American RV Motorhomes that have hydro boost brake servos, frequently produce low-efficiency brakes. This particularly applies to Workhorse and some Roadmaster chassis.
In America, the process of refacing the disc on a brake pad replacement is common practice, although in this country it usually depends on the price. If the brake discs are re-faced then the brake effort is improved dramatically.
Brake Effort Calculation
An American RV motorhome requires a class 4 MOT test once it is 3 years old. In order to pass the test, it must have a minimum of 50% effort recorded during the brake roller test. This is calculated by taking the maximum gross weight that the vehicle can carry, usually, this is found on the spec plate often located next to the driver’s seat. The vehicles brake effort calculation needs to add up to 50% of the gross vehicle weight.
While the vehicle is on the brake tester the front wheels are rotated by the brake tester rollers, but when the Motorhomes brakes are applied they slow the rollers down. When both wheels are rotated and the brakes are applied there should be no more than a 25% difference between the two sides, any more than that then the vehicle will fail its test. If both brakes lock then you have achieved 25% of the brake effort target.
When the gross weight of the motorhome is 22,000 lbs (approx 9800kg) with the front brakes locking, then in order to pass the test the rear brakes need to lock (stop the brake rollers) or achieve 4900 kg brake force collectively. This is the lowest requirement needed to pass the MOT test.
A few things need to be taken into consideration, one very important thing is how much force you need to apply to the brake pedal to achieve these minimum MOT brake forces. If you need to apply that much force you are in danger of breaking the back of the driver’s seat, and the brakes on the road would be dangerous but would pass the test.
When LAS technicians replace the brake pads they use good quality pads and also machine the brake disc. This will then give the vehicle the most efficient brakes possible, as well as in some cases with the use of a particular brand of the brake material, better brakes than a new vehicle. The driver will then need to use less force on the brake pedal to slow the vehicle down, making for a more confident drive.
The problem with American RV Motorhomes is that they spend a lot of time standing, the brake discs then get much corroded and pitted, which does not help the brake problem in any way, in fact, it causes the problem to get worse.
At LAS we reface the brake discs on the vehicle so as not to spend time removing the disc and then replacing the hub seals. With the disc still on the vehicle, it can also alleviate what is called brake disc run out.