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Contributor
Location: Washington State | This is an important advisory to FMC motorcoach owners of a very serious and potentially life-threatening catastrophic failure of the steering bellcrank. I own an MCC/Barth, which many of you know is based on the FMC design and tooling. I was completing the setup of my rebuilt MCC front end and making adjustments. While turning the steering wheel back and forth something didn't feel or sound right. I had my wife turn the wheel back and forth while I was underneath and I traced the problem to the bell crank. The bellcrank is essentially a section of steel tube inserted into the steering arms then welded together. The welds on mine are broken, allowing the steel tube to rotate inside of the steering arms. It only rotates a few degrees until the jagged edges of the weld catch, but over time this will loosen up. Eventually the steering arms will no longer be "linked" to the steel tube and there will be no steering. Mine broke where the arms that connect to the tie rods are welded to the steel tube. It is possible that the welds connecting the drag link arm could break, so I recommend checking that as well. I removed my bellcrank (again) and took it to a certified welder to repair. IMHO these factory welds are pathetic. It looks like a single-pass, marginal quality weld. If others, including FMC are as poorly constructed as mine, this could be a looming problem for a number of us. I am going to attempt to attach a picture showing the broken weld.
 (IMG_8462.JPG)
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 IMG_8462.JPG (105KB - 54 downloads)
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Regular
Location: Opelika, Alabama | Thank You, unfortunetly it rained today but will check Mine soon! | |
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Extreme Veteran
Location: Scottsdale, Aridzona | Hello Roy. An amazing and significant find ! Have you also examined the IDLER ? It is the same fabrication with one less arm. It too would be suspect. How many miles are on your MCC ?
Long accepted non-destructive testing for cracks of any kind like weld, stress, corrosion, etc. is the "red" dye penetrant method. It is accepted for virtually all metals/welds and is cheaper than zyglo (similar method) and magnaflux inspection.
About the cheapest ($73+ship) dye penetrant kit I have found is the Magnaflux Spotcheck Sk416 Kit -
http://www.amazon.com/SPOTCHECK-SK-416-Penetrant-Kit/dp/B0086ANFC6.
There are instructions in the kit, and/or review a good "how to" such as -
http://www.nationalboard.org/Index.aspx?pageID=164&ID=374.
Getting the part clean is always a problem, and the two cans of cleaner get used up a lot faster than the penetrant or developer. Aerosol can Brake Cleaner is a cheaper replacement for the cleaner, and many use that for the initial clean up and reserve the kit cleaner for wiping off the penetrant. Just make sure you wait at least 4-5 minutes for all the brake cleaner to evaporate, before applying the penetrant. Clean the penetrant, while it is still wet. The penetrant should be wiped not squirted with cleaner, as the squirted cleaner may wash the penetrant out of a crack, and the developer would show nothing. These "kits" are made offshore now, so there may be even cheaper ones available. The Magnaflux Spotcheck Sk416 has been around before I used it in the USAF as a Jet Mechanic in the 60s, and many times since. Most welding supply shops will also have the Sk416 Kit or something comparable, as will most good welding shops. Individual cans of cleaner, penetrant, and developer are also available. You, of course, can get a Dye Kit and check for cracks yourself, or take the Bell Crank and the Idler to a welding shop for inspection, and repair as necessary.
I really wish you had not discovered this manufacturing defect, but it is real and has unacceptable consequences. Examination of the welds "in situ" is essentially impossible as both pieces are "up in there" and the welds, particularily the top of the welds, are very difficulty to even see, much less clean, penetrant spray, clean, developer spray, and then inspect. The difficulty is to get both the Bell Crank and the Idler out so the welds can be inspected. We are all now compelled to remove and carefully inspect the welds, with one of the accepted non-destructive methods (red dye penetrant, zyglo penetrant, magnaflux) of the Bell Crank and the Idler on each and every FMC and MCC. Damn ! Well, so be it. If anyone else discovers weld cracks or other issues with the Bell Crank and Idler . . . please share your findings (with pictures please !), and your repairs, with all FMCers and MCCers. One way or the other . . . it is probably time to replace the bushings in the Bell Crank and the Idler anyway . . . but that is another story.
I really thank you for bringing it up in a timely manner with clear evidence as shown in your excellent picture and narrative.
Lou #120.
Edited by hemi354az 2013-01-01 10:01 PM
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Extreme Veteran
Location: Scottsdale, Aridzona | http://www.rotax-owner.com/pdf/spotcheck2.pdf
Another "how to" by Magnaflux Spotcheck.
Edited by hemi354az 2013-01-01 9:48 PM
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Contributor
Location: Washington State | My odometer shows just over 37k original miles, but my speedometer no longer works. I was told when I bought it that it has about 50k total, and this may be accurate based on the story verified by MCR, as they sold this one back in the '90s and that owner ended up owning two MCCs and essentially parked this one. So best guess is 50k miles, which I suspect is significantly less than many FMCs and MCCs out there. I haven't pulled (again) the idler out and checked it yet, but I will because I agree that given the construction is virtually identical, the idler is also at risk. The idler does see less stress, though, since it is only controlling the right wheel. I've already had these parts out once and had new bushings machined for the idler. The bellcrank bushings were in good shape so I reused those. I have to admit that it never occurred to me to closely inspect the welds. Just goes to show you, don't take anything for granted. I tell you, I had to do a double and triple check when I saw that tube moving inside of the arms. I could not believe what I was seeing, that was the last thing I expected. | |
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Extreme Veteran
Location: Scottsdale, Aridzona | Send me a regular E-mail please. I have another issue to discuss. Thx, Lou.
< xjetmec@cox.net > | |
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Expert
 
Location: Cottage Grove, OR | One thing to remember is that MCC did not use FMC manufactured parts to my understanding. They purchased the tooling and design, but not the parts inventory. This means that, most likely, MCC manufactured their own bell cranks and idlers so what applies to MCC coaches in this regard MAY not also apply to FMC coaches. I, personally, have not heard of this issue applying to any FMC coaches - worn bushings, yes.
Also, MCC coaches are heavier on both axels and have the 22.5” wheels and tires and, therefore, more average force would be transmitted through the MCC coach's steering assembly than for the FMC. | |
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Contributor
Location: Washington State | I had to take another look at the idler arm to realize that, while being similar in construction, it operates on a different principle and is very low risk. The bell crank relies on connection of the drag link arm at the top of the shaft (tube) and the steering arms at the bottom. The shaft transfers torque from the bellcrank to the steering arms, therefore great amount of force is applied to the connections of these parts.
The idler arm is constructed by welding the steering arms together, one stacked on top of the other with an offset, then connecting the arms to the shaft. All torque is transferred from arm to arm and the shaft serves only as a pivot point. No torque is transferred via the idler arm shaft.
So, to sum it up, I feel good about the idler arm now.  | |
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