Smokin'' Tag Wheels, Batman!

[ghanson]

I could use a little help here. I'm out on the road with the bus and the tag adjustment is out of whack.  Hit the brakes and the left tag locks up. I know there is a valve that adjusts this in the middle of the engine compartment, between the tags, but I don't have a pressure gauge, and probably don't know what to do with it if I  did. An email explanation would help, since I'm typing this out on my phone and not the computer, or my cell number is 812 399 9444.  I can limp it home like this but I'd rather adjust it.  Thanks.......g

[ghanson]

Smoggy?!?   Who wrote that?  Blast that auto word fill function!  It's supposed to be Smokin' Tag Wheels! This thing is makin' me look like an idiot!




Fixed it. DML

[JackConrad]

We had a problem with our tags smokin' when we made a HARD brake application (like when that idiot pulls out right in front of you). First thing to check is the tag unloader valves located just inside the right side door on the engine compartment. There is a separate valve for each wheel. Since only your left tag is smokin', it sounds like maybe that air bag is not appling adequate pressure. Possible causes include unloader valve, broken air hose to tag air bag, leaking air bag or broken tag air bag bracket. Or it could be a brake problem. Jack

[buswarrior]

Sliding tag tires under braking is usually an air bag pressure problem, as Jack has noted.

If the tires aren't being squeezed to the ground hard enough, they'll lock up under braking.

You can check to see if one has been accidentally shut off by checking the manual shut-off valves in the curb side engine access door. If they are good, ideally, a scale where you can get each tag on the scale alone let's you check both sides, but both together on the scale alone is better than nothing. You want to see closer to 4000 pounds bearing down than under that, depending on your total coach weight, on the MC7-8-9.

happy coaching!
buswarrior

[Dallas]

Not to be contrary,

Check your bake adjustment. It is really super easy to over brake with an MCI tag. This is because the tag doesn't carry as much load as the drive axle. If they've always worked before, and you haven't made any changes other than brake adjustment, or  wear, the brake adjustment will take care of the problem....

My method is to tighten to brakes up until thee is no clearance between shoe and drum, then back off 1/8th turn. Some people back off 1/4 turn. some back off until a whack on the drum produces a ringing sound.

Do you have auto slack adjusters? In my opinion, those are almost as worthless as a first date when your 13. They are just another method to fail.

Of course, I have only driven 3.5 million miles in 29 years, and owned at most 5 trucks as a fleet. I was known to my drivers to be very picky, when they came in with their trucks, it was a rule that the driver was the one who adjusted his brakes.


Good Luck,

Dallas

[buswarrior]

I'm hoping that if recent brake adjustments had been attempted, that we would have had that shared with us for trouble shooting purposes....

However, the strength of squeeze is fairly equal over the active part of the brake chamber stroke, and then weakens a bit as the chamber stretches out towards the regulated pushrod stroke, and of course progressively degrades to nothing if the chamber over strokes and bottoms out.

So a tight adjustment, say 1" of applied stroke, doesn't squeeze any more than around 1 1/2", beyond that the graph starts to droop for a Type 24 and it squeezes a little less. We shouldn't let it stroke beyond 1 3/4" or it is out of compliance, and not doing its intended share of stopping the coach.

Now, a relay valve that is directing a disproportionate pressure or is sticking and sending a sudden shot to the tag brake chambers may wreak havoc...

If the rubber on the tire has some issue and isn't gripping the way it should....

Unusual road surface at that moment? Did it do it once or a bunch of times? Polished interstate concrete can do funny things...

And the original suggestion of a lightly loaded tag suspension...

A properly functioning brake should not slide a tag tire by itself under moderate brake applications. It has to have some help....

Something is amiss...

How about it ghanson? Anything been worked on or changed recently?

happy coaching!
buswarrior

[Tony LEE]

Seized up tag axle bearing?

Reverse up over a low curb and then back down and make sure the wheel is not hanging up.

[belfert]

Apparently, Dina considered tag axle brake lockup to be a big enough issue to include ABS only on the tag axle.  I haven't noticed any issues with my tag brakes and I'm not even sure the ABS is working.  (The brakes will still work without the ABS working.)

[ghanson]

Thanks for all the replies, gents, and a few phone calls.  It turns out that the only problem I had was that the tag valves were shut off.  Yes, I do check them from time to time, but I never close them.  No real reason to under normal conditions.  It seems that some zaney funster got into there when I was out, or something, or maybe the squirrels did it.  Anyway, open valves, problem solved.  I have had problems with the tag adjustment in the past, so that's where my brain went, and not to the simple solution.  Again, thanks for the help.

ghanson

[Nick Badame Refrig/ACC]

I had a feeling that was it.

Last year, I drove all the way to Florida with no air in the tags and was wondering why my brakes were smoking too...

Nick-