Ask the MAC – 18 Dec 2025

Timber…

Q) We have a 26 tonne drop side truck on our fleet which is due for its annual test. A pre-MOT check has revealed that the exhaust brake is inoperative. Can we have it removed as the driver never uses it? The service provider has said it is a mandatory device, and a testable item. An inoperative device will be a reason for failure. Would it be a mandatory device on our 26t drop side truck which we only use for transporting timber?

A)  With regard to exhaust brakes, the test criteria are listed under IM58 Additional Braking devices in the Heavy Goods Vehicle Inspection Manual.

Any inoperative device will be a deficiency irrespective of whether it is mandatory or not. 

If the device has been removed and it is mandatory this will be a reason for failure. If the device is not mandatory, the operator should be informed to complete a VTG10 form (notifiable alteration). Where an exhaust brake operating cylinder and lever are completely removed, the housing containing the butterfly may be retained with the butterfly fixed in the open position.

This type of device is mandatory on ADR vehicles and passenger carrying vehicles. If your 26t drop side truck is not an ADR approved vehicle, you can remove the device if you comply with the criteria in IM58.

Testing… testing… 

Q) We are a local authority who have our own in-house workshops but no annual test facility. As all the government test stations in our area have now closed, we are now relying on a local ATF (Authorised Testing Facility) to carry out all our annual testing of our fleet of vehicles.

It is not always easy to take the vehicles to test with a load on, especially the refuse collection vehicles. The RCVs are usually presented for test clean and empty as we have always understood the weight of the body would be enough to produce a satisfactory brake test reading.

A recent tester at the site has said that if we present the vehicles unladen they will be unable to produce a satisfactory brake efficiency reading and will fail. What are the rules governing this?

A) While whenever possible a vehicle should always be presented for test in a laden condition to achieve the most effective and meaningful brake test, there may be occasions when this is not possible.

If this is the case, due to the vehicle design or type of cargo carried (RCVs being a good example), this is one such category of vehicle which can be presented unladen for annual test. To pass the brake test, the vehicle would have to meet the required brake performance criteria or rely on the vehicle’s brakes locking out to obtain a pass. Please see below taken from IM71 in DVSA’s Heavy Goods Vehicle Testers Manual:

If more than half the number of wheels lock, the specified brake effort can be considered to be met. On a motor vehicle where not more than half the wheels lock, where applicable the front wheel allowances must be taken into account.