Applying maximum speed doesn't work?

So I'm making a Model that is hovering on the ground (thanks to a BodyPosition that's Position is set a little above the ground and it's MaxForce is set to 0, 40000, 0) and can be steered. The model consists of a Part (in which is a Script, a BodyGyro, BodyPosition and a BodyVelocity) and a VehicleSeat that is welded to the Part. The Script makes it so the signals sent by the player to VehicleSeat are changing the properties of BodyGyro and BodyVelocity. This is how it looks:

local RunService = game:GetService("RunService")
local part = script.Parent
local bodyGyro = part.BodyGyro
local bodyVel = part.BodyVelocity
local seat = script.Parent.Parent.VehicleSeat
local goBack, goForward = false, false
local turnLeft, turnRight = false, false

local maxForward = 20
local maxBack = -10

seat:GetPropertyChangedSignal("Occupant"):Connect(function(char)
	local currentSpeed = 0
	local currentAngle = 0
	RunService.Heartbeat:Connect(function(step)
		bodyVel.Velocity = (part.CFrame.LookVector  * currentSpeed)
		bodyGyro.CFrame =  CFrame.Angles(math.rad(0), math.rad(currentAngle), math.rad(0))
		if seat.Throttle == -1 then
			if goBack then return end
			goBack = true
			repeat wait(.1)
				currentSpeed = currentSpeed - 1
			until seat.Throttle ~= -1 or currentSpeed <= maxBack -- The 2nd statement doesn't seem to do anything.
			goBack = false
		elseif seat.Throttle == 1 then
			if goForward then return end
			goForward = true
			repeat wait(.1)
				currentSpeed = currentSpeed + 1
			until seat.Throttle ~= 1 or currentSpeed >= maxForward -- Here too.
			goForward = false
		end
		if seat.Steer == -1 then
			if turnLeft then return end
			turnLeft = true
			repeat wait(.01) 
				currentAngle = currentAngle + 1
			until seat.Steer ~= -1   
			turnLeft = false              
		elseif seat.Steer == 1 then 
			if turnRight then return end
			turnRight = true
			repeat wait(.01) 
				currentAngle = currentAngle - 1
			until seat.Steer ~= 1
			turnRight = false
		end
	end)
end)

The Model speeds up fine and rotates fine too, but the maximum speed I applied to it doesn't do anything. The speed easily goes above 20. I tried doing other things to fix it but nothing worked. Thanks for reading.