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Old 07-08-2019, 10:27 AM   #1
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DOT brake fitting failure at 60mph

The brass elbow came apart while traveling 60 mph on I29 near Omaha. The brakes locked the right rear Tag an wore it through in seconds. My wife managed to pull to the shoulder where we waited (1 foot from the white line) 7 hours for Progressive pro roadside assistance. (press
You see in the attached picture the 1/2 npt part came out of the elbow part. I do not see what held them together. It just slips in and out. there is an Oring in the elbow but i see no mechanical retention feature that failed. Perhaps the failed portion disappeared.
You can see on the elbow a symbol which i guess represents the manufacturer's logo. I would very much like to see and understand the feature that held it in and failed.
any help?
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Old 07-08-2019, 10:46 AM   #2
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I'm not a fan of those Push-to-Connect fittings because the o-ring will eventually leak and it can't be replaced. Those P-T-C fittings are only good for assembly line workers. IMO

The P-T-C fittings (if made by reputable company like Parker) are pretty robust. I have not seen or heard of one coming apart like yours. But since those fittings have the "extra machining" (for the swivel and o-ring) it adds an additional point of failure.

Of course any fitting can fail. I always replace the P-T-C fittings with a standard DOT air-brake compression fitting when I have to replace one for leaking.

I suppose it is a good idea to go under the coach during your annual inspection and grab/wiggle all the brake fittings to check for any pending failures.

P-T-C fittings on top, and standard compression fittings in the middle and bottom of photo.
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Old 07-08-2019, 02:22 PM   #3
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the push to connect feature end is not the one that failed. the failure is on the NPT end.
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Old 07-08-2019, 04:34 PM   #4
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But it is the same fitting.
A P-T-C swivel fitting has two o-rings inside and a gripper to hold the hose, so it has more parts to fail than a standard compression fitting.

But they lasted 14 years (at least on my coach - you didn't say the age of your coach) before some started leaking, so if you want to use the style again I think you will be fine for the rest of the coach's life.

good luck
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Old 07-09-2019, 09:38 AM   #5
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Glad you found the problem. I am curious, what caused your right tag wheel to lock up?
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Old 07-10-2019, 03:52 PM   #6
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brakes on an air system are clamped down by springs. When you press on the brake, air is let off at the wheel cylinders and the springs clamp the brake according to the remaining air pressure. Let up on the brake and the increased air pressure opens the springs to allow rotation. When the Tag air line came apart, the air holding the tag brake escaped first and the springs clamped on the brakes. You wont believe what that did to the NEW 550$ tag. I will attach a pic.
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Old 07-10-2019, 04:05 PM   #7
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Quote:
Originally Posted by wsmcycle View Post
brakes on an air system are clamped down by springs. When you press on the brake, air is let off at the wheel cylinders and the springs clamp the brake according to the remaining air pressure. Let up on the brake and the increased air pressure opens the springs to allow rotation. When the Tag air line came apart, the air holding the tag brake escaped first and the springs clamped on the brakes. You wont believe what that did to the NEW 550$ tag. I will attach a pic.
I see. Thought the spring brake was usually on the drive axle and not the tag axle. I guess yours is different.
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Old 07-10-2019, 04:11 PM   #8
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Your explanation of how air brakes work is not correct.

Air pressure applies the brakes, to all wheels, when you step on the brake pedal.

Rear brakes ( typically only the drive axle ) have dual chambers with spring sections that apply the brakes when air pressure is lost or the parking brake is applied.
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Old 07-10-2019, 04:31 PM   #9
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Twinboat is correct. Pressing on the brake pedal applies air pressure to the brake cylinders to stop the coach. This is the service brake system.
If the air pressure drops out of the system, the springs clamp the brake shoes to the brake drums.
Just like when you park your couch, pull the yellow brake valve which drops the air pressure out of the system to set the brakes for parking.
Great system.
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Old 07-10-2019, 05:38 PM   #10
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Did the brakes apply to your drives as well? I'm wondering if the tag locked up and not the drive axle because it's carrying much less weight than the drive.
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Old 07-15-2019, 04:32 PM   #11
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I am embarrassed by my ignorance. I am glad to have been straightened out.
The failed fitting was part of the right-side tag brake. I do not know why the other brakes did not clamp but the tag sure did.
thanks
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Old 07-15-2019, 04:39 PM   #12
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My original question was directed at the failure of the swivel joint on the NPT end, not PTC female on the opposite end. I can appreciate the disdain for the PTC end but that end did not fail. what was the design of the swivel joint? any drawings available?
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