I saw a guide that used 75w90 synthetic gear oil for the rear end plus the gm limited slip additive.

I bougt some plain 75w90 and got the GM additive. Is it alright to use the 75w90 because on autozones site it says to use 80w90.

Can i use it and will it matter it i use it or not?

 

Its OK to use 75w90... Some manufactures do not recommend synthetic in the rear end... Do some research first.... Its has been discussed in the Drivetrain section....

 

i use quaker state 75w 90 with limited slip additive with no problems. The book at autozone is just what the manufacturer reccommends it.

 

I didn't use synthetic because some people in the forum told me not to. I was just wondering if 75w90 is acceptable when it says use 80w90 on autozones site.

 

I use the same but it was Mobil 1 and my differential needs a replacement or repair the inside of the differential because it's whinning for days now. I use the gm additive as well.

 

Recommendations against synthetic are usually because of a clutch type posi(Auburn, Eaton, when used with those synthetics can cause noise or slipping, synthetic is fine with a geared posi(like Torsen or I am sure others). Something many seem to forget is that while yes synthetics are better dinos these days are very good as well and will do an adequate job of most things asked of them unless you are pushing a lubricants very limits.

 

75W90 should be fine.

Rich

 

I agree, 75w90 is suitable. I've always used Mobil 1 and the GM additive in the rear diff of my car, but your choice is fine too.

 

Any auto parts store is just going to show what the manufactor recommends, as mentioned above.. IE: If you ask for spark plugs for the LT1, its going to say "platinum" tipped, because thats what came factory....

Its good to ask advise, just be careful, and conduct research on the project that you are working on.. I have noticed the threads, that you have posted... Knowledge is the key.... Have fun, and use only the information that you are sure is correct for your project....