rear brakes lock up first??

i just did the rear brakes on my 94voyager.new cylenders,drums,shoes.i've got the primary shoe in the front(short shoe).
know the rear brakes seam to lock up on gravel,and wet slipery roads.
can somebody help me with this prblm.i have no air in the system.
all possible sugestions appriciated.
my long shoes are the thickest should they be in the front??

Welcome to AF!!

Actually air may not be the issue but a fresh bleeding of the brakes may be the culprit. Bleed the front brakes too. Also check to make sure that the front brakes are in good shape. It is possible that the pads are worn and not giving enough braking allowing the front to do the majority of the braking causing the lock-up. One other problem may be with the master cylinder. If not enough fluid is going to front brakes then the rear will lock. Check the brake lines to make sure there are no kinks or damage to any of the lines going to the front brakes. I would concentrate on the rubber lines going to the calipers. They will go bad internally and cause problems. I hope this gives you somewhere to look.