Has anybody ever skimmed the face of the drum where the magnets rub.Having to put new magnet in and drum face slightly scored.I see a problem if done the magnet will sit out further on the arm and may cause it to rock around more.Of course too much off and the studs will beva problem
Chassis Alko 12 inch electric brake drum skim
- Thread starter BJM
- Start date
If they are that bad just take them into a shop and get the bumps shaved off, its not a friction surface and the magnet just needs to float, unlike the brake surface .............. The magnet should have plenty of movement as they can wear a fair bit before they start to cause problems and they will wear down more than you could machine off .......... just never heard of anyone machining the surface.... I'd like some discs on mine but they are a pain to set up on a van.
Just be careful sometimes the arm the magnet on, might get slightly bent and the face of the magnet is not fully attaching to the disc. This may be the cause of the scoring??
Checked the magnet arms seem to line up when sitting on the backing plate.Taking the backing plates in to get re powder coated.The trouble is the drum surface obviously gets worn when the magnet is applied,as well as the magnet surface.Must be a lot of pressure on both when braking,especially down hill.I would say dusty conditions would also speed up wear on both surfaces.Amazing they dont wear out quicker
Hi @BJM , I am sure that a man of your experience is familiar with brakes of all types, so the following is not new to you, but might be helpful to others.
When you put your foot on the brake, the electric current in the brake coils are energised and immediately are strongly attracted by magnetic force to the steel brake drum. This pressure does not vary - it stays constant while current is going through the coils. However, the arm attached to the brake coil moves the primary shoe against the inside of brake drum. The rotation of the wheel drags the primary shoe away from the anchor (at the top) and this in turn forces the secondary shoe against the brake drum and also against the other side of the anchor pin at the top. Both shoes are then in contact with the drum and the more speed, the more the brake shoes are dragged/forced against the brake drum as friction/retardation tries to move the brake shoes in the direction of travel. The anchor pin at the top prevents this happening and so the brake shoes are locked/jammed harder and harder against the inside of the brake drum. So a lot of pressure is created (and heat too!) . Dust from the brake shoes unfortunately cannot easily escape and tends to remain within the drum. This causes more wear on both the magnet coils and the drum and reduced braking ability. Water (worse if muddy) and dust from the road can also get into the braking system. That is one of the reasons the covers for brake adjusting slots should always be in place to prevent/reduce dust entry.
Hope this helps those who do not fully understand the concept. Those that do, please ignore my waffling. Sorry @Drover , I could not find your great diagram on caravan brakes on previous posts.
Good description of how they work BIA.The number of people who have trouble with electric brakes never ceases to amaze me.However if every part is in good condition ,fitted correctly ,and adjusted correctly there should not be a problem.! Using non genuine brake shoes,fitting other Alko parts such as springs .magnet etc.Getting the 12 inch backing plates blasted and powder coated for $40.00.Still working out miles cheaper per side than full replacement non genuine backing plates complete.Living near the coast certainly increases the corrosion underneath on ,JTech suspension ,springs ,etc
It would help if they painted the gear properly in the first place..... If you drive thru roadworks some of the stuff they use will corrode even the gal off chassis rails so the beakes would get hammered....the right mix combination add a bit of moisture and its off an running....I just flush my brakes with metho and air, if backing plate was in need a quickspray with galmet and engine black but $40, now thats cool.