1946-1949 Rear Differential 1949 club coupe

[Phil J]

Is 1/4 inch of play excessive for the 1949 rear pinion when rotated?  Are parts available for this rear if needed?  Please let me know your thoughts and thanks in advance

[The Tassie Devil(le)]

G'day Phil,

Play in a pinion should be measured at the teeth contact with the Crown Wheel with a dial gauge.

There will always be an amount of backlash so the gear teeth aren't tightly bound together.

Most backlash measurements will be around .010"   As in 10 Thousandths of an inch.   The Shop Manual will have the correct measurements.

There should not be any fore and aft slackness as these bearings need pre-loading to maintain life.

Bruce.

[Jay Friedman]

Aside from replacing the pinion seal and bearing, the '49 rear differential cannot be taken apart.  If it goes bad it must be replaced as a unit, so parts are not available.  (Something to do with special pins that hold it together that only the factory could work on.) 

Differentials were the same from about 1941 to about 1956, the ratio being the only difference. A '49 with Hydramatic should have a 3.36:1 differential ratio, which was probably the most a common ratio used 41-56. If needed just find another one. I had to replace the differential on my '49 some years ago.  I found and bought another and installed it as is since I figured chances were that the seal and bearing were
good.  I lucked out and they were. 

[Phil J]

thank you Jay--good information

[Jay Friedman]

Phil, in my experience they are relatively easy to find since they were the same for many years.  Just make sure it's the correct ratio.  You can do this by counting the teeth on the gears. Only problem is how heavy they are, so expensive to ship.  I was lucky as I found mine at Hershey so brought it home in my car. 

To install, you jack up the rear wheels/axle reasonably high.  Take off wheels and brake drums.  You'll see behind the hubs 4 bolts that hold on flanges which hold in the axles.  Unbolt these and pull out the axles.  Then get under the car and remove the driveshaft.  I usually wrap a cord or piece of tape around the rear universal joint so it doesn't come apart.  Then unscrew the circle of bolts that secure the differential.  Be careful of the special washers behind the bolts.  Using a transmission jack or good floor jack, manipulate the differential out onto the jack and lower it.  There is a large round gasket between the circle of bolts and the axle housing.  I think Olsen's Gaskets in Washington State sells this gasket.  Replace the gasket and install the new differential.  Circle of bolts should be torqued to 30-35 foot-pounds.  Before putting the axles back in I would replace the axle seals at the outer end of the axles just inside the housing.  I think Olsen's sells these.  If not, I think southshorebearing.com sells them. You can remove the old seals by prying them out with the axles.  Drive in the new seals and I suggest coating the rubber with a bit of chassis grease so sliding in the axles does not damage them.  Replace driveshaft, axles, brake drums and wheels.   

[Phil J]

The rear diff is shot so I am actually thinking of installing a more modern unit.  It will be under the car and unseen to most and I like the idea of being able to source parts and repairs more efficiently. I am keeping the car as original as I can but since the rear is not a serviceable item, it seems like this would be a logical change. Has anyone completed a swap and if so what assembly did you use? In my 30 plymouth I found a 9 inch from a bronco fit the bill without major modification, and in my camper I used a 14 bolt for a specific year gm van that fit without major modification.  Leaning toward a 9 inch since it has the same bolt pattern .  Any input is appreciated

[toybox]

Too bad I just sent a nice one to the scrap yard. I have a 46 and if it only had 1/4" back lash I would be stund. Between the ring and pinoin , spider and axle gears and axle gears to the axel splines it's closer to 3/4" in a rebuit rear end. A good used will have even more.  Tim