Reverse Uphill with Disc Surge Brakes

[Horigan]

I just had my drum brakes replaced with disc brakes and just picked the trailer up from the shop today. The forward braking is much better and smoother. Unfortunately, the reverse lockout solenoid doesn't appear to be working and I'll have to take it back. This is with a Titan disc surge coupler with electric lockout. I've confirmed power to the lockout solenoid in reverse and I don't hear or feel any actuation in the solenoid when putting the car in reverse. I also can't back uphill.

The issue got me wondering how the system works when stopping going downhill and going into reverse. I understand the solenoid blocks the master cylinder actuator flow to the brakes, but what about the pressure already in the brakes when you stop going downhill? Does the solenoid have a small cavity that relieves the brake system pressure when the solenoid activates and shuts off the surge actuator flow?

 

[tpenfield]

The reverse lockout is more/less a valve actuated by the vehicle reverse light circuit. If you stop going forward on an incline and then immediately go into reverse to try to back up, the brake system would not have any chance to release itself.

In order to back-up properly, you would need to start from a relatively flat area.

 

[dingbat]

They make two types of solenoids....

A simple in-line blocking solenoid requires you to start from a level, no pressure, position.

The second is a by-pass valve. When actuated, the valve “short circuits” the residual pressure from the trailer back into the master cylinder fluid reservoir. Back up anytime and anywhere you want

Easy to identify which type you have. By -pass valves have a line running back to the fluid reservoir. The others don’t

 

[Horigan]

Thanks dingbat. The bypass version is the one I need as some of my parking situations require starting from an incline.

Now to find one that works with a Titan coupler...

 

[alldodge]

I installed a lighted switch in the truck, (powered by cig lighter wire) so as I get close to where I'm going to backup the switch is flipped. Didn't use the backup light connection

 

[dingbat]

Thanks dingbat. The bypass version is the one I need as some of my parking situations require starting from an incline.

Now to find one that works with a Titan coupler...

The solenoids are generic. Worst comes to worst you need to drill and tap a hole in the coupler for the return line.

Most couplers I’ve seen as of late come come with the hole and a plug installed

 

[Horigan]

Unfortunately, my Titan doesn't have a port in the reservoir to plumb the bypass to. It looks like main actuator manufacturers that offer the bypass lockout solenoid are Demco, Champion, and Tie Down. I'm leaning towards Demco.

I'm frankly surprised the bypass design isn't the baseline for disc brake couplers. Having to start reverse from a level surface is not always feasible. I guess being an aircraft brake engineer has raised my expectations.

AllDodge, the separate switch is a novel idea. I'll have to chew on that.

 

[briangcc]

Some trailers have a spot in the coupler for a pin to lock out the brakes while backing up a hill. Both my Four Winns and my Chap (Eagle) have this provision. Does yours have that as well to avoid modifying your braking system?

 

[Horigan]

My Titan does not have lock pin option. I was able to fashion the equivalent with some wood wedges I made that I wedged into the coupler and held in place with duct tape. This allowed me to back it into my driveway to work on it, but it's not something I'd want to do long term.

Researching this further, all I need to do is drill and tap a hole in my current master cylinder to accept the bypass solenoid return line. Project for this weekend.

 

[Lowlysubaruguy]

Sadly the bypass solenoid alone is not a fix for all applications. My tow rig does not give power in reverse for a brief moment. My driveway is steep and off a down hill approach meaning I have to really work at it to get into reverse long enough with no brakes applied before backing. Its compounded by the fact that my boat and trailer weighs close to 11,000 pounds and has brakes on all six wheels. I may have to run a switched power source for the reverse bypass to work. my trailer came with it new and it does work if given a moment to turn on and if there is no pressure built up in the system first. However if theres pressure it cannot dump it after the fact.

 

[dingbat]

Sadly the bypass solenoid alone is not a fix for all applications. My tow rig does not give power in reverse for a brief moment. My driveway is steep and off a down hill approach meaning I have to really work at it to get into reverse long enough with no brakes applied before backing.

Something is not right....doesn't matter how long after the fact the power is applied. A by-pass valve blocks the port from the master cylinder and opens the trailer to source, effectively short circuiting the braking system when powered.

Perhaps you have a blocking valve or the power is not being maintained while backing

 

[Horigan]

Lowlysubaruguy,

If your solenoid doesn't have a third port with a hose going back to the master cylinder reservoir, you only have a blocking valve that will behave as you're stating. I'm finding most disc surge actuators only come with the blocking valve, not the bypass valve.

 

[Lowlysubaruguy]

No it’s a factory installed return style solenoid built right into the master cylinder not an add on. Im assuming it cant release the pressure that builds before I get the reverse electrical voltage I’m tinkering with adding a push button switch to get it released before I get to my driveway. Mind you this is new equipment and a heavy boat. When theres a certain force reached the valving can’t make the switch. The road into my driveway has just enough downward angle to put quite a bit of force on the brakes as I come to a stop. While I don’t know it for a fact I think my reverse lights must get power via hydraulic switch on the trans not from the shifter its an Allison so the delay is just enough to let the surge brakes build a lot of pressure. If I am on a flat surface and give it a second they work flawless every time. If you have ever tried to unscrew a co2 cylinder without releasing the pressure it’s hard to do but drop that pressure and it’s screws right off I think the same principle here. I don’t want to run a full on or off switch so I can’t forget and leave it off I’ll do a spring loaded momentary switch. I pull out of my steep driveway and head right through my neighbors house or worse the next road ts at a highway then a railroad track and then the Columbia River. Its on my list to fix as soon as the boat starts to leave the driveway again. It won’t be much longer. Ive figured out how to time it right but the real issue is if I get my trailer swinging off and have to pull forward then I have to deal with a hefty angle however it’s long enough I don’t suffer from a trailer that over corrects easily.

 

[dingbat]

No it’s a factory installed return style solenoid built right into the master cylinder not an add on. Im assuming it cant release the pressure that builds before I get the reverse electrical voltage I’m tinkering with adding a push button switch to get it released before I get to my driveway. Mind you this is new equipment and a heavy boat. When theres a certain force reached the valving can’t make the switch. The road into my driveway has just enough downward angle to put quite a bit of force on the brakes as I come to a stop. While I don’t know it for a fact I think my reverse lights must get power via hydraulic switch on the trans not from the shifter its an Allison so the delay is just enough to let the surge brakes build a lot of pressure. If I am on a flat surface and give it a second they work flawless every time. If you have ever tried to unscrew a co2 cylinder without releasing the pressure it’s hard to do but drop that pressure and it’s screws right off I think the same principle here.

Your CO2 analogy really doesn't apply here. To avoid said condition, solenoids operate at right angles to the force. Your effectively shearing the valve off the cylinder, not unscrewing it.

Brake systems are high pressure, low volume systems. Backing solenoids are a simple vent to port configuration. Properly functioning, there is no lag or delay to drain off pressure when actuated. Response times are immediate. Measured in milliseconds not seconds.

Possible scenarios...
1. Your valve isn't opening up all the way from a defect or under voltage condition
2. Your brakes need bleed. Air trapped in the braking system acts like a sponge, causing delays in response
3. The master cylinder isn't vented properly. Are you sure the master cylinder is designed for use with disc brakes? Is the cap vented?

When troubleshooting the problem, don't assume anything.New by definition is unproven......

IMHO: Built in systems sux. Valves can and do go bad on a regular basis. Especially on braking systems prone to water incursion. Instead of changing out a $40 stand alone value, you now have a master cylinder to deal with. No thanks

 

[Lowlysubaruguy]

First thing im going to do is borrow my neighbors truck and see if that is a fix if so its the truck not the trailer I am not sure why Gm has wired this in a manner its got such a long delay for the reverse circuit and I have not even looked to see if its from the trans or if a module has to wake up and power this circuit. Its also quite possible there isnt enough current from whatever is supplying this reverse voltage to power that solenoid when its got hefty brake pressure on it so thats something ill figure out.

Its quite possible the circuit is powered via a module and may not have the current to make that solenoid open under load. I had not thought about that until you mentioned it. If thats the case Ill probably have to wire in a relay that turns on via the reverse lights but gain power from a better source and heavier wire. Which is not that big of a deal.

Curing this is on my lists of things to do as soon as the weather clears a little more. your insights been a lot of help.If I find its in the trailer its under warrantee ill make arrangements to get it either fixed or them to ship me a new solenoid.

It does work just fine if I can alllow the reverse circuit to power up. Which still makes me think its related to the trucks wiring and not the trailer. Thanks your thoughts have given me som directions to go.