I am trying to do a brake job on a 1991 Chevy 4X4 on the rear brakes. I can not get the brake drum off.

install,
so they are off now, I'll pretend, REPLACE.

axle job, brake job what? "CONTEXT" helps.; sure does.
easy, have even videos of axle pulls too.
get 2x 8mm bolts to do the ejection
see photo one,
92 on up looks same.
http://www.fixkick.com/axles/axle_rear_R&R.html

btw , on that same site is the full 1996 fsm,
click search and manuals, then click FSM.
bingo , factory brake pages, , all.
same as 98

Did you check the park fuse, or the orange wire going into the headlight switch for power ?

To replace pinon bearing you need to pull wheels and the brake drums off next pull cover off the back of the rear end (make sure you have a drain pan under rear end) next turn dive shaft till you see a small bolt remove bolt pull center pin out push axle in pull c clips out pull axels out remove four bolts holding ring and spider gears remove gears assembly next remove drive shaft remove bolt from pinon push pinon in remove seal and bearing

Its likely you eighter lose a hold down spring for the shoe or poped a wheel cylinder pistion out so it can't return properly Your brake shoes in eighter case are spend this caused the problem Try to apply the parking brake you may be able to lossen it up but the rear brakes need to be replaced . To get the drum off if the parking brake dosn't work you will need to look at the back of the rear brake plate inside of the tire where the brake lines hook up. There will be a rubber plug at the bottom of the plate remove it inside there is a part called a star wheel you can turn it with a stright head screw driver . This will release the tenistion on the shoes and allow you to remove the brake drums . But keep in mind that one of the star wheels turns right handed and the other turns left handed so if it feels like its is getting tighter your turning the wheel the wrong way it should get easyer to turn Good luck you need new rear brakes

1990 Chevy 4.3 l engine runs rough at idle half the time-- sometimes it's OK, other days it's rough and can smell raw gas, as tho it's running rich... any ideas?

adjust the rear brakes up manually ,and grind the lip down on the edge of the brake drum so you can adjust brakes right up before you refit the drum

on the 04 chevy silverado theirs cable equilizers that stable your cables of your parking brakes check to see if those arent loose or damaged in anyway if so replace if not remove the rear wheels and use a brake spoon to spin the adjuster nut on the o4 chevy their is not slots in the sides of the brake drum or the dust shield so it is a hastle trying to find if your on the adjuster or not but once you tinker with it for a while you will get the hang of it

Common cause is the drums and brake shoes need to be replaced. When there no longer within the the specification for the brakes to work properly, the self adjusters will over adjust the brake shoes and you'll have the feeling of the rear drum brakes lock up as the shoes will bind up along the drums. Replace both Shoes and Drums and this can be done on your own will common tools and a simple brake spring tool that you can pick up at Auto Zone or Parts Source and both can give you the step by step instructions to replacing the rear brake system. Good luck and be safe.

Can you tell me which type of axle you have?

Full Floating Axles To remove the drums from full floating rear axles, use the Axle Shaft Removal & Installation procedure in Section 7. Full floating rear axles can readily be identified by the bearing housing protruding through the center of the wheel.


Semi-Floating Axles

1. Raise and support the rear end on jack stands.
   
2. Remove the wheel.
   
3. Pull the drum from the brake assembly. If the brake drums have been scored from worn linings, the brake adjuster must be backed off so that the brake shoes will retract from the drum. The adjuster can be backed off by inserting a brake adjusting tool through the access hole provided. In some cases the access hole is provided in the brake drum. A metal cover plate is over the hole. This may be removed by using a hammer and chisel.
   

You may have to back off the automatic adjuster before you can pull the drum from the brake assembly

To install, reverse the removal procedure.

If you are familar with a front brake drum on a rear wheel drive vehicle, the procedure is the same, if you have not seen this in the past it might be wise to have a professional do the job. Brakes are not something you want to take a chance with.