Poor Man's Electric Over Hydraulic

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Dora~Jean

Active member
I just thought of something that might work for surge-brake trailers with a "Reverse Flow Solenoid" like mine. Sorry, tried to post a picture, couldn't. Here's a link to the device on Tie-Down Engineering: http://www.tiedown.com/pdf/c1034.pdf

I have 4 wheel disc brakes which require either a reverse lockout or reverse flow solenoid in line with the brake lines in order to back the trailer up an incline or even on level ground sometimes. The solenoid is activated when the backup lights come on (preferred hookup). The system has worked great for many years and I'm very satisfied.

The reverse "lockout" type, when activated by the backup lights, closes a valve to prevent hydraulic pressure to the trailer brakes. The reverse "flow" type, when activated, returns the hydraulic fluid through a line back to the master cylinder. This is the type I have. It has a slight advantage in that if you stop the trailer while going downhill (applying surge brake pressure), then put the tow vehicle in reverse, the brake pressure will remain in the trailer lines preventing the trailer from backing up. Or, when backup up a driveway, if you have to move forward for a moment to make a correction, the brakes will lock up the same way. With the "flow" type solenoid, the brakes are fully released.

So here's my idea. Instead of hooking the solenoid to the backup lights, hook it to the brake lights through a relay that activates (energizing the solenoid valve to release) when the brake lights are OFF and deactivates when the brake lights are ON (de-energizing the solenoid valve for normal braking).

The only downsides I can think of is possibly some latency in the brake fluid flow, but shouldn't be much, and having the solenoid energized most of the time -- possibly heating it up causing premature failure (if it fails, the brakes will work correctly, just without the uphill backing feature).

What do you think? I prefer opinions before messing with something that works right (except long, downhill runs) -- and messing with braking systems in general... :shock: [/img]
 
I assume that your idea is to prevent the surge brakes from activating when you are going down long grades?

Why not put in a switch, to activate that solenoid, with a diode to prevent back flow to the back up lights. Seems easier and more fool proof.

I do have a question. My new truck( GMC) has a built in manual break controller--I have a 7 pin round to 5 pin straight adaptor. I suspect that the controller will be actually going directly to the lock out solenoid. Rather than changing the wiring on the truck. Can I manually activate the brake controller to activate the lock out selenoid--especially on long grades or when backing up?
 
On the 7 to 5 adapter, the control wires from the brake controller are not connected to anything. The signal to the lock out solonid will still be coming from the back up light.
 
Bob, yes, long downgrades is what I'm trying to solve. I also thought of adding a switch and diode (and red dash light) to switch it off on long downgrades, but I imagined the situation (rare) of coming to a pile-up and having to quickly swerve or stop. Then I thought of myself trying to find that toggle switch while in this panic mode -- I don't think so...

But still, if I could make the red light BIG enough, maybe it would be in the forefront of my pea brain to flip the switch just BEFORE panicking. Also would want to remember to flip it back when at the bottom of the hill.

Thanks Bob. And looking forward to seeing you again at the Delta get-together.
 
Thanks Matt.
Some 7 pins I have had from stock trucks have not had the back up lights connected to the 5 pin. I have to check this one out with a volt meter and test light.

Let me reframe the question--since I can easily make a 7 to 5 adaptor--would it work using the contoler (again something I can measure) to lock put the brakes on long grades or manually on back up. As I understand the tow haul mode in the new truck, it does increase engine/transmission retard on the down grades. Since I rarely use service brakes on my trucks--I want to let the truck compression slow the trailer as much as possible.

Granted that in an emergency we want to have full breaking power. In this case a (4500 lb. max) 22 behind a truck which weighs 6000 lbs--

Thanks for the thoughts.
 
Bob,

If your truck works like my Chevy/Allison in tow mode it will definitely apply engine braking and even downshift if you touch the brakes in tow mode which is really great for keeping things under control but you will definitely need something to keep the surge brakes off during that time.

I find that on most mountain grades I can hold back the RF which is 9000++ by downshift and engine braking with the occasional touch on the brakes. One more advantage of electric over hydraulic is that I can manually apply a touch on the trailer brakes from the cabin if it is slippery. After all there are 6 BIG disk's back there.

I use the Tekonsha P3 controller which gives really excellent control over the max braking force plus the amount of "boost". You just have to remember to dial the settings back after you unload the boat or you will have a large blues cloud of tire smoke at your first traffic light.
Works wonders on tailgaters :shock:

M
 
I see what you're trying to do Bob. I think the problem would be that the brake controller sends a variable voltage signal. More voltage = more braking power. So I wonder if the lower voltage would be enough to trip the solonoid, or if the low voltage would damage the solonoid?
 
On further reflection, I believe that solenoid is much like an electrical relay. It's either open or closed. I don't think a low voltage from the controller would damage it but I don't think it would cause it to close part way and restrict flow. It would just do nothing until the voltage was sufficient to close it and then it would "snap" shut.

You may be able to find one that is a variable position one, i.e. one that closes proportionally to the voltage applied to it. Isn't that how the electrical braking system works anyway? Or is that just "electric over hydraulic".... :roll:

Charlie
 
The electric over hydraulics I've seen use the 12V charge line from the tow vehicle to provifr the power for the actuator, and the signal from the brake controller to tell the actuator how much brake to apply.

One problem with some of the new brake controllers is that they are "smart". They send out a small signal to verify that the electric brakes are back there. The problem is that with the electric over hydraulic systems this just confuses the controller, as it can't see enough resisitance on the line.

We had one customer add a second controller to his new truck, and a second plug at the back to run the "stupid" controller for his boat trailer brakes.
 
Here is what the volt meter says--the 5th pin is activated 12 volt plus when back up lights are on--not related to the controller--as Matt says. I could put a switch in the back up circuit, with a diode--or just manually lock out the surge brakes with a bolt or pin if necessary. I'll not complicate things.
 
The switch sounds like a better idea Bob. It's not simple when you're going down hill and really NEED the brakes to go back and pull that pin. I doubt if the lovely Marie would volunteer to "ride the tongue", nor would you ask her to, in order to "pull the pin" when needed. :shock:

This is an interesting discussion....

Charlie

BTW, do you folks that have laptops and IPADS have fingerprints on both screens? :oops:
 
Charlie,
Fingerprints are OK it's when you get white-out on the screen that you know you are Irish.

Ooops get the fire hose....

M
 
Sorry to interrupt the other discussion, but Bob, you just gave me another idea that makes the best sense for me anyway.

Install a dash-mounted switch, and light, to activate the brake-relay-solenoid circuit relay I was proposing ONLY when needed, like for long downhill runs and backing up a driveway, etc. When the switch is OFF (brake-relay-solenoid reverse flow circuit deactivated), the brakes work normally, all day long, all the time.

I know this is a bit complicated with 'activated' vs 'deactivated' (reverse thinking needed). But to sum it up, the switch in the ON position would allow the cab brakes to control the trailer reverse-flow solenoid: Cab brakes applied, reverse-flow solenoid inactive (through relay) thus applying trailer brakes; cab brakes off, reverse-flow solenoid active (through relay) now releasing trailer brake fluid pressure and returning to trailer's master cylinder.

Leaving the dash switch ON or OFF still gives you full trailer braking at all times. But ON means solenoid will be activated for long periods for no reason. OFF, everything works normally but with no backup relief valve.

I like it, at least at first blush.
 
What you are proposing is to get rid of the back up light activation of the bypass, and use a switch. I agree. With the Honda Pilot, which did not have a lock out hooked up for the 4 pin connector (did for a 6 pin), I just put the pin in the trailer frame when backing up. The new truck has the lock out in reverse. I'll have to see how it goes on the long down grades. The back up light is redundant and not necessary if you have this switch (and the red light! to remind you) You could even rig a circuit so that if you were going on down grades and hit the service brakes, that it would then turn off the bypass solenoid. (two way switch--lock out or lock out, except when you hit service brakes)--that would be easy to do.

Charlie--some of these grades are quite long--and up to 7% grades. Yes, it could happen that you had to hit the service brakes hard, but I suspect very unusual. I guess the biggest problem I have is that I like to drive at 55 or less down these grades, and occasionally I get behind a truck going slower, and have to use the service brakes to slow until I can pass.

I have "manual" in the 6 speed transmission, so I can select the gear and it will be locked in that gear, using engine breaking power. Somewhat similar to what I have in the RV with the 6 speed Allison, Cummins diesel , and an exhaust brake--except the gas engine does not have an exhaust brake.
 
Well, so much for my 'great idea'! I did manage to measure the solenoid engagement current at 12.5 volts, it is 705 mA, or 0.7 Amps. Which is fine, I'd go with a 5 Amp rated relay to do this circuit, still might, not sure.

However, after thinking about it awhile, I found a serious flaw in the concept. Say you're going on a long, downhill run, you flip the disengagement switch to have the surge brake master cylinder's fluid pressure released (except if you apply the tow vehicle's brakes). The problem is that you now have a compressed, or completely compressed surge brake master cylinder on the trailer, it is useless for further braking in this condition. You'd have to accelerate quickly to pull out the tongue before applying the brakes. Who is going to do THIS just when you get into a situation that you need your brakes???

Big flaw, sorry. The good side is that you'll spare your brake pads/shoes on long, downhill runs. The bad is you'll have no trailer brakes all the way down and then some until the tongue is pulled back out and reset.

There might be some way to use the other type solenoid, the stop valve type that holds and blocks further trailer brake pressure, not sure.

My conclusion, true electric over hydraulic braking systems are still the best and only safest way to do this -- so far...
 
It seems to me that there would still be travel in the surge brakes when you released the solenoid. The hydraulic fluid is non compressible--thus the coupling has moved little if any at all. You would still have the full travel of the cylinder, and braking ability.

All bets are off if you have something other than a simple lock out solenoid, which is what I have.
 
Yes, the lockout solenoid might work in this configuration, just hadn't thought it through yet. I have the "bypass" type solenoid which simply reroutes the fluid back to the master cylinder. This allows you to "pause" while backing up an incline, taking it out of reverse, straightening up the vehicle, then continuing backing without having a locked condition in the trailer brakes.

When I had brake drums, the lockout solenoid worked OK, but with disc brakes, it was nearly impossible to overcome the braking force that is 'locked' into the system when it is taken out of reverse backing uphill. But you can overcome this by either putting an object in front of the trailer tires, moving forward to release the brake pressure, or, install a brake lockout mechanical device for backing up. The latter is what I did for years.

Not sure the lockout solenoid is the answer either though. Because if you have to brake a little going downhill (disengaging the solenoid), then when you release the service brakes (reengaging the solenoid), it will "lock in" the trailer brake pressure and continue to apply the brakes...hmmm.
 
I have never had any problems with the lock out type of solenoid--on 2 C Dory 22, C Dory 25 or Tom Cat 255. The first 22 had drum brakes, the rest had disc brakes. However, I have not backed up any steep inclines (backing down a launching ramp would be different).

I would only use a switch--again--having not critiqued the circuit which would be safe for application of the service brakes.
 
The other problem I see is that if you switch the solonoid after you've begun going downhill, you may trap fluid in the brake lines after the brakes have been partially applied, which maight create more heat problems, not less.
 
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