I have a 68 Big Block Camaro with front Drums. A previous owner upgraded it to power assistance. The problem I have is when I need to brake suddenly, It pulls to the right quite severely and is quite difficult to keep in a straight line. Any suggestions as to what could be the problem?

Sounds like the front drums need to be adjusted so they are both equal... Adjust the them till the drums lock up, then back them off the same number of turns till they just barely rub. Test drive & re adjust if needed.

Each time you back the car up and stop, the self adjuster should adjust the brakes if they require adjusting. Sometimes this mechanism becomes rusted or worn so it won't work. If this is the case, you can adjust the brakes through the access slot in the backing plate and that will resolve the problem for a while. You would have to keep up with manual brake adjustments though and the parts to repair it are not expensive and the repair is not complex.

You could also have a more serious issue with your brakes. It's unusual for the car to pull violently to one side from only adjustment issues. It would be worth pulling both front drums off for an inspection. You would look for brake cylinder leaks, wheel bearing grease or brake fluid contamination on the linings, worn out linings and broken springs. You can also check to make sure the self adjusting system is free to operate.

You should also check that the rubber brake hoses are in good condition on both sides. They can perish from the inside and cause an obstruction. You may be looking for a brake that is grabbing on the right or a brake that is not functioning on the left. Either issue will cause the right pull you describe.

There is also the remote possiblity that they were assembled with the primary and secondary shoes mixed around. Each brake should have one short and one long shoe. It's a fairly common DIY mistake to put them in the wrong places.

The front brakes receive equal pressure from the master and distribution block, so your power brake booster upgrade is not likely to be related to your pulling problem.

tired, what you say makes sense, and is "by the book", but my old drums are not. They are in perfect shape, including the self-adjusters, if they weren't, they'd be replaced with discs by now.
For 6 years now, I've had to adjust all 4 drums every 6 weeks or so. If I don't, the pedal drops, and it gets real "darty." I never know which way it's gonna go, and of course it only pulls when I NEED it to stop. If I keep em tight, she stops straight and true.
Aussie, check em anyway, everything that tired said. Then adjust them.

Most likely is the brakes with adjustment problems, I have also seen the backing plate worn to a point where the shoe sits in a grove and causes uneven breaking. Or could also be worn control arm bushings steering linkage with some play in it. Check those too!

One other thing is check and see if both drums are worn to the SAME diameter!! B/c if one is small, like new, and the other is bell-shaped and almost worn out, the same thing might happen.

And the short shoe fits to the front and the longer one to the rear..

Up to when I pulled my drums off for my pdqCBB set-up, my car NEVER darted!! BUT the SOB needed to be down-shifted and I also just about had to drag my left leg out my door to haul her down from speed!!

It was always exciting when my slapper-bars were slapping and my rearend was hopping up and down as I was stabbing my brakes AND down-shifting at the same time, trying to keep her straight!!

My wife used ta have an absolute fit whenever I had to haul her down AT SPEED!!

NEVER AGAIN!!!

pdq67

whenever my Nova started doing that crazy stuff when it had drum brakes, i would just do 4 or 5 hard stops in reverse at about 10-15 mph, and it would fix it.

I had this same problem with my 1968 4-wheel drum no power assist. I tried literally everything, (replaced shoes, resurfaces drums, new drums turned to same diamter, new master cylinder, new rubber hoses, (cleaned and replaced solid lines) new brake springs, new wheel cylinders, blah blah blah, even got bored one day and switched all the right side stuff to the left and all the left side stuff to the right) The car still pulled to the HARD right with the brakes, I could make RH turns without toughing the wheel, just pump the brakes. I also rebuilt the front end (new coils, new upper and lower ball joints and bushings) still brake pull. I finally did a disc brake swap and crisis averted! There are lots of great kits out there to convert and it will make your car stop so much better. I did the junk yard upgrade and got spindles, calipers and rotors from a '72 chevelle it bolts right on, just keep your camaro's steering arm. Good luck and let us know how it works out.
steve