Friday, September 22, 2006

Crimson Tide

I am in Alabama, at a Wal-Mart in Saraland, just north and west of Mobile (map).  I reached my projected stop of Greenville yesterday around 2:15, well ahead of schedule.  I decided it was too early to stop, and, even though the next Wal-Mart was past the Mobile River, that was only two more hours away.  With rest stops, I still made it here by 5.

One of the strategic errors of this plan, however, was that I had to run the A/C all night -- it is much warmer and more humid here than up north.  Thus it will remain now as I proceed through "LA" (that's Lower Alabama, don't you know) and the gulf coast of Mississippi and on to New Orleans.  I am seriously considering an RV park there just to have full-time power for the air conditioning, especially since it will be two or three nights.

The major news I have to report from here is that the upper windshield suffered major cracking last night.  The bad news is that I don't think we have the time or resources to get it replaced before Mexico.  The good news, if you can call it that, is that I definitely know now why it cracked.  As I suspected, it is a stress fracture.

As you recall, the windshield was installed improperly (in fact, I have been speculating for some time that the improper installation has been responsible for the leakage we have been experiencing).  To be more specific, the installers ran a bead of adhesive around the steel window frame, and then glued the window to the frame, filling in the remaining gaps with adhesive sealant.  This is the way most automobile windshields are installed, and these guys had never experienced anything different.

The correct method is to place the glass, dry, onto small rubber blocks that stand the glass off from the frame by about 3/8" on all sides.  A special, flexible urethane adhesive is then injected into the gaps, resulting in a 3/8" cushion of urethane all the way around the glass.  By contrast, with the glass glued directly to the steel, as it is now, any flexion or stress in the steel is transferred directly to the glass.

Last night this fracture mechanism was confirmed in a dramatic way.   After I parked, in a spot that was sloped both to the front and to the right, I set the level controls to get more-or-less level, and went upstairs to prepare the coach for the night and start making dinner.  Now, the leveling valves are very slow to respond, so I am accustomed to setting them by experience to where I think they need to be, then doing something else for five minutes while they settle in to position.  Then I re-check level and adjust as necessary.

While I was going about my business, I heard a popping sound from the front, and the cats were staring in that direction, wide-eyed and alert.  My first thought was that some pranskster was throwing rocks at the windshield -- I ran forward and drew the drapes.  "POP" -- a crack happened right in front of me.  I raced downstairs to put air into the rear leveler as quickly as I could.  Unfortunately, the damage was done -- cracks now extend about a foot from the upper right corner, diagonally down towards the center.  One set of cracks has even made a complete loop, creating a loose piece of glass held in only by the safety laminate.  The cracks are open-ended, and I expect that they will continue to spread across the windshield from wind pressure on the glass.

What happened is this:  The rear suspension is controlled by only one ride-height valve.  This allows the coach to roll left or right as needed and dictated by the front air bags, which are controlled separately.  If, however, one side of the rear suspension "bottoms out" onto the hard stop, then that hard stop, combined with the pressure of the front suspension in the diagonally opposite corner, will impart a twisting stress on the coach -- with the front of the coaching trying to roll left, for example, while the rear is trying to roll right..  Apparently, the left side settled onto this stop last night.  This same sort of stress is induced when the air system empties with the coach on anything but flat ground, or when jacking one corner to remove a wheel, or if the suspension bottoms while driving, due to potholes or whatever.

Putting more air into the rear system, to get it up off the stop, removed the flexing torque.  So things are stable -- for now.  We will see how much spreading occurs in the next few days.  I have a spare windshield standing by in Nashville -- if the problem becomes emergent, I can have FedEx Custom Critical pick it up and bring it to some location along our route, such as Houston or El Paso.  The challenge then will be to find a shop that can remove the damaged glass and properly install the new one.

I'm hoping the thing will just hold together for the Mexico trip.  At least that way I won't be worrying about breaking a brand new windshield, either on the Mexican roads, or on the piggyback train.

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