Hi,
I'm rebuilding a 67 mustang fastback that had most of the mods done by the previous owner. It just needed a few last touches. The previous owner put on a new rear diff, however he never put in any seals. When i brought it over from texas it was leaking. It had 250 miles on it when i purchased it.
I drained the oil, but didn't measure how much. As i was examining the empty axle housing i see a lot of steel 'shavings.' I say that with " because they are super fine, to the point where you can barely feel the grit between your fingers.

My questions are
1 should i flush the grit out? Is some amount of steel shavings normal in there?

2 If so what should I flush it out with (flushing means removing the seals again, flushing and re-installing) I assume whatever i flush with is going in the pumpkin and coming out the axles....?

3 what kind of oil do you use to fill the rear diff with? its a 347 stroker.

thanks in advance.

 

If it was me i would pull the diff out and look at every gear see where the metal is from.If everything looks fine clean out the housing new seals and gear oil.

 

Best approach is to remove the axle shafts and the third member to allow easy access. Swab the axle tubes using a cleaning solvent of your choice. The more time you take, the better off you will be. Clean the center section out by hand as clean as you can get it. After you have wiped the interior out really well, spray paint the inside of the center section and the axle tubes with a good spray paint. I have used red oxide primer successfully, or consult your local engine builder for advice as to what he uses to seal paint engine blocks. The paint will seal off any unseen particulate you are unable to remove from cleaning alone. You could also use a hot steam style pressure washer. Regardless of what you use, a paint sealer would be advisable. If you choose to service the gear set while it is out, clean and seal the inside of the third member in the same manner. You simply can't get all particulate out of cast iron.
Best,
Al

 

Thank you for the advice. Would you replace the seal on the pumpkin? it looks like its leaking from there as well.
Is some amount of steel filaments in the oil normal?
What kind of oil do you use to refill?
thanks again

 

It's not unusual to find some particulate in the gear oil, especially if the oil has been in there a long time. Also, you don't have a way of knowing what, if any, failure has been in the rear axle in the past.
As for gear oil, the in favor lubricant these days is some type of multi-viscosity synthetic oil. As for me, I would use a standard 90 GL5 or GL6 rated oil. I don't see any true advantage in the synthetic; in fact, it should not be used with new gears, as they will not break in properly. Standard gear oils have lasted for hundreds of thousands of miles in these cars, so how are you going to improve on that. I even heat tested standard vs. synthetic in a closed track racing Mustang and found no discernible difference in the gear set's temperature after racing for thirty minutes.
Best,
Al