I am going to be replacing my differential fluid in a couple days and I could not find what to use in my car in the repair book I have. I see a couple different watts and synthetic and am not sure which one to use. I wasn't sure if synthetic oil shouldn't be used in the rear. So I need to know what watt to use and if I can use synthetic. Thanks.

 

if you have a limited slip (aka posi) then you DO NOT want to use synthetic. other than that any 80-90w will work fine. if it is posi you will need to add limited slip additive.

 

No posi, yet. It also shouldn't matter the watt? I see 75-90, 80-90, 85-90, and 85-140 in both synthetic and natural. It is a daily driver but I get into it sometimes so what would be the best choice? I don't know the details of what the diff prefers. Or if it should be a bit different for winter/summer ect. Thanks for the help. I couldn't believe the book didn't say a word about the watt or capacity the diff needed.

 

if you are in a area where it gets very cold you will want to use 75-90, otherwise use 80-90 of either dino or synthetic oil.

 

Thanks. Would you happen to know the capacity too? I would imagine it says it in the shop book but I have the Haynes.

 

there is a 4th gen capacity post in the how to and faq sticky at the top of the 4th gen general section. found it, 1.75 quarts, here it is https://camaroforums.com/forum/93-02...acities-70171/

 

Thanks, I didn't think to check for a sticky like that lol.

 

I knew that 4th capacities list would come in handy. Saw it on here twice now. Good thing Craby remembered where it was at cause I forgot. Lol.

But Craby, I noticed the first time you mentioned not to use synthetic in a LSD. I was just curious as to why? The Lucas I used was and I haven't had trouble yet.

 

it will ruin the clutches in the center section and turn the posi into a one wheel wonder. i speak from experiance.

 

The thinking behind the no synthetic in a "clutch style" LSD is you may not want a super duper lubricant worked into the clutches, for fear of making them slip. Is that an absolute fact that can happen? I think the jury's still out on that one, but why take a chance. The biggest threat with any oil is thermal breakdown (where synthetic shines), more important in engine oil than gear oil. Using good old dino oil for the gears (with the additive) will be fine and dandy. The additive by the way, helps to prevent the clutches from getting gummy and sticky, which will give you a clunk-clunk-clunk when you take a turn.
However, GM started using Torsen (non-clutch) LSD units starting in the 1999 model year, so if you have one of those, you can use either oil and the LSD additive isn't needed.