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Introduction of Trailer Slack Adjusters

Views:0     Author:Wondee Autoparts     Publish Time: 2021-12-09      Origin:Wondee Autoparts

A slack adjuster is an important component used to transfer braking force and compensate the design clearance between a brake lining and a brake drum.

As shown in Figure 1 below. It plays a vital role in vehicle safety driving, It is mainly introduced from the following aspects:

A slack adjuster for semi trailers and trucks

(Figure 1. A slack adjuster for semi trailers and trucks from a China supplier/WONDEE Autoparts)


1. Function of slack adjusters

The function of the slack adjuster is to adjust the brake clearance of the brake.

During the use of the vehicle, frequent braking will lead to the increasing wear of the brake drum and brake lining, resulting in the increase of the braking clearance between the brake drum and brake lining, the extension of the brake pedal stroke, the decrease of the braking torque of the slack adjuster, the braking lag and the decrease of the braking torque of the brake.

In order to ensure the driving safety of the vehicle, maintain the relative stability of the brake pedal stroke and the work balance between the brakes, the brake clearance needs to be adjusted. A slack adjuster can adjust the brake clearance increased by wear and keep the brake clearance within the design range.

As shown in Figure 2 below. The slack adjuster is installed on the camshaft, and its tail is hinged with the air brake chamber push rod.

slack adjusters installed on the axle

(Figure 2. slack adjusters installed on the axle from a China supplier/WONDEE Autoparts)


2. Classification of slack adjusters

At present, there are two kinds of slack adjusters commonly used :

(1) Manual slack adjusters

As shown in Figure 3 below. For vehicles equipped with manual slack adjusters, the wear of brake drum and brake pad increases after driving for a certain distance, resulting in the increase of brake clearance. It is necessary to manually adjust to ensure that the brake clearance is within the design range.

Manual adjustment of brake clearance has the problems of untimely adjustment and randomness. When the problem is serious, it may lead to prolonged brake response time, inconsistent brake clearance, wheel deviation, vehicle tail swing and even brake failure, and even traffic accidents. Therefore, it is necessary to regularly check and manually adjust the brake clearance and keep it within the design range.

The advantages of manual slack adjusters are that the price is relatively low and the market share is high. Its disadvantage is that it cannot meet the continuous, efficient and consistent braking effect required by heavy duty vehicles, which is easy to lead to braking lag, eccentric braking, and even cause the brake lining to loosen and fall off, which brings potential safety hazards to the running vehicles. Therefore, the automatic slack adjusters will become a new trend.

A manual slack adjuster for semi trailers

(Figure 3. A manual slack adjuster for semi trailersfrom a China supplier/WONDEE Autoparts)


(2) Automatic Slack Adjusters


As shown in Figure 4 below. Automatic slack adjusters can record the increase of braking clearance caused by the wear of braking elements during operation, and automatically adjust the braking clearance to the designed working range.

The automatic slack adjuster does not need to manually adjust the brake clearance, with less maintenance times and long maintenance interval. At present, it is more and more used in various vehicle models.

An automatic slack adjuster for semi-trailers

(Figure 4. An automatic slack adjuster for semi-trailers from a China supplier/WONDEE Autoparts)


3. Composition of slack adjusters


(1) Composition of manual slack adjusters


As shown in Figure 5 below. The manual slack adjusters consists of the following parts:

Composition of a manual slack adjuster

(Figure 5. Composition of a manual slack adjuster from a China supplier/WONDEE Autoparts)


(2)Composition of an automatic slack adjuster


As shown in Figure 6 and table 1 below. The automatic slack adjuster consists of the following parts.

Composition of an automatic slack adjuster

(Figure 6. Composition of an automatic slack adjuster from a China supplier/WONDEE Autoparts)

S/N

Descriptions

1

Tubular Rivet

2

Bearing Housing

3

Thrust Bearing

4

Cone Clutch   Housing

5

One Way Clutch Spring

6

Pinion

7

Thrust Bush

8

O Ring

9

Worm Shaft

10

Grease Nipple

11

Body

12

Bush

13

Spring Seat

14

Coil Spring

15

Spring Retainer

16

Return Spring   -inner

17

Return Spring   -outer

18

Rack

19

O Ring

20

Worm Gear

21

Gasket

22

Cover Plate

23

Control Disk

24

Control Arm

25

Cover Plate   Assembly

26

Countersunk   Screw

27

Welch Plug


(Table 1.Accessories list of an automatic slack adjuster)


4. Working principle of automatic slack adjusters


It is introduced as follows:


As shown in Figure 7 below. When the vehicle is braking, the air chamber push rod pushes the camshaft to rotate. The rotation angle stroke can be divided into the following three areas:

(1) H = clearance angle: corresponding to the normal clearance between brake drum and brake lining, the slack adjuster does not adjust the angle;


(2) E = elastic angle: corresponding to the elastic deformation of the braking system and its transmission components, the slack adjuster does not adjust the angle;


(3) V = excess clearance angle: corresponding to the clearance caused by the wear of the brake drum and the brake lining, the slack adjuster will automatically adjust and compensate the corresponding angle through the built-in adjustment mechanism.

Schematic diagram of brake clearance

(Figure7. Schematic diagram of brake clearance)


5. Installation, commissioning and inspection of slack adjusters


(1)Installation of slack adjusters


The installation steps of slack adjusters are as follows:


Installation of air chambers

As shown in Figure 8 below. According to the installation requirements of the axle and the air chamber, fix the brake air chamber on the air chamber support of axle. During assembly, the push rod of the brake air chamber shall not be pushed out, that is, the extension stroke of the push rod is 0 mm.

Installation diagram of brake air chamber

(Figure8. Installation diagram of brake air chamber)


Clean and grease the camshaft splines

As shown in Figure 9 below. Before installation, clean the impurities and dust on the camshaft spline and apply lubricating grease.

Clean splines and applying grease

(Figure9. Clean splines and applying grease)


Installation of the slack adjusters


As shown in Figure10 below. Pay attention to two points: A. adjust the direction of the slack adjuster to ensure that its tail end can be hinged with the push rod of the air chamber; b. Ensure that the angle between the axis of the wear indicator and the horizontal center line of the shaft tube is 90 °.


Fasten the slack adjuster to the camshaft according to the structural sequence in the picture, align the end hole of the slack adjuster with the fork hole of the brake air chamber, insert the locating pin and fix it.

Fixing and installation of slack adjusters

(Figure 10. Fixing and installation of slack adjusters)


(2) Commissioning of slack adjusters


① Adjust the slack adjuster

As shown in Figure 11 below.

1. Hang the return spring according to the specification;

2. Completely press the clutch sleeve with a socket wrench to separate the clutch sleeve;

3. Rotate the paddle so that the indicator sharp angle of the paddle is aligned with the convex point of the cover plate.

Adjust the slack adjusters

(Figure 11. Adjust the slack adjusters)


② Tighten the slack adjuster


As shown in Figure 12 below. Lock the shift rod support with the self-securing nut according to the specified torque. After fixing, check whether the indicating sharp angle of the shift rod is aligned with the convex point of the cover plate.

Fastening of slack adjusters

(Figure 12. Fastening of slack adjusters)


Adjust the clearance of the slack adjusters

As shown in Figure 13 below. Completely press the clutch sleeve with a socket wrench to split the clutch sleeve; After locking the slack adjusters clockwise, rotate the adjusting bolt counterclockwise for 3 / 4 circle.

Adjust the clearance of the slack adjusters

 (Figure13. Adjust the clearance of the slack adjusters)

During the above installation and commissioning, it is forbidden to use an impact wrench. The adjusting bolt can be turned only after the clutch sleeve is fully pressed in, otherwise the slack adjuster may be damaged.


(3) Inspection of slack adjusters


As shown in Figure 14 below. Under normal use, check the working condition of the slack adjuster every three months, including visual inspection of the position of the wear indicator, and add grease every 6 months.

For vehicles running under harsh conditions, the frequency of inspections shall be increased according to the actual situation.

Schematic diagram of wear indicator

(Figure 14. Schematic diagram of wear indicator)

Compiled by  WONDEE Autoparts

2021-12-8


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