Crunching sound when full throttle & brake hard?

[superek4]

hi,

i just convert my friend's Losi8T Version 1 using Losi conversion.

Test run the car it gave out a crunching sound when full throttle & hard brake.

When low speed its ok. May I know what went wrong before I strip the car? The race is this sun & I still have another car to test?

Pls help thxs!