95 nissan hard body front brakes lock up ive replaced the proportion valve, master cyl,brakes and calipers,even the brake booster...and they still lock up while driving...please help

Need year make and model. In most newer vehicles the valve is located in the master cylinder. It will not normally lock up the front wheels. It usually controls one front and one rear wheel at a time in the event of a brake fluid loss. If front calipers are locking up you could have seized caliper pistons/slide assemblies. The flex hoses may be deterioated internally due to contaminated brake fluid or the master cylinder may be defective

there is a proportioning valve to the rear brakes that only allows them to operate fully under load or heavy braking. If it is faulty then full brakes will be applied to the rear which will allow them to lock up first.
Check pad/shoe condition and rear drum/shoe adjustment as well

To and from the master and calipers. Did you replace the calipers also? Lock ups usually occur when a brake hose is bad or the caliper is bad/binding. Drive it and check the wheel the gets the hottest. Short drive. They get really hot, be careful( will take the skin off your finger). You can get new, bad calipers. The booster and proportioning vavles will not cause a lock up.

did you check proportion valve and reset it

what is the year ,make and model.? does it have abs brakes

If the pads are being applied and you are not pushing on the pedal, it could be something going on with the ABS.

did you check the brake booster ? how long you use the brake booster? may be have no enough pressure in vacuum brake booster. get more details here for help : http://www.fiverhope.com/
http://www.fiverhope.com/category-67-b0-Brake-booster.html

The only things I can think of is ether a kink in the right side brake line or the proportioning valve is clogged or stuck or the ABS valving is clogged or stuck. Its possible the system has become contaminated with moisture???

A bad brake booster will result in a hard brake pedal, stiff and more effort required to stop the truck. Here are my questions to you, first, you said you replaced the master cylinder, did you bench bleed it before you installed it? If not, there IS still air in it, regardless of how much you bleed the brakes at the wheels. Second, when you bled the brakes, after changing the calipers and master cyl., did you also bleed the proportioning valve? Sometimes air can get trapped in the valve, and its almost impossible to get it out bleeding just the wheels. And lastly, when the brake light comes on, does the abs light also come on with it? Air can also get trapped in the abs control module too.

here is a 96 taurus


Item Part Number Description 1 2C296 Anti-Lock Brake Tube 2 2C219 Anti-Lock Brake Module 3 2005 Power Brake Booster 4 2263 Front Brake Tube 5 2B091 Brake Pressure Control Valve 6 2140 Brake Master Cylinder 7 2B547 Brake Load Sensor Proportioning Valve 8 N802191-S60 Bolt 9 2L568 RH Rear Brake Tube 10 2L569 LH Rear Brake Tube 11 2C287 Brake Fluid Distributor Tube 12 N808531-S301 Bolt 13 — Front Side Member 14 N802324-S56 Bolt 15 18124 Front Shock Absorber 16 2B121 Front Disc Brake Caliper 17 2078 Front Brake Hose 18 2264 Front Brake Tube 19 2553 Rear Disc Brake Caliper 20 2A442 Rear Wheel Brake Hose 21 N808728-S60 Bolt 22 — Side Rail 23 N802324-S60 Bolt
Brake Load Sensor Proportioning Valve


Item Part Number Description 1 2B547 Brake Load Sensor Proportioning Valve 2 — Body 3 N802191-S56 Bolt (2 Req'd) 4 2L568 Brake Tube Assy 5 2L569 Brake Tube Assy 6 2265 Brake Tube Assy 7 2B255 Brake Tube Assy 8 5500 Rear Suspension Arm and Bushing 9 W611634-S301 Bolt A — Tighten to 11.4-15.6 Nm
(8-12 Lb-Ft) B — Tighten to 10-14 Nm (7-10 Lb-Ft)

Brake Hose, Rear —Drum


Item Part Number Description 1 — Rear Side Rail 2 2L569 Rear Brake Tube 3 N602324-S60 Screw 4 N611193-S60 Screw 5 2C023 Left Hand Rear Hose and Connector 6 2210 Rear Drum Brake Backing Plate 7 18125 Rear Shock Absorber 8 2267 Rear Brake Tube A — Tighten to 16-20 Nm (12-15 Lb-Ft)