Recommended Differential Fluid for 77
12-10-2012, 09:45 AM
#1
Le Mans Master
Thread Starter
Recommended Differential Fluid for 77
Hi guys, I am working on a friends 77 and need to know the factory recommended gear oil weight and need to know if I need 1 or 2, 4oz bottles of the GM LS additive? Searching on here I here I am reading different things, use 80W90 or 80w140 syn or non-syn and 1 or 2 bottles of LS additive, no one has a set answer on what needs to be used! Rear end chatters/grinds pretty bad so need to change it out (its been sitting for a long time too).
Also looking at the fill plug its square, what tool/socket do I need to buy to get it off?
Also looking at the fill plug its square, what tool/socket do I need to buy to get it off?
Last edited by Corvette Don; 12-10-2012 at 09:47 AM.
12-10-2012, 09:53 AM
#2
Hi guys, I am working on a friends 77 and need to know the factory recommended gear oil weight and need to know if I need 1 or 2, 4oz bottles of the GM LS additive? Searching on here I here I am reading different things, use 80W90 or 80w140 syn or non-syn and 1 or 2 bottles of LS additive, no one has a set answer on what needs to be used! Rear end chatters/grinds pretty bad so need to change it out (its been sitting for a long time too).
Also looking at the fill plug its square, what tool/socket do I need to buy to get it off?
Also looking at the fill plug its square, what tool/socket do I need to buy to get it off?
If I remember correctly, a 5/8 open end wrench will turn the fill plug. Take a few yoga classes first.
12-10-2012, 10:07 AM
#3
You can get a 8 point socket at sears that will fit a square head and wont round it off like an open end.
12-10-2012, 10:25 AM
#4
Le Mans Master
Thread Starter
I dont think it has deteriorated, the LS still works and it does not whine at any speed, just get the grinding at slow speed turning (1-2 mph) anything over that it goes away, searching shows that most of the time replacing the fluid with the correct stuff (and I am sure the prev owner did not use the correct stuff) will fix it.
12-10-2012, 10:48 AM
#5
Melting Slicks
I dont think it has deteriorated, the LS still works and it does not whine at any speed, just get the grinding at slow speed turning (1-2 mph) anything over that it goes away, searching shows that most of the time replacing the fluid with the correct stuff (and I am sure the prev owner did not use the correct stuff) will fix it.
Adam
12-10-2012, 01:17 PM
#6
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I have been using 80/90 gear weight oil and one 4 oz bottle of GM posi lube for 40 years in my original 65 rear end. It's never been rebuilt and still makes no noise. (I know that's the kiss of death now that I've said this 
) Same thing in my 68 and 61 and every older Corvette I've ever owned. Never had a rear end issue. Forget the synthetics on the old cars. This is what they were designed to use. Do your figure 8's in a parking lot after you do the change to work the posi lube into the clutches 
) Same thing in my 68 and 61 and every older Corvette I've ever owned. Never had a rear end issue. Forget the synthetics on the old cars. This is what they were designed to use. Do your figure 8's in a parking lot after you do the change to work the posi lube into the clutches
12-10-2012, 02:00 PM
#7
Le Mans Master
Thread Starter
I have been using 80/90 gear weight oil and one 4 oz bottle of GM posi lube for 40 years in my original 65 rear end. It's never been rebuilt and still makes no noise. (I know that's the kiss of death now that I've said this ) Same thing in my 68 and 61 and every older Corvette I've ever owned. Never had a rear end issue. Forget the synthetics on the old cars. This is what they were designed to use. Do your figure 8's in a parking lot after you do the change to work the posi lube into the clutches
) Same thing in my 68 and 61 and every older Corvette I've ever owned. Never had a rear end issue. Forget the synthetics on the old cars. This is what they were designed to use. Do your figure 8's in a parking lot after you do the change to work the posi lube into the clutches