UFP discs: locking brake on reverse

[JeffJuneau]

Hi, After looking through the Mac archives on trailers with disc brakes I didn't find an explanation for my most recent issue with my UFP disc brakes and hydraulic brake actuator. I have UFP Model A-60 actuator, and Model DB35 disc brakes on my Mac trailer. I haven't experienced this reverse braking problem in the previous two years of owning my 2009 aluminum Macgregor trailer. When I back up the trailer, the driver side brake applies braking pressure. It takes some force to overcome that pressure. I noticed it this winter/spring while I had the trailer blocked up to remove weight from the axle. Periodically I would spin the wheels to make sure they were staying free. While the pads on the calipers rub on the rotor going forward, the driver side would lock up partway when I tried to spin the wheel backward. This also showed up when I recently parked the trailer. When going slightly uphill in reverse or on soft ground, the driver side was applying pressure.
I bled the brakes, and that seemed to help a bit, but it still partially locks the driver side trailer brake when driving backward. My trailer light connector was plugged in during this procedure, though I am not sure if that makes any difference. I think the surge brake system is all hydraulic on my vehicle. I also released the push rod release a couple of times to see if that would help. I also inserted the key that is supposed to help keep the actuator from fully closing. That helps some, but does not fully stop the driver side from applying some brake pressure. The brakeaway cable has not been triggered and the clip is in place. Not sure what else to try. Like I noted, this did not happen in the previous two years.
Thanks in advance for any suggestions of things to try.

[JeffJuneau]

A correction, one additional piece of information, and an apology:
I incorrectly assumed in my previous post that the UFP brake actuator only operated mechanically, from hydraulic pressure during braking. After cutting open my wiring lead to the trailer plug, I see another blue wire going from the bundle of trailer lines into the end of the surge break assembly. After a little more searching, I see that part of my issue is discussed in a 2017 mac post. Apologies for not tracking that one down. The blue wire goes to a solenoid in the brake actuator that bypasses the surge brake lock out when backing up. The problem is that my blue wire is not connected to any of the 4 leads from my plugin to the trailer, and just sits disconnected in the plastic housing that covers the trailer wires . My 26M came used with only a 4-pin trailer plug. (1) green R blinker and brake, (2) brown L blinker and brake, (3) running lights, and (4) ground. Perhaps the solenoid failed and this was the previous owners temporary fix. I am not sure what to do at this point, but I am a Mac out-of-water for this year so far, until I get this fixed. Also, here in Juneau, I am unable to find a mechanic who is willing to even work on a boat trailer. So, I am stuck with my rather meager mechanical skills, and this forum has helped me out of a black hole before. Thanks for any ideas. Jeff

[Jimmyt]

Jeff,
Your trailer should have a 5-pin connector. I believe that solenoid takes the reverse light signal to valve off the brakes on the trailer when backing. You don't mention your tow-beast, but my Silverado has the circular trailer interface. I bought an adapter that converts to 5-pin.

Suggest you get a 5-pin pigtail and get the solenoid working again.

You should be able to defeat the brakes mechanically, though. Maybe post a pic of your brake/coupling assembly showing how you tried to mechanically defeat reverse braking.

Your post puzzled me. You seemed to say that you could spin the trailer tire forward (assumed on a jack, or stands, and the pads would drag. However, when you spun the tire backward, the pads locked. I couldn't make heads or tails of that, so I didn't have a decent reply. Disc brakes, in good condition, should spin in either direction equally, with some slight pad drag. You may have bearing or brake issues if yours spin forward, but not backward when blocked up. I would remove the wheel and take off the caliper and try to determine what is going on. Spin the hub without the caliper in both directions to check the bearings.

Verify that your bearing nut has a cotter pin in it. Just on the off-chance...

If I don't have the mechanical defeat in, or the reverse wire hooked up, I can't move my trailer up any incline in reverse.

[Russ]

My understanding is when backing (or braking) the tongue moves forward depressing the brakes. The 5th wire (backup lights) is supposed to bypass this functionality with a solenoid. Many wiring harnesses (like mine) do not have a 5th wire so using that "key" is the only way to prevent this.

I think this is all that you have described.

My thoughts are that your problems are not from the brake actuator, but rather something in the disc caliper. That's where my input ends. I don't understand anything beyond that.

[JeffJuneau]

Thanks so much for responding JimmyT and Russ. Your post helped to clear up some things for me on the operation of the trailer surge brakes and what to check next. To answer some of your questions:
Tow Beast (not much of a beast): My tow vehicle is an older Chevy Trailblazer, with 4 hi/ low. I only tow my mac for two miles on flat roads to the Suzuki outboard service and less than 3 miles to the Auke Bay Harbor. From there I have access to all of the inside passage, so I don't need anything more than it's 4,800 lb capacity.
Connector: JimmyT, I have what I assume to be the same Chevy round 7-pin connector on my SUV that you do. Here is an image of how I use the mechanical defeat device to prevent reverse braking. I retain it with bungees so it doesn't fall out when backing up an incline. Like I noted, it helps, but I still get some resistance from the driver side disc brake of the trailer.
Reverse resistance on driver brake & bearings: This problem only occurs only in the drivers side. The defeat device seems to work 100% on the passenger side. I am pretty sure that my bearings are good on both sides. There is no play in the wheels. I use bearing buddies religiously. They both spin forward with just slight rubbing on the caliper pads as I would expect, but when I hand spin the drivers side wheel backward, it goes about half a turn before increasing resistance quite a bit. I can still turn it backwards with a lever in the openings on the wheel.
Trailer stands: For winter, I block the trailer with wood blocks at 6 points. One in front of and behind axle on each side and the front and rear bottom of transom. Then I can freely spin the wheels all winter, and work on it in a secure position.
Solenoid: Also, I just hooked up my motorcycle 12 volt battery positive terminal to the lead going to the solenoid, and grounded the battery on the grounding screw on the trailer hitch right where everything else is grounded. Heard and felt no response from the solenoid. Maybe it is not working correctly, or maybe I don't have it grounded correctly. Do I need to ground to somewhere else on the solenoid? I is hard to see anything up there now. Should I assume that I have to install a new solenoid with this test?
New Connector: I looked at the alternatives of connecting a flat 5-pin flat pig tail to the trailer lines, but then I have to use an adapter from the 7pin round connector on the tow vehicle to the 5pin flat for the trailer. Or I could connect the trailer wires directly to a round 7-pin male connector. Just the appropriate 5 of 7 pins of course. This is the connector I just bought to do that. Is this an acceptable solution?
Caliper inspection: Yes, removing the wheel and inspecting the whole caliper sounds important. When I get the boat in the water, that is on my list.
Thanks again for your help, Jeff

[Jimmyt]

This is the adapter I have (there are plenty of places to get it other than the jewelry store, but the price isn't bad).

https://www.westmarine.com/buy/west-mar ... LcQAvD_BwE

Alternatively, your idea would be fine also. Just put a 7 pin connector on the trailer. You just have to figure out the pinout.

Let me tell you what I'm thinking on your one wheel braking. With the brake defeat in place, you're getting resistance out of one brake only. The symptom can be duplicated on blocks,rotating the wheel by hand - totally eliminating any possibility that the brakes are being activated. This leads me to think that the bearing nut may have been overtightened when installed, and may be turning enough to cause jamming in the bearings when you rotate the hub backwards. Even if there is a cotter pin in the nut, it can turn slightly. Also, you need to check to make sure the washer is installed between the nut and outer bearing AND that the washer has a key to prevent it from turning.

If that checks out, I'd have to pull the caliper and try to figure it out (possible rotor or pad damage?), but it makes no sense that it would grab in one direction and not the other - if you have disc brakes. They are not directional. Not saying it's not possible, just saying I haven't seen it before. And... since I've had grease under my fingernails since I was in diapers, I've seen some brake issues. But, I'm keenly interested in seeing how this shakes out. I try to learn something new every day.

[Russ]

I lost that reverse lockout "key" a long time ago. I would stick a big washer or nut in that space and tape it in place.
Its purpose is to physically prevent the travel of the brake "plunger".

I have plugged into a 5 pin connector and never heard that solenoid make a noise when in reverse. I have no idea how it even works.

I would focus on the brake caliper on the driver side. Maybe the calipers are not opening up. Or the brake pads are warped or some such thing.

It sounds like you don't trailer very far and maybe, like with other things, lack of use can cause problems. Hopefully, someone who knows more about brake systems can chime in.

[kenfyoozed]

I keep one of these in place on my pontoon trailer. My tuck is big enough to not need the help in braking

https://www.amazon.com/Noa-Store-Compat ... s9dHJ1ZQ==

[Russ]

I keep one of these in place on my pontoon trailer. My tuck is big enough to not need the help in braking

https://www.amazon.com/Noa-Store-Compat ... s9dHJ1ZQ==

Nice. But not $27 nice. I'll keep using my washer and tape when/if I need it. And I ONLY need it when backing up on a hill. Heck. I bet if I added a magnet to my washer I could eliminate the tape holding it in place.

The Amazon link DOES have a great video demonstrating how the key prevents the travel of the surge.

[Be Free]

I agree with Jimmy that the problem is not in the brake lockout since you can duplicate the problem by turning the wheel in reverse. I'm going to go out on a limb here and guess that you have a damaged wheel bearing.

I've seen drum brakes lock up in reverse when the emergency brake mechanism is broken but I can't think of any way a disc brake could fail in a similar manner. If the brakes are not what's keeping it from moving by only other suspect is the bearing. I think it's time to take it apart.

[JeffJuneau]

Sure appreciate your collective insight regarding my driver-side backup resistance problem on my Mac trailer. Thanks to your advice, I will be taking apart the hub and removing the calipers for inspection after I put the Mac in the water. I hooked up the 7-pin round connector that matches my Trailblazer, and it connected up all 5-contacts much more cleanly than going through an adapter to a 5-pin flat pig tail. I played around with it a bit, and it seems to back up easier than before. Maybe my imagination. The solenoid brake defeat switch goes to the middle pole, and I was able to confirm that the wire to the solenoid is getting 12 volts when the SUV is in reverse. Can't verify much more till I test it without the boat on the trailer. The Pacific Trailer supply, says that the old solenoid is self grounded, and the new ones have a dedicated ground wire. Also, it says that the solenoid makes an audible click when the valve opens. Apparently, when the valve opens it allows for brake fluid to go from the master cylinder to the to the reservoir, releasing pressure on the brake. I am just regurgitating what is in the item description, because this has all been a slow learning curve for me. I've lost count of how many times I've been helped by the knowledgeable folks in this group. Indebted again, Jeff