electric brakes

[va_camper]

I recently bought a used tt with tandem axles and noticed that the brakes didn't seem to be working as well as they should. I checked the voltage (12vdc), and current at 100% output(about2.8amps) at each wheel. All that appeared normal but braking still seemed lacking quite a bit . It won't even come close to locking the wheels at 20mph test. My question is do the brake magnets(coils) actually drag on the brake drums to move the brake lever that in turn spreads the brake shoes? The reason for asking is I'm wondering if the levers are actually moving correctly if the magnet levers have been bent somehow and they are keeping the magnets from actually contacting the brake hub . Plus I would like to know more about how my brakes work for future reference. Thanks!

[Bigbird65]

As long as we are talking about brakes here is my story. Our TT is only about 3 months old. I have a Tekonsha P3 controller. When we first got the TT the brakes were pretty insensitive. The brakes got more sensitive as miles piled up and I would have to keep reducing the voltage on the controller. I'm now down to about 3.5. If I move it up above 4 the brakes really get grabby as I come to a stop. At 3.5 it is not too bad. TT now has about 1000 miles on it and I think the next thing I'll do is pull the drums and have a look see. I appreciate any comments that you have.

[aluminum_flyer]

I was going to add... but someone already mentioned it. Grease contamination to start, then magnet condition / shoe condition, etc.

[Aluminum_Siding]

You should pull off the drums to inspect for anything goofy bad magnets etc. It's an eazy job if your fairly handy. I recently swaped out my drums, shoes, magnets and bearings on my old TT.

Here is a great vid on adjusting breaks.

You Tube Travel Trailer Break Adjust

[ChooChooMan74]

Gdetrailer wrote:

va camper wrote:
I recently bought a used tt with tandem axles and noticed that the brakes didn't seem to be working as well as they should. I checked the voltage (12vdc), and current at 100% output(about2.8amps) at each wheel. All that appeared normal but braking still seemed lacking quite a bit . It won't even come close to locking the wheels at 20mph test. My question is do the brake magnets(coils) actually drag on the brake drums to move the brake lever that in turn spreads the brake shoes? The reason for asking is I'm wondering if the levers are actually moving correctly if the magnet levers have been bent somehow and they are keeping the magnets from actually contacting the brake hub . Plus I would like to know more about how my brakes work for future reference. Thanks!

2.8A per magnet is NOT 100%.

3.0A per magnet IS 100%.

You are only getting 93% braking due to voltage loss in the wiring and or corroded splices.

However you should have enough braking to feel it working when you use the manual override.

Where do you find how many amps a magnet is suppose to be pulling? Is it on the magnet itself? And how did you come up with 93% voltage drop? He said he had 12 volts, and I didnt see where he tested the voltage at the controller vs the voltage at the magnets to see what, if any, voltage drop he was getting.

[va_camper]

Thanks for the info everybody . I'll know what to look for now . It'll make my job a lot easier!

[Lynnmor]

DieselX wrote:
I would pull the drums and rule out grease contamination from a blown grease seal, happens all the time.

That right there is your starting point.

[DieselX]

I would pull the drums and rule out grease contamination from a blown grease seal, happens all the time.

[Old-Biscuit]

Manually adjust your brakes........

Jack one wheel at a time off ground
Remove plug in brake slot....inside/lower area of drum
Using a wide blade flat screw driver turn star wheel to tighten brake shoes while turning tire until tight
Then backoff on star wheel until tire rotates 3/4-1 turn freely with slight drag noise of brake shoes

When energized magnet 'sticks' to face of drum and as wheel rotates the magnet travel engages lever which forces brake shoes outward to contact drum.
Magnet/lever only has so much travel and if brakes shoes are not adjusted they can not fully engage drum.

Should adjust yearly/12,000 miles.

[Gdetrailer]

va camper wrote:
I recently bought a used tt with tandem axles and noticed that the brakes didn't seem to be working as well as they should. I checked the voltage (12vdc), and current at 100% output(about2.8amps) at each wheel. All that appeared normal but braking still seemed lacking quite a bit . It won't even come close to locking the wheels at 20mph test. My question is do the brake magnets(coils) actually drag on the brake drums to move the brake lever that in turn spreads the brake shoes? The reason for asking is I'm wondering if the levers are actually moving correctly if the magnet levers have been bent somehow and they are keeping the magnets from actually contacting the brake hub . Plus I would like to know more about how my brakes work for future reference. Thanks!

2.8A per magnet is NOT 100%.

3.0A per magnet IS 100%.

You are only getting 93% braking due to voltage loss in the wiring and or corroded splices.

However you should have enough braking to feel it working when you use the manual override.

[rbpru]

I had a clicking sound in one of my brakes that I could hear when driving slow or parking. When I got home I put a hydraulic jack under the frame and lifted each wheel off the ground.

I spun the wheel and had my wife squeeze the brake actuator; sure enough one of them made a clunking noise compared to the others. They all stopped the spinning tire. My next move is to pull the hub and find out why the noise.

[naturist]

I don't think you want to be able to lock the wheels up on dry pavement. In a panic stop (tree jumps out in front of you, for example), you want the trailer to stay straight behind you, not slew around sideways because it is skidding. If you are gonna hit something, anything, you always want to hit it front first, never sideways. Injury protection from the side is poor compared to from the front.

[Ron3rd]

You're correct in how the brakes work; the magnets engage the face of the drum and move a lever. You need to take it all apart to see what's going on. Could be worn magnets, shoes, shoes out of adjustment, etc. Good time to repack the bearings too.

BTW, you probably will not be able to lock the brakes up at 20 mph so just make sure the brakes are providing good stopping power.

[opnspaces]

Yes the magnets contact the face of the drum (where the wheel is sitting). The magnets get dragged on the drum which forces the shoes out to contact the drums.

You may not be able to get the wheels to lock up, as I believe even Dexter says they may not depending on load. But have you adjusted the brakes up to make sure there is not too much clearance?

[ChooChooMan74]

http://www.hitchweb.com/blog/post/2013/01/07/how-electric-brakes-work

Yes they do drag on the drum. There could be a few things. Everything is frozen, shoes out of adjustment, or bad magnets (although you seem to have tested that)