Ford Repair: rear drum brakes..., rear drum brakes, ford ranger 4x4

Question
QUESTION: Hi,
I have a 99 Ford Ranger 4x4 4.0L auto truck. At start up, the rears will lock up if applied semi hard. This will occur for a little bit then go away. Almost as if the wetness/moisture is causing this then goes away when the interior parts are dry. All parts are/were new not long ago and no leaks noticed. Any ideas? Thanks.

ANSWER: Several components could cause this, including a master cylinder. If indeed you replaced all of the parts, do they include the wheel cylinders?

---------- FOLLOW-UP ----------

QUESTION: Hi,
I didn't replace the wheel cylinders. They weren't leaking, but could they still be bad?
Thanks,
Mike

ANSWER: I doubt that both of them would be bad. Are both sides locking up.or is it just one side? Did you have the drums turned? If they are both locking up, and you did have the drums turned,replace the master cylinder.

---------- FOLLOW-UP ----------

QUESTION: Hi James,
Thanks for the responses. I don't know if both were locking up, just that it did it for a few minutes until the brakes etc heated up. But just for good measure and to save you some time could you tell me what to do for several conditions? If drums weren't turned, could it be them? If drums were turned and both sides are locking up, could it be the master cylinder and why? I'm just wondering, I never would have thought of that one. If it is just one side, then would it be a bad drum? Or master also? Thanks in advance. You have been very helpful. I'm no stranger to brake issues, but I know my knowledge limitations and two heads are definitely better than one. I'm thinking everything was new (everything minus wheel cylinders), but I could be wrong about the drums. It's not too often I buy those, rotors many, but drums rarely. However, no expense was spared with this truck and they might've been replaced also. I will know by looking at them. So, if you can give me tips on the possible scenarios, I should be able to remedy the situation. Again, your knowledge has been extremely helpful and I am greatful.
Many thanks,
Mike

Answer
The drums are circular shaped of course. Over time, they get egg shaped. This can be turned out, nut just slapping a set of shoes on is just asking for it. Usually purchasing the drums is not necessary, all that should be required is having them turned. You can still do that.  This is what I would do. I would take the drums off, and have them turned. More than likely, it sounds like this is you're problem.