Rear Axle Oil Seal Repair

Plymouth used a common approach to sealing axles from 1928 through about 1942. While reasonably straight forward it is different enough from modern vehicles that I thought a write up would be useful.

You will know that you have a seal issue when you notice gear lubricant dripping down the inside of your rear tire. There are actually two seals:

1. A felt “oil washer assembly” located on the inside of the bearings. This is to keep the gear lubricant from washing out the grease on the bearings.
2. A “oil seal assembly” that is supposed to keep the wheel bearing grease from escaping into the brake drum. This seal is made of leather.

In this case we are getting gear lubricant leaking out of the joint between the axle housing and the brake backing plate. This indicates that either insufficient grease was kept on the bearings or that the inner seal has failed and the grease is being washed out. Since the inner seal is not available, we will simply be sure to grease the rear bearing at regular intervals. But we will fix the leak into the brakes.

The Procedure

1. The axle hub and drum are a single assembly that are removed together. The hub is held to the tapered shaft by a castle nut. And the castle nut is made safe with a cotter pin. Remove and discard the cotter pin.
   
2. The nut should be on tight. Really tight. So break it free while the car is still on the ground and the weight of the car can help hold the axle still. We are not removing the nut at this time, just breaking it free.
   
3. The lug bolts should be broken free at this time too. After they are broken loose raise the car using a jack and remove the wheel and tire. All the tires that remain on the ground should be chocked and it is a good idea to have both a jack stand and the jack in place. You don’t want the car to move or come down on you.
   
4. Remove the axle nut and washer. Replace the axle nut just enough to do two things:
   1. Protect the threads on the axle shaft from the puller.
   2. Keep the drum from flying across the garage when it pops free.
   
   
5. You will need a real, honest drum puller. Not cheap if you want to buy one but you might be able to rent one from a local tool supply. These were used on Ford as well as Chrysler products so they were pretty common at one time.
   
6. A single jack or other large hammer is used to tighten the puller. Some lubricant on the puller’s threads will help translate the force from the hammer into pulling force the axle hub. Some hubs can be very difficult to remove. It has been suggested that leaving force applied overnight can help. It has also been suggested that hitting the side of the hub when the puller is tight can help. I have personally never had a hub that would not come off with just using the strong blows on the the puller.
   
7. The outer seal leaked and we will have to clean or replace the brake parts before we are done.
   
8. The original seals are a bolt on assembly consisting of a pressed steel carrier and a leather seal. The gasket material appears to be 1/64" thick. The seal, Chrysler part number 601487, is not available new. The “New Old Replacement Stock” (NORS) seals that might be available are likely to be dried up and non-serviceable. We will have a machine shop disassemble the original seal assembly and press in a modern Timken 350936 seal. This is a rubber seal that is listed for timing chain case seals. My thanks to Robert Davis, the Plymouth Owners Club’s technical advisor for 1933 for finding that this seal will fit.
   
9. Gaskets are not available so we will make one. We start with cutting out a couple of circles.
   
10. Mark out the flat and the location of of the bolt holes.
    
11. Using a hole punch for the bolt holes we finish off the gasket. Actually, this gasket wasn’t quite good enough to use, but the procedure to make it was used for the final gasket shown in the next photo.
    
12. We now have our seal ready as well as the gasket.
    
13. The original seal did not look all that bad, so we need to figure out what went wrong. The surface that the hub shaft the seal runs on is damaged.
    
14. A “Speedi-Sleeve” (part number 99189) was installed over the sealing area. It is a bit long.
    
15. The machine shop used a disc sander to bring the sleeve down to a reasonable height. This drum was still standard size but was slightly out of round so it was turned just enough to make it round.
    
16. Since the drums were turned we will need to do a “major adjustment”. It is possible to do it without special tools, see the brake adjustment page. But if you have the tools, you can do it the factory way and measure the drum.
    
17. The pivot end of the shoes should have 0.004" clearance while the end by the cylinder should have a clearance of 0.010".
    
18. Install the hub and drum assembly.
    1. Put some grease on the lip of the rubber seal so that the axle hub will slide easily into place without damaging it.
    2. Do not use grease or anti-seize on the tapered shaft. The key is there for alignment, the tapered shaft transmits the torque between the axle and the hub and needs to be a tight fit.
    3. There are no torque specifications in the 1933 Operator’s Manual nor in the 1933-36 Mechanic’s Manual. However the hub bolt and washer are the same for 1933 through at least 1948. And the torque specification for those is listed as a minimum of 142 foot-pounds.
    4. Install a new cotter pin.