3rd and Drive slipping bad

[TomsSVX]

Looks like the case cracked.... drained the fluid and burned up the pinion bearing thus killing the gears... I would put money on the pinion bearing being loose and noisy

Tom

[dan_j_b]

Yeah the pinion bearing doesn't sound too good when I turn it. My only question with your theory is how did the case crack? I think the crack was the result of the damage, not the cause.

[TomsSVX]

Could have been... The #1 cause for gear wear is the pinion bearing taking a crap... I guess the cracked case was just a result of the worn gears meshing inproperly and breaking the case... How do the seals look on the axles?? If those go bad, the gear oul leaks out and that can cause bearing failures.

Tom

[oab_au]

I would say that the failure started with the crown wheel being forced away from the pinion gear. Unfortunately the front diff isn't very strong, the pinion is firmly held in a steel plate, that is bolted to an aluminum housing that holds the crown wheel.
Any extreme or sudden loads, like front wheel spin will distorting the aluminum case, allowing the crown wheel to move away from the pinion. This moves the tooth load out to the tip of the tooth, that eventually breaks off from the load. The broken tooth piece jams between the two gears forcing them apart to break the case.

They did reinforce the case to help with the distortion, at some stage, so it may be only in early models.

Harvey

[crotchrocketony]

I did my diff swap last ngiht. not bad at all. so when this trans mission blows up (I have no faith in it being this is #3) Im guessing I could buy a legasy trans and then just swap the front diff so I dont have to mess with the rear

[dan_j_b]

oab_au - Thats true, but how can you explain the fact the the pinion gear is sheared off on one side, but the rest is perfect and the crown is bad all the way around? the pinion had to be locked in that position while the crown continued to turn.

crotchrocketony - The SVX uses a gear ration of 3.545 for the front and rear. As far as I know, there is no other subaru box that uses that. you could swap in some 3.90's or 4.11's for extra fun, but you have to change the rear diff too.

[oab_au]

Originally Posted by dan_j_b

oab_au - Thats true, but how can you explain the fact the the pinion gear is sheared off on one side, but the rest is perfect and the crown is bad all the way around? the pinion had to be locked in that position while the crown continued to turn.

crotchrocketony - The SVX uses a gear ration of 3.545 for the front and rear. As far as I know, there is no other subaru box that uses that. you could swap in some 3.90's or 4.11's for extra fun, but you have to change the rear diff too.

The loading on the pinion teeth, is at least 3.5 times higher than the loading on the crown wheel teeth. The diameter of the gears, makes the difference.

As the case distorts the crown wheel moves away from the pinion gear to move the load out to the pinion tooth tip. So the pinion breaks a tooth off first, keeps rotating to damage the crown wheel teeth. The next pinion tooth is then impact loaded to break off next, until there are a number of pinion teeth off.

Harvey.

[dan_j_b]

Yes, but if you look at the picture, there are only a few teeth broken on one part. 2/3 of the teeth are still perfect. The pinion gear obviously stopped turning before the teeth were broken off.

[Trevor]

Originally Posted by oab_au

The loading on the pinion teeth, is at least 3.5 times higher than the loading on the crown wheel teeth. The diameter of the gears, makes the difference.

As the case distorts the crown wheel moves away from the pinion gear to move the load out to the pinion tooth tip. So the pinion breaks a tooth off first, keeps rotating to damage the crown wheel teeth. The next pinion tooth is then impact loaded to break off next, until there are a number of pinion teeth off.

Harvey.

Not a correct answer.

The exact loading being questioned is the lateral forces involved, as would be required to distort the case. Not subsequent loading on the pinion teeth, which involves gear diameters.