trans fluid

hello, hope everyone is doing great and enjoying the ride
one question... should i drain the trans fluid or should i just top it off?
its old, the van was last tagged in 81...
and what grade should i use.
and last.. can i use the same gear oil for the differential housing?
thanks y'all

if it were me i would replace it all trans as well as the reearend i would go with 90 wt. gear oil. and i would stay with o'e'm' i here a lot of guy's that replace with senthatic have a problem with the seals so i would stay with the gear oil it came with. thats my 2% worth

hey, thanks a bunch.

im sure this is a given. but i got confused. how many seals for the differential and the trans.

I didn't know that Chevy trannies had backing plates :-)

However I was once told that one can "clean up" a manual transmission by draining the gear oil, filling the tranny with automatic transmission fluid, running it just a few miles, draining the auto fluid out and replacing with good old 85-90 gear oil.

Is this a good idea?

I tried it once with my '79 mitsubishi manual tranny, but it was still noisy. I wound up replacing a few bearings inside the transmission (a local parts store/shop helped) and that fixed the problem.

Didn't have any leaking problems as a result, but it did require renewing various bearings (mainly one, as I recall) to fix the original problem). It was about 16 years ago so my memory is hazy on whether we replaced any o-rings or seals. I haven't tried this "fix" since, as I absolutely agree that noisy bearings can only be fixed by new bearings.

this moves a bit from the OG posting but deals with gear fluid as well
this morning i was happily changing the gear oil in the differential cassing,
took the cover and was whistling and cleaning, just like a happy vanner
but then the wether turned on me...
i got dust, not much, but still dust inside the diff. i cant clean it now and have not check how far inside this dust is in the apparatus..
i know i have to clean it, but how do i do this, whats the best way to get that out?
thanks

thanks i never thaught of this but i never checked nevermind changeing the rear end fluid in my 65 going to go on the top of the list for spring tune-up!