Romain Grosjean confirmed that's the brake issues which plagued Haas in 2016 have still not been completely resolved.
The French driver had his first day in the team's VF-17, clocking in at 56 laps and with the eighth fastest time on the day.
"Right now we are not 100 per cent happy with the braking still," Grosjean explained.
"But we are going to work around and hopefully find some solutions early in the year."
His day at the office was a bit upset by an issue that kept the beautiful VF-17 in the team's garage but Grosjean joined the action out on the track later on.
"There were a few things that held us back in the garage so we need to work and get better in the future. But I got the first few laps in the car and learned to drive it a little bit."
Grosjean was pleasantly surprised by his 2017 charger at the outset.
"It feels pretty good. High speed [corners] are going to be interesting this year, much more than it was in the past.
" I think some of the circuits are going to be more exciting. I'm looking forward to doing more."
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