Unstoppable Custom Entity

Hey,
I tried to create a custom entity class in 1.12 to make a ridable cow. So basically I can control the cow but it is still a bit buggy

1. For the first minute on a new cow I can only control it forward
2. After that minute it gets super sanic speed, even if I tried to prevent that by multiplying the motion (motX, motZ) with backToNormalSpeed

here is the class so far:

Code:

public class DisabledCow extends EntityCow{

    private static final float backToNormalSpeed = 0.5f;

    public DisabledCow(World world) {
        super(world);
        //stepHeight
        this.P = 1f;
    }

    //movement       x      y      z
    @Override
    public void a(float f, float f1, float f2) {
   
        //if has passenger and its is alive
        if(isVehicle() && cV()) {
            EntityLiving entityliving = (EntityLiving)bE();
       
            this.lastYaw = this.yaw = entityliving.yaw;
            this.pitch = entityliving.pitch * 0.5F;
            this.setYawPitch(this.yaw, this.pitch);
            this.aQ = this.aO = this.yaw;

            //be, bg, bh - Player WASD+Space?
            f = entityliving.be * 0.5f;
            f2 = entityliving.bg;

            //slow down backwards
            if (f2 <= 0.0f)
                f2 *= 0.25;
       
            //calculate in which direction cow should go
            if (f2 > 0f) {
                float f3 = MathHelper.sin(this.yaw * 0.017453292F);
                float f4 = MathHelper.cos(this.yaw * 0.017453292F);
           
                this.motX += -0.4F * f3 * backToNormalSpeed;
                this.motZ += 0.4F * f4 * backToNormalSpeed;
            }
       
        }
        super.a(f, f1, f2);
    }


    //is passenger a living entity
    @Override
    public boolean cV() {
        return bE() instanceof EntityLiving;
    }

    //get passenger
    @Override @Nullable
    public Entity bE() {
        return bF().isEmpty() ? null : (Entity)bF().get(0);
    }

Well I copied the majority from EntityHorseAbstract as good as possible and did not change methode names. I hope the code is selfexplanatory with the comments.

Any idea how to fix these bugs or where they come from?
Any help would be appreciated.