Marcos Ambrose will return to a more conventional brake set-up after enduring a tough first day of competition in his V8 Supercars return at the Sydney NRMA 500.

Stopping his #66 Xbox-backed Falcon has proved a bugbear for the former double series champion.

The 38-year-old is competing as a wildcard ahead of his full-time return to spearhead the DJR Team Penske outfit in 2015.

Ambrose logged crucial laps, completing the 125km distance of the opening leg in 20th ahead of a 21st place finish in the rain-shortened second race.

It was a tough initiation back into the V8 Supercars fray for Ambrose who started both sprint races off the back after his qualifying crash earlier in the day.

The Xbox crew will revert to a smaller master cylinder for Ambrose, reflecting more of the set-up used by DJR runners Scott Pye and David Wall.

With a larger master cylinder Ambrose was struggling for feel through a much stiffer pedal.

“We are going to change the brakes around and see if we can get a bit more comfort there for me,” Ambrose told Speedcafe.com

“That’s the biggest area. I just can’t seem to stop the car consistently well.

“I’m just not synched into the brakes. We are going to get back to more conventional stuff and start again tomorrow.”

Struggling to come to grips with the brakes has taken Ambrose by surprise after his lead-up track time in the Falcon at a Lakeside ride day and twin full day tests at Queensland Raceway in recent weeks.

“I’ve been surprised. It’s been the achilles heel all weekend,” he said.

“It certainly wasn’t what we were hoping for that’s for sure.”

Ambrose instigated clean getaways in both heats, passing three cars in the second race before contact with Craig Lowndes sent him spinning, leaving Jack Perkins to make contact with his left-hand front door.

“We made some good starts which was a positive I guess,” he said.

“I had some car speed when I had clean track. I’m trying to learn on the run.”