Looks like you collected some beaters! I love vehicles and your deck looks awesome!
Ok, let's think about them. The main benefit of vehicles is that they aren't creatures, so their power/toughness to cmc ratio is quite high compared to regular creatures and they have a clear advantage in combat in the early stages of the game. The disadvantage of them is that you need to tap additional creatures to let them attack/block. And this is a problem.
Siege Modification and
Armed and Armored can be a very powerful tool, but rely on them to attack basically increase massively the effective casting cost of your vehicles.
I really like the choice of cards you came up with. The Ox is amazing.
Path to Exile and
Lightning Bolt look out of place here, but hey, they're good removals!
Here's my current cheap build with vehicles and dwarfs:
https://deckstats.net/decks/88072/1298278-vehiclesDepala, Pilot Exemplar and
Heart of Kiran are an absolute blast in this deck.
Built to Last add some protection to my vehicles and
To Arms! increase the defense side of the deck.
I hope I gave my help. Have fun!