Not good. The battery can flip over spilling acid or breaking things or the battery (+) post can touch metal parts and arc causing a fire.

Tie it down with bungee cords or rope before you drive.

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That cube barely works. A knuckle buster.

If you are doing lots of brake jobs the disk brake caliper piston compressor is the way to go.

Well worth the money.

You can also rent this kit from your local autoparts store.

Drum brakes on the rear?

If yes then either the shoes are worn or the the rear brakes need adjusting or both.

Do your rear brakes look like this?

https://www.youtube.com/watch?v=PGh879YscPA

Buy the repair manual for your car. It will tell you how to replace the pads as well as where to jack the car and where to place the jack stands.

Gather together all of the tools you will need.

If special tools are required you can rent them from your local parts store.

Do one side at a time so you can use the other side as a reference on how the parts fit together.

Keep the rotors/pads clean and grease free.

Safety: Support the car on jack stands and not just the jack.

Are the plugs gapped correctly?