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Old 06-30-2008, 05:09 PM   #1
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Smile Brakes-Have tried most everything.

My trailer brakes in 28', '99 Airstream Excella do not apply firmly. Regardless of the Prodigy controller setting, when I test them by operating the controller lever I drift very slowly to a stop.

I have replaced the controller. We thought there might be a problem with it - the Prodigy tech rep said to replace it under warranty. Changing controllers did not help.

The output at the controller is 13.6V, 5.5Amps. The readings at each of the brake magnets is 10.6V, 3.8Amps (with controller set at full gain of 13). These magnet readings are within the specs listed in the Airstream manual. When I test the breakaway switch, the trailer brakes are locked at a standstill.

The trailer never had a great deal of use. The brake linings and the drums are in very good condition. There is no shiny glaze on the linings. They are smooth and even.

I have used a corrosion block to free up the movement of the mechanical brake shoe components so that all work smoothly.

I have applied a straight edge to the lengthwise dimension of the magnets. They have not worn unevenly at one end. However, they are somewhat rippled on the wear face, and a similar uneven wear is on the surface of the drums. I asked a very experienced Airstream mechanic about this, and he stated that he sees this condition sometimes. His opinion is that if these grooves are fairly minor it should be okay. I would say that two of the magnets have very little - but some - uneven wear. The other two are definately rippled.

Other than the voltage and amperage loss at the magnets, the uneven face of the magnets is the only thing I can find.

Mind you, I was an accountant by training. I'm not great at mechanical stuff.

Is my ONLY next step to replace the magnets and have the drums resurfaced? Do most machine shops have the capability to do this resurfacing work?

Help would be greatly appreciated. Steve
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Old 06-30-2008, 06:13 PM   #2
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Are the shoes adjusted to the drums properly?
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Old 06-30-2008, 06:23 PM   #3
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Originally Posted by bluegrass-girl View Post
My trailer brakes in 28', '99 Airstream Excella do not apply firmly.
Please define "firmly". Electric brakes do not have the braking force of hydraulic or disc brakes. Don't expect the trailer brakes to lock up. A gradual stop if you are using the controller only may not be unusual. Remember you are then using the trailer brakes to stop both the trailer and TV. The amperage going into the brakes sounds like it is right on the money.
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Old 06-30-2008, 06:57 PM   #4
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The brakes were adjusted recently by a mechanic who frequently inspects and works on heavy trailers. I then had the trailer at an Airstream dealer a month ago, and they changed the brake adjustment slightly. They were aware that I was having problems with braking efficiency.

During the time that I have owned the trailer, I have followed the Prodigy directions in setting the controller. Find the point at which the brakes just lock up, and then back back off on the gain very slightly. Up until recently, I could lock up the trailer brakes if so desired in a road test at 25 mph. I can set the gain all the way to 13 and the best I can do is slow the truck/trailer down slowly with the trailer brakes. The trailer brakes should stop the truck and trailer in a 25 mph test.

Thanks, Steve
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Old 06-30-2008, 07:13 PM   #5
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Brake Problems

Try this and let me know what you get.
Get a long piece of wire, #16 lamp cord will work.
You will need access to a brake magnet +12 Volt supply wire.
Connect the trailer to the tow vehicle and plug in the trailer plug to the
tow vehicle.

1. Measure the output voltage of the Tow Vehicle (TV) battery. It should be around 13 Volts DC. Write this value down.

2. Clip an alligator clip wire to a bare brake wire at the wheel.

3. Run the wire alligator clip wire to the TV.

4. Clip the end at the tow vehicle to the negative lead of your volt meter.

5. Connect the POSITIVE lead to the + output terminal of your brake controller.

6. Turn the Ignition Switch of the TV to the ON position.

7. Fully depress the panic stop button on the Brake controller. While holding the button fully depressed and the volt meter still hooked up to the + lead on the battery and the brake wire read the voltage. It should be close. Release the panic stop button. Turn off the ignition switch.

If the voltage is not close (within a volt) we will make more measurements.

8. Remove the positive lead from the Brake controller

9. Gain access to the back of the trailer plug mounted on the tow vehicle.

10. Connect the positive lead of the volt meter to the brake wire coming from the controller (on the TV side of the trailer plug).

11. Have a friend:
A. Turn on the Ignition Switch.
B. Depress the Panic stop button.

12. Read and write down the voltage. This voltage should read less than .5 volts.

13. Turn off the Ignition Switch

If it does not read this low, you have high resistance somewhere between the plug and the brakes, which is what I suspect. The resistance that I am referring to is so low you may not be able to measure it with your ohm meter, so you measure the voltage developed across it.
You measured 13.6 volts at the back of your brake controller. You measured 10.6 volts at the brake magnet. Doing the math there is approximately .5 ohms resistance caused by a bad connection probably.

14. Gain access to the trailer Plug cord (the one that connects to the TV) in the trailer.

15. Connect the + lead of the meter (other end still connected to the brake magnet wire) to the brake wire at the end of the trailer cord on the trailer.

16. Again have you assistant turn on the TV Ignition Switch and depress the Panic switch fully.

17. Read and record the voltage.

18. Turn off the TV Ignition Switch.

19. Voltage .5 volts or less? If so you have a problem somewhere between where your + meter lead is connected in the trailer and the back of the truck (female) plug.

20. Scratch clean a piece of metal on the TV. Place the + meter lead on this clean spot
(other end still connected to the brake magnet wire)

21. Have your Assistant turn on the Ignition Switch and depress the Panic Button.

22 If you read .5 volts or less then the problem is in the +12 volt brake wire going to the brake magnets somewhere between where you measured the voltage in step 17.

23. Turn off the Ignition Switch.

If you read more (especially 3 volts) the problem is a bad ground, usually in the trailer plug and cord or where the ground wire from the trailer plug receptacle on the tow vehicle is connected to ground or in the plug itself. The easiest thing to do first is clean the ground spot where the ground wire is connected to the frame of the TV.
Next clean the spot on the Trailer where the ground wire is connected to the trailer frame.

Hope this helps.

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Old 06-30-2008, 07:24 PM   #6
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This is a stupid question but I have to ask. Is the prodigy set on B1, B2 or B3? It should be on B3.


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Old 06-30-2008, 07:40 PM   #7
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Hey bluegrass-girl,

From your posting I could tell you take your Airstream braking system as seriously as I take mine. I think is a safety matter not to be patched or half-assed engineered because I love my Vintage Airstream, but I love the people riding in the tow vehicle attached to the trailer much more.

I'm not an Airstream brake guru, so please do not take my observations as someone of authority that knows all about Airstream brake systems, because I do not.

I did noted the tech. spec. details of your posting and wondered..why the Volt /Amp. loss was so great in such a short wire run from the controller to the brake magnets? That loss could only occurr if there was a short / partial short.

I had a sim.problem with my Airstream TT. What I experienced with my 1968 Tradewind TT was an unexplained loss of braking power with no common causal factor that I could reproduce static. After many attempts, I was getting really annoyed.

I tried and tried to reproduct the factors that caused the brakes to fail or to partially work without finding the common cause.

Long story short, a previous owner had dropped the belly skin and stray foamed the entire underside of the trailer, including the brake wiring and junction points. The spray foam had trapped mositure and corroded the wiring. Shorts developed, on and off, as the trailer moved and twisted.

To test this theory in application a dedicated wire run was made from the tow vehicle wiring harness to the brake system wiring drums.

Poof..the Airstream trailer electrical brakes activated and locked up and a 3/4 ton diesel turbo tow vehicle just spun it's wheels trying to move it.

As an ecomonic choice, rather than remove all the spray foam and replace the wiring and junction points above the belly pan, a new brake wire was run through a PVC conduit attached to the outside of the trailer's frame to the brake system.

Total cost for materials was approximately $25.

Just something to think about and test.

I hope it helps,

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Old 06-30-2008, 08:03 PM   #8
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I just scanned through this, and didn't see it posted, but check to see if the magnets or magnet contact areas are covered in brake dust or grease.
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Old 06-30-2008, 08:04 PM   #9
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From your description it sounds like the braking efficiency has degraded from a formerly adequate performance level. If so, then you must have developed a poor connection somewhere along the circuit. Remember that the ground return is as important as the wiring out to the magnets. You'll need to do some sleuthing to find the problem. Look at any/all connectors and especially the umbilical plugs at both ends. signs of discoloration due to heating are a good clue to high resistance.
"Not all who are laundering are washed" say Bill & Heidi

'78 Excella 500,"The Silver Pullit". vacuum over hydraulic disc brakes, center bath, rear twin. '67 Travelall 1200 B 4X4 WBCCI 3737
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Old 06-30-2008, 08:10 PM   #10
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Excellent description of the problem, bluegrassgirl, in terms of what has been checked thus far. You may not be "trained" in these mechanical arts, but your ability in description is EXACTLY the way to look at RV systems, be they mechanical, electrical, gas, fluid and/or combinations. A systematic approach works wonders once one gets the hang of it, one then is "ready" to consider, test and eliminate. You're more than half-way to the solution with this sort of approach. A cluster of details to attend, your training was ideal.

Good luck.
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Old 06-30-2008, 09:10 PM   #11
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I have received some excellent suggestions. I'll continue to search for electrical problems tomorrow.

For your information, the tow vehicle is a heavy, 2003 Chevy 2500 diesel with Allison transmission. It weighs nearly as much as the trailer. I have used a Prodigy setting of B1 in the past with excellent results. In the tests over the last several days, I switched to B2 with no discernable improvement. I'll try the B3 setting.

I thoroughly cleaned the surface of the magnets. There was a fair amount of brake dust on the shoes and drums. All has been cleaned.

The direction that the comments seem to be taking is to look at the considerable voltage and amperage loss between the controller and the magnets, to include possible ground problems. This is just the kind of steering that I need.

Thanks, Steve
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Old 06-30-2008, 09:39 PM   #12
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You might want to check the 7 pin connectors for corrosion as well. If something was going to change in the electrical circuit, that would be the most likely place.


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Old 07-01-2008, 09:16 AM   #13
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When I checked my brakes, I found 3 of the four magnet ground wires broken, PO had not allowed long enough wire when axles moved up and down, so make sure you have a god ground to each magnet. Just my $.02.
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Old 07-01-2008, 05:33 PM   #14
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You are losing three volts somewhere.
It could be caused by almost broken wire, corrosion at the plug contacts,
corrosion where the wire goes into the back of the contact or a bad ground. The resistance is so low that you cannot measure it reliably with a regular volt meter, so look for voltage developed across it.
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Old 07-01-2008, 09:11 PM   #15
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Be sure to check the ground wire on the TV you may be getting the ground through the trailer ball. Pulling the brake-away pin provided the brake power from the trailer battery and uses the same wiring only a different path so that is a good clue on where the problem is.

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Old 07-02-2008, 05:22 PM   #16
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Thanks for the many helpful replies.

Last evening I replaced the break away switch. It was origonal equipment in a "99 trailer, so I thought that it would be a good step. I also applied some fine sandpaper to the brass leads in the electrical hookup cord on the trailer. They were a dull brass color: they are now shiny. The receptacle side on the truck appears as new.

This morning I went on a test drive. If anything, the braking ability seemed to be a bit worse. At 25 mph, regardless of gain setting (tried 6 and 10), or B1, B2, or B3 boost setting, the trailer brakes do little to stop the vehicle. When I returned from the drive I pulled one drum off and again checked the numbers at the magnet. The results were a little higher than I earlier obtained. With engine running, at full gain (13), voltage is 11.0, amperage is 4.1.

This evening I have recorded the following data (all with engine running):

-Battery voltage - 14.3
-At input to Prodigy - 14.3
-Output wire of Prodigy (full gain) - 13.7
-With lead run from brake magnet to Prodigy output wire - 12.6 volts. Used #12 wire with lighter wire clip wires on one end. This result falls within your definition of being close.

There are more measurements to be performed as listed in the post. More data to follow! I'm heading back outside.

Thanks, Steve

This evening I proceeded to start the diagnostic procedure laid out by Beginner. This is a progree report on the first couple of steps.
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Old 07-02-2008, 05:42 PM   #17
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The posts and data seem well rounded. Don't forget the other half of the circuit. Make sure all is well grounded. The controller, trailer plug and the grounding points of the brake circuits at the axles. The current must make it back to the TV.
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Old 07-02-2008, 07:59 PM   #18
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Voltage Checks

You are measuring voltage, not current.
The lighter #16 wire will work just fine.
Remember, you have a resistance somewhere between the brake magnets and the controller or between the ground wire of the brake magnets and the negative post on the tow vehicle battery.
Only have the full gain selected long enough to make the voltage measurement (10 seconds or so), for this you need an assistant/helper.
You don"t need to have the engine running, just the ignition turned on.
Post results as soon as you get them.
Describe the points at which you made your voltage checks fully, this will help me.
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Old 07-02-2008, 09:57 PM   #19
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If you test the break away switch make sure you unplug the umbilical or you may fry the controller
Sail on silver girl. Sail on by. Your time has come to shine.
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Old 07-03-2008, 12:52 PM   #20
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I solved a similar issue by following any exposed wiring with my Radioshack infra-red thermometer. It showed a hot spot at a soldered connection inside many turns of insulating tape. Ten years of very slight moisture ingress had caused electrolytic corrosion between the solder and the copper wire. This caused the hotspot, the resistance, and the poor performance. A common problem is corrosion or a loose wire inside either part of the 7-way connector. I fixed this on an Argosy in the Florida Keys last winter, when the distressed owner had useless brakes.
Nick Crowhurst, Excella 25 1988, Dodge Ram 2500 Cummins Diesel. England in summer, USA in winter.
"The price of freedom is eternal maintenance."
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