Q.
Dear Sirs,
I have a 2 year old trailer and I am having problems getting it through the MOT on the service brake, can you give me any tips what to look for.

A.
Dear Customer,
A lot of customers first blame the electronics because it is something they can’t see or understand but 9 times out of 10 it is a mechanical problem. Firstly don’t present a trailer for MOT if you have not removed the hubs and drums and overhauled the brakes, if you have been carrying light loads the linings could have suffered from glazing, if they have don’t bother to try to file the glaze off just replace the linings. Dry brakes will have problems in passing the MOT, remove the pins and rollers, clean them down and lubricate prior to assembly. If you find the lower linings are thinner that the top linings check the return springs, a stretched spring can allow the bottom shoe to sit on the brake drum. It is important with modern vehicles the foundation brake has to be in top condition, the way to check the ABS or EBS is to turn the ignition and make sure the warning light comes on and then goes off, if it stays on when moving you know you have a problem with the ABS or EBS, also when you turn the ignition on your should hear the truck and the trailer modules clicking.
A tip for when you go into the test station, provided you don’t have a drawbar trailer which has to go in loaded, if it is a semi trailer take it in un-laden, before you go onto the brake rollers turn the engine off and start the engine with your foot on the brake then the EBS system gives full braking without load sensing, this is more important if you have a part load on the trailer.

Regards
Fred the Fitter. 

 

Q.
Dear Sirs,
I have a 3 year old trailer and I am having problems getting it through the MOT on the park brake. I did have a trailer with a mechanical park brake but this one has spring brakes and I thought that would end all my problems.

A.
Dear Customer,
Many thanks for you e mail regarding your parking brake, I hope you find the information below of help.
I think what you are suffering from is tired springs inside each chamber, firstly never try to take the spring section of these brakes apart, the spring is strong enough to take your head off.
Spring brakes work well if you are able to relax the springs when you park the vehicle up but that is very difficult, so many customers tell me that the parking brake on the trailer goes on when they apply the parking brake in the truck, not so. Some truck braking systems put air down the service line with the truck parking brakes but that applies the service brake on the trailer not the parking brake. If there is air in the service line it is not possible to apply the parking brake. While you have the park brake off the springs are compressed and you know as well as me if you keep a spring compressed for 36 months there is no way it will go back to where it was when it was new.
Firstly check to see how the braking system works on the truck, put the park brake on and remove the yellow air line from the trailer to see if there was air in it. If the was no air like the Volvo when you park up at night you could apply the park brake on the truck and then apply the park brake on the trailer and that will relax the springs and help the chambers to keep their power. If your truck does apply the service brake to the trailer, apply the park brake to the truck and then remove the service air line to the trailer (the Yellow line) do not remove the emergency or Red air line, then you can apply the trailer parking brake. Please remember when you have air in the parking section of the chamber the air keeps the brake off and the spring compressed, when air is exhausted the park brake goes on and the spring relaxed.
If your foundation brake is in good order (you have pass figures for your service brake) and your park brake is low all you can do is to replace the chambers.
When ordering a new trailer please remember there are two types of chamber, a normal trailer spring brake chamber is cheap and will not last as long as the piston type chamber, these are more expensive but well worth looking at, they last for years without much trouble.
I hope this is of help, please do not hesitate to write if you have problems.

Regards
Fred the Fitter.