Recently had clutch and flywheel and since then the speedo just shakes and doesn't say the correct speed I purchased another speed sensor that goes into the gearbox and same happening but when I took this one out it looked like it had been bent inside so I've just got another one put that on and when I drive the speedo was shaking at around 20mph bit when I press the clutch it goes down to 0 then goes back to shaking around 20mph then just says 0 all the time now does anybody know what is wrong and what I can do as the mechanic who did the car cannot be trusted