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Old 02-20-2023, 05:54 PM   #21
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Originally Posted by thewarden View Post
It is a brand-new unit. The first thing I would do is take it back to the dealer rather than trying to sort this out yourself.
I be a bit wary of taking it anywhere without checking ALL the axle mount bolts.

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Old 02-20-2023, 06:13 PM   #22
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Dual axles place considerable strain onto the tires, especially when backing/turning.
Sure there's tire scrub when turning sharply, but I don't see how there can be any more strain when backing.
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Old 02-20-2023, 08:26 PM   #23
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Thanks for all the suggestions, it gave me things to look at and think about.

As for the too tight or jackknifed turn, the diagram I drew was pretty accurate as to the angle of the trailer centerline compared to the truck centerline. I do an S turn, but the ‘far end’ of the turn before I start backing is pretty shallow so the truck and trailer are not in line, but not all too far out of line with each other, I am just trying to start the beginning of the turn to get the back end towards the driveway. If I were to guess, I would estimate the angle to be 5-10 degrees, closer to 5. One thing I failed to mention is I have a cap on the truck so seeing the front of the trailer is a bit difficult because the cap blocks the view.

As for loose bolts and witnesses marks, I have turned my share of bolts, but consider myself a ways from being an expert on mechanical things (I am much better with electrical and electronic stuff). I pulled out the creeper and spent some time looking around, I saw nothing which appeared loose, nor anything that looked like it had been shifting or sliding from where it seems to belong. I did not check the torque on the axle mounts because I do not know what the spec is, but is was pretty clear they are tight, not sliding and an extra tug with a wrench does not move them.

The one thing I saw that seemed a little off was the driver front mount which connect the shocks to the torsion axle connecting arm has a bit of a warp in it, see pictures below, while the other ones do not appear to. I am thinking this might be evidence that something torqued, or may be totally inconsequential.

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Old 02-20-2023, 08:28 PM   #24
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Humm I somehow put the pictures in twice
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Old 02-20-2023, 08:41 PM   #25
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Oh, I forgot about the trailer brakes being locked. Yes I can see if one of the trailer brakes got locked this could occur, especially if there was something loose inside. As for the gain for the brakes, once the whatever makes the jarring sound and the tire goes back to the pavement, the remaining backing goes smoothly without any adjustments to the trailer brake controller. This being our first trailer, we had DP motorhomes prior, there is a good amount of brake usage getting the trailer into it’s spot.

This only seems to happen the first time backing after driving a while.
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Old 02-21-2023, 05:15 AM   #26
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This is just a guess but I think the front wheel’s brakes are binding when backing up. This is causing the front axle to be pulled down to its fully extended position - the arm of the front axle being moved from horizontal to more vertical. This action pushes the trailer up and the trailer is pulling the rear axle up with it and lifting the tire. Pulling ahead releases the bind.

Possibly a broken spring inside the drum.
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Old 02-21-2023, 05:33 AM   #27
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I know every brake system is different so. I can't believe with a new trailer your brake gain is at 5 ? My 10 year old FC25 is only now at 4.
5 on my setup would be locking tires on flat ground. Have you tried just turning the gain down to 0 and backing in? At that slow of a speed I would hope your TV can control the trailer without aid from the brakes. You may be riding the brakes and if the gain is to high the unload wheel on the inside would definitely be locking up and pushing the axle around. I know everyone is guessing, but thinking simple is usually the path, as a major problem doesn't just come and go and is usually obvious


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Old 02-21-2023, 06:37 AM   #28
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I know every brake system is different so. I can't believe with a new trailer your brake gain is at 5 ? My 10 year old FC25 is only now at 4.
5 on my setup would be locking tires on flat ground. Have you tried just turning the gain down to 0 and backing in?
Joe D

On a new set of brakes I have had to turn up the gain until the brakes were properly seated and adjusted. This has taken several hundred miles until the brakes really would feel like they were working properly. Then the brake controller could be dialed down.
The next time you perform this maneuver pull out the umbilical cord to see what happens. Also jack up the trailer and start spinning the wheels. Listen for metal on metal or grinding sounds.
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Old 02-21-2023, 06:44 AM   #29
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Originally Posted by AldeanFan View Post
This is just a guess but I think the front wheel’s brakes are binding when backing up. This is causing the front axle to be pulled down to its fully extended position - the arm of the front axle being moved from horizontal to more vertical. This action pushes the trailer up and the trailer is pulling the rear axle up with it and lifting the tire. Pulling ahead releases the bind.

Possibly a broken spring inside the drum.
I had this situation with my boat trailer. It had surge brakes on it, not electric. When I apply TV brakes the weight of the boat and trailer cause the trailer to surge forward and that surge applies pressure to the trailer brakes.

When I first bought the boat, I put the TV in reverse and the brakes on the trailer locked up and lowered the front of the trailer. There was supposed to be a wire that should be connected to my brake lights so when I was in reverse the trailer brakes would be de-activated. Once I had this installed , no more problem.

All of this to say, with your electric brakes, disconnect your umbilical cord when backing up. This way you should have no brakes on your RV. If you still have the issue you know it’s not brake relates and vice- versa.
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Old 02-21-2023, 06:47 AM   #30
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A very simple and quick way to see if the brakes are not set properly is to simply unplug the trailer before backing in next time. Of course this will only check the brake operation, not a loose or damaged brake part, but it will check off one box in the process of elimination.
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Old 02-21-2023, 07:34 AM   #31
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The trailer brake controller has adjustments for gain and for "boost" it is called on my controller. Backing there should not be any proportional braking from the gain so the boost that initiates the braking when the brake lights come on must be locking up the brakes. So too much setting there or a mechanical problem in the brakes. I have never seen a wheel lift or felt my trailer lock the brakes when backing. So I would check the way the brake controller is set. And the brakes. If I dial in too much "boost" my brake will sometimes lock a wheel going forward at low speed.
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Old 02-21-2023, 08:47 AM   #32
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On the topic of brake controllers, perhaps the following will help explain the operation a bit better.

The 'gain' setting determines the maximum amount of brake force that is ultimately applied.

The 'boost' setting determines how quickly the trailer brake controller ramps the braking force from the minimum setting to the maximum setting.

The 3rd variable is out of your direct control, and that is the impact of the brake controllers built in accelerometer.

Most proportional brake controllers start by applying a fixed percentage of the maximum braking force (say... 15%). Braking force ramps at a fixed rate as a function of time to a maximum value determined either by the gain setting (if deceleration is high) or to an intermediate maximum force determined by the level of deceleration (if deceleration is low or moderate).

The boost function only serves to increase the ramp rate of braking force as a function of time. It does not change the maximum braking force that is applied (that is determined by the gain setting). With some controllers, the boost level will also increase the starting percentage of braking force that is initially applied (such as changing the default of 15% to something like 25% at boost level 3).

Given the behavior outlined above, when backing at low speed, the trailer braking force level will be low (like 15%) and will not ramp up because the reported deceleration rate by the accelerometer will be neglible) and thus the impact of the boost setting will also be neglible (some controllers even disable the boost function when the tow vehicle reverse lights are activated).

So, unless your brake controller is malfunctioning, it is unlikely to be the source of your problems. At the extremely low speed you are moving at in reverse, you don't even need trailer brakes. So I recommend that you disconnect your 7 pin cable and eliminate the trailer brake controller variable from your setup. If the problem continues, the brake controller and trailer brakes are not contributing to the problem. If the problem goes away, then you need to look closely at the controller or brakes.

I agree with others that a gain setting of 5 is likely way too high. Above 3.2, my GT 27FB Twin brakes lock up immediately at 25mph with minimal brake application.
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Old 02-21-2023, 11:03 AM   #33
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Not sure why your brakes wold activate when backing? Are you riding one foot on the brake pedal while backing? It sounds more like the brake is sticking or locking mechanically, Is the break away cable too short?
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Old 02-22-2023, 05:26 AM   #34
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I doubt brake controller settings has anything to do with this problem.
I have two trailers, one I tow at 7.5 and the other at 6.5 on my Tekonsha P3 brake controller with the boost on level 2 of 4. The readout rarely exceeds 4 when actually braking. There is no “normal” brake controller setting, it’s what works for your combination.

If this problem were caused by the brake controller gain being set too high I would expect the brakes to be locking up going forward as well as reverse.
My guess is a mechanical issue inside the drum.
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Old 02-22-2023, 07:12 AM   #35
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Another setting not mentioned yet is for hydraulic over electric breaks.
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Old 02-22-2023, 09:37 AM   #36
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My guess is a mechanical issue inside the drum.
Easy enough to figure out.

Rolling you might hear grinding or clanking (loose parts). I've heard both on mine. Lift. Spin a wheel.

Ultimately, remove the drum. 1 7/16 (IIRC) socket (36 mm) and snap ring pliers. Torque it back on at 150 ft.lbs.
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Old 02-26-2023, 10:03 AM   #37
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I don’t own an Airstream (yet)… so take this FWIW…

Do Airstream electric brakes actually work in reverse? On our current FW the brakes only apply while the trailer wheels are turning in the forward direction…

I’m in the “something’s broken inside the drum” camp… something similar happened on my drum brake motorcycle… spring broke and wedged between the “following” brake shoe and the drum
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Old 02-26-2023, 10:22 AM   #38
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POI there is no such thing as "never adjust" brakes.

Nothing mechanical is for never.

They must be taken apart inspected,repaired & adjusted as needed.

If the street side rear wheel is lifting up it's unlikely IT'S the problem, I would look at the brake and mount bolts on the opposite side of said axle....BUT ALL should be examined!!!!!!!

Bob
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Old 02-26-2023, 10:34 AM   #39
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Originally Posted by ROBERT CROSS View Post
POI there is no such thing as "never adjust" brakes.

Nothing mechanical is for never.

They must be taken apart inspected,repaired & adjusted as needed.

If the street side rear wheel is lifting up it's unlikely IT'S the problem, I would look at the brake and mount bolts on the opposite side of said axle....BUT ALL should be examined!!!!!!!

Bob
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Not be contentious but in my experience I have never had to (or been able to) "adjust" disc brakes. In my shop we have done hundreds of brake jobs over decades and only the drum brake jobs ever need adjusting.
It is true that nothing lasts forever but if I have to "adjust" a disc brake job, then I am replacing parts........
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Old 02-26-2023, 10:43 AM   #40
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Not be contentious but in my experience I have never had to (or been able to) "adjust" disc brakes. In my shop we have done hundreds of brake jobs over decades and only the drum brake jobs ever need adjusting.
It is true that nothing lasts forever but if I have to "adjust" a disc brake job, then I am replacing parts........
One exception. Rear disc parking brakes. There have been designs with either a "tophat" drum within a disc (with shoes) and mechanical piston pushers. They occasionally need adjustment. Not often.
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