Differential Nightmare

The differential is a major driveline assembly which doesn't get much attention until it gives trouble.  Fortunately the Rambler differentials are heavy duty and very reliable.

They seldom give major problems - however, six years ago when I bought my first hobby Rambler (I had Ramblers 15 years ago but they were my transport) it had a terrible oscillating drive line noise.  It sounded just like the differential gears/bearings were worn.  The noise was the right frequency for differential problems.

So I was recommended to a mechanical workshop that had experience with Ramblers and on a test drive he confirmed that it was the differential.  So the cost was $1,150 to remove and overhaul the differential.  Well the car was no good to drive as it was so I gave him the go ahead.  Four weeks later the job is completed with new differential bearings, matched crown and pinion and rear wheel bearings.  The shop that overhauled the differential ran the diff up to speed to ensure it was quiet.

So I pick up the car and go for a test drive and to my disappointment it is still fundamentally the same.  A little quieter but all the same!!

So in the end I found it was the torque tube drive shaft that was source of the noise not the differential.  The shop that did the work never even checked the drive shaft even though they would have had it in their hands and it is easy to inspect.  But things didn't improve.  Three months later I accelerated hard on take off and heard a sharp wrenching sound from the differential.  I later found this to be the rear axle slipping and shearing the hub splines.  The repair shop had not torqued the axle hub nut enough!  The story gets worse as this differential later got driven without any oil (my screw up).  So this differential seemed to be doomed.

What work is required on the differential?

If you do not know the history of the differential in your car it is recommended that you change the oil as a minimum.  One Rambler I had the diff oil was totally brown/red when I removed it.  I believe the car had been idle for some time and the upper section of the crown wheel rusted.  On driving the car the rust would have worn off giving the oil the red colour.  Interesting the diff was still good and gave no trouble.  The differential place I now use and respect recommends the use of multi grade differential oil.  Single viscosity oil is also acceptable.  Take care that gasket surfaces are clean when installing a new diff housing gasket and that you fill the differential up with oil.

Changing rear wheel bearings requires removing the rear axle and removing the hub from the axle.  This is no mean feat.  The hub is secured to the axle via a taper and spline arrangement with a key to locate the assemblies.  It is very difficult to remove a hub and axle that has been together for 40 years.  A special heavy duty hub puller or a 30 tonne (minimum) press is required.

Important items for reassembly is setting up the axle end play with shims on the left had side.  Flange sealer also needs to be used between the brake backing plate, the housing and outer oil seal to prevent diff oil leaks.

There is an inner seal that should be checked and replaced if necessary.  The axle needs to be removed to be able to drive the seal home square.  This seal prevents differential oil getting to the wheel bearing area.

The outer seal is less critical as this seals the grease used in the wheel bearing from the brake linings.  If you use a modern high temperature wheel bearing grease this seal should be adequate to seal grease flowing to this area.

The rear axle to hub nut needs to be torqued to a minimum of 250 ft lbs (170Nm).  My method of ensuring this is correct is to have a 1m bar on " drive socket and stand on the 1m bar until you are satisfied that it is tight.  Anything short of this and you risk shearing the hub axle drive.
Differential after sandblasting and being painted with 2K black.

It is interesting to note that a second differential I had overhauled initially had a slight whine at about 50 mile per hour.  After 5,000 miles the noise disappeared.  A successful example of ignoring it and hoping it goes away!

Contributed by Rohan Borrell Technical Officer