Car stalls when braking..

Just got my car back from the shop. It had some transmission work, brakes, and a fuel filter done.

They found that the speedometer gear was pretty torn up so they ordered a new one. It hasn't come in yet but I needed the car so they let me take it without the gear in it. The speedometer doesn't work which is not that big of a problem but when I brake somewhat firm the car dies.

Would the lack of a speedometer gear have anything to do with this? What else could it be?

Thanks for your help.

Thanks hissin I really appreciate it.

I acutally have the old one that has 2 teeth left on it I might throw that in for now.