Saturday, December 22, 2012

Top tip: Properly sealing the inboard CV drive flanges

A common problem on both Dino's and Ferrari 308/328 cars is the contamination of the inboard CV joint by poorly sealed drive flange splines. If gear oil leaks through the flanges it dilutes the grease in the CV preventing proper lubrication and causing premature wear.

To prevent this I would like to share a procedure that I thankfully learned from David F. at Ferrari Service of Bedford (

First up is using the correct sealant and in this case we use Permatex RTV sealant that is resistant to gear oil. Gear oil has certain friction modifiers that attack regular RTV sealants so it is necessary to use the appropriate material for the application.

Next up is a look at the spline that leaks. The outside diameter is kept dry by means of a seal but oil can still creep through the splines and into the CV.

The RTV sealant is spread neatly but liberally on the inside of the splines of the CV flange. Note also the mark made to show the location of the indexing hole.

The CV flange can now be slid into position. Leave the overflow of RTV as it will serve to act as a final seal.

With the drive flange installed now the mounting bolt and washer must be installed. Note that the notch in the large washer goes in the hole marked by the line. Also you can see the overflow of RTV has been flattened by the large washer making a nice large continuous seal under it.

Lastly using some bolts and a large pry bar, the flange is held stationary while the prescribed torque is applied to the fixing bolt.

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