QUESTION: We have a really well broke western, 6 year old gelding. We purchased a buggy and single horse harness at a country auction and decided to train him to drive too. It is the first horse we have trained to drive. He finally got fairly good at it and no longer was spooky. He was really hard to control at first before he settled down. Trying to run away and hard to turn. But now, he is not as nice a horse to ride? He is harder to stop, opens his mouth when asked to back up and no longer responds as well at neck reining? Our Vet couldn't find anything wrong with him. His teeth are fine. So Why?
ANSWER: His Mouth. Plain and simple. When you could not control him to stop or turn him which was because he was so frightened, you naturally had to do a lot of hard pulling on his mouth. First that would have caused him pain. Then the bars/corners of his mouth would have gotten sore. Then when they healed up, he would then have what we call a "Tough Mouth, meaning he no longer has as much "Respect" or even "Feeling" to give to the bit correctly. Plus you were direct reining him during driving. Side pulls to his mouth, not neck reining.
So then the horse resists or fails to respond to the bit/reins as well as he used too. Have a Professional Trainer try him in a couple of different bits for riding to try and find one that he will respond too like he used too.