Question about the differentail. If it ain't broke don't fix it?

[cretin90]

'66 300 w'/ 38k on the clock. Running now, but prior to the re-awakening, it sat for 27 years.'
Is there a compelling reason to change/not change the differential oil?. ..so far (digits crossed) everything runs fine. ...but .....27 years.

 

[HWYCRZR]

Change the oil in case there’s been water or condensation. It is cheap insurance. There is probably sludge in the bottom. Get a good sucker gun

 

[413]

It’s nice to change it. Lowest labor time is to use a suction gun. Drive it to get it warm and it comes out easier and then the particles are mixed in with the oil.

 

[gyknot]

Although no harm can be done by changing it, I'm going to break with the crowd and say leave it alone. What little condensation there is likely to be can be evaporated with a good long hot drive down the hiway.
I have broad shoulders. Let the criticism begin.

 

[Davea Lux]

If the car was stored someplace dry and reasonably warm, there probably won't be much condensation. That having been said, the oil is now well over 50 years old and has probably oxidized some over that long period of time, so it would probably be to your advantage to change it. If the car was stored on the dirt someplace, the oil is likely full of moisture and should be changed immediately. The top of the gear set that is out of the oil bath sometimes rusts over time and all that accumulated rust will come off as the vehicle is driven. The rust particles are a fine abrasive and can destroy the bearings in fairly short order. It would also be a good idea to pull the rear axles and repack the bearings, the grease that is in them is also likely deteriorated. With the axles out, it is a fairly quick job to pull the 3rd member for inspection and charge it with some fresh oil.

Dave

 

[cretin90]

If the car was stored someplace dry and reasonably warm, there probably won't be much condensation. That having been said, the oil is now well over 50 years old and has probably oxidized some over that long period of time, so it would probably be to your advantage to change it. If the car was stored on the dirt someplace, the oil is likely full of moisture and should be changed immediately. The top of the gear set that is out of the oil bath sometimes rusts over time and all that accumulated rust will come off as the vehicle is driven. The rust particles are a fine abrasive and can destroy the bearings in fairly short order. It would also be a good idea to pull the rear axles and repack the bearings, the grease that is in them is also likely deteriorated. With the axles out, it is a fairly quick job to pull the 3rd member for inspection and charge it with some fresh oil.

Dave

Great analysis, Dave. Quite logical. Yes, the car stayed in a garage for nearly three decades, undriven. But in Wisconsin...as in butt-*** cold.

While that may exclude the issue of rust, the sheer amount of time sitting surely would degrade any dino-oil.

Do you guys have a favorite for this application?
Synthetic ? Or dino?

And thanks to all of you for the replies. This group is great.

 

[Davea Lux]

Conventional 85w-90w is fine. You won't hurt anything by using synthetic, but that is overkill for an 8.75 unit. If you want the synthetic, avoid the ones with the friction modifiers for limited slip.

Dave

 

[cretin90]

Done. Oil was old, but clean and no sludge. wheel bearings done, upper and lower ball joints greased. Discovered all my wheel cylinders are either leaking or seeping. yay me.

 

[mopar440]

Done. Oil was old, but clean and no sludge. wheel bearings done, upper and lower ball joints greased. Discovered all my wheel cylinders are either leaking or seeping. yay me.

Change brake hoses if old too, can look good and still fail