I have about 750 miles on a rebuilt 8" rearend/differential. When I change the fluid, can I get away with simply pumping the old stuff out or will that leave metal flakes behind? Or do I really need to take out both axles and disconnected the pumpkin?

 

Not sure you need to R&R the fluid at all...

 

Definitely should replace the fluid, but there should be a magnet in the bottom of the case to pick up any shavings. If so, I wouldn't worry too much about simply sucking the fluid out and dumping new stuff in.

 

I doubt there are any metal flakes in there in the first place.

Most of the stuff is a black dust the comes off the gears. I think it could be a surface coating left on after the carburizing process. I would imagine these gears are carburized to created a hard face to resist wear but still have a softer tougher core that can take shock loading with out shattering.

I could be way off but Im betting that most of the deposits are graphite/carbon with some metal dust. Drive it around then empty the fluid and most of the stuff should be in solution when you suck it out.
Thats what I did on mine and I drove it for a few days then check the fluid and it was still yellow. The stuff that came out was black.

-Gun

 

Yeah, just coatings and any dust etc from the install. Change it out by sucking/pumping and you should be fine.

 

This is definitely good news hehe . .

 

if the rear was done correctly then you shouldn't need to change the fluid for another 30,000 miles!

 

Curious do you know if you have a magnet in the diff? But regardless I would not worry about just replacing the fluid. Its recommended!

 

I know there is no magnet. I didn't think about it until after.

Maybe I'll just slap one on the bottom of the pumpkin haha!