Brake Drum Failure

[hsykes]

We have had several cast iron air-brake drums crack with pieces of drum a falling off while driving during the past couple months. If anyone is aware of this type of problem or its resolution please contact bitb@nc.rr.com Thanks.

The drums are Webb 66661 with Meritor brakes on a 27000# rear axle.

Howard Sykes
Maintenance Officer
Lebanon Volunteer Fire Department
bitb@nc.rr.com

[arhaney]

Few questions for ya......

Are the drums having chunks come off of them, or is it scale coming off the outside of the drum?

What is the condition of other drums on this truck? Cracks? A lot of wear? Deep grooves from worn out shoes?

Any pictures? I was in class 8 truck maintenance for 18 years and I've only seen a couple of busted drums in all those years......even on trucks with 750,000 to a million miles.

[spearsm]

Originally posted by arhaney
Few questions for ya......

Are the drums having chunks come off of them, or is it scale coming off the outside of the drum?

What is the condition of other drums on this truck? Cracks? A lot of wear? Deep grooves from worn out shoes?

Any pictures? I was in class 8 truck maintenance for 18 years and I've only seen a couple of busted drums in all those years......even on trucks with 750,000 to a million miles.

MR. ALAN HANEY....Tha MAN!
Go Alan!
Go Alan!!!

[lvwrench]

I tried sending you an e-mail so I hope you got it. If not I can be reached at kbraker@lasvegasnevada.gov I have seen this problem on our 31,000lb axles but not on our 28,000lb or less axles. I do know that you have to be careful on crossing over from the Meritor to the Webb on some drums due to a difference in the pilot hole diameter. We have had great service from Webb drums except at the 31,000 lb. level we had to go back to the Meritor which was a heavier cast for the stress and heat.

[hsykes]

Attached is some additional information on our brake failure. I will update this indicating whatever we find as a final resolution. Photos of failing parts are also attached.

1. Chunks are coming off.
2. Drums and shoes were in good condition. Failures have occurred within weeks of installation and with only a few hundred road miles.
3. Failures have occurred on both rear wheels.
4. All parts used have been newly manufactured. They have been the same part numbers as used by the original truck manufacturer (E-One).
5. We have confirmed with Webb, Meritor and E-One that we are using the correct parts for this application and weight.
6. While the brakes have been used hard, they have not had any use that is abnormal for a fire truck. The drums did not have discoloration or other signs of extreme heat.
7. The truck is one of two 2002 model year sister pumper/tankers. Only one is having this problem and it has gone through multiple sets of drums. All brake components on an axle have been replaced at the same time (not just drums or one side).
8. The factory-installed brakes on both trucks have been replaced as they wore out. None of the factory-installed brakes had problems with cracks.
9. Due to driver rotations, both trucks have been driven by all of the same drivers, so no differences here.
10. We are aware of the two pilot hole designs and are using the correct drums.

So the bottom line is, we are still trying to determine the cause of the problem. Any ideas are welcome.

[hsykes]

This close-up should make it easier to see the full thickness crack in one of the drums.

[arhaney]

Question, are the front brakes on this truck working correctly. It could be that they are working very little and placing too much strain on the rear brakes. Just a thought.....

Have you contacted the manufacturer of the truck and brakes, with a problem this serious they may get very involved in finding the problem. This is very unusual I have to admit, good luck!

[BirkenVogt]

Originally posted by hsykes
We have had several cast iron air-brake drums crack with pieces of drum a falling off while driving during the past couple months. If anyone is aware of this type of problem or its resolution please contact bitb@nc.rr.com Thanks.

The drums are Webb 66661 with Meritor brakes on a 27000# rear axle.

Howard Sykes
Maintenance Officer
Lebanon Volunteer Fire Department
bitb@nc.rr.com

After reading your list my suspicion is on a failure or lack of anti-compounding in the rear brakes.

What relay/quick release valves are installed in the rear emergency/service system and how are they connected?

What type service and spring brake chambers are there?

What are the lengths of the slack adjusters?

In the future you might try the bulletin boards at www.evta.info/forums. It is a format similar to this one but specifically for maintenance and there is a category specifically for brakes. I will also post this reply over on the NAEVT but most of us internet aware mechanics are now at the EVTA one.

Birken

[lvwrench]

Good call Birken and glad to see you on this chat line forum as well as the EVTA. The drums looked just like the ones on our 31,000 lb axle did. Ours actually fell into usually three major pieces if not just thouroughly cracked through as per the photo. There is a possibility of compounding at thr rear brakes although that is not supposed to happen with a rig that new. Too much pressure applied to the brakes could crack the drums. The other thought would be to go back to the original factory parts too see if that cures the problem. If it is a Meritor set up then their factory techs should be able to help. We had Rockwell techs down once to help on a problem years ago and they really helped. Are the backing plates on or do you take them off? In the heat here we remove them per the factory techs to aid in cooling the brakes.Good luck, keep em safe and let us know the outcome.

[hsykes]

We still have not found a root cause of our brake problems. Attached are some updates of additional items that are now known.

1. Our anti-compounding valve has been tested and confirmed as working correctly.
2. Current certified weights (fully-loaded truck) have been taken-by truck, axle and wheel. They are very close to the manufacturer’s gross weight rating but do not exceed the ratings.
3. Temperature readings have been taken of all four drums immediately following heavy braking. This occurred after it had been driven as it is for a code-3 (emergency response) run. Temperatures of each drum were very close to 500 degrees Fahrenheit.
4. The engine is equipped with a Jake brake that is used and has been confirmed to be working normally.
5. The truck manufacturer has informed us that they are aware of several other trucks experiencing this same type of brake failure, but the failure is not seen in the vast majority of their trucks. At this time, they are not aware of what is causing the problems, which are occurring in different parts of the country.

I will update this item again as I have additional details or a resolution.

[lvwrench]

Very interesting. I am sort of a loss but was interested in the fact that you said you were in talks with both Webb and Meritor so I assume it is a Meritor axle system. Have you tried using only the Meritor drums? Since the rigs weighed in within the limits of the axle rating without going over it should be okay there. Are the tires rated for the weight? Have you actually vertified that the axle is the right axle via the tag on the axle? Have the two units been absolutely verified one against the other that they are identical? Good luck and please keep us informed as to the outcome.

[BirkenVogt]

Originally posted by hsykes
We still have not found a root cause of our brake problems. Attached are some updates of additional items that are now known.

1. Our anti-compounding valve has been tested and confirmed as working correctly.

You said the drums were 500 degrees which I believe should be well within their design limits. I am still interested in where this anti-compounding trail leads. Some systems are set up in such a way that if the service brake is applied when the spring brake is already on, then the spring brake release pressure, which is supposed to be equal to the service brake pressure more or less, rises quite slowly because of restrictions, and so it is possible for there to be a brief period of time when the forces on the brake are more than they are supposed to be (spring + service). Most likely to happen when the operator steps in and jams his foot down on the service brake real hard and fast with the spring brakes still applied. This can be visualized by installing a pressure gauge on both the service and emergency ports of the rear brake can and watching to see how fast they both go up when the service brake is applied with the spring brake still on.

Birken

[Peetmoss]

In my opinion I would look at the mating surface of the drum and hub. Is it clean and smooth.? Compounding seems an unlikely cause of your drum fractures to me. I personally have never seen a drum crack in that fashion.

I would however check the stroke of all slack adjusters,and I would also look for galzing of the drums. Also maybe try changing shoes. I use an aftermarket shoe that has elemenated 90% of our heat checking issues and most of our glazing issues.

[tomwnh]

I have seen brake drums crack like this one other time and it was caused by heat (expansion) and the cooling (contraction) of dissimilar materials. If the parking brake is set when the brakes are still extremely hot the drum cools quicker than the shoes and causes the drums to crack as they meet resistance. Taking the dust shields off the axels helped. I’m surprised the manufacture has not suggested a different lining for your shoes or a different drums.