Replacing a Pinion Seal

 

Replacing a Pinion Seal

 

 

Replacement of the differential pinion seal on a Chevelle can be performaned by more than one method.  Of course, it should be replaced any time the pinion gear is removed, such as ring and pinion replacement.  This article deals with replacment of only the seal in event of a pinion seal leak on a 10 or 12 bolt rear.  First, be sure it's the pinion that is leaking.  A leaking cover gasket will sometimes appear to be a leaking pinion seal from lube running forward on the bottom of the housing and dripping off the seal flange.   For any replacement method, a pinion yoke holding tool must be available or fabricated.  If none available, a large pipe wrench with a pipe "cheater" extension will work in a pinch.  CAUTION: It's recommended the rear of the car be supported by more than 1 pair of jack stands, due to the forces to be exerted on the differential during the work.  It's not an easy job.

The first method is per the Chevy Chassis Service Manual and is preferred.  The rear tires and brake drums should be removed.  Drain the lube by removing the rear cover.  After removing the driveshaft, utilize a small scale (0-50) INCH-POUND torque wrench and turn the pinion yoke clockwise.  IMPORTANT STEP:  Record the inch-lb figure required to turn the yoke and gears, etc.  Install the pinion holding tool (or pipe wrench) with the extension of the holder to the passenger side of the pinion and resting against the floor.  Remove the pinion nut (turn CCW) and yoke.  It may take a few taps with a hammer cushioned by a piece of wood to get the yoke off.  Pry out the old seal.  Put a thin coating of silicone gasket sealer on the new seal and tap it into place.  Put new gear lube on the seal lips.  BE SURE to not seat the seal flange all the way into the housing.  Replacement seals must be installed so an approximately 1/8" gap remains between the seal fanage and the housing front edge or it will rub on the pinion bearing.  Claen and put a thin coating of gasket sealer on the pinion gear splines of the yoke.   Reinstall the yoke and start the nut using either a new self locking nut or the old one with red Loc-Tite on the threads.  Now comes the sensitive part.  Install the yoke holding tool with the extension on the driver's side of the pinion, resting against the floor.  Tighten the nut (CW) to the point where the turning force of the gears as measured by the inch-lb torque wrench is exactly the same as before the nut was loosened.  It will require frequent checking with the torque wrench.  Slightly more (1-3 inch lbs) turning force is acceptable but less force is not.  That is important to put the same or slightly more pressure on the crush sleeve which is behind the front pinion bearing.  The purpose of the crush sleeve is to pre-load the inner bearing race of the front pinion bearing and prevent it from turning on the pinion gear.  After the nut is tightened the proper amount, reinstall the driveshaft, cover, and replace the lube with new to the bottom of the fill hole.  Either use a new cover gasket or no gasket with silicone sealer applied to the cover before installing it.  Removing the front pinion bearing and replacing the crush sleeve with a new one is an alternative, but that's no picnic (crushing the sleeve requires about 300 ft-lb of torque) and should be avoided.

The second method is per a Pontiac Chassis Service Manual and does not require a small inch-lb torque wrench, which can be very difficult to find.  The steps are essentially the same but instead of using the torque wrench to measure turning force, a mark must be made on the pinion stem and nut before the nut is loosened at all.   Use a chisel and hammer to make a continuous indexing line on both the nut and stem.  The old nut must be re-used.   BE SURE to make those marks before touching the nut or you're screwed.  Marks made with a felt tip won't work.  They disappear.   When reassembling and tightening the nut, tighten is so the marks line up the same as before it was loosened, then tighten an additional 1/32".  No more or the gear tooth contact pattern may be disturbed and gear noise will result.

The third method, as used successfully by some, is the least technical but is reported to work.  I don't recommend it except as a last resort.  Same steps as the first method but without the inch-lb wrench.  When assembling and tightening the nut, use a regular ft-lb torque wrench and torque the nut to 100 ft-lb.  That reportedly puts the right amount of pressure on the crush sleeve but obviously is approximate.