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Old 07-25-2011, 02:53 PM   #1
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Disc brake lag

I have a 2007 31í Classic with disc brakes, and an Actibrake heavy duty electric-hydraulic actuator (that Airstream tells me is not on the recall list). Since I had it new, it has had an approximately 1 second brake lag between application of the TV brakes, and activation of the trailer brakes. Iíve bled the brakes twice, had two different brake controllers (first was a Brakesmart controller which tied right into the hydraulics of my old suburban, the next is a Tekonsha P3 on my Toyota Sequoia) and I've checked that the ground is good from the actuator to the TV.

I was hoping that someone might be able to tell me if this is normal or not? All of the actuators that Iíve researched show an approximately 1 second lag between electrical signal, and full pressure output, so Iíve been thinking this is normal (except for the Al-Ko Sensabrake which boasts a .3 sec lag ). However, what worries me is that healthy shove I get from the trailer when I hit the brakes hard before the trailer kicks in (and then its brakes are great), especially when rounding a corner.

Thanks,

Paul
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Old 07-25-2011, 03:13 PM   #2
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Originally Posted by trvler View Post
I have a 2007 31í Classic with disc brakes, and an Actibrake heavy duty electric-hydraulic actuator (that Airstream tells me is not on the recall list). Since I had it new, it has had an approximately 1 second brake lag between application of the TV brakes, and activation of the trailer brakes. Iíve bled the brakes twice, had two different brake controllers (first was a Brakesmart controller which tied right into the hydraulics of my old suburban, the next is a Tekonsha P3 on my Toyota Sequoia) and I've checked that the ground is good from the actuator to the TV.

I was hoping that someone might be able to tell me if this is normal or not? All of the actuators that Iíve researched show an approximately 1 second lag between electrical signal, and full pressure output, so Iíve been thinking this is normal (except for the Al-Ko Sensabrake which boasts a .3 sec lag ). However, what worries me is that healthy shove I get from the trailer when I hit the brakes hard before the trailer kicks in (and then its brakes are great), especially when rounding a corner.

Thanks,

Paul
Sounds like your controller has a little extra delay.

Andy
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Old 07-25-2011, 03:26 PM   #3
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One trick you can do is apply the MANUAL button on the brake controller first, then apply your foot brake.....I know this won't work in an emergency situation, but all other times it will work....
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Old 07-25-2011, 04:08 PM   #4
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Wow, I thought the Brakesmart was great, but I used it with conventional electric TT brakes. Never noticed any delay at all. Maybe the interaction with disc brakes is different.
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Old 07-25-2011, 05:43 PM   #5
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I have used the BrakeSmart unit for about 8 years now....first with electric and then with Kodiak Disc in 2007.....no problems at all....I am also using the Titan BrakeRite actuator unit....
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Old 07-25-2011, 06:04 PM   #6
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Controller Settings?

I am not using your controller so it could be that none of what I'm about to say applies to your situation. But I do have the ActiBrake system installed at Jackson Center.

Our controller is Hayes Genesis. First, it has a setting for electric over hydraulic brakes. Check to see if you controller has something similar.

Second, the Genesis has an initial brake setting. That is, when I touch the brake pedal lightly, just slowing down a little, this setting tells the ActiBrake unit how hard to apply the brakes. As an example, if I'm driving at highway speed and I very lightly touch the brake pedal I want to feel the trailer brakes engage slightly. I want to know it's getting the signal. I don't want to feel a push.

The third factor is something that Genesis does not allow me to control directly. It's the rapid deceleration factor. This takes into account how agressively the trailer brakes engage during a quick/hard stop.

The fourth factor is controlled by a setting on Genesis to indicate how quickly the brakes go full on. I change the setting to indicate the amount of braking at maximum brake pedal action.

I may not have done a good job describing the settings but I think you get the idea. Check to see if your controller has something similar. My guess is you want the initial setting to react with a lighter pedal touch.

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Old 07-25-2011, 08:11 PM   #7
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Paul,

I own an '07 30' S/O and I personally have done a lot of work on the system. Upfront, I have never driven a different trailer so nothing to compare to.

My observations:
Brake hose routing. Inspect the hose where it connects to the caliper for kinking. Inspect with axle loaded and remember, its only going to go up bit higher and make the line even shorter. My research on Airforums has found several cases of short brake hoses, can cause pinched line, create new problems. It happened to me, I feel it caused a hot brake from being pinched.

The mere flow of fluid out of a bleed screw does not guarntee that all air bubbles have been purged.

Brake hose connection to caliper and brake hose to elbow or tee connection. This connection does not have any IMHO reasonable option to bleed the inboard side caliper to aid in purging air bubbles. If you try to crack it, then tighten it, you risk having the hose twisted.

Reason for concern on above statement. Draw a sketch of the hose routing, comes off of the chassis from an elbow or tee, arcs UP then down into inboard caliper. Inboard caliper cavity-> cross over line at BOTTOM of caliper -> outboard caliper -> and finally up to bleed screw. Now, color into your sketch an air bubble : If I was an air bubble, where would I hide? And what would you have to do to make me leave my natural home that would be at the highest points of the circuit, and then how do you push a bubble down and get it out the other side? For comparison, look at a motorcycle rea wheel swing arm, the line comes off of the frame and follows down the swing arm, now come off of the frame and route the line in to the caliper from BEHIND the rear tire, it has to swing thru a larger arc.

I have a list of experiments and experiences on my AS, from replacing the actuator myself that "tested and passed" only later to find it was drilled in wrong place to buying a Carslile from Andy, no complaints, to installing longer hoses at home, to having both axles replaced (long story) to later creating my own hose (all brake line components) connection that allows me to crack the line where it connects to the inboard caliper to compliment the bleeding process, to having a three person team to bleed them, controller operator, fluid watcher topper offer and bleed screw operator me. I used the inboard line connection first, cracked it, bled fluid, then switch to outboard bleed screw. Concept is to purge the inboard caliper independent of outboard caliper. I also highly recommend using a tube to catch the old fluid rather than spray away, DOT 3 is nasty stuff.

Also, I think we have one other major difference to consider as we work with or assess this system. The master cylinder on our TV (w/o TT) gives us one stroke and creates a displacement of fluid to create pressure to create braking forces, we feel the feedback and can determine no air bubbles or concern that it has air bubbles. Our electric hydraulic system keeps pumping and pumping compresses any air bubble = time delay and eventually we get brake pressure. So all of the factors that I have learned, many here at Airforums, wiring, (feed it a strong clean 12V) correct controller (my 1st controller was not listed for hydraulic brakes) correctly tuning controller and probally a few things I don't know about.

W/O having driven pure electric brakes, I have no comparision, but I can drive my rig (granted still a low mileage rookie) and using my best Scan Identify Predict Decide and Execute (SIPDE for the MSF RSS crowd) feel pretty darn good when I'm hooked up. I also feel the most coordinated braking so far with the Max Brake, I have no plans to alter this setup now, just maintain it.

Brakes are a serious issue, just because this is what I chose to do does not necessarily make it what you should do, just my observations and actions.

Good luck and be carefull.
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Old 07-26-2011, 07:48 AM   #8
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Thanks for all your replies.

Andy, about controller delay - the Brakesmart controller I used with a previous trailer with electric drum brakes had no delay, but plugged into the electric/hydraulic there was a delay just as there is with the Tekonsha P3.

Dwight and Nvestysly- is there not a delay when you hit the trailer brakes with your manual control?

GCinSC2 - I have been thru the hose routing woes already with this airstream - replaced all the hoses and rerouted them a couple of years ago (and posted my dissatisfaction with Airstream engineering that allowed the routing of brake hoses where they could get pinched by the trailer frame!). And then I poured a couple of gallons of brake fluid thru the system to bleed it. Although it may still have air in it somewhere - I'm just trying to figure out whether it is worth my time and effort to keep bleeding the system, or am I reaching the physical limit of this type of braking system?

thanks again,

Paul
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Old 07-26-2011, 08:33 AM   #9
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I believe it is a normal occurrence, although I don't think my delay is more than 1/2 second. I don't believe (but I haven't really researched it) the Actibrake "stores" pressurized brake fluid, like some automotive "Hydroboosts" do. In other words, I believe the Actibrake must receive a signal, fire up the pump to build pressure, and decide how much to apply, based on the input from the controller. This takes a little time.

I use the Hayes Genesis, and have always had a little "lag". I was told by the dealer it is normal.
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Old 07-26-2011, 08:55 AM   #10
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@Paul......to tell you the truth, I have never noticed any delay with the BrakeSmart when I had the electric or now the disc.....I am sure there is some delay just to to the design of the system....but I do know that my BrakeRite unit works so much smoother and seems to activate the brakes quicker than the ActiBrake (version 2) that I had prior.....
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Old 07-26-2011, 01:14 PM   #11
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Quote:
Originally Posted by trvler View Post
Dwight and Nvestysly- is there not a delay when you hit the trailer brakes with your manual control?
I don't recall sensing a lag. I won't have the trailer and TV connected for another week or so - when I do hook them up I'll confirm the presence (or lack of) a delay.

In any event I can't imagine the delay is one second - one Mississippi - is a long time.

I'll let you know what I find.

Lucius
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Old 07-26-2011, 01:34 PM   #12
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Some delay is inevitable. The pump motor has inertia, and the brake pads need to be moved out to push on the rotors; the hoses have a small amount of compliance, etc, and the power input from the motor is not infinite.

I did find that thorough, repeated bleeding of the brakes was essential. This seemed a little surprising, until I thought about the amount of lines, calipers, etc, involved. One tool that made this a lot easier to do by myself was a momentary contact switch temporarily wired in such a way that it would engage the break-away circuit when pressed. I could then engage pump, open bleeder, watch for clear liquid, close bleeder, disengage pump.
I did need to refill the master cylinder between wheels, of course.

If you wish to measure the brake delay, simply engage the trailer brakes when coasting; you'll feel the pressure ramp up in response to your control input. I don't think mine is anywhere near a second, but it is definitely there.

The only way to make this really imperceptible I think would be a system w/ much higher instantaneous power output - something like a heavy duty voice coil setup controlling a vacuum boosted master cylinder. In this case, the voice coil provides very rapid response, and the servo effort is made possible by the stored energy in the vacuum reserve. Of course, thorough bleeding of the brakes would still be essential.

- Bart
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Old 07-26-2011, 04:45 PM   #13
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Sounds like some delay is inevitable, and experienced by others. Maybe my problem is trying to figure out how to estimate the lag time - never thought of "1 mississippi"! Maybe if I get to "1 miss.." I'm under one second, and I don't have to rebleed brakes (thanks Lucius).

Dwight - thanks for the impromtu comparison with Brakerite - I'll think of that if the Actibrake ever needs replacing (hopefully not some time when I really need it!).

Bart - the Al-Ko Sensabrake is an electric/air/hydraulic actuator built in New Zealand using compressed air held in a cylinder to give near-instantaneous pressure to the hydraulic fluid in addition to a pump. Sounds like a great idea (and will apparently allow break-away locking of trailer brakes without a battery), but I gather it is getting not so good reviews in Australia. Don't know if you can get this in North America. Guess I'll have to wait until I tow the trailer to New Zealand!

Paul
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Old 11-06-2011, 01:12 PM   #14
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Is bleeding brakes part of regular maintainance I liked the electric brakes but now I have disc brakes and I have a delay and partial lock after applying and releasing them . Fluid does become contaminated and asorbs moisture . I am talking about automobiles but this should be the same . Can they be bled with a vacuum pump or do they need pressure applies ?
Don
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