Draining the rear axle

[Author nameAuthor names are only available to PAS members.]

Another question for you helpful guys. What would I do without you?!

How do you drain the rear axle oil?

The 1929 handbook on p28 says “Lubricant in rear axle should be drained out through plug on base of case every 10,000 miles.”

OK I give up!

---

My 1929 125 (133) does not have a plug on the bottom of the case!! The only way I can see to drain it is via a suction device OR take out the rear axle & tip it up! Once the axle is out a simple modification to fit a drain plug would be a doodle. The oil that is in there (about an egg cupful!!)I think is genuine Pierce Arrow factory oil! Pretty foul! Thank you for your expertise. Jak.

[Author nameAuthor names are only available to PAS members.]

G’day Jak,

This appears another example of the handbook having been written before the engineers were completely finished with the design!

No need to drill and tap! To drain, remove the bottom three bolts on the rear diff cover–with drain pan in place, of course. The oil/glue will drain through the bolt holes.

Given the state of the lubricant, I suggest you remove the entire rear cover and scoop out all the hardened or semi-fluid lube. If the diff originally had 600W steam cylinder oil, that stuff tends to thicken over time and no longer lubricates well.

After you have cleaned the inside of the housing as well as you can, you may wish to flush. I use 20W-50 motor oil and drive **slowly** around two or three blocks, then allow it to drain overnight and re-clean the inside of the housing.

In my climate (SF Bay Area, no freezing), I use 140 weight GL-4 hypoid oil in 1929 and later Pierce differentials. Don’t use GL-5 (for limited slip diffs) or GL-6 (synthetic) because their chemical composition will eat away yellow-metal (bronze and brass) bushings and thrust washers. This I found out the hard way, and a Sta-Lube PhD chemist was wrong….

Rather than making a gasket, you can use RTV sparingly to seal the cover/diff housing surfaces.

Please keep us posted!

George

[Author nameAuthor names are only available to PAS members.]

You might speed up the draining of the thick old oil by shining a heat lamp on the differential housing, or use a heat gun to warm up the housing.

Greg L

[Author nameAuthor names are only available to PAS members.]

G’day George & Greg

---

Good info thank you. Removing the bottom 3 bolts seems obvious now that I put my glasses on plus a good light!! They have a beautifully shaped head to look like nuts & studs.

I have done it and at least there was some lube in there! Unique smell though! Like something burnt! I will fill with engine oil as George suggests to give it a clean & run it up on jack stands for a while. As for the bronze eating exercise I learnt that one the hard way 50 years ago! So much for so called experts who seem to be only interested in selling stuff to you. I have 140 mineral trans oil sans bronze eating additives. Thanks again.

Jak.

[Author]

Posts