915 8/31 ring and pinion build in dimensions

[Roslin]

I'm seeking the two values, to calculate a different final drive for a 915 transmission.-

- The length "Ro" from pinion front to crown wheel / diff. centerline ?

- The length "B" from the back side of crown wheel, to the pinion centerline ?

See attached photo of a VW final drive. I don't know if Porsche uses the terms "Ro" and "B"

Hope anyone have access to these two dimensions in a book. I tried too see if i could google it, but so far not.

Thanks

Roslin.

[Mark Salvetti]

Ro is calculated (Porsche uses the variable E).

R = 66.30mm. The end of each pinion shaft has a value etched into it, such as N2, where "2" is the deviation from R in hundredths of a mm. N is determined by the factory for each ring and pinion set. They ran them on a jig adjusting Ro until the pair ran with the least amount of gear noise. Then they measured Ro, calculated N, and etched that on the end of the pinion.

In this example, Ro = 66.30+0.02 = 66.32 mm.

I don't know where to find a value for B. It's not something that you need to measure to set up a 915. Instead, you adjust backlash on the ring gear, also determined on the factory jig and etched onto the edge of the ring gear.

Mark

[Roslin]

Thanks Mark !

Is the 8 teeth Pinion diet. to centerline "R" always = 66.30 + the Hundreds ?

Roslin

[Matt Monson]

Yes, R is always the same and then the deviation of the individual unit is scribed on the ring gear.

[blue72s]

And what is the Po distance?

Thanks.

[Matt Monson]

Ro+A.

[blue72s]

Thanks but I don't have the A specs.

Anyway, I needed to know the overall diameter of the crown wheel because I was wondering if it's possible to retrofit a 915 r+p into the 901 mag transaxle by machining the 915 pinion shaft to 901 specs (cutting it to length if the basic shaft diameter and spline pattern are the same) but only if the crown wheel diameter is small enough to fit into the 901 mag housing.

Is the 915 crown wheel (7:31 or 8:35) considerably larger diameter than the 901 version?

[Matt Monson]

Won't fit.

[Roslin]

Does anyone know the "B" dimension for 8:31 setup ?

Thanks Roslin