I don't see the hydro boost unit causing the pedal to push back like that. That is something an ABS pump would do.

Also you say the pedal goes down after this happens but you didn't say if it goes down to the floor, lower than normal or just back down where it was.

What kind of noise does it make when this is happening?

"Follow me the wise man said, but he walked behind"


'92 D250 Club Cab CTD, 47RH conversion, pump tweaks, injectors, rear disc and hydroboost conversion.
'74 W200 Crew Cab 360, NV4500, D44, D60 and NP205 divorced transfer case. Rear disc and hydroboost conversion.
2019 1500 Long Horn Crew Cab 4WD, 5.7 Hemi.