Pulsating brake pedal

Got my new 70 gremlin project to run for the first time today. Took it for a short ride around the block and the brake pedal has a heavy pulsation when brakes are applied.  Car has 4 wheel drums. Is it most likely a warped drum? Thanks

Gotta agree with Bill...  98% probability that's it.  The only other common culprit doesn't apply to classics; ABS sensor tone rings that get metal dust all over them.

Thanks guys. Is it more likely the rear drums over the front or are either possible? 

The fronts see harder use and more heat, so it's usually the front drums.  If the car has been sitting it could be either end.  Make sure the wheel cylinders move freely.  I recently did brakes on a car that had been sitting about 10 years.  All but 1 piston in the right front wheel cylinder were completely frozen up.  3 wheels were completely inop, and it was being driven.

Bob
tufcj

tufcj wrote: The fronts see harder use and more heat, so it's usually the front drums.  If the car has been sitting it could be either end.  Make sure the wheel cylinders move freely.  I recently did brakes on a car that had been sitting about 10 years.  All but 1 piston in the right front wheel cylinder were completely frozen up.  3 wheels were completely inop, and it was being driven. Bob tufcj

Although sitting for extended periods is one of the worst things you can do to brakes (aside from getting them really hot and then holding the pedal down hard) - you should have seen what I saw while doing brakes working my way through college - and later working on Iowa Highway Patrol cars - talk about brakes being abused. I saw my share of disc brake rotors fried - and with one side worn completely off and the pad backing worn half-way gone. Any further and some would have been into the caliper's piston. "car pulls to one side while braking"  Oh, really?? Gee, wonder what is causing that - does it make any noise??
"Oh, a little, I guess - sort of a grinding sound".

A far less common reason for pedal pulsating with drums is bent axle or hub - slide and hit a curb or hit a good ol' Des Moines city pot hole. 
The idea with a true pedal pulsation - sort of like a slow-motion anti-lock brake thing, is that something is causing the fluid to periodically be pushed back at the master cylinder - pedal pushes master, master piston pushes fluid out to wheel cylinders and something out there as the wheel rotates wants to push back on a regular basis and suddenly you feel like you are playing a base drum with the pedal going up and down.