What sort of tracks you are having trouble with ? What car do you drive when you have this issue ? Tires used and did you use ABS ? What sort of brake balance you are usually running ?
First of all, most understeer when hard braking is caused by too much front bias brake balance, low grip tires were used, and too late braking into the corner.
A bad braking technique is also great contributor, try to do threshold braking. You can watch my videos, they could give you ideas the sort of braking technique that would help. Check the Maserati, Countach and Stratos videos, they have several nice hard braking into difficult corners. I'll link them here, I hope you don't mind :
Maserati GranTurismo S '08 at Motegi Full Road Course, 2:22.683 - CM tires
Watch the full lap to see how early braking should be and most of them in straight line.
Lancia Stratos '73 at Nurburgring GP/F, 2:47.090 - CH tires
With difficult to handle like Stratos unique handling, trail braking is a challenge, giving smooth braking early is a good practice.
Lamborghini Countach 25Th Anniversary '88 at Rome, 1:23.518 - CM tires
Heavy car like Countach will need extra care when braking, sometimes finding the right braking line defines a good lap.
For more videos, you can check my thread over at GT5 videos sub forum, I'll be uploading video at Daytona Road Course with Dodge Viper GTS - stock, CM tires-no ABS, the difficult to approach 1st left hander is one of it's unique challenge.