Ian - I don't know of any mountains in the Dandenong area, nor any off road mountain type trails. But if you take the bike path out to Ferntree Gully, Belgrave, there are some beaut trails in the Dandenong Ranges. Sorry, I don't know exactly where they are, just heard of them from guys who use them.
The steepest is a fire trail, I think, which starts somewhere near the T.V. tower/s. What about if you ask at Ian Brown's bike shop in Dandenong, they might know.
There is a good path, starts at the bridge over the creek in
Hammond Rd., and heads out to Carrum. Hard fine gravel. Food shop there. Fairly flat, this path is a good, fast ride, as it
follows the creek.
What about Abbots Rd, which runs from Frkstn - Dnong Rd to
the Sth Gippy Hwy. By the bridge over the creek, or main drain, there are grassed ridges, where the drain has been dredged in years past. We need to have these ridges opened up for public use i.e. off-road bikes. Let's hear of your explorations, huh? Cheers.
The Warburton Rail Trail is a really good ride. Suits both road and mtb's. No hills, gentle gradients. You can choose your starting point from the Melways. This path is shared with
walkers, joggers and horses.