Calculus is very heavily dependent upon algebra, trigonometry, and precalculus. If you have a D+ in precalculus, you very likely are not ready for calculus.
I know a student who took calculus based physics, and who also took physics without calculus. She says that it is easier with calculus than without. While I only took calculus based physics in university, this makes a lot of sense to me. The two are quite closely intertwined as others have said.