How trailer brakes work

[tdonoughue]

@flyin_dutchman asked about how #trailer_brakes worked on another thread. That seemed a topic it's own, so I have started this. Unfortunately right now I have no pics, but I am sure I or others will add later...

A trailer beyond a certain weight capacity is required to have an active braking system. All of our boats (I think) came with hydraulic brakes that are activated by the weight of the trailer pushing against the vehicle when the vehicle slows. Just aft of the coupler there is a piston that compresses, just like your car compresses a piston when you push the brake pedal. Compressing that piston pushes hydraulic fluid down hydraulic lines to pistons at each wheel. The pistons push brake pads against rotors or drums to stop the trailer.

All that works pretty well, except when you try to back up the vehicle. If you try to back up, the piston compresses and activates the brakes on the trailer. For this reason, trailers hook to the car light system through the 4, 5, or 7 pin connector and sense the backup lights coming on. When those lights come on, an electrical valve closes and prevents the hydraulic fluid from going to the brakes, essentially shutting them off while you are backing. When you put it in drive, the lights go off, the valve opens and everything is back to normal.

If you don't have the lights hooked up, you can still back the trailer. However, first you must temporarily deactivate the brakes. The trailers of this type provide a little nickel-size key that fits in the side of the coupler. The key stops the coupler from compressing (thus stopping the piston from compressing and the brakes from working). There are some aftermarket caps that can go on top to do the same thing, as well.

#Brake_fluid should be checked periodically, just like your vehicle's. However, note that brake fluid absorbs water very, very well. And when it absorbs it, it stops working. So do not check in the rain, and if it is humid, check very quickly. The reservoir is under a cap on the top of the trailer neck, right behind the coupler. Pry that off and you will see below the reservoir cap. Unscrew that to see the level, which should be about 3/4 full.

Note that brakes are a closed system. Brake fluid does not get used or evaporate. If your fluid is low, refill it, but then you need to find the leak. You also need to check more frequently and be prepared to refill, because the level will continue to drop.

Ok, what did I miss?

 

[tdonoughue]

Ah, yes. The brake system is called #surge_brakes...

 

[Joshb723]

Are we supposed to check the brake pads or rotors periodically?

 

[tdonoughue]

#Brake_pads, yes. I would say probably 1x year would be sufficient. Unless you put lots of miles on the trailer, you will rarely replace them. #Rotors or #drums, not necessarily. They will let you know they need to be turned or replaced by beginning to pulse the brakes.

I have to check whether I have drums (I think so) or disks. Not sure what everyone has for trailers, so I have written it generically for both. Disks have a rotor in the middle and the piston at the wheel squeezes a #caliper. You will find them on most front wheels of cars. #Drum brakes have a drum and the piston pushes pads inside the drum out against the inside of the drum.

 

[Ronnie]

Nice write up Tim.

 

[Geiger41]

that little nickel sized tool is a pita to get into place. I have a 4 pin in my jeep and a 5 pin on the trailer. I read the trailor manual and a quick way to backup w/o any other connectors is put the blue wire with the brown, turn the vehicle lights on and when you put the vehicle in reverse it releases the brakes. works every time.

 

[tdonoughue]

@geiger41 , this is true. Anything that energizes that backup light wire will work. The only downside to the way you describe is that you don't want to accidentally leave that in place and trailer your boat at night or in the rain... You will have no trailer brakes on the road. So you wouldn't want to make the change permanent on the vehicle or trailer.

 

[maboat]

put the blue wire with the brown, turn the vehicle lights on and when you put the vehicle in reverse it releases the brakes. works every time.

This works as far as disabling the trailer brakes, but it has nothing to do with putting the vehicle in reverse. If you connect the plug this way, and turn on the lights, then the trailer brakes will be disabled whenever the lights are on, regardless of vehicle being forward or reverse.

 

[Sacamano]

Should we use DOT 3 brake fluid when topping off?

 

[Julian]

" For this reason, trailers hook to the car light system through the 4, 5, or 7 pin connector and sense the backup lights coming on."

Trailers with brakes all have 5 or 7 pin connectors (not 4 pin) - the 5th wire is the reverse light connection.

Almost certain that all our trailers have drum brakes.

 

[Boat Crazy]

I am almost positive my trailer 2010 MFI has disk brakes. I would check, but my boat is up the road in locked storage.

 

[Ronnie]

I think the 2010 mfi trailer brakes are disks but they are surge brakes not electric. Here is a link to site which has a short animation on how surge brakes work. Below are pics of my surge brake assembly I had to replace the emergency/breakaway safety cable because it snapped on my last year while I was on the freeway (different story). The brake fluid reservoir is a lot smaller than I thought it would be. I ended up buying a c-clip tool that makes removing and installing the three on the unit easy. The blue wire on the harness is attached the solenoid on the back of the assembly and it is supposed to lock out the reverse automatically when it is hooked up correctly. In my case it was not so I've been using D keys to back up my driveway since I got the boat. The button on the bottom just pushes the cylinder out less than a quarter inch, enough to keep it from sticking.

http://www.pacifictrailers.com/UFP-A-60-Brake-Actuator-Replacement-Parts-for-Disc-Drum-brakes/

 

[maboat]

Almost certain that all our trailers have drum brakes.

I'm 100% certain that MY trailer has DISC brakes. And I'm almost certain that all the Yamaha-provided trailers came with disc brakes too.

 

[Julian]

Awesome....are those with disc brakes also Shorelander trailers not MFI? Perhaps I can add this tidbit to the "Differences" spreadsheet!

 

[maboat]

I have an MFI trailer (from Yamaha) and it came with UFP disc brakes.

 

[Julian]

Cool......I'll start another thread with this question....thanks!

 

[tdonoughue]

Should we use DOT 3 brake fluid when topping off?

Yes.

Note that DOT 3 so less good than DOT 4 is less good than DOT 5, but they don't mix! He difference is in their boiling point (boiling hydraulic fluid is bad), if I recall correctly. But do note the other correct post above that the reservoir is small. One little can will set you for a top off. But it does not keep, so top it up with the DOT 3, wait a week or two to make sure you are not topping up more (leak!) and toss the can.

 

[txav8r]

The book on the old and new 210/212/230/240/242 all use the same UFP surge brake actuator with minor exception. The hitch lock is the only major difference between them but the surge brake unit is the same. And no, it isn't electric on any of them, they use the reverse light signal from the tow vehicle as @tdonoughue mentioned, to block the solenoid to prevent the brakes from activating when backing up, and that is the only "electrical" connection. All of these same models use the UFP DB35 disc brake unit as well. So that is the same on MFI or Shorelandr trailers. @Julian , I didn't understand your question above, but I think this answer covers it as they all are the same. The model number of the surge brake actuator on the newer Shorelandr is the A-60, and the MFI is the A-75, but the guts of the actuator is the same on both, with exception of the hitch latch and the way the safety cable hooks in and routes...here they all are together...

You can also go to the UFP website and look at your equipment and download service manual and other service guides. This is the actuators page link...
http://www.ufpnet.com/Actuators/tabid/54/Default.aspx From their index, you can download the disc brake manual, the axles, the bearing buddies, the springs...all of it, they are the manufacturer of these products.

Also, I had an A-160 manual in my Shorelandr paperwork, but I have the A-60 unit on my trailer. Could it be that the upgraded A-160, that does away with the requirement to disassemble the unit to reinstall the C-clip break away cable clips if the unit is activated, is installed on some of our trailers...this is what it looks like...

The safety actuation cable hooks to the chain on top of this unit. So in the event it is tripped, you just replace the safety cable externally and reset the safety unit actuator lever without disassembly.

 

[txav8r]

Also, the book says Dot 3 or Dot 4...not Dot 5. What comes from the factory isn't stated, but it does say not to mix, but you can use Dot 3 or Dot 4. @tdonoughue , I knew that the fluid could go bad, but I didn't think it would go bad if you kept it sealed. I have used a container for several years without ill effect, but I kept it sealed and didn't leave it open long when using it. I know that brake fluid absorbs moisture fast! I may have to replace mine now dang it! It is also a good idea to completely replace all brake fluid ever few years on these trailers.

 

[Julian]

All of these same models use the UFP DB35 disc brake unit as well. So that is the same on MFI or Shorelandr trailers.
.

This is not the case as I have an A75 actuator with drum brakes on my trailer. The other thread I created was to determine which models have drum vs disc brakes. My guess they switched to disc in 2006 (based on answers thus far). But it is entirely possible that MFI could have switched in the middle of production year....

Thread for what type of brakes your trailer has:
https://jetboaters.net/threads/what-kind-of-brakes-does-your-stock-trailer-have.1916/