Flushing Trans and Diff:

So, I drained the Trans and Diff, and what I see looks pretty yucky.

Is it recommended or possible to flush with something before refilling?

~Ed.

Doesn't look too yucky. Any chunks or pieces of metal? If not, just refill.

So, I drained the Trans and Diff, and what I see looks pretty yucky.

Is it recommended or possible to flush with something before refilling?

~Ed.

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The oil from the transmission and differential will probably be quite dark to begin with since what is there is probably not modern gear oil.

Dunk your fingers into each and see if you feel anything like metal bits or whatever. Run your fingers along the bottom of the pan, too. That's all assuming that you drained each into a clean container, which is what it looks like from here. Also look for shiny bits of metal, although there will always be some metal wear in the drained oil.

What I'd do is make sure it all drains thoroughly --- let it drip for a few days --- then refill with an appropriate gear oil. This time, perhaps you could fill it with a cheap 85W-140, run the car for a few dozen miles, then drain it again. See what it looks like. If what comes out is pretty much what you put in, then refill it with whatever you'd like to have in there for the long haul.

Be aware, though, that if you use a modern 85W-140, it may run out of the seals on the back of the transmission or out the axles on the rear end. Watch for that, and if it's excessive, just stop and drain it then. Refill with something thicker. I use Shell Valada 680 with about 25% Lucas Oil Stabilizer. Seems to work for me.

You want the thicker oil in the transmission if needed to allow for smooth shifting.

You want the thicker oil in the transmission if needed to prevent excessive leaks.

You want the thicker oil in the differential if needed to minimize leaking.

But you don't want oil that's too thick as it will not lubricate well. Exxon makes a steam cylinder oil in TK-1000 and TK-1500 viscosities. I think both are too thick. The Shell Valada seems closer to the 600W that was recommended originally.

--Scott Dwyer

I use a small amount of marvel mystery oil before draining. Add it to the rear end and transmission. Put the car on jack stands and run it up to 5-10 MPH for a couple of minutes. Then let drain for a few hrs. This works really well and removes a lot of the sludge build upon the gears and case. After taking the top cover off a transmission ive seen a notable difference.

The MMO is a good idea. I never heard that one before.

Works very well to remove the sludge from an oil pan also. Just don't run that long and never under any kind of load.

Be aware, though, that if you use a modern 85W-140, it may run out of the seals on the back of the transmission or out the axles on the rear end. Watch for that, and if it's excessive, just stop and drain it then. Refill with something thicker. I use Shell Valada 680 with about 25% Lucas Oil Stabilizer. Seems to work for me.

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As a follow up, the Series 10 instruction manual recommends a 600W steam cylinder oil for both the transmission and differential (in summer use). Franklin Service Bulletin 567 from March 1930 (attached) also recommends 600W steam cylinder oil for both Series 10, 11, 12 and the 130 transmissions. Same for the differential except that Series 11 recommends a lead-based lubricant. I don't know why.

From what I can determine, the closest thing to 600W steam cylinder oil today is the Shall Omala 680 (the new name for Shell Valvata J 680).

As a friend privately pointed out, it's always best to use what Franklin recommended unless modern technology has clearly given us something better, like using Mobile 1 for the valves.

--Scott