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Author Topic: Broken brake drum  (Read 3310 times)
Sam 4106
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« Reply #15 on: March 12, 2013, 01:38:11 AM »

Rick and Chessie,

Thanks for your input. I think you are right about the reason for the drum cracking. The drum has the small holes for the flat head screws. Stud piloted. I took the drum back off and found that it is peeling metal off the hub flange for about 1" at every stud. I had only managed to force the drum onto the flange about 3/32". So I think the inner nut on the studs were over tightened when they were installed. I think the studs were changed when the PO had aluminum wheels put on. There is nothing wrong with the drum, the problem is the hub.  The drum fits easily over the brake shoes and the hub spins freely. I did back the brakes completely off to remove the cracked drum and the cracked drum is still the original size of 14.5," as best I can measure it, so I think the shoes are standard too. I will try filing the hub flange by each stud and try to put the drum back on. There will still be plenty of surface between studs to center the drum and the tapered, slotted screws will also help to center the drum. If that doesn't work, I'll have the flange turned so it is concentric, or look for a different hub.

I often lay awake at night pondering a problem and often arrive at a workable solution. But, input from others is valuable in broadening my thought process. This is a case where reading your input got me to thinking in a new direction. Your input is very appreciated.

Thanks, Sam
« Last Edit: March 12, 2013, 01:50:02 AM by Sam 4106 » Logged

1976 MCI-8TA with 8V92 DDEC II and Allison HT740
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« Reply #16 on: March 12, 2013, 06:14:26 AM »

I have only removed a front drum.  It required a few few raps with a hammer to break the rust loose.  It slid back on quite easily by hand.  Is it possible that your old drum was the wrong part number and that is why it cracked?
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Jim Keefauver/1985 Wanderlodge PT36/6V92TA/MT654CR/East Tn.
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« Reply #17 on: March 12, 2013, 07:46:37 AM »

Could it be that someone has installed the wrong hub (hub piloted) on your bus?  The difference between hub bores on the wheel is 8.669" for hub pilot and 8.722" for stud pilot.  I'm guessing that the drum bores would be the same.
« Last Edit: March 12, 2013, 07:54:42 AM by Len Silva » Logged


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Sam 4106
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« Reply #18 on: March 12, 2013, 09:53:24 AM »

Jim, thanks for the info on how easily the drum should slide on.

Len, you could be right that the front hubs are hub piloted with stud piloted studs. Both the drive and tag axles had hub piloted hubs with hub piloted studs and nuts, but with stud piloted wheels when we got the bus. That allowed the wheels to be off center in any direction and the ride was not smooth as a result. Those were changed to stud piloted hubs and studs from an MCI 9 that a friend was parting out. Since the front axle has stud piloted studs I didn't change those hubs. Even if the front hubs were originally hub piloted they still work as stud piloted with stud piloted studs. The flange that the hub piloted wheels ride on is not the problem. As you point out the hole in a stud piloted wheel is larger than that of a hub piloted wheel. The problem I have is that the outside of the hub flange that the inside ledge of the drum sits on is enlarged at every stud location. The bore of the drum inside the stud holes doesn't rest on the hub flange, there is at least a 1/2" clearance there. Nor are the stud holes in the drum tight fitting, some clearance there too. I hope I have explained the situation adequately, if not ask more questions.

I appreciate all the thoughts that have been offered. Thanks, Sam
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1976 MCI-8TA with 8V92 DDEC II and Allison HT740
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« Reply #19 on: March 12, 2013, 09:42:11 PM »

Jim, thanks for the info on how easily the drum should slide on.

Len, you could be right that the front hubs are hub piloted with stud piloted studs. Both the drive and tag axles had hub piloted hubs with hub piloted studs and nuts, but with stud piloted wheels when we got the bus. That allowed the wheels to be off center in any direction and the ride was not smooth as a result. Those were changed to stud piloted hubs and studs from an MCI 9 that a friend was parting out. Since the front axle has stud piloted studs I didn't change those hubs. Even if the front hubs were originally hub piloted they still work as stud piloted with stud piloted studs. The flange that the hub piloted wheels ride on is not the problem. As you point out the hole in a stud piloted wheel is larger than that of a hub piloted wheel. The problem I have is that the outside of the hub flange that the inside ledge of the drum sits on is enlarged at every stud location. The bore of the drum inside the stud holes doesn't rest on the hub flange, there is at least a 1/2" clearance there. Nor are the stud holes in the drum tight fitting, some clearance there too. I hope I have explained the situation adequately, if not ask more questions.

I appreciate all the thoughts that have been offered. Thanks, Sam

Sam,

Are the stud retainer nuts installed correctly and with a proper flat washer? The correct nut is a locking nut. One end is rounded. If they were installed backwards without a washer, it would probably bulge the hub flange as you have mentioned. I was thinking the hub is aluminum, but it's been a few years since I had mine off.

craig

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Craig Shepard
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Sam 4106
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« Reply #20 on: March 13, 2013, 08:17:38 AM »

Hi Craig,

I just went to the shop to see if the nuts are locking, the washers are there, and are installed correctly. They are. I have no idea if the hubs are the right ones for an MC 8, but the ones currently on the bus are cast iron.

I know it is possible to distort cast iron by over tightening bolts because when my brother was helping me change the manual transmission in our 4106 he overtightened the bolts holding the flywheel to the crankshaft. When I installed the new pilot bearing it would not turn freely so I had to put on the flywheel that I got with the transmission. I can't fault my brother because he was in the early stage of Alzheimer's disease and had already lost some of his former capability. He had been a good mechanic his whole adult life and was always willing to help me with projects. He lost his life to Alzheimer's 2 years ago.

I will update when I learn if filing or grinding off the high spots works. Thanks for your thoughts. Sam 
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1976 MCI-8TA with 8V92 DDEC II and Allison HT740
Sam 4106
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« Reply #21 on: March 13, 2013, 03:50:33 PM »

I used my Dremel tool and a small grinding wheel to slowly take off the high spots of the hub flange. It took five tries but the drum finally slid into place using the five slotted screws to nudge it on. I did the final tightening with the lug nuts before I put the wheel back on and torqued it on. I will have to readjust the brakes after the shoes conform to the new drum. I left them a little loose initially.

Thanks everyone for your help, Sam
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« Reply #22 on: March 17, 2013, 05:09:04 AM »

Sam, I'm kind of concerned about your studs. If the backing nuts were overtightened to the point that it distorted the cast iron hubs, then surely the studs have been stretched which will result in weakened studs that could break. I'm not sure I believe that it's possible to distort the cast hub before the stud breaks, but obviously something is causing the distortion.
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Craig Shepard
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http://bus.gumpydog.com - "Some Assembly Required"
Sam 4106
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« Reply #23 on: March 17, 2013, 12:23:27 PM »

Craig,

Thanks for bringing that to my attention. I had not previously considered that, but I don't think I will change the studs at this time. If there is a problem with them and they do start to fail, I doubt that they will all fail at the same time. If one ever breaks, then I will replace them. There are so many things on a bus that have the potential for catastrophic failure that we live with every day, I am not going to worry about something that is unlikely to fail catastrophically.

Good luck, Sam
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1976 MCI-8TA with 8V92 DDEC II and Allison HT740
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« Reply #24 on: March 17, 2013, 12:42:07 PM »

Without any wheel installed, run a lug nut all the way down the stud by hand.  It should spin on easily and without any change in resistance.  If it starts to bind up anywhere along the stud, that's an indication it may have been stretched.
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« Reply #25 on: March 17, 2013, 03:48:50 PM »

"If there is a problem with them and they do start to fail, I doubt that they will all fail at the same time. If one ever breaks, then I will replace them"
A number of years ago I was getting my 4106 ready for a trip from Vancouver, Canada to California for a race. I had the bus in for service and apparently the tech told me I had 2 broken studs on driver's side rear duals.  I was quite new to buses and I'm sure I thought that even though 2 were broken that left 8 good ones.
Anyway, we were travelling down the I-5 and had just decended from the Sykyous Pass from Oregon to California and I notice a vibration. My son was travelling with me and he suggested I speed up to see if it would go away.  I sped up to 75mph and then returned to 55. A few moments later all hell broke loose as both rear wheels came off the bus and it ground to a halt dragging the left rear. One wheel hit the side of a car with a man and his son in it. Luckily the wheel and car were going the same direction so only minor damage. I remember vividly seeing the second wheel go spinning past me from the fast lane where I stooped to the right lane and into the ditch and a field 1/4 mile away. The cops came and a wrecker hauled the bus to Yrecka where I was able to get it a week later.
When I got home from the trip I mentioned to the mechanic what had happened and he said "I told you that you had 2 broken studs". As I mentioned earlier I am sure my thoughts were that "I still had 8 good one left".

Regards

Fred
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Sam 4106
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« Reply #26 on: March 17, 2013, 06:46:03 PM »

Len,

Your method is reasonable for the wheel end of the studs, but the end through the hub flange is what caused the distortion. I had the lug nuts on and off 5 times, grinding a little off the hub flange until the brake drum would go fully on. The lug nuts didn't ever bind. The tires that were on the aluminum wheels, when we got the bus, were dated 2003, so I think that is when the longer studs were put on. I have no way to verify that because the guy that converted the bus is dead and his widow, that we bought the bus from, knows very little about the bus. The bus was his project. We got a picture book with the bus and there are no pictures with the aluminum wheels showing. No broken studs in nearly 10 years, but I will watch them closely.

Fred,

Thanks for sharing your experience. It I see a broken stud I will have all of them replaced.

Thank you both for your thoughts, Sam
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1976 MCI-8TA with 8V92 DDEC II and Allison HT740
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