Problem: Vehicle pulls to one side during braking
Cause: There are many causes of brake pull. here is a list of possible causes:
- Friction problem
- Rotor friction surface problem
- Caliper problem
- Restricted brake hose
- Hydraulic restriction higher than brake hose
- Rear brake imbalance
- Loose front end part
Solution: Determining the actual cause of the pull condition relies on approaching the problem in a methodical fashion. When faced with a brake pull condition follow these steps:
1. Confirm pull condition (see Figure 56.1). Drive vehicle on typically crowned roads. Note vehicle handling during both braking and non-braking. If pull is duplicated proceed to next step.
2. Before suspecting brakes check tire size, condition and air pressure. If not within acceptable levels side to side swap tires accordingly and road test vehicle. If pull is still present go to next step.
3. Perform an inspection of the steering and suspension components. Pay close attention to those that will allow a toe or caster change during braking. If any component shows excessive wear that could contribute to the pull repair is suggested before continuing. If front end parts are tight go to next step.
4. Line lock rear brakes with approved line lock. Test drive vehicle to check if pull is effected. If pull is gone, cause is in rear brakes. If pull is still present go to next step.
5. Perform brake inspection. Pay close attention to the operation of the calipers. Check caliper housing’s ability to move freely. Check piston condition by pulling back dust boot. If significant difference exists from side to side service calipers and road test vehicle. If pull is still present go to next step.
6. If front pads have friction material left on them swap brake pads from side to side and test drive vehicle. If pull is gone or switches directions friction is source of your problem. If no change in pull swap brake pads back to original position and go to next step.
7. With brake pads back to their original position, swap rotors and test drive vehicle. If pull is gone or switches sides rotor’s friction surface is the cause. If no change in pull go to next step.
8. If pressure gauges or clamping plate gauges are available perform aside to side pressure check. Pressure readings should be within 50psi at pressure above 500psi. If pressure readings are not within 50psi of one another go to next step or if pressure gauges are not available proceed to next step.
9. Determine possible points of restriction. One front to rear split hydraulic systems this will include the brake hose, ABS modulator (if equipped) and combination valve (rare but possible) and steel brake line to side opposite the direction of the pull. If diagonal split hydraulic system the list will include brake hose, ABS modulator (if equipped), steel brake line to side opposite the direction of the pull and master cylinder.
10. The most common point of restriction are the brake hoses. The hose on the side opposite the direction of pull is the most likely cause. If the hose has a mounting bracket clamped around it, check the bracket for signs of corrosion. If corrosion is present pry the bracket apart, squeeze the hose in the direction opposite the crush pattern and then test drive the vehicle. If the pull is eliminated or substantially reduced the brake hose is the cause. If no external signs of restriction are visible the decision has to be made to replace the hose(s) or perform additional diagnostic steps. Those steps could include switching hoses from side to side or trying to blow through both hoses to check if there is a difference. Usually the time necessary to do either test would be better spent trying a new set of hoses. If the hoses are shown not to be the cause of the pull by diagnosis or replacement the system should be checked for an upstream restriction. Go to next step.
11. Brake pull still present after performing steps 1 to 10 – This should not happen very often. If steps 1 to 10 have been followed correctly and the vehicle is still exhibiting a brake pull then identify hydraulic components between master cylinder and front brakes. These will usually include the ABS modulator and/or the combination valve. On vehicles equipped with combination valves the outlet lines of the valve could be switched using the necessary line adapters to determine if valve is source of restriction. If pull is still present after step 11 it is advisable to recheck previous steps.