In whole of Mumbai route I know only that Dadar is the station where both Central and Western Railways train meet. Visited Mumbai in 2013. I still remember from Mumbai CSMT I boarded afternoon train which goes towards Chennai. After boarding train our train had a great parallel run with Suburban train from masjid to some station I dont remember exactly. Our train was in lead GY WDM3D that time in 2013. And it had loco changed at GTL from GY WDM3D to ED WAP4.