The Final Drive housing that contains the differential is prone to having the bores for the two main roller bearings "shagged" into an ellipse. This elliptical shape can no longer maintain the bearing interference fit required for accurate crown wheel and pinion set-up, long bearing life - or maintain the accurate shaft spacing required for minimal gear friction and maximum power transfer.
The WEVO solution is to machine a pocket into the pinion bulkhead and shrink fit a stainless steel alloy bridle insert into the case. The bridle is designed to harness the two bearings together - similar to the way the late model G50-50 911 Turbo transmission is manufactured. The exact spacing of the Input shaft and Pinion shaft can be maintained under much more stressful service conditions.
The Bridle is also designed to install the superior input shaft roller bearing (930 302 391 00) from the 930 transmission that was also featured on the last series of 915 transmissions. This bearing has a smaller outside diameter than the original 915 input shaft roller bearing and can only be installed after the bearing bore diameter is reduced by the WEVO bridle insert.
After the Bridle is installed by a shrink fit and two retaining screws - the Maincase is final machined, blue printing the interference fit for the input shaft and pinion shaft roller bearings and the precise shaft spacing. The pinion bulkhead is faced to ensure the case is square, flat and perpendicular to your crankshaft.
We then install 10 carbon steel thread inserts for the positions of the Bearing Retainer, allowing the use of 12.9 grade M8 x 20 cap screws to firmly anchor this important part of the transmission bearing package. WEVO always cross drills and lock wire these 10 bolts when building a 915 transmission and recommend this practice.
Alll new studs installed.
The Final Drive modification suits all 915 transmissions 1972 through 1986 magnesium or aluminum and 930 transmission.