"I was downchanging to first and I heard it go 'crunch, crunch'. It put a hole in the gearbox casing and we were spraying oil everywhere. I didn't want to oil the track and make a mess so I just came in and parked it.
"It's a sad end to a great day. I'm just really proud of the Wood Brothers and this whole team. They gave me a great car today. I'm so grateful to Little Debbie and the McKee family for giving me this opportunity. I had a great time out there today. It's just really unfortunate it had to end that way."
Despite the disappointment, Ambrose said he was proud of how he had performance on his Cup debut and said he was looking forward to a run on the oval circuit at Loudon next weekend.
"It was my first go at one of these Cup deals and we held our heads high," he said. "We didn't get to run right to the end but they certainly knew we were there and we showed what we're capable of in Cup.
"My next run with Wood Brothers and Little Debbie in Cup is next weekend in Loudon. It will be a lot easier to run both my cars at the same place without all the travel. It will be another challenge to run Cup on an oval and have to qualify to get in the show but after today I'm really looking forward to it."
