This post describes my hard pedal braking issue, but the string didn’t reach a firm conclusion.
https://driveviperforums.com/forums/threads/29275-Hard-Pedal-no-brakes-weird-ABS-feel-What-is-going-on?highlight=brake+booster
I have a 2008 Viper (3-channel ABS, not 4 like Gen 5) and during an autocross had the same hard pedal, no braking experience. I have stiffer springs front and back, shocks set to full rebound stiffness, but don’t think this is bump-related. It rides great on the street and I’ve never had the hard pedal just driving around. For the summer I put on OEM size Toyo 888’s and went to ~8 AX events. I got the hard pedal at maybe 3 of them, and then only once during the day. I can’t be left foot braking because I’m not good at it, but since all courses are only 1st gear, I don’t have to pretend to heel & toe anyway. Despite this, I suspected the vacuum level and replaced the booster check valve, but saw no change. I added a vacuum reservoir, and surprisingly made it better. Now, under conditions when the hard pedal might have occurred, the pedal was somewhat harder than usual, but felt 80% normal instead of 0%. Has anyone else had this or have any recommendations? Replace booster? Does the Comp Coupe use a different booster? Thanks for any advice or comments.
