1) General Principle of Brake Setting
The basic number one rule with the modern over run braking system is that on completion there should be no clearance whatsoever in the linkage system, generally speaking only couplings older than 20 years require clearance to be set in the linkage/rod system. If in doubt please contact us. To achieve a correctly set up Auto Reverse Brake System, correct adjustment of four main areas is necessary. These are as follows:-
1. All brake back plates
2. Brake compensator
3. Brake Linkage
4. Coupling and clevis
2) Before Starting the Procedure
All Indespension couplings are fitted with spring loaded handbrake systems which, upon application of the handbrake automatically apply further pressure should the trailer roll backwards. The system ensure adequate force is applied to the brakes.
Many manufacturers now use this type of handbrake system as it self controls the forces going from the handbrake spring energy store into the brakes once the handbrake has been applied.
NOTE- It is very important the correct safety bolt is installed prior to commencement of any work on the brake system or coupling. Use an M10 bolt or setscrew (min 25mm long) or longer to ensure the handbrake cannot move.
A tapped hole is provided close to the handbrake plate as per the images below.
Please ensure that the appropriate fastener is correctly located prior to any service work otherwise personal injury may occur.
Prior to commencing the adjustment, ensure that the coupling head is fully extended into the start position.
The adjustment should ideally be carried out on level ground and disconnected from the vehicle.
Ensuring the trailer cannot move, release the handbrake fully to the off position as shown in the photo above.
Jack up on one side of the trailer and place an axle stand under for safety reasons. Chock the wheel on the opposite side to prevent the trailer rolling during adjustment.
Starting with the wheel (or wheels) that are off the ground, adjust the back plate as described in the following procedure.
3) Setting Your Knott Back Plates
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IMPORTANT! Always rotate in a forward direction when setting the brakes.
Commence by tightening the back plate adjuster nut to bring the shoes in contact with the drum whilst at the same time rotating the wheels in the forward direction. The wheel must not be rotated in the reverse direction otherwise the auto reverse mechanism will be engaged and the procedure will need to be re-started.
You will feel the shoes contact the drum. Continue revolving the nut until such a time that the wheel cannot be rotated with heavy hand pressure in forward direction.
The nut should then be backed off by only half a turn. Care must be taken to ensure the backing off is only half a turn, backing off further increases the amount of cable pull required for the brakes to actuate.
Repeat the procedure for all the remaining drums.
You can check the setting by pulling on the relevant Bowden cable for the brake you have just set. When correctly set there should be 4mm to 6mm of free movement as shown. This procedure needs to be repeated for all remaining wheels and a careful check needs to take place for each setting as described.
Once all the back plates have been set and checked on the Bowden cable, the next step is to ensure there is no clearance in the brake rod. All modern couplings should have zero clearance in the brake rod. To remove any clearance, tighten the front swivel nut (with domed face).
Check that all the clearance has been removed by moving the rod backward and forward. support the brake rod whilst checking so that it does not sag under the weight of the rod and the compensator.
Once you are certain all the clearance has been removed tighten the locknut up against the swivel nut to lock in place.
4) Final Checks on Brake System Setup
This procedure should be carried out on level ground with the trailer detached from the vehicle such that the coupling head is fully extended as shown. Chock to ensure the trailer cannot roll AND ENSURE ALL WHEELS ARE ON THE FLOOR.
Once the system is fully set and secure, remove the red safety bolt.
It is now possible to carefully check the setting. Apply upward pressure on the handbrake as shown in the photograph, below, lifting from position 1 towards position 2. The over centre action should be noticeable in that the handbrake should gently automatically apply after the handbrake has been lifted approximately 100mm.
If the handbrake is very difficult to apply then it would suggest that there is not enough clearance in the drums and you would need to reset the brakes using the earlier brake setting procedure. If the handbrake flies on too quickly then there is either clearance in the brake rod or too much clearance in the drum and again you will need to reset the brakes following the instructions earlier.
The perfect handbrake action should be that the handbrake gently applies itself having lifted approximately 100mm once applied. When in the ‘on’ position, the shaft of the handle should be vertical.
If the trailer is now pushed backwards whilst the handbrake is applied then the handle should move into the vertical auto reverse position. You must be very careful at this point to ensure that you trip all brake drums into auto reverse. If the handle is not fully 90degrees then this would suggest that not all the drums are tripped out. Should this happen, you would need to take the handbrake off, pull the trailer forward then reapply the handbrake and attempt to roll the trailer backwards.
A good check at this point would be to look at the compensator and if all the back plates have correctly tripped into auto reverse then the compensator would be level.
If you are sure that the brakes are tripped out and the handle is not vertical then the brake are too tight and you need to reset the brakes. It is highly probable that one or more of the drums have not been backed off correctly.
If your handbrake travels to a similar position as shown in this photograph then there is far too much clearance in the system and the trailer could roll backwards on a hill as there will not be enough energy remaining in the spring to withstand the forces on the brake system.
if this conditoon ecists in your brake set up, you must have the brake system adjusted correctly as soon as possible. If in doubt consult your nearest Indespension or call the sales line on 01204 478591.