pre-load/torque 915 gearbox

[alexandervdr]

I have the diff of my 86 targa separated from motor and transmission.
The specs for pre-load toque are somewhere between 300 and 650 Ncm (not sure what that is in pound-lbs). I assume that his number gets lower by the miles driven due to wear. How low can it go and still be ok?

PS: I got this picture from another thread. Anyone can tell me which manual this is taken from?

[Zuffenwerker]

[Zuffenwerker]

The procedure your referring to is for the older transmissions. There is a different procedure for checking the taper roller bearings of your 86. It involves removing the pinion shaft and measuring the the diff movement with an indicator

[alexandervdr]

Originally Posted by Zuffenwerker

The procedure your referring to is for the older transmissions. There is a different procedure for checking the taper roller bearings of your 86. It involves removing the pinion shaft and measuring the the diff movement with an indicator

I know, the illustration was for just for clarifying what I was referring to. My question was to know how/if the initial pre-load/torque setting changes with time and miles.

[Zuffenwerker]

Well there is no preload torque setting for your transmission the preload is measured in up and down play. As the bearings we’re wear the play increases which is less preload

[kevingross]

Originally Posted by Zuffenwerker

Well there is no preload torque setting for your transmission the preload is measured in up and down play. As the bearings we’re wear the play increases which is less preload

This procedure is all but useless. It does not produce reliable and consistent results. The original factory procedure works just fine, and is what I use. There really is no difference between the earlier 915 transmissions and what came in your Carrera, and so no reason to alter the methods used.

One thing to understand is that Porsche frequently revises these sorts of procedure when they realize that dealerships and indies don't purchase the tools originally specified. The techs do it "by feel", get it wrong, transmission/engine/etc fails, Porsche takes a hit on warranty and reputation. So they come up with a simpler method in the hope that their techs will at least follow it.

Correct that as they break in, the bearings lose turning torque. Will drop to about 10% of the new bearing torque. I always set up with new bearings, much easier to measure good number on turning torque.

[alexandervdr]

tnx all for the feedback, very helpful as ever!