Date: Wed, 25 Nov 1998 19:51:56 -0600
Reply-To: Joshua Van Tol <jjvantol@USWEST.NET>
Sender: Vanagon Mailing List <vanagon@vanagon.com>
From: Joshua Van Tol <jjvantol@USWEST.NET>
Subject: Re: Bearing load on reverse driven transaxles
In-Reply-To: <33826e80.365cab90@aol.com>
Content-Type: text/plain; charset="us-ascii"
>Joshua Van Tol wrote:
>
>(again, out of context on the quote)
>
><< Flopping the diff in no way results in any change that
>the diff cares about. By backwards I mean turning the input
> shaft the wrong way, not flipping the diff. >>
>
>Yes, but the end result is the same. By not flipping the
>ring gear over to the other side of the pinion and reverse
>rotating the input shaft you are now driving on the coast
>side of the ring gear. I do a lot of the Type I style transaxles
>and do not see any unusual wear patterns on the ring gear
>or pinion head that I can attribute to driving on the coast
>side vs. the regular thrust side. Also, keep in mind that
>the newest gearbox of this type is now 31 years old.
Regardless of which side you put the diff on, as long as you turn the
transmission input shaft the same way, you load the gear teeth the same
direction. I had to draw a diagram to prove this to myself, but it is true.
Think of it this way, all you are doing when you put the diff in the other
side of the case is to rotate the diff around the output shaft by 180
degrees. The same side of the gear teeth is still loaded, provided the
input shaft still turns the normal direction.
Reversing engine would result in reversing the side of the gear teeth in
the final drive that's loaded, which would probably result in damage to the
teeth, or at least a shorter lifetime, and more noise.
>The only bearing that I would be concerned with would be
>the mainshaft ball bearing, however, I do not think that there
>will be enough of a load along the length of the shaft to
>worry about. The pinion shaft and it's double tapered roller
>bearing should be just fine in either direction.
Yup, the double tapered roller bearings, and the mainshaft ball bearing
would be just fine. But how about the thrust washers or thrust bearings on
the gears? If you reverse the direction you turn the input shaft you'd have
to be sure that the thrust surfaces on the other side of the bearing could
take the load. Either that, or cut some reverse pitch gears to reverse the
axial force. Or use straight cut gears, but those'd be noisy.
I decided just now to pull out the bently manual and take a look.
Specifically, I'm looking at diagrams for the 091 4 speed. The diagrams I'm
interested in are on page 35.25. Looking at second gear, you can see that
it has a needle bearing, to take care of tangential loads (i.e.
perpendicular to the shaft) and smooth machined surfaces to the pinion end
and towards the 3rd gear. Towards the pinion, the thrust surface contacts a
thrust surface on the 1-2 synchronizer hub. This is the interface that
would be loaded while power is applied to the input shaft. To the other
side is a similar arrangement. Thus it looks like vw used more or less
equivalent bearing surfaces for the forward and reverse load surfaces of
2nd gear at least. I haven't studied the diagrams completely, so I don't
know for sure that the rest of the gears are provisioned likewise.
On some transmissions, such as Borg Warners, one or both sides of the gear
would have a flat needle bearing for a thrust bearing, rather than just a
polished metal to metal contact. If only one side had such provisions, it
could be bad to apply much power to the input shaft in the wrong direction.
Joshua Van Tol -- jjvantol@lear.csp.ee.memphis.edu
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