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How to kill a Sundstrand hydro

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Well, I had posted a while back that "this can't be good" with a pic of a piece of metal found in the filter inlet when changing out the fluid on a new to me late model Sovereign.  So I finally pulled the pump today and found the problem.  A problem I will bet daiseys to donuts that no one has ever seen.  It has to be a rare freak failure.  When the pump was pulled the drive gear was missing.  Looking at the "new" pump I can see why.  The washer and bolt holding the gear in place were abviously gone too.  If ished the gear out of the transaxle housing, and proceeded to pull the rear end.  After removal, I turned it upside down and rattled out the missing parts.  It is AMAZING that there was no catastophic loss of the gears.  On inspection, not one nick or chipped tooth I could find.   Now that I have completely cleaned and flushed the rear end, I went to install the "new" pump, but have an issue.  The "new" pump is from a 7117, an older model.  The "old" bad pump does not have the two bolts seen in the pic.  The cast iron rear end housing on the 7117 is drilled to accomodate these two bolt heads.  The late model Sovereign rear end is not.  ANy hydro guys ou there have any answers as to when and why the change?  Anyway, what are the odds of that bolt coming loose?  Anyone ever hear of this?  






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Never heard of such a failure but it is similar to the bolt holding the BGB driver bearing/shaft coming loose leading to BGB failure.  

Nor do I have any idea when the change occured but I'm guessing cost reduction. 

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The original pump is bad, that is why I can't use it.  The one picture is of an internal plate and you can see the damage.  There was bits of metal throughout in the fluid, and I am sure that's what killed it.  It still worked, but was sluggish when climbing hills, etc.  

I can drill the transaxle casting to allow for clearance, but I now want to make sure there aren't a number of other things that differ on the pumps.  I suppose I can pull the rear end again, and use the donor rear end.  However, I hate to split the case, and the donor has a broken axle tube.  

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I do have a question:  Why wouldn't the filter have protected the pump?  I would think the pump is drawing fluid post filter, no?   It would seem to me that's the whole idea behind the filter. Bypass?

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