How bad is it to run with only four lug nuts on a wheel?

The studs are replaceable. I have had several on my 94 Camry break in the past. You should have them replaced.

Did you, by chance, use an aftermarket wheel on that hub? Sometimes, if the centre bore of the wheel is larger than the hub, you can break studs like that on a pothole. It's quite a dangerous practice to use a non-hub-centric wheel, in my opinion, because all the load is taken up by the studs, but many people still do this. It's best to have a hub-centric wheel from the dealer. I bought one a few months ago for $CAN 60, so they're not expensive.

How do I replace one? Can the bad one be driven out while the hub is on the vehicle or does it have to come off? Need a press?

It's pressed in/out while still attached to the vehicle. I tried driving one in myself but I didn't like all the banging and force I was putting on the axle with the hammer. I think Pep Boys replaces the stud for under $40.

Any reputable tire shop should be able to change the stud for you. You should get it replaced. I've seen cars drive with four lug nuts, but wouldn't recommend it. It can cause rotor to warp because of uneven torque.

Butzmark wrote:

Not necesairly... they probably cross-threaded it... They put the nut into the air-gun socket and bbbzzzzit. Instead of puting the nut by hand, turning it at least 3 times and then use the air tool for torque. Just the constant chase for precious time and lack of liability for the broken cars... How can you prove they cross-threaded your lug-nuts ? You can't, and they know it perfectly, so they do not care.

You have drums or rotors on the rear breaks ?

I had drums, and I have replaced the stud myself after watching how they do it at Pepboys one day. They just hammer it out... Of course I had to remove the drum to expose the studs and see what is really inside... It is relatively easy. Then they put the new one just enough to catch the grooves and then put the wheel tightening stud in place with a lug nut... Just get the right replacement stud. The work is quite easy and you do not need very big hammer :-)