why do my 1989 GMC one ton brakes lock up on front wheels ?

Question

on gravel or wet pavement they just slide. i have put new rotors and calipers new shoes and cylinders on back, brake equalisation thingie under master cylinder,
back brakes are adjusted properly

it doesn't take much to lock the front disc brakes up.

i need to fix before i have an accident someday

Answer 1

the reason for this is when you are on gravel or wet pavement there is just not the same amount of traction as there is on pavement and dry pavement. you have a one ton vehicle it is equipped with heavy duty brakes that have a lot of stopping power. When you do not have much weight on the ie just the truck alone it is very easy for them to loose traction and lock up. The tires you have may also contribute to this if they are hard tires such as tires rated at 80,000 mile rather than a sof tread tire rated at fewer mile you may hust not get the traction required to keep this from happening. remember it is hard to slow down that much weight it is very normal for vehicle without abs to do this. This is why almost all vehicle built today have abs.

If you have been losing brake fluid it is possible that this fluid soaked into the pads and are causing them to lock up. Brake fluid soaked pads are more proned to this behavior due to the friction values created by this fluid.

Answer 2

Check your caliper slides, check for a plugged front brake hose, and make sure you haven't overfilled your master cylinder. an overfull master cylinder will cause front brake lockup.

Answer 3

You probably need to bleed the front brakes.

Answer 4

check your calipers and hoses