SO I just finished some rear brakes here at work and it made me think of this thread. If the contact points where shoe meets rear plate are rusty, dry, grooved or just gunked up this can cause a jerking feeling when the hydraulic pressure finally over comes what may be holding them back.

If you have to you may need to take a whizzy wheel and smooth them out bur more than likely they are rusty which would just a be a clean and lube.

As far as the front yes you can have a vacuum leak on either side of the booster. The most likely side would be the front. There is a gasket or Oring where the master meets the booster. I could see with them being upset and you supplying parts this being over looked or just not installed, if say the booster you brought them didnt have one in it. kinda like "f*** it this is what he brought us."

Im not saying anything about the shop but it does get sketchy most of the time when customers supply parts.

Have you taken the drums off yet? If you want to post pictures we will do what we can to help.

 

As far as I can tell they replaced all the rear brake components. I can't really do anything till this weekend. I have heard of people having to try a few times before finding a good booster.

 

Thought just came to mind. It might not be anything wrong with the rear brakes, but it's now obvious that the fronts are working LESS than 100%, or anywhere close to it.