HGV/PCV Annual MOT test question
Discussion
When subjected to the annual test approximately 22% of PCVs and 38% of HGV's fail the test first time.
For artic trailers the failure rate is even worse with approximately 1 in 2 failing.
Yet the maintenance outfits of some operators manage to get a 97% pass rate which for these outfits is not a flash in the pan.
Do you know why?
OK the easy answer to this is because of good maintenance and attention to detail.
However there is one overwhelming reason why these garages avoid the high failure rate.
Do you know what it is, and how they manage to get such a good pass rate?
Have a guess.....
For artic trailers the failure rate is even worse with approximately 1 in 2 failing.
Yet the maintenance outfits of some operators manage to get a 97% pass rate which for these outfits is not a flash in the pan.
Do you know why?
OK the easy answer to this is because of good maintenance and attention to detail.
However there is one overwhelming reason why these garages avoid the high failure rate.
Do you know what it is, and how they manage to get such a good pass rate?
Have a guess.....
OK obviously folks either need some hints or aren't interested, fair enough whichever.
The main reason for failure is ineffective brakes.
Even firms who do check and service brakes including replacing friction material still have the high failure rate. Most of these vehicle use drum brakes though discs are gaining market share.
The firms which have the 97% record do what is known as brake profiling.
This means that when the brakes are overhauled a complete new kit of parts is fitted shoes, springs, clips and drum. The new drum is specifically machined to a good profile fit to the shoe friction material thus maximising contact area of the friction material.
Without this technique the area of friction material/drum contact is not enough (can be as low as 10%) to get effective brakes and insufficent time to bed in.
Fitting new brakes a month before the test and sending the vehicle out so the brakes can bed in means vehicles with inefficient brakes are on the road. Making a fitter drive up and down the yard avoids this but is an ineffective use of man/machine time. In both cases high wear rate of friction material and drum until things are bedded in.
Using the matched component route a) means the vehicle passes the test first time, b) actually reduces costs due to reducing wear of friction material and less crazing / distortion of drums which often have to be scrapped anyway.
As for discs a modified technique gets similar results.
We don't see the same effect on cars so much as the braking capability of light vehicles is so much better, but its a technique to consider if you want to have maximum performance out of your stoppers on any vehicle straight out of the box.
OK I'll get my coat now.
The main reason for failure is ineffective brakes.
Even firms who do check and service brakes including replacing friction material still have the high failure rate. Most of these vehicle use drum brakes though discs are gaining market share.
The firms which have the 97% record do what is known as brake profiling.
This means that when the brakes are overhauled a complete new kit of parts is fitted shoes, springs, clips and drum. The new drum is specifically machined to a good profile fit to the shoe friction material thus maximising contact area of the friction material.
Without this technique the area of friction material/drum contact is not enough (can be as low as 10%) to get effective brakes and insufficent time to bed in.
Fitting new brakes a month before the test and sending the vehicle out so the brakes can bed in means vehicles with inefficient brakes are on the road. Making a fitter drive up and down the yard avoids this but is an ineffective use of man/machine time. In both cases high wear rate of friction material and drum until things are bedded in.
Using the matched component route a) means the vehicle passes the test first time, b) actually reduces costs due to reducing wear of friction material and less crazing / distortion of drums which often have to be scrapped anyway.
As for discs a modified technique gets similar results.
We don't see the same effect on cars so much as the braking capability of light vehicles is so much better, but its a technique to consider if you want to have maximum performance out of your stoppers on any vehicle straight out of the box.
OK I'll get my coat now.
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