Key cellular functions depend on the transduction of extracellular mechanical signals by specialized membrane receptors, including adhesion G-protein coupled receptors (aGPCRs). While recent structural studies support aGPCR activation through shedding of the extracellular GAIN domain, shedding-independent receptor signaling has also been observed. However, the molecular mechanisms underlying these distinct mechanosensing and signaling functions remain poorly understood. Here, we combined single-molecule force spectroscopy, molecular simulations, and cell signaling assays to elucidate the structural and dynamic underpinnings of ADGRG1 mechanotransduction. Under different regimes of mechanical shear stress, the isolated GAIN domain experienced two alternative modes of structural deformation, resulting in distinct loop motions and surface exposures of the tethered agonist prior to shedding. In the full-length receptor, specific GAIN orientations and loop interactions with the transmembrane domain were sufficient to partially dislodge and couple the tethered agonist to extracellular loop 2, promoting potent allosteric communication. These findings aligned with the observed significant basal activity of the receptor and enhanced signaling upon collagen-mediated mechanical shear stress. To validate our mechanistic predictions, we rationally designed ADGRG1 variants with reprogrammed GAIN motions and resistance to mechanical load. These variants displayed the intended shifts in constitutive activities and signaling responses to collagen. Our study reveals a molecular blueprint of ADGRG1 activation, highlighting how GAIN structural plasticity and adaptation to mechanical shear stress, the orientation of the extracellular region, and specific motions at the GAIN-7TM interface enable a rich gradient of signaling responses to chemical and mechanical stimuli. Our findings reconcile allosteric and mechanical views of aGPCR activation and pave the way for developing precise medicines that regulate aGPCR functions.