of September do you think there might be rooms available last minute? I see what you mean about not going on a rainy day! Maybe I'll need to have Plans A and B?

We travel mostly in October and I’ve never made last minute bookings or just went hoping to find something. So I can’t comment. Sorry. Both Zell am See and Heiligenblut are worth visiting. That’s all I can say.

Yes, it's doable if you start early.

We last drove the High Alpine Road in summer 2021. We started very early in Munich (it was a Saturday in August, when the highways heading south are always jammed) and were in Fusch an der Großglocknerstraße at around 8 am and on the other side in Heiligenblut at around 1 pm.
That included a breakfast stop at the Edelweisspitze (https://www.edelweissspitze.at/en/), a 90 minute stop at the Franz Josef Höhe (https://www.grossglockner.at/gg/en/grossglockner/kaiserfranzjosefshoehe) and a few more short stops along the road.

From Heiligenblut it is another 2.5 to 3 hours to Ljubljana if you follow the main road.
I would still recommend an overnight stop after the high alpine road as there are many little gems along the route.
You could stay the night in Heiligenblut or continue to one of the many lakes in Carinthia. How about Millstadt on Lake Millstätter See or, if you are a nature lover, Techendorf on Lake Weißensee?

If your destination is Ljubljana, I would drive around Wörthersee the next day, visit the Pyramidenkogel and then drive over the Loibl Pass to Slovenia.
If your destination is Kranjska Gora, I would recommend taking the detour via Tarvisio (Italy) and visiting the Laghi di Fusine, one of the most beautiful spots in the Julian Alps.
https://www.moonhoneytravel.com/laghi-di-fusine-italy/

Excellent suggestion, thanks. I think I will go to Kranjska Gora ahead of Ljubljiana, so a night in Heiligenbrut or Techendorf (we are indeed nature lovers) looks lovely.

My advice to offer is to have a backup plan!

We were there in September about 5 years ago and our plans to drive it (on route to Admont from Lienz) were cancelled (by us) when a rare and early storm blew in and it was snowy and icy.

We're from Colorado, used to driving in such conditions, but it was just a little too much for us to push forward on the plan.

If/when you experience it, experience it for me too!

Danb I've traveled all over that area mid to late September with no reservations - no problem whatsoever - plenty of vacant rooms. I'd usually pick a room around lunch time. If you have a car in particular, you don't have to book anything ahead in that area at that time of year.

The Grossglockner High Alpine road is a fabulous drive and I wouldn't pass up the chance unless the weather is bad. I have driven it 4 times with the last being August 2023 and the volume of motorcyclists and bicyclists was alarming. I am not sure if it will be as busy in September but be aware of the possibility.

Grossglockner