Auto Parts: Chevy Cavalier brakes, chevy cavalier, rear drums

Question
I did a complete brake job on my daughter's 2001 Chevy Cavalier about 1year ago. I replaced all parts, to include, front calipers, rotors, pads, hardware etc, the rear drums were turned, all other parts, including the wheel cylinders were replaced. I even replaced the master cylinder and power booster. All wheels were bled accordingly.

The problem is this, when the brakes are applied the rear of the car appears to dive. If the brakes are applied hard, the rear wheels appear to lock up. I took the car to a local just brakes and they found all of my work was proper. The only thing they suggested was the possibility of bad new rear wheel cylinders. I replaced them and still the problem persists. The rear diving is bad enough it causes the car to slide in wet weather. I was then told it may be the rear shocks. Am I missing something or what would be causing this problem. Could it be in the front wheels and not the back?
The Cavalier is a 2001 base model 2.2l.  

Answer
    The 2001 Cavalier has 4-wheel anti-lock brakes as standard equipment.  It is a low-cost ABS that GM developed specifically for the small J-body cars.  Rather ingenious in design, it is not as sophisticated as that employed on the larger ABS-equipped cars.  Nevertheless, if it were working your rear wheels wouldn't be locking up.  It's possible that the sensor in one of the rear hubs has malfunctioned.  The system does not have the large capacity for adjustment that the more expensive systems have, however.  The first thing I would do is buy two new rear drums and replace the turned ones.  These drums do not have much leeway for wear and, if they needed to be turned, are probably beyond the wear specs.  Before you replace the drums remove the shoes and make sure that the curve of the shoe closely matches the curve of the drum.  If they are not very close the shoe will not bed into the drum properly and will only touch the drum at the edges or in the middle.  This would result in increased pressure on the contact patch between the shoe and the drum which could cause locking.  When replacing the shoes measure the inside of the drum with a drum gauge (they are fairly cheap and one of your auto-minded buddies is liable to have one).  These gauges measure both inside and outside diameters.  The idea is to then adjust the shoes so that they are only a thousandth or so smaller than the drum.  This ensures that there is no adjustment needed after the drum is installed.  On the subject of adjustment: drum-braked cars built after the early '80's self-adjust their brakes via the use of the parking brake.  They do not adjust by driving backward and stopping like the older cars did.  Occasional use of the parking brake is therefore necessary to keep everything working properly.  I would also be tempted to have the brakes pressure-bled by a pro (not at a franchise auto shop, a real pro).  This would ensure that the bleeding did not compromise the  ABS.  If, when installing new components, the fluid is forced back into the ABS unit it will gum up the works and cause a problem much like you are seeing.  If these measures do not solve the problem then the whole system needs to be checked for pressure and function.  A real pro will have a variety of fittings and gauges that allows him to check the pressure in the hydraulic system while in use.  If there is a deficit then he will look for the cause.  He can also use his computer equipment to scan the ABS computer and determine that every electronic part of the system is functioning properly.  Go ahead and do the drums and shoes first, though, they are more than likely out of spec if they were turned.