ALLEN PARK, Mich. --They don't work together anymore, but when you've spent as much time together as Jim Caldwell and Peyton Manning did, the friendship will remain.

Communication is now through an occasional text message instead of daily conversations about everything, but there will be a mini-reunion Sunday night of the coach and quarterback when Caldwell coaches his Detroit Lions against the Manning-quarterbacked Denver Broncos.

It's a close relationship that started when Caldwell was hired as Manning's position coach with the Colts by Tony Dungy in 2002. By the time the Lions inquired with Manning about hiring Caldwell as their head coach in 2014, Manning fully endorsed his former position coach and head coach after working with him for a decade.

Simply, Manning said Caldwell made him a better quarterback.

In Indianapolis, Caldwell stressed fundamentals, the importance of routine and that everything -- from drills in practice to discussions in Wednesday and Thursday meetings -- had a specific purpose.

“The discipline of having that routine really made an impact on me,” Manning said. “I really felt like I just sort of took a step up during the years that he was my quarterbacks coach.”

So understand they are intertwined. Even the way they speak -- measured, careful not to give too much away but also adding stories here and there -- is similar.

One of the things Caldwell possibly took from Manning in Indianapolis was a desire for completions. This seems bizarre -- everyone wants completed passes -- but when Caldwell arrived in Detroit, completion percentage was one of the two things he stressed most to Matthew Stafford.

Part of that could come from Caldwell’s experiences with Manning.

“The thing that Peyton has done that has been really good is he has always been completion-driven,” said Lions backup quarterback Dan Orlovsky, who also played in Indianapolis in 2011. “Getting the ball out of your hands and into other players’ hands, and I think that is a thing that Jim has always stressed is being completion-driven and completions are good.

“So I think that’s one thing that you don’t want to be safe, you want to be smart. I think that’s a thing that has transferred over. Fundamentals. Basics.”

Fundamentals were a Caldwell trademark with Manning. The daily drills started to mirror throws Manning would make in games. It made Manning become a more accurate quarterback -- he never had a season under 65 percent completion percentage with Caldwell as a coach -- and a better decision-maker. Manning’s interceptions were consistently lower during Caldwell’s tenure than they were prior to his arrival.

A lot of that has to do with Manning, who was relentless in preparing for games, practices and individual drills. That’s what stood out to Caldwell when he first met him -- along with Manning’s ability to recall everything.

Caldwell tested this early in his time with Manning, reviewing every interception the quarterback had thrown before Caldwell and Dungy’s arrival after the 2001 season. Manning remembered the situation, play call and what happened in almost every one before the tape went on.

Once they got familiar with each other, they split game studies of upcoming opponents. Then the two would help present to each other. That in itself is not unusual, as the Lions quarterbacks essentially have similar roles during game weeks.

But the way Manning would be able to use the information gleaned from reports was way different than anything Caldwell had seen.

“We would go in and kind of present to one another,” Caldwell told ESPN.com last year during reporting for a story on Manning. “Then he’d be like, ‘OK, yeah, yeah, I see that one. It’s a strong safety cheating, so you know what I’m going to do, all right, Jim, this is what I’m going to do with that one. If they show us that one, I’m going to check to this particular protection, flood protection, and I’m going to block things up, I’m going to make number 59 MIKE and I’m going to throw a post over the head.’

“He was always trying, teams blitz ya and a lot of times guys are trying to get completions. He’s trying to go deep on you and often times he would succeed. So what he would do in those situations, he’d write those things down. I can’t tell you how many times it happened but it happened enough where you knew, some guys just work and take in that information for show. This guy can utilize it.”

There’s little doubt Manning is doing that again when Denver faces Detroit on Sunday. The difference, though, comes in the influence.

It’s likely no one in the NFL, other than Manning’s brother Eli, knows Manning better than Caldwell. There’s a good chance no player in the NFL knows Caldwell better than Manning.

And their impact on each other is undeniable.