Wedge Expander Solutions

一、Introduction to wedge spreaders

1. Brief description of wedge spreader:

The wedge spreader is an important assembly in the automobile brake system, which is applicable to medium and small trucks, trucks and trailers equipped with air chamber wedge brakes. This product utilizes the principle of gap change sensing to automatically compensate for the increased brake clearance between brake shoes and hubs due to abrasion at any time during the vehicle driving process, providing a constant and correct clearance between shoes and hubs to keep them within the standard range (the constant clearance is set in advance according to the different technical requirements of the users) and keeping the clearance between the hubs. And keep the clearance of each wheel hub consistent, overcoming the hidden danger of accidents caused by the vehicle braking out of synchronization and runaway or malfunction, so that the braking effect of the vehicle in the driving process to maintain the best, greatly improving the safety and reliability of vehicle driving. The wedge spreader is configured in the wedge brake, installed in the whole axle to use, first understand the wedge brake structure.

2、Basic structure of wedge brake:

1、Brake base plate 2、Brake clearance self-adjuster 3、Return spring 4、Unequal thickness friction pad 5、Shoe assembly 6、Pin 7、Dust retaining disk 8、Brake air chamber

A. The wedge brake consists of brake air chamber, wedge assembly, brake base plate, brake shoes, friction pads and return spring. B. The wedge brake belongs to the collar-from-shoe brake, the air chamber pushes the wedge lever, and the wedge block converts the push force into the braking force on the shoes in the vertical direction. Each side of the wedge spreader has a set of independent clearance self-adjusting mechanism to control the brake clearance of the lead-follower shoes separately.

3、Principle of wedge spreader:

- When braking: step on the brake pedal, the air chamber push rod is pushed to push the wedge-type push rod, the wedge-type push rod will be driven by the roller to transfer the braking force to the brake shoes directly, the brake shoes will open and hold the brake drum to realize braking.  

- Brake return: release the brake pedal, brake shoes and wedge push rod by the return spring force, so that the brake shoes and brake drum separation, to realize the brake release, when the excess clearance exists, in the process of brake release, to realize the self-adjustment function.

The set braking clearance of the wedge spreader is 0.7~1.4mm. when the friction pads wear to the point that the braking clearance is larger than the preset clearance value, the wedge brake clearance self-adjustment mechanism will activate the self-adjustment function to adjust the clearance to the set value.

二、Wedge spreader disassembly, installation and adjustment method

1. Wedge spreader disassembly:

a）Remove brake air chamber	b）Remove the tension spring. Remove the spring by inserting a pry bar into the gap underneath the spring and lifting up.
c）Use a wrench to remove the attachment screws on the brake shoe plate	d）Remove wedge spreader

2. Wedge expander installation:

a) Install the expander assembly on the brake base plate so that the brake base plate mounting holes correspond to the expander assembly installation.

b) Bolt the spreader assembly to the brake base plate.

c) Remove the retaining rubber bands from the spreader assembly and ensure that the shoe support blocks can be fully placed in the bracket grooves at each end of the spreader.

d) Install one end of the return spring into the hook post of the shoe first, and use a screwdriver to pry the other end of the return spring into the hook post of the shoe.

e) Bolt the brake air chamber to the brake base plate (tighten the 4 locking screws).

2. Adjustment after installation of wedge expander:

a. After replacing the friction pads, because the self-adjuster at this time the two ends of the outstretched amount is large, the need for preliminary adjustment of the braking gap (installing a new expander this step can be omitted).

b. Coarse adjustment method: rotate the push rod threads clockwise to the end in counterclockwise rotation 1.0~2.0 turns. Then adjust the positioning plate to the correct position (this step can be omitted when installing a new expander).

Step 1: Rotate the positioning plate and adjusting screw clockwise to the end as shown on the left until it can't be rotated, with the direction of the positioning plate curl toward the end.
Step 2: Return 1-2 turns counterclockwise as shown in the right figure to adjust the orientation of the positioning plate on both sides. After adjustment, make sure both sides are the same size and both sides of the positioning plate are facing the same direction.

c. After installing the brake drum, the wedge expander for fine-tuning, adjustment method: counterclockwise toggle gear, brake clearance becomes smaller; clockwise toggle gear, brake clearance becomes larger; each rotation of a tooth brake clearance adjustment amount of about 0.03mm, fine-tuning brake clearance requirements in the 0.7 ~ 1.4mm between the two sides of the adjustment method is the same.

1. Insert the screwdriver into the square hole of the hoof plate.	2. Toggle the adjusting gear clockwise and the gap becomes larger.	3. Toggle the adjusting gear counterclockwise and the gap becomes larger.

三、Wedge spreader failure determination methods

1. Failure detection of wedge spreader:

Vehicles under standard load due to weak braking, drag brake, holding, runaway and other faults, before determining whether the expander failure, should ensure that:
1. the air pressure at the end of the air chamber of the whole vehicle ≥ 0.6Mp, and there is no air leakage, stringing and other phenomena in the brake air chamber.
2. Brake air chamber return normal, no stagnation phenomenon.
3. There is no obvious loosening and damage to the connecting bolts of the brake air chamber.
4. The air pressure of the left and right tires is consistent and meets the standard requirements.
5. Brake drums and friction pads have not reached the wear limit and there is no abnormal wear phenomenon such as pulling grooves and bias grinding.

2. wedge spreader test rules:

 四、Maintenance and Precautions for Wedge Expander

1.Maintenance
1.1 The wedge brake assembly is recommended to be inspected once a month or 10,000 kilometers, mainly checking whether the brake clearance meets the requirements. Because of the characteristics of wedge brake itself, the braking clearance at the end of the collar shoe is often smaller than that at the end of the shoe, which is normal. If the brake clearance of the collar shoe is larger than 1.4mm, it is necessary to disassemble and check.
1.2 It is recommended that the self-adjuster assembly be inspected every 2 years. The main inspection is to check whether the parts are damaged (the life of the internal parts may be lower than the design requirements in case of poor road conditions, heavy loads and frequent braking) and whether the lubrication and sealing in the chamber are normal.
1.3 Brake clearance overhaul mileage of the brake, recommended l ten thousand kilometers. Measure the stopper through the inspection hole in the dust pan. Mainly measure whether the brake clearance on both sides is in the adjustment range of the self-adjuster (≤1.4mm), if the brake clearance >1.4mm, it is necessary to dismantle and inspect the self-adjuster to find out the cause and repair it.

2. Precautions:
2.1 When removing the brake drum is strictly prohibited to step on the brake, it will lead to the top lever of the self-adjuster to punch over the top, and then step on the brake again brake drum no action, brake failure.
2.2 When replacing the friction pads, you need to strictly follow the above instructions to adjust the braking clearance within the specified value, and the collar from the shoe clearance is uniform; if the clearance is too large, it will also lead to the self-regulator overshoots the top of the line, so that the brakes fail.
2.3 In the process of maintenance and warranty, once the dust cover is found to be damaged, the dust cover must be replaced immediately so as not to enter the dust and cause the failure of the self-regulator.
2.4 The material of the outer dust cover is high temperature resistant silicone rubber, not oil resistant, it is strictly prohibited to contact with solvent cleaning agents, such as diesel fuel, kerosene, gasoline and so on.
2.5 Self-regulator overhaul must be carried out in a qualified service station, shall not be disassembled and overhauled privately.