Introduction of Trailer Brake Drums

A brake drum is the core component of vehicle braking system. Its function is to generate braking force and hinder vehicle movement or movement trend.

A brake drum is a matching part of internal tension shoe friction brakes. It should not only have the strength and stiffness, but also have as high and stable friction coefficient as possible, as well as appropriate wear resistance, heat resistance, heat dissipation and heat capacity.

Brake drums are widely used on axles of semi-trailers.

As shown in Figure 1 below. The brake drum is connected to the axle hub by tire bolts. When the vehicle is braking, the air brake system pushes the camshaft to rotate to spread out the brake shoes to apply pressure to the brake drums, so that the friction force between the brake pad and the brake drum generates braking torque, and finally stop the vehicle. The reliability of brake drums directly affects the driving safety of a vehicle.

Figure 1. Drum type brake system

A brake drum is one of the important parts of a trailer axle, It is mainly introduced from the following aspects:

1. Technical standards of brake drums

(1) The technical standard of brake drums shall comply with China national standard GB / T37336-2019.

(2) The technical standard of brake drum casting blanks shall comply with China national standard GB / T9439-2010.

2. Technical parameters of brake drums

As shown in Figure 2 below. Common technical parameters of brake drums are as follows:

Figure 2. Schematic diagram of brake drum parameters from a China's manufacturer WONDEE Autoparts

(1) A：（Overall Diameter of Drum）

(2) B：（Dust Shield Recess Diameter）

(3) C：（Brake Surface Diameter）

(4) D：（Overall Depth）

(5) E：（Brake Surface Flat）

(6) F：（Depth of Dust Shield Recess）

(7) G：（Squeeler Band Thickness）

(8) H：（Distance from Outside of Backface to Start of Taper）

(9) I：（Inside Finished Diameter）

(10) J：（Bolt Circle Diameter）

(11) K：（Pilot Diameter）

(12) L：（Outside Finished Diameter）

(13) M：（Diameter at Taper）

(14) N：（Backplate Thickness）

(15) O：（Bolt Holes: Number and Size）

3. Classification of brake drums

According to structure types of the brake drums, it can be divided into the following two types:

(1) Common brake drums

1) Single material brake drums

As shown in Figure 3 below. This kind of brake drums has the advantages of simple manufacturing process, stable performances and high cost performance. It is widely used in trucks, tractors, full trailers, agricultural vehicles and semi trailers.

Figure 3. Single material brake drums from a China's manufacturer WONDEE Autoparts

2) Bi-metal brake drums

As shown in Figure 4 below. As the name suggests, the braking part of the bi-metal brake drum is composed of two different metal layers inside and outside. The inner layer in contact with the friction lining is a cast iron part to ensure a good braking performance. The outer layer is made from high-strength steel to improve the strength and toughness of the brake drum. At present, this brake drum is currently in the trial stage in the market.

Figure 4. Bi-metal brake drums from a China's manufacturer WONDEE Autoparts

(2) Brake hub-drums

As shown in Figure 5 below. A brake hub-drum combines the wheel hub and the brake drum into one. This drum is mostly used on light-duty trailers.

Figure 5. Brake hub-drums from a China's manufacturer WONDEE Autoparts

4. Selection of brake drums

How to choose a brake drum in need correctly can be determined from the following aspects:

(1) Determine drums according to the OEM number of the automobile manufacturers, axle manufacturers or brake drum manufacturers.

As shown in Table 1 below, the OEM number of common trailer brake drums of well-known manufacturers.

Model	OEM number	Model	OEM number	Model	OEM number
MERCEDES BENZ	3014210501	BPW	310667290	MAN	81501100194
	3014210701		310677040		81501100195
	3014210901		310677590		81501100175
	3014211301		310677670		81501100216
	3014230001		310677630		81501100229
	3014230101		310667120		81501100212
	3014230301		310677720		81501100219
	3014230801		310677940		81501100116
	3014230901		310679060		81501100231
	3524210401		310977720		81501100226
	3524210501		310687150		81501100223
	3544210001		310967050		81501100213
	3544210101	BPW	327280140	Volvo	1134817
	3544210301		327280860		1590313
	3544210401		327280100		1075305
	3604210601		327262200		1599678
	3604210701		327262190		1599679
	3604230101		327248460		1577439
	3644210001		327248400		3171743
	3814230001		327248780		3171744
FUWA	3602.A	FUWA	3601.A		3171745
	3602.B		3601.B		3171746
	3602.C		3601.C		3171747
	3602.E		3601.E		3171748
	3602.R		3601.R	SCANIA	1414153
	3602.S		3601.S		1361331
	3602.Q		3601.Q		1333117
	3602.S1		3601.R1		1414152
	3602.R1		3601.S1		1334075
	3602.H	MITSUBISHI   FOSO	MC807783	NISSAN	40203-90104
ISUZU	1-42315314-0		MC807781		43204-90545
	1-42315336-0		MC828491		43204-90106
	1-42315365-1		MC060504		43204-90071
	1-42315377-1		MC838284		43204-90176
HINO	43512-2660		MC838283		43204-90215
	43512-2830		MC865370		43204-90110
	43512-2860		MC308941	FRUEHAUF   TRAILOR   TRAILER	AJA 595001
	43512-3020	WEEB	66814F		AJA0489001
	43512-3490		66816F		AJA0489002
	43512-4011		66827B		AJA0490001
	43512-4090		66852F		AJB0465001
ROR	21018963		66854F		AJB0465002
	21018986		66864F/B		AJB0026001
	21020038		66864B		AJB0335001
	21021114		66865B	SAF	1064012800
	21021114A		66873F		1064013000
	21021164		61527B		1064014900
	21223852		61528B		1064019700

Table 1. Common brake drum OEM numbers

(2) Determine drums according to brake drum drawings.

(3) Determine drums according to the basic sizes of a brake drum.

As shown in Figure 2 above, at least several parameters such as C, D, E, J, K, and O are required to determine the product.

5. How to measure a brake drum

As shown in Table 2 below. Relevant parameters of brake drums shall be measured as shown in the figure below.

1. Diameter of brake surface (C)	2.  Width of brake surface (E)
3. Overall  height of brake drum (D)	4. P.C.D.of bolt holes (J)
5. Diameter of bolt holes (O)	6. Diameter of center hole (K)
7. Outline characteristics of brake drum	8. Number of bolt holes

Table 2. Schematic diagram of brake drum measurement

6. Maintenance of brake drums

In order to achieve the longest service life and the best service performance of a brake drum, regular maintenance shall be carried out according to the maintenance manual of the vehicle manufacturer or axle manufacturer.

7. Replacement of brake drums

If one of the following problems occurs, the brake drum needs to be replaced. The brake drum must be replaced in pairs to ensure that both ends of a trailer axle have basically the same braking effect.

(1) The brake drum is cracked;

(2) Hot cracks, grooves or wear on the friction surface of the brake drum exceeds the limit of the brake drum;

(3) The mounting surface of the brake drum is cracked;

(4) The bolt hole of the brake drum is damaged;

(5) The brake drum is out-of-round.

8. Troubleshooting of brake drums

Troubleshooting table-problems, causes and troubleshooting methods are shown in Table 2 below:

No.	Problems	Pictures	Characteristics	Causes	Troubleshooting
1	Oversized Drums		The brake surface diameter is in excess of its specified maximum diameter.	The brake surface diameter is in excess of   its specified maximum diameter.	Replace the drum immediately.
2	Cracked Drums		A drum which has cracked completely through a section of the braking surface.	1. Excessive heating and cooling. 2. Excessive shoe pressure.	Replace the drum immediately.
3	Uniform excessive   wear		The edge of the brake drum forms an extremely obvious step.	The brake drum is rapidly and evenly   worn due to heavy braking resistance, braking imbalance and the entry of dust   and impurities	Replace the brake drum in time.
4	Unilateral abnormal wear		There are obvious wear marks on one side of the brake drum, but there are no obvious wear marks on the other side.	The Brake drum and brake lining are not concentric.	It is necessary to adjust the brake base   plate, brake support plate, brake shoe pin and other parts.
5	Heat Checking		A broken network of fine hairline cracks on  the braking surface of the drum, is a normal phenomenon of braking surfaces.	It is caused by regular heating and cooling of the surface.	Examine heat checks  frequently to make sure they have not grown deep  enough to weaken the drum.
6	Partial hot(black) spots		The spots neatly cover the entire friction surface of the brake drum,   forming a uniform parallel ring, or appear or form evenly distributed small round spots in a larger local area.	Uneven wear due to material and   structural errors of brake drum.	Replace the brake drum in time.
7	Martensite Spotted Drums		Martensite spotted drums have extremely hard, slightly raised, dark colored spots on the braking surface, shown uneven wear and the surface is out-of-round.	The spots are caused by very light brake applications with nonasbestos organic linings that are contacting the drum at a few  lining high spots.	Unless this is detected very early, the   brake drum should be Scrapped.
8	Brake drum grooves		Deep nicks or grooves are formed on the working surface of the inner circumference of the brake drum.	The wear of the brake lining exceeds the limit, causing sharp objects such as rivets to form pull grooves on the   working surface of the inner circumference of the brake drum.	Replace the brake drum and brake lining.
9	Scored Drums			Scored drums are signified by   circumferential grooves on the braking surface and excessive lining wear.	Replace the drum immediately.
10	Blue Drums		A bluish disfiguration on the brake parts   (shoes, drums/rotors or bolts) indicates excessive heat.	This is usually caused by an oversized brake surface diameter/undersized rotor width or by weak or broken return springs.	Replace the drum immediately.
11	Brake drum backplate dropped		The circumferential brake part   (cylinder) and flange part (disc) of the brake drum are separated	Improper structure and material during brake drum manufacturing.	Replace the brake drum in time.
12	Brake drum bolt holes are worn		The bolt holes of the brake drum are abnormally worn, which are   elliptical holes.	The flange bolts (wheel bolts) are not fully tightened, and the brake  drum has relative movement impact with respect to the radial and axial   direction of the wheel hub.	Replace the brake drum in time.
13	Hub grease contamination		The lubricating oil / grease is thrown   onto the working surface of the inner circumference of the brake drum.	The hub oil seal fails, and the   lubricating oil / grease is thrown to the working surface of the inner   circumference of the brake drum.	Replace the brake drum in time.
14	Grease Stained Drums		Brake drums with discolored spots on the   braking surface, and oil or grease splattered on the brake assembly.	Over-lubrication of the cam or camshaft, or by an oil seal failure.	Replace the drum immediately.
15	Out-of-round drums		Variations in drum diameter at different points on the braking surface indicate out-of-round drums.	Variations in drum diameter at different points on the braking surface indicate out-of-round drums.	Replace the drum immediately.

Compiled by  WONDEE Autoparts

2021-11-25