tag brake "sticking"

bobofthenorth · July 17, 2011, 08:39:37 PM

So we're barrel-assing down #1 highway west of Swift Current tonight, windows open, enjoying the sunshine and warmth that has been missing from our lives these last 6 months. Hear a funny noise, steering feels funny and I pull over. Go back to the trucklet expecting to see another wheel has fallen off but all is well. Marilyn gets out, walks along beside the truck, all seems well. Start to get back up to highway speed and suddenly hear a tire shriek. Stop again and this time when I try to move the curbside tag doesn't turn.

So the workaround for tonight was simple - raise the tag and pull into a rest area. I was ready to quit anyway. But why only one side hung up? No maxis on the tags so that isn't the problem.

Suggestions?

luvrbus · July 17, 2011, 09:27:20 PM

Bob, you probably lost a diaphragm that is where I would start then check the relay valve,and the quick release valve plenty to choose from with that problem,you didn't throw George under the bus lol did you
www.Bepco.biz has the best trouble shooting guide for air brakes if you need one

good luck

Sean · July 17, 2011, 10:50:58 PM

Hey, I didn't know Defevers had tags?

Seriously, though, in addition to what Clifford suggests, you should also look to make sure it didn't "cam over." Although I would assume those units had automatic slacks ...

-Sean
http://OurOdyssey.Blogspot.com

bevans6 · July 18, 2011, 05:16:03 AM

I don't understand why a plain brake chamber would apply or hang on if there is a bad diaphragm. I can't quite figure that.

Brian

buswarrior · July 18, 2011, 06:14:34 AM

Tag brake components live a hard life, with the drives blasting road crap at them constantly.

Broken return spring or binding mechanicals, particularly the clevis pin, maybe the camshaft needs r&r?

happy coaching!
buswarrior

bobofthenorth · July 18, 2011, 12:07:44 PM

Update:

I couldn't see anything obvious in daylight so when we pulled out this AM I put weight back on the tags and everything was OK. Marilyn ran along beside and we did a stop 10 miles up the road. Everything was good for about 50 miles and then the same thing only this time there was no doubt - I could see the black stripe in the mirror.

I'm with you Brian - I can't see how a blown diaphragm on a non-spring pot would do this. I'm more inclined to blame Prevost's stupid and needlessly complicated system of relays to the tag axles. It seems to me that I must be getting supply air to that chamber somehow. But I'm open to all ideas because troubleshooting my idea is going to be a bear. I was expecting this after the bus sat for 7 months but that doesn't make it any easier to take.

Iceni John · July 18, 2011, 12:26:22 PM

Quote from: bobofthenorth on July 18, 2011, 12:07:44 PM
Marilyn ran along beside and we did a stop 10 miles up the road.

You made her run ten miles? You northerners are tough.

John

luvrbus · July 18, 2011, 01:10:38 PM

I never saw a service brake on a Prevost tag that didn't have a spring return the disk on the end of the rod wears the diaphragm out and the spring has no tension to release the brake but it could be the relay or the quick release not just a Prevost thing, are those type 16 like the H series use on the tags,bet you a cold one you replace that chamber your trouble goes away but if I lose you come here to collect lol I would replace it before working on the 2 relays at the tags spend the 30 bucks Bob and replace it probably time anyway Marilyn will front you the money if you have been nice to her

good luck

rv_safetyman · July 18, 2011, 03:41:33 PM

I had a bogey with a failed automatic slack adjuster that had the same symptoms. Didn't quite put rubber on the ground, but you knew that something was hung up. The brake was way out of adjustment. I don't think it "camed over", but it sure did not release cleanly at times.

Ever since that event, I no longer trust my auto-slack adjusters. I climb under the bus before every long trip just to make sure the brake adjustment is correct.

Jim

bobofthenorth · July 18, 2011, 06:02:05 PM

Well now that I understand it I like Clifford's idea a LOT better than mine. At least I can troubleshoot it so I'll start there whenever I can get the bus up on blocks.

bobofthenorth · July 25, 2011, 11:56:48 AM

Confession is supposed to be good for the soul:

I went so far as to pull the rim and get a new tire mounted - the original had a fairly large hole, just in the bottom mind you but its hard to put a boot over a 10" gap. All the while I was trying to make this a brake hardware problem. I had crawled in behind the wheel, inspected the brake hardware and everything seemed to be OK. That was pointing me toward a Prevost relay problem which I was dreading.

However, when I went to remount the tire I finally noticed that the hub was frozen solid. From there it was a pretty short journey to figure out that I had a piled up inner bearing. I'm baffled why that happened - I know it didn't run hot because I stopped a couple of times to check everything and there was still oil in the cap when I took it off. I assume it had something to do with the bus sitting for 7 months. Whatever the cause the inner bearing is lying on the ground in pieces. Now I've got everything pulled apart and I'm waiting for the local welder to return home so I can get him to cut the inner bearing off the axle. Time to phone Prevost parts - nothing that money won't fix.

Melbo · July 25, 2011, 05:28:18 PM

Glad to hear you figured it out and that Marilyn doesn't have to run along side to figure it out for you.

Melbo

Van · July 25, 2011, 05:51:44 PM

Look at it this way, at least he is not bobbin' up-N- down at sea trying to fix it

mustta been the salty air up there Bob, glad ya got a handle on it

Van

bobofthenorth · August 13, 2011, 03:44:04 PM

Yesterday I got back from a project in Brazil, picked up the frenchy-parts from UPS and today I was raring for tearing. John-the-welder didn't show up "early" like he said he would so around 9:00 I went looking for him. I found him along with several locals drinking coffee in his shop. About an hour later we got the acetylene torch loaded and commenced cutting. Now John is an elderly gentleman and his eyesight isn't what it once was so there was a moment when I seriously considered calling the whole project off. In the end he nicked the axle a couple of times but I've seen worse. The bigger issue was that the bearing had obviously run hot enough to weld itself to the axle and it was the worst prick I've ever dealt with to break free. For a couple of hours I was seriously considering packing the whole works off to my favorite machine shop to have them cut the spindle off and weld on a new one. But I persevered and after a lot of beating with a large hammer and larger punch and a lot of bleeding when I missed either of the above items, I finally got the first piece of the bearing broken out. I'd love to say that after the first piece came out it got easier but it didn't. Eventually to get the final piece out I ground the remains of the bearing down to about 1/4" thick and at that point it finally bent enough to break free.

Now everything is cleaned up ready for reassembly but I have to wait for one more frenchy-part. The spacer behind the inner cone took the brunt of John's misses with the torch and has to be replaced. I could probably cobble up something that would work but I think I'll wait for the right part.

I still don't know why the bearing failed. Obviously it had to have run dry but there was oil ran out of the cap when I took it apart so I'm not sure how that worked. The outer bearing could have been dry with the inner bearing still having oil but it was the inner one that failed. Whatever happened there's not much else to do now but put it back together and hope it doesn't happen again.

One of the nice things about boats is no GD wheel bearings.

Stormcloud · August 13, 2011, 04:34:13 PM

Glad you're on the 'good' side of the repair now.