On Fri, 2009-01-02 at 01:06 -0500, Phil Chambley Sr. wrote:
> I do not believe the issue with the Ten Tec PTO mechanics is one of wear in
> the planetary drive, and I will explain my reason. The drive is made up of
> ball bearings, tracking in a bronze race. We've all seen electric motors
> with ball and bronze bearings run for years without a problem. An electric
> motor will rotate more in a day than a PTO shaft will be turned in twenty
> years, and it will do it without noticeable wear.
There was a serious groove in the bronze race in my PTO bearing. The
replacement had no such groove and drives the shaft through the whole
range that the old one didn't. Remember the balls contact area is far
smaller than in a motor bushing. The PTO frame is made from an extruded
aluminum channel and the inside surface is not exactly perpendicular to
the shaft. So that bronze cup sits at an angle to the shaft. With the
three balls carrying the load, only when the cup is aligned properly, in
this PTO only one ball is loaded at a time.
>
>
>
> The real culprit with these PTOs is a combination of using a grease with
> poor aging properties, along with the use of a PLASTIC THRUST BEARING CUP.
Poor perhaps compared to what? We tend to keep these around for much
longer than most consumer products are expected to last.
In my PTO, I left out on of the thrust washers and came up with a pretty
good shaft load. I'd force that one in, if I ever took it apart again
and still had the thrust washer to go in.
>
>
>
> It is the latter that causes the greatest problem.
>
>
>
> The thrust bearing cup keeps pressure on the planetary drive. The friction
> between the balls and the shaft/race assembly must always be greater than
> the resistance of the return spring and other frictional losses, otherwise
> the drive will slip. As the grease thickens, the need for better contact in
> the planetary drive assembly is multiplied.
>
>
>
> The problem is, the thrust bearing cup is made of plastic, and it is mounted
> via two screws in its "ears" which are out of plane with the shaft. This
> allows the mounting ears to stress-relieve, and reduce the pressure on the
> end of the shaft, and consequently, on the planetary drive. When this
> happens, the drive will begin to slip, whether or not the grease has
> thickened, but thick grease will magnify the effect.
>
>
>
> I recall seeing one bearing cup so deformed that it was necessary to
> re-surface it by scrubbing it on a flat emery surface. I've repaired quite
> a number of these drives and have never had one fail again.
>
>
>
> The drives I've corrected only required cleaning out the grease and removing
> one of the washers under each ear of the thrust bearing cup. This restores
> the pressure on the ball/race assembly. Removing the PTO is not usually
> necessary for this operation.
>
That would not have fixed my PTO.
>
>
> Phil C. Sr.
>
> k4dpk
>
73, Jerry, K0CQ
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