I have a 1970 F-100 with power brakes.When I put on the brakes especially on a dirt road or slick surface I have to be real careful or the left side will lockup on me.I just got this truck and don't know what all has been done as far as brakes.I need some pointers guys!
James

 

We're assuming that you have 4 wheel DRUM brakes, if this is the case then your locking up could be a couple of things:
1 being it is possible that one of the brakes on that side may be adjusted too tight, to check this jack up your truck on the right side & give the wheel a spin it should spin easily, but have "some" drag, then do the same for the left side & compare it to the right side, if it is tighter then you'll simply need to back off on the adjustment until you get them both equal.
2, it is also possible that you've got a stuck, or sticky wheel cylinder on the right side, not letting the brake shoes work smoothly, thus causing the left side to lock.
Hope this helps a little.

 

James,
Misadjusted brakes drums are the most likely problem. They can be adjusted with a screw driver through the backing plate.
There is another possibility. You could have worn flex lines. Your vintage truck sets you up for this. The flex line will collapse and allow forced fluid in and not let it out. The brakes will drag and wear prematurely. They will get so hot that they will liquidfy the grease in the drum. It will then burn the grease seal and the grease will escape into your brakes. When you step down on the brake, only one side works. The other side is lubed. Check for a grease leak. If you see one, remember what you've read.
Good luck, have Fun,
KingFisher