HiCustomer Thank you for asking your question on JustAnswer. The other Experts and I are working on your answer. By the way, it would help us to know:-What year is your Ford?-How many miles are on your Ford?-What type of engine is in your Ford?-What have you already tried?Thank you again for trusting us with your problem. Please reply as soon as possible so that we can finish answering your question.Thanks,
1994 Ford Explorer
Changed the fluid and filter, and the vacuum modulator so far
Are you saying that the trans is slipping? What exactly do you mean when you say "it will not engage the gears"? Does it shift late? Does it shift harsh? Does it not want to engage in forward or reverse? Does it just rev up and not move? I just want to have a clear understanding before answering your question.
If it will not engage at all, it has an internal mechanical issue. Most likely it is a forward clutch issue. I am afraid you are looking at either an overhaul or replacement. The modulator only affects the shift harshness and timing, not the engagement. There are no electrical concerns either that will cause a no engagement. Make sure it is full of fluid, which I am sure you already have. Beyond that there are some tests that can narrow it down to which internal issue is causing your concern, but it is internal. Let me know if there is anything else I can help you with.