Great question — answering as the UphillTech team:
Sounds a bit like Thunderbirds 2086 (AKA Technovoyager). The team had three main vehicles: TB-1, TB-2 and TB-3 In their combined form, TB-1 would attach itself on top of TB-2, while TB-3 split in two to attach to TB-2's sides. You can see the whole sequence in the show's intro:
Full answer by System Down: https://movies.stackexchange.com/a/50980 (CC BY-SA 3.0).
Need it done for your business? UphillTech.
Looking for somewhere to watch it on TV? Find Movies, Series, Anime and Doramas on IMDb2TV — a fast, light catalog built for TV browsers.