ariba

Hello
I had an issue with my 77 L48 50k miles 350T trans. I drove the vet it was fine but after driving about 25 miles there was a sound when I was driving slowly about 5-10 miles but after I accelerate above 20 Miles the sound go's away. It felt like one of the tiers was bad even when I was inside the cabin I felt it. I Checked the rear axle it looks fine.
Just to make sure after this incident I put about 20 more miles going back home but I didn't hear or felt a thing.
1. I hope someone help me to diagnosed the issue.
2. Do you think It's the diff?
3. If you think it the diff, do I need to change fluid?
4. Is it easy to remove the drain plug? & where is it located?
5. for the fluid & additive can someone give me a part #
Lucas OR GM?
75W-90 OR 80W-140
Non Synthetic OR Synthetic
Thanks

Wee

Drain plug for a 72 can been seen in the photo below....That is with the RR tire and wheel removed. I used a funnel with a long hose attached to fill it back up. You have to suck the old fluid out.


Here is a photo of the funnel/hose setup....This was the first time I changed mine....Don't use the cheap oil seen on the floor....I ended up changing it again shortly after when I pulled the differential and put in a new seal.



Here are the Gm part #'s I preferred to use Sta-Lube 85W90 GL-4 instead of hte GM oil. You will need (2) bottles of the additive, or at least I did.
GM gear oil part#89021671
GM posi additive part#88900330

As far as I know the 77 should require the same.

Brian

resdoggie

Buy an oil suction gun to suck out the old oil and put in the new.

derekderek

there are 6 u-joints. replace them all. a really bad one will give an out of round tire feeling soon before it leaves the car all by itself.

0Willcox Corvette

We have a hand held pump that sucks the fluid out of the rear end, and when filling we put the additive in the lube and then pump it back in.

Willcox

ariba

Thanks All
Wee, Resdoggie , Derek, Willcox.
I did ordered 2 GM gear oil part#89021671=left
2 GM posi additive part#88900330
I will plan to change oil & additive this week
The funny part I drove the Vette yesterday about 4 miles and no sound. But I still going to change it.
Thanks

resdoggie

Rule of thumb: If you can't remember when a fluid was changed, then it's time to change it.

Tripower delight

You can change the oil in the rear,but that might not be the problem. Ujoints when they go bad they make noise.
check out the side of the car were you think the noise is coming from.

ariba

Update

Thanks All & especially Brian

I did change the diff oil
It took a loot of time to suck out the old oil, even when I drove the car for 10 min to make the oil worm.

1.5 bottle GM gear oil part#89021671
2 bottles GM posi additive part#88900330


The problem was gone. I drove the 77 about two times a week nothing happened, sometimes I drive for an hour, no noise.


Very happy with the result.

HeadsU.P.

Good God dude! I hope that's a misprint.

Its 2 of the large bottles of GM Lube
and 1 small bottle of GM posi modifier.

BKarol

I assume he meant 1 & 1/2 bottles of fluid and 2 of additive? hopefully

ariba

Yes that was I meant
1 and half bottle of GM gear oil part#89021671
2 of the small bottles GM posi additive part#88900330

HeadsU.P.

You guys still have it backwards.

Not sure what could happen if you are short on the GM lube. (should be 2 large bottle)
Not sure what would happen with too much posi modifier. (only need one)

Should you pump it back out and do it over with the correct ratio? I don't know.