Want to change the fluid on both axles. Don't know what type or amount to used since i bought the vehicle used w/ no manual. Can someone recommend a brand and amount to use. Would like to go synthetic. Thanks!

Welcome to AF. 75-90 Mobil 1 synthetic is your best choice here, should do the tranfer case also. GM has a special fluid for that , Autotrak to be exact.

it don't take fluid it takes grease. you probabley going to have to buy new boots if your removing them just to change grease. the easy way is just buy both half shafts. but if you want grease you can buy at any parts store it's usually green.

Mobil 1 75W-90 should work just fine for front and rear differentials. I don't recall the type of limited slip differentials (G-80 option code) used in these vehicles, but if your vehicle has limited slip, look in your Owners Manual to see if a limited slip additive is required. Routine service of the front drive axle joint grease is not required. Your Owners Manual will also give you the required amount of lube.

The Eaton locking diff. does not reqiuire any additive. BTW I don't think he meant the cv joints.

The Eaton locking diff. does not reqiuire any additive. BTW I don't think he meant the cv joints. no i wrote him told him i should have knowen that. i had a ruff night lastnight and a hanover the smorning when i wrote that. hell my niece has one dono what i was thinking exsept for trying to drink coffee.

Stay away from synthetic gear lube,too hard on gears.I know of 3 rear ends going due to synthetic gear lube.I know a guy that has replaced ring and pinions due to synthetic gear lube,down to pencil tip

Synthetic causing this, I don't think so, used it in my pictured race car, 650 hp, never did any damage to the ring and pinion that could be attributed to the syn fluid, plus I have 120k on my TB no issues. Service customers trucks in my shop also with no issues.

I agree, the guy is rebuilding rear ends for other reasons. Synthetic lube is an upgrade over regular petroleum lube. General Motors has been using synthetic differential lube for a long time now on millions of differentials with no lubrication issues. Just be sure you are using the correct weight and lube rating (GL-4 Vs. GL-5).

Thanks for all the info guys. I bought M1 75W- 90. I also bought some "Equa Torque" limited slip additive (made by CRC). It says it's for GM #1052358 diff's. Since i don't have an owners manual i have no idea as to what type of diff's. it has. Is there an axle tag somewhere that i can decode? I guess i could just call my dealer. It's a 20003 TB- "LT" with AWD. I'm assuming it takes 2 qts. per axle.

This is true,this guy,my father's friend Rich worked on one customer's rear end replacing the ring and pinion due to synthetic gear lube.The rear end was fine before the switch to synthetic gear lube and was really noisey after switching to synthetic gear lube with the teeth down to a pencil tip.Synthetic gear lube is not recomended for detroit lockers either and my father's friend Rich was told this where he got a 9 inch ford with a detroit locker for a 1983 Monte Carlo he has.

This is true,this guy,my father's friend Rich worked on one customer's rear end replacing the ring and pinion due to synthetic gear lube.The rear end was fine before the switch to synthetic gear lube and was really noisey after switching to synthetic gear lube with the teeth down to a pencil tip.Synthetic gear lube is not recomended for detroit lockers either and my father's friend Rich was told this where he got a 9 inch ford with a detroit locker for a 1983 Monte Carlo he has.
Not being argumentive here, but the stated failure is anecdotal evidence at best, I rebuild/modify diffs quite often in trucks and race cars, no issues with the proper weight syn fluid. The locker has it's own parameters when it comes to fluid use and operating characteristics completely unrelated to the issue of syn usage in the the trucks we are discussing.