HELP - Need help with hung brake in Kansas City, Kansas

[bevans6]

The application pressure in an air brake system is strictly related to a couple of things, aside from basic sizes, friction material, etc. as I understand it.  If I'm wrong I'd like to learn, hence this post.

There is a variable leverage effect on the brake shoes relative to the position of the S-cam against the rollers, but it's minimal.  Leverage is greatest at the base of the S-cams and less at the tips, so as the brakes wear and the rollers move out, leverage and efficiency drops.  This is accommodated within the design of the air brake system, where you can simply apply more air pressure to compensate.  Adjusting the slack adjusters does not change the position of the S-cam relative to the rollers, that is strictly a function of brake shoe thickness relative to brake drum inner diameter.

The thing that adjusting the slack adjusters does is change the leverage ratio of the push-rod to the slack adjuster.  Within the range of adjustment the difference in leverage ratio is only one or two percent, so again close to irrelevant.

About the only thing that does change the pressure developed is air pressure and cannister size.  That completely overwhelms the other possible differences.  You develop a certain amount of pressure in the system that is  delivered equally to all of the cannisters, and they develop push based strictly on their size.  So adjusting the slack adjusters, which I might do if they were manual but would not do if they were automatic and in range, won't actually do anything to change the amount of pressure on any of the brakes relative to the one having a problem.

Now what you could do is just disconnect the pushrod from the slack and let the cannister fully extend as soon as the brakes are applied, or adjust that slack to be very loose, so the can bottomed out as the brakes are applied, the idea being that you don't have a way to  disconnect that can and you don't want it to cam-lock or cam over again.  Making that one brake ineffective won't affect any of the other brakes at all.

If this is wrong, let me know in what way so I can correct my thinking!

Brian

[belfert]

I talked to Bryce and he directed me to Arrow Stage Lines in Kansas City.  They said they could send someone out to look at it.  But first, the gentleman told me to try tightening the slack adjuster all the way and then doing a full pressure brake application.  He said that frees up stuck brakes 9 of 10 times.  That seems to have worked.

Now that the brake is freed up I need to find a place to fix the problem.

[prevosman]

Don't mix up brake application pressure and volume.

If you step on the brakes you are essentially telling the system how much pressure the brake chamber is going to see, not how much volume it is going to get delivered.

All a long stroke does apart from running the risk of overtravel on the S cam is lose mechanical advantage. The volume of air delivered is that which is required to provide the pressure you called for with your foot. The greatest mechanical advantage comes from properly adjusted brakes and when the slack adjusters are adjusted all you are doing in essence is rotating the S cam, bringing the shoes closer to the drum, while positioning the arm on the slack adjusters so its travel is in the range of greatest mechanical advantage.

[Joe Camper]

Yes inevitably the applicacation pressure will equall out but making all the other brakes tighter will have them grabbing first or quicker and that will give some "cushin" to compinsate under normal braking. If you have to make a panic stop all bets are off.
Or if a maxi is doing this every time you set the parking brake it may hang up again.

On trucks they have appplication pressure gauges and brakes that are adjusted tight require way less application air to stop. If good 10 lb of application air will stop you nice. If a truck is loaded heavy or say a panic stop you get to 60psi or so of application air.

I do not disagree with anything you mentioned Bri

[John316]

Now that the brake is freed up I need to find a place to fix the problem.

Ummm, Brian. You told me that you were stopping to get it fixed right away. There is no way, you should continue like it is.

Think about it like this. Say you are driving. You have a panic stop to make. You don't make the stop and either injure or kill somebody. An investigation ensues, and it is discovered that your one of your brakes is compromised. That could be real trouble!

It is one thing to bypass a brake until you get to a city. But I really don't think too many people will have much sympathy if a brake is bypassed, and you continue driving until you get out of town.

I would have been MUCH stronger on the phone, if I would have guessed that you were going on.

Some of the gents on here might disagree with me, but safety is a big concern.

FWIW

John

[Len Silva]

All of these suggestions are fine for solving the immediate problem and getting underway again.  They do nothing for the underlying cause which is lack of proper maintenance.

You cannot inspect brakes from the back.  The only way to be sure is to pull the drums on every wheel and thoroughly inspect and repair every part of the braking system, including drum diameter and roundness.

If the tag brake overheated enough to make visible smoke, there is a good chance that the linings were damaged, the drum was warped and/or the bearings and seals compromised.

You were very lucky to see the smoke.  If it had happened at night, you might not have discovered the problem until it was flames.

[John316]

///////////snip////////////////
You were very lucky to see the smoke.  If it had happened at night, you might not have discovered the problem until it was flames.

Len,

Brian said that they smelled the brakes. It was dark, when they figured out they had a problem. He had the guy, who was driving, stop. That is when they found the issue (so I understand).

John

[Len Silva]

John,

I didn't get that from the original post,

Smoke started pouring out of the tag axle brake and we pulled over

but it doesn't really change anything.

You were lucky to have smelled the brakes burning before there was a fire.

The point is that when you buy a used bus, among the very first things on the agenda should be a complete and thorough axle service all around, regardless of what the PO might have said.

Brian may have thought that was what he was getting, but that was not the case.

The thing is that brake and axle service is so cheap compared to the safety value, it is not something to compromise on.

[John316]

Len,

I know, what he told me on the phone didn't exactly match what he wrote. He said that it was dark, and it was only when they smelled the brakes, when they pulled over.

I do not know where the "smoke pouring out of the tag axle brake" came from. Maybe that was the assumption, or maybe they saw it after somebody else smelled it....who knows. If they didn't see if until somebody smelled it, I gotta wonder about the guy driving that bus. If it is dark, and you see the smoke (remember, they just went through downtown KC, plenty of light, or somebody else's headlights), then they should have seen the smoke before somebody else smelled it. When I drive, I am always checking my mirrors. Day or night.

John

[luvrbus]

Anyway he was in good hands I know both of those young guys Wade and Matt and they are well versed in brakes I can assure you of that and there is no sense in Brian having the repairs done on the road and spending a small fortune.
He just needs to watch and be sure the seal is not pouring grease one brake on a tag bad is not going to make that much difference in his stopping ability 

good luck

[John316]

Clifford,

I agree with you. But, I think Wade would have worked him in today, given that side a once over, and been set. He broke down less then 15 min from the Arrow shop in KC.

That is true, the tag isn't as big a deal as some of the others. They were still so close....

John

[luvrbus]

If he was that close John he should of let Wade look at but Brian is Brian what else is new lol

good luck

[John316]

http://maps.google.com/maps?saddr=Exit+232A&daddr=Manchester+Trafficway&hl=en&sll=39.059392,-94.501272&sspn=0.007439,0.016512&geocode=FTrKUwIdjK5b-g%3BFSoCVAIdXAVe-g&vpsrc=0&mra=dme&mrsp=1&sz=17&t=h&z=17

That close, Clifford....

[Busted Knuckle]

I gave him the # and told him that's where I send or take my buses when we have issues in that area. I couldn't do any more over the phone.
 BK  

[Len Silva]

BK,

I'm just curious. What do you do when you buy a used bus and before you put it in commercial service? And, how much do you expect to spend, over the purchase price before you put a used bus on the road?

I think that would be some valuable information for many folks here.