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Old 04-26-2003, 07:26 AM   #1
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Join Date: Jul 2002
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Vacuum disks locking unexpectedly

After years of faithful service, I relined my disk brakes and install new rotors last fall. This week I pulled my 78 Excella out of storage and headed for the Ozarks. About an hour down the road, my brakes unexpectedly locked up, and pulled my tow vehicle to a crawl before I figured out what was wrong. I stopped, walked around, and could find nothing wrong except hot brakes. I started the truck up and head down the road for a half hour when the same thing happened.

Suspecting my brake controller (I'm not sure why) and being on mostly level ground, I disconnected the controller and again drove on. Half hour later, same thing, so the problem has to be in the brake actuator on the trailer.

The lock-up seems to occur after a period of downhill coasting (high vacuum), and is "cured" by simply pulling over and stopping. I replaced a cracked truck to the brake acuator hose (the truck hoses are fine), and reconnected the brake controller after checking it. That seem to improve things; but I still had a unexpected stop or two on the way home.

What should I fix? The breakaway valve? Vacuum reservoir? Hoses in the acuator (which look fine).

I'm hoping Andy at Inland or some other disk brake expret will see this and give me some ideas. I'd prefer not to tow that way again.
Bill & Jeanne Miller
78 Excella 31 CB
St. Louis
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Old 04-26-2003, 10:12 AM   #2
Rivet Master
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Inland RV Center, In's Avatar
Corona , California
Join Date: Feb 2002
Posts: 16,497
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Disc brakes can be actuated whenever there is a sudden loss of vacuum. You could perhaps have a bad "breakaway" switch.

You could also have a defective check valve in the vacuum line from your tow vehicle.

You could also have a defective brake controller or wiring related to it.

Andy Rogozinski
Inland RV Center
Corona, CA
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