I just purchased a 77 Ambassador with the hydralic brake system and after several disappointing calls to Airstream and a local dealer thought I had bought a camper that I couldn't travel with, having said all that and waiting for my printer to print out the thread. I understand that the vacuum controller that eliminated the vacuum link can be purchased or salvaged and eliminate the need for the vacuum hookup that was originally on the trailor? Is there a place that I can purchase one of these new? Would like to start out with completely reliable brakes. I'm completely new at this and excited about my purchase. Would like to get it on the road this spring.
I have been mulling this one over for several weeks. What Andy said makes some sense, but I'm having trouble with the terminology of a 'partial short'. No such thing. Either it's intermittent or it's shorted. Fuses should not be used in the brake controller power feed. However, circuit protection is necessary. A Type 1 circuit breaker is preferred because it does continually (automatically) reset. This continuous reset feature is mainly for the protection of the moving trailer. Should a short occur the breaker will continuously reset until you disconnect the source of the short or unplug the circuit breaker. This resetting should provide some braking to the trailer, if the short is intermittant in nature. The CB will provide fire protection because it will not allow the wire to overtemp (if sized correctly) due to a constant short. If a dead short occurs remove the CB to open the circuit. If the CB is activated STOP and resolve the problem before continuing.
Tekonsha Prodigy recommends a 20amp Type 1 CB for 2 axles and 30amp for three or more. I would recommend placing the CB in an accessable place if quick removal becomes necessary. Type 1A CBs are manual reset by taking power off of the CB. These are not recommended because they are like fuses, once off they remain off until you do something to replace/reset them.
Take care,
Sean
__________________ Old trucks and old trailers . . . a comfortable combination! AIR 1446
W5CDR A-6E All Weather Attack Driver, BUFF USN Aircraft Maintenance Officer, Ret. '91 Suburban R-2500 w/BBC '78 Honda GL-1000 '72 Triumph T-100R Daytona
A very very low or zero resistance circuit that is abnormal is a "short.'
Partial shorts occur when there is a measureable amount of resistance, which is appreciably greater than a dead short, consistant with the type of circuit in question.
As an example, the current oval type brake magnets measure an average of 3.5 ohms. Four of them wired in parallel, calculate to be .875 ohms. At 13 volts DC, the current draw will be 14.86 amps.
In my judgement, should a resettable circuit breaker be used, a 20 amp breaker will not provide an adequate reserve.
Should one of the magnets be worn beyond it's normal wear pattern and a partial short developes, lets say for sake of discussion 1/2 ohm, then the total circuit resistance will be .35 ohms.
At 13 volts DC, a .35 ohm load will draw 37.15 amps. That will blow your circuit breaker quickly.
However, by actual tests, with the exact example that I stated, some braking will still occur.
Why 13 volts DC? That is the voltage you typically have when the engine is running.
Therefore, in conclusion, it is far better to risk a smoldering wire, and/or a destroyed controller, should a partial short occur, and still have some brakes, as opposed to "NO" brakes.
Please don't assume, that all owners have the electric brakes checked or bearings repacked as they should, "THEY DON'T."
They usually wait until they have zero brakes, before they become aware of a problem.
Try to make a panic stop with a loaded 31 foot Airstream trailer, without brakes, just once. You will "never" want to experience that feeling again.
And besides that, your clothes washing machine, will appreciate your thoughtfulness.
Perhaps now, you may better understand, "WHY" a fuse or circuit breaker should never be used.
A manufacturer of controllers assume a liability if they tell you that a fuse or circuit breaker should not be used.
There will be many opposed to what I contend. But, they cannot ever say, that no brakes is "better" than some brakes.
Andy
inlandrv.com
airstreamparts.com
airstreamcandy.com
A update on my brake job. I am back in St Paul for a couple of weeks taking care of Biz, then back to Scottsdale to the trailer. I sent off the sync. valve to Inland RV for rebuild. Andy seems to know his stuff! Upon inspection of valve they found hydrolic fluid, he advised me to rebuild master cylinder. I have taken the whole assembly back here to repair. Since I have yet to get a manual from Helen, I am not sure if I have to disasemble the air canister at the seam, and if so does that have a diaphram in it. Anyway am excited to get it working and keeping it Stock! attached are few pics. It is on nice Mag wheels also.
Glad to see that you are getting the right help on your brakes. I really like the braking power of my discs.
__________________ Craig
AIR #0078
'01 2500hd ext. cab, 8.1 litre gas, 5 sp. Allison auto
3.73 rear end
Mag-Hytec rear diff cover
Amsoil Dual by-pass oil filtration system
Amsoil synthetics all around
265 watt AM Solar, Inc. system
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I just purchased a 77 Ambassador with the hydralic brake system and after several disappointing calls to Airstream and a local dealer thought I had bought a camper that I couldn't travel with, having said all that and waiting for my printer to print out the thread. I understand that the vacuum controller that eliminated the vacuum link can be purchased or salvaged and eliminate the need for the vacuum hookup that was originally on the trailor? Is there a place that I can purchase one of these new? Would like to start out with completely reliable brakes. I'm completely new at this and excited about my purchase. Would like to get it on the road this spring.
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