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scary observation...a nut that was sheared in half

January 10, 2011, 01:44:25 pm

I pulled the 02 u270 out of the shop yesterday to take it for a little exercise, heat the fluids and to move some stuff around in the shop.  With it out of the shop, I kicked something across the floor-- it was a 3/4" bolt / nut that was sheared in half...

Very concerned with what this massive bolt was likely intended to do, I carefully put the coach back in the shop to do some looking around in the suspension area.  It ended up being one of the ( fasteners (4 on each side) that holds the steer axle to the front suspension.  YIKES!  Based on the corrosion that covered half of the shear section of the bolt, it looked as if it had been cracked for awhile and the suspension inflation (at start up) stressed the bolt to breakage.    In looking at the mounting surface, the bolt hex is captured by the vertical plate-- however, there is a weld bead that may have kept the bolt from sitting square to its clamp surface.  I supposed as the bolt was torqued, be began to bend and crack. 

I'm going to have a talk with FT about their thoughts on this.  Needless to say, I'm a little concerned about the others... 

As anyone else seen such a thing?? 

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Re: scary observation...

Reply #1 – January 10, 2011, 05:33:45 pm

The bolt was destined to fail the day it was torqued. That bolt would stand tremendous amount of tention when properly torqued, but when stressed with a side load it was just a matter of time before it fractured. A soft bolt might take the abuse, but not a hard heat treated bolt.
  During assembly often bolt holes do not line up perfectly so the pieces are pryed into position and the results are fractures radiating away from the holes. Just the nature of hand built equipment by unskilled labor. Its not like they are highly skilled technicians building race vehicle's.
  Other places to look for problems are  the fluid hoses ( coolant and hydraulic) touching and rubbing on various components. I have also found several (4) hangers that were installed under side stress and broken. replaced by (pros) only to break again. Sometimes its better to do the small suff yourself, take your time and do it right.    Gordy

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Re: scary observation...

Reply #2 – January 10, 2011, 08:22:44 pm

I checked mine and all 8 bolts are there.  Bet you are glad you found it.  That is the kind of thing I go under the MH and look for.  So far I have found a set of brake pads that needed replacing, a leaking shock, leaking front wheel seals, and a few other things.  Sounds like a simple fix,  file or grind the suspect area flat and install a new bolt of the correct size and grade.

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Re: scary observation...a nut that was sheared in half

Reply #3 – January 11, 2011, 09:59:35 am

That would get my attention big time too.  The only time I have seen such an issue was after a wreck where the front end took a very big hit on the left front wheel, from a Isuzu pickup truck driven by a drunk who ran into the left front wheel on a loaded tandem loaded dump truck.  Most interesting, the drunk driver did not get hurt, he went thru the windshield and down the road about 50 ft, not hurt, scraped up a bit. Most interesting fact was finding the valve springs from the Isuzu 150-200 ft away.
The dump truck also suffered cracked spindle and bent drag link.
Should have taken pictures of this one.
Scary stuff indeed.

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Re: scary observation...a nut that was sheared in half

Reply #4 – January 11, 2011, 10:34:45 am

I haven't gotten back under the rig to look at the area, but I need to review how I will torque this bolt.  The bolt is rated to approx 375 ft/lbs and will require another shop to put the necessary torque on the nut.  My torque wrench is only good for about 250 or so.    I've got a few weeks to figure it out....

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Re: scary observation...

Reply #5 – January 11, 2011, 10:55:46 am

A possibility for proper torque maybe found in the instruction manual or the steering gear, called the "Torque-Turn" method.  Like some head bolts may be spec'd for 110ft lb PLUS 120 degree turn or that type torque requirement.  I am not sure for the steering gear, but there are lots of specs for different NEW bolts.  This torquing always requires new bolts, this is a stretch of new bolt.
We have the 3/4" torque bars.

For a funny, Cat engine 353 series 6 cylinder, 6.25" bore, 1200 rpm max,  mains are torqued to 1350 ft lb if I recall from the old days.  Aint no fun
That is no longer a big engine.
Wonder if Brett ever played the 353?

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