Car MOT Manual 2012 onwards

Body, Structure and General Items - 6.6 Towbars

This inspection applies to: all types of towbar fitted to the rear of a vehicle. It does not include emergency towing eyes.
Tow ball covers must not be removed to facilitate inspection of the tow ball. Some tow bars are hidden behind an access panel in the bumper or bodywork. Unless requiring the use of tools or specialist equipment, these panels must be removed to facilitate the inspection of towbar components, as well as checking inside the luggage compartment, including lifting of loose fitting mats or carpet.

Retractable towbars should be tested in their inuse position unless this requires the use of tools or specialist equipment. If a tow ball or pin is not fitted at the time of test, e.g. because it is detachable, has been unbolted or otherwise removed, but the attachment brackets are still in place, these brackets should still be assessed unless they have been deliberately rendered unfit for further use. There may be play in some detachable tow balls between the receiver socket and the tapered swan neck fitting, with up to 3mm movement measured at the ball end. Reason for Rejection 4a should only be used where play is greater than this. Quick release mechanisms must not be operated, only visually assessed.

Wear in a pin, jaw or hook should be regarded as excessive if the thickness of the metal at any point is reduced by more than 25% of the original thickness. Pin locating holes should be rejected if they are worn or elongated by more than 25% of their original diameter. These criteria also apply to pins and brackets for any height adjustment or swivel devices. For tow balls the amount of acceptable wear is considerably less. However, a tow ball should only be rejected if a visual assessment indicates that the tow ball is obviously excessively worn. Many bolt-on type tow balls have accessory devices sandwiched between the tow ball and its mounting flange. These are not to be considered as inappropriate modifications unless their fitment is clearly likely to adversely affect the roadworthiness of the vehicle/trailer combination. Trailer electrical couplings are tested under Section 1.9.
Method of Inspection
1. Visually assess the towbar for wear and pull on the towbar and/or its mountings to check for security, corrosion, fractures or damage.

2. Check the towbar assembly is attached to the vehicle structure using mountings, supports and fixings of an appropriate size and type.

3. Check the presence and security of:
a. retaining devices e.g. nuts bolts b. locking devices e.g. split pins, R pins.

Note: It is not always possible to determine the presence and effectiveness of certain types of locking devices eg locking fluid or nyloc nuts.

4. On detachable tow balls:
a. check for play between the tow ball arm and its receiver socket
b. visually assess the condition of any quick release mechanism.

5. On height adjustable or swivelling towbars, check:
a. for presence, and security of locating or swivel pins
b. locating or swivel pins and brackets for excessive play or wear
c. locating or swivel pin retaining devices for presence and security.

6. Check the condition of the body and chassis in the vicinity of the towbar mountings.

7. Check the towbar assembly for any inappropriate repair or modification.
Reason for Rejection
1. A towbar component insecure, fractured or e xcessively:

• worn
• corroded, or
• damaged.

2. Towbar assembly is attached to the vehicle structure using a mounting, support or fixing which is obviously of an inappropriate size or type.

a. Retaining device missing or insecure
b. locking device missing, insecure, inadequate or damaged to the extent that its operation is impaired.

a. Excessive play between a detachable tow ball and its receiver socket
b. a quick release mechanism that does not secure the tow ball arm as intended.

a. A locating or swivel pin missing or insecure
b. excessive play or wear in a locating or swivel pin or bracket
c. a locating or swivel pin retaining device missing or insecure.

6. Any deliberate modification, excessive corrosion, damage, fracture or inadequate repair of a load bearing structure or supporting panelling within 30cm of the towbar mountings, which affects its strength to the extent that the security of attachment of the towbar is significantly reduced.

7. A towbar assembly inappropriately repaired or modified such that it is likely to adversely affect the roadworthiness of the vehicle/trailer combination.

Reproduced from the MOT Inspection Manual by kind permission of THE VEHICLE INSPECTORATE.

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