I have a 88 and hear everywhere I check that when changing the oil on the rear differential you should add the 4oz bottle of AC Delco LSD additive. Though the FSM only mentions the additive for Camaros, and says to use straight 80w-90 for all other applications. I suppose it couldn’t hurt to just add the additive anyways but thought I’d ask here, thanks.

 

Some bottles include the additive. Just check the back of the bottle, to make sure. Otherwise add it.

 

My cars were totally fine with the LSD in it already and not adding extra. Some could be different give it a try.

 

Yes

i seized up my d44 doing a peelout in the rain where one side of the road was slick patching cmpd and the other side was tar/chip

changing the fluid , and adding 2x the amount of posi additive . Then doing a bunch of figure 8 turns in cul de sacs unseized it

 

Thanks everyone, just ordered a bottle of the additive.

 

I wonder if that is part of your source of slow 60' times.

 

Read the label on the oil very carefully. A lot of modern oil companies include the additive in synthetic gear oil. For example Redline and Amsoil do (or did) but to my knowledge Mobil does not. Doubling up on the oil additive isn't good either. The old rule of thumb was to add two 4 ounce bottles with conventional gear oil. Following this rule with some modern synthetics can cause the LSD to slip and you would do the dreaded one wheel peel. But to add more to the confusion is that the companies that do include it don't put in the same amount. Some use more than others. I feel its a good idea to research it just a little. Do a search on the forum for the brand you like and see what others have said worked for them. I personally used Redline (which has a small amount of limited slip additive already) and I added a 4 oz bottle to that. So far everything seems fine but if I wouldn't have read the label and instead followed the old rule of thumb and put in two 4 ounce bottles of additive I may have had issues. Also if you can, try and add the same brand of additive as the base oil. This will eliminate the possibility of oil incompatibility that can cause foaming and oil break down. I know in today's world that's rare but I've seen it happen in industrial gear boxes a lot over the years. It certainly could happen in your car.

 

I know not to use synthetic oil, just using standard STP 80w-90, and pretty sure that stuff doesn’t have additives but I will check just in case. I ordered one 4oz bottle and that’s all I’m adding, thanks for the info.

 

I wouldn't say to not use synthetic oil. I only use synthetic in mine. Just be cautious what additives come in it.

 

Moble also has the additive.

 

You'll actually need two bottles. I went with Valvoline that has the limited slip additive in it and added a bottle of the AC/Delco limited slip additive, and ended up having to add a 2nd bottle of AC/Delco limited slip additive.

 

Why do I need 2 bottles ? GM only calls for one 4oz bottle

 

Many have to add two. But you can add one and see if you get any grinding or noise when turning.

 

The additive is a friction modifier.
If the clutches grab too much they will stick and you will notice most when turning at slow speed.
The clutches will stick, release and stick and turning will not be smooth.
The modifieer reduces friction between clutches. It will at the same time make the LSD looser.
Too much additive and one wheel burnouts are more likley.

I bought the bottle when changing oil, but I did not use it. No problems yet.
Could be that the friction discs were already solked with enough additive from the previous oil.

If the LSD starts binding in the future I will add the additive at that time.

 

I have no issues with the rear end, just doing maintenance, so one bottle should be fine. Thanks for the info.