jlashley2001ss

iTrader: (5)

how often should you have your rear end fluid changed? Any recommendations as to which fluid? thanks guys

blueorb

I think the general guide line is 25,000 miles. Do rear end at the same time you do the transmission fluid.
A lot of people, myself included, use the Mobile 1 with the gm slip diff additive (if that applies to your set up). I don't think you can go wrong with Royal Purple or Redline either.

luvmeZ28

iTrader: (3)

ive been doing about a 60/40 mix of royal purple and lucas. just did mine again yesterday, as a matter of fact.

Ryan02SS

iTrader: (3)

30K for me. Mobil 1 75W-90 Synthetic The Mobil 1 has the limited slip additive allready blended into the oil. 9-10 times you will not have to add any extra.

RPM WS6

iTrader: (3)

30K sounds good, maybe more often if you race the car hard or live in a real dusty area.

I always use non-synthetic 80W90 + GM additive. That is what GM recommended for the '98 rear.

In my '00, I used the 75W90 synthetic.

jlashley2001ss

iTrader: (5)

what about the 2001's?? Is there better weights to use for certain year cars?

RPM WS6

iTrader: (3)

I beleive it was only the '98s that GM recommended using the non-synthetic 80W90. These rears apperently had a different limited slip unit (Auburn for '98 vs. Torsen for '99+ I beleive). I'm not a rear diff. expert, but that is the information I've discovered.

IIRC, for all '99+ rears, the 75W90 synthetic was recommended for the standard limited slip rears. Not sure if the cars with the optional SLP (Firehawk/SS) diff. have a different fluid recommendation or not.

SladeX

My 98 was built early in the 98 model year and it has a zexel torsen differential. Quick test of this is that they will spin in opposite directions when in the air. I'm pretty sure that 98+ has zexel torsen's installed.

I'd only add the additive if you suffer from "the rusty nail" effect. It's just some clicking during turns with a zexel-torsen. Some diffs have it, others don't. I have 2 of those differentials, 1 in my 88 as well and have not needed the additive.

ULTIMATEORANGESS

iTrader: (4)

if you race your car regularly i recommend changing it once a yr or around 12-15k.


thats if your rear lasts that long.


i went with lucas with GM additive.

luvmeZ28

iTrader: (3)

i thought the auburn diff. was just an option for 98+ fbodies.

RPM WS6

iTrader: (3)

Only thing I can say for sure is what the GM manual states for the year. My '98 lists non-synthetic 80W90. Both the '99 and '00 that I owned stated synthetic 75W90.

I've read before that some '98s received auburn diffs. I haven't tested mine personally, but I just go with what the manual tells me.

fasteddyss

iTrader: (1)

I would do it every year or 10k. I am hanging on to my stock rear as long as possible. If you change it every year you may catch the bearings going before the whole rear goes.

Good Luck

bad6as

iTrader: (17)

so how would i know for sure if my 98 should get synthetic or standard

RPM WS6

iTrader: (3)

Personally, I just go with what the GM manual states. It says to use a non-synthetic 80W90 + GM additive for '98. For '99 and up, it recommends synthetic 75W90 + additive. Not sure how many (if any) '98s actually got a different rear, but just in case I follow the GM suggested fluid useage.

I've never had any issues following the GM fluid recommendations for these rears, so I plan to continue following that practice.

bad6as

iTrader: (17)

i just looked in my manuel and it says both v6 and v8 rears take the synthetic 75w90 and add the limited slip addative to the lsd

RPM WS6

iTrader: (3)

Very strange. That's not what my '98 states.

Mine lists: Rear Axle Lubricant (limited-slip diff), GM part #12345977. That part number has since been updated to #89021669. Both parts are 80W90 non-synthetic lube.

Shadow Assassin

We do it every 15K miles around here. I just go to GM and get what they give me. Did it for my 98 and now following the same plan w/ the 99.