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I have a 98 Z28, I recently had my transmission rebuilt and they had concerns about play in the rear end, so they opened it up, but didn't see anything wrong.
I have concerns I may be getting some noise on slow speed turns (had issues before I'm trying to fix, suspension and I think maybe parking brakes so it's hard to tell if it's a new sound)
On my invoice I see 2 3/4 80/90 synthetic lube, and nothing about separate additives.
So the question is, since i have a 98 I believe I have an auburn, and everything seems to say it you have to use dino oil and an additive in older forum posts here. But when I look at my GM service manual and the alldata service manual, both show the recommended oil is 75/90 synthetic with 4 oz additive.
I read the most synthetics already have the additive (good enough for an auburn?) ... so is this ok or did they mess up? Based on the service manual says probably couldn't convince them it's wrong for a chance to get it replaced at no cost...
how does it feel? you'll know if something isnt right, I forgot to add the additive once with my auburn unit and going slow around corners or backing out of a parking spot made it groan really bad lol. it would moan, pop and make all sorts of weird nosies. so if yours is quiet in those scenarios youre fine
how many miles on the 98 Z28 ?
80/90syn,75/90syn,interchangeable-no problem.
add the additive,even though the lube is supposed to contain it.
GM viscosity modifier additive,http://www.summitracing.com/search/d...rder=Ascending
It does make noises as I slowly back out and turn out of a parking spot, but it did that before the change. I don't really hear it on the street.
I think I may be hearing new noise now - but I could just be paying more attention and only notice it now. I'm pretty sure my parking brakes are making some noise.
I'm guessing I can't just add the additive now since it's probably full? It would need a full fluid change?
You can add the fluid. Take a 1 minute ride after it's(the rearend) cooled down overnight and then add the additive,if possible,within a few minutes. The thicker cool oil will then still be coating the parts inside and slightly lower the level to allow the addition. OR parking the car on a slope with the right side higher will shift the fluid to the left. The fill plug is on the right side.
overfilling by a few ounces won't matter.
Auburn recommends non-synthetic in their OEM units. The GM manuals may be referring to the fluid specs for the Torsen which shows up by far the most often on LS-1's (1999-2002) with the exception of some SS's and Firehawks. Auburn has tested their units extensively with the recommended fluids. Other choices could lead to differential (cone) clutch chatter.
All Auburn Gear differentials require a high quality non-synthetic 80W90 GL-5 gear oil. Treat the oil with Auburn Gear, GM, or Ford additive. 3 ounces of additive per 1 quart of oil. A 6 oz. bottle of additive comes with each Auburn unit.
This is what confused me earlier, here is a screenshot from alldata, my 98 service manual shows the same chart. They lump the 98-99 together. It seems strange GM is recommended something the oem doesn't?
I'd go by what the 1998 Camaro Z28 service manual (or owner's manual) stated. I've seen some snap shots on here of 1998 service manual charts that stated the non-synthetic + friction modifier. Nothing says you can't use synthetic in the Auburns if clutch chatter or other noises isn't an issue. No doubt there are people who have used synthetics with no negative results. But, I'd rather see that evidence after the car was driven 80K-100K miles. Fwiw my '99 owners manual only references the synthetic diff fluid....doesn't seem to know that not all '99's come with a Torsen.
When I had to change my fluid I went with Auburn's recommendation. And it didn't hurt that the forum had plenty of posts of people that didn't have good luck with synthetics. Didn't find anyone saying that non-synthetics ruined their differential.
One other thing; IF the shop actually installed 80W/90 gear oil, I am 99% sure it is mineral based gear oil, and NOT synthetic, since there are NO 80W/90s I know of which are synthetic based, ONLY 75W/90s (even though there is at least one {Valvoline white bottle} 75W-90, which is also mineral based, but hard to find).
I looked a parts store web site, I see some 80/90 synthetic blends? Maybe this makes it not as bad?
Looking at the invoice again it does say synthetic 2 3/4 (seems like a lot?) @ 11.15 = $30.66, and doesn't list any separate additive.
Still deciding what to do ... I found a 1oz syringe, so I think it would be easy to take out 3-4oz and replace it with the additive. I don't really want to take the cover off, but maybe it's safe to pump it out since it should be clean inside only being a few weeks old?
Is it that synthetic could be noisier/not work as well, or can it actually cause damage/extra wear?
This 1998 owner's manual doesn't specifically mention synthetic rear differential fluids (page 6-26 or 284/402). It lists only own GM #12345977 or SAE 80W-90 GL-5 gear lubricant for standard differentials. For the LSD option it mentions the same GM fluid + LSD additive. 1.75 quarts to fill it.
Is it that synthetic could be noisier/not work as well, or can it actually cause damage/extra wear?
All 3 of those have been mentioned in historical posts on this site. Doesn't mean it will happen to you though as some have reported no issues. The synthetic fluid is sometimes cited as being "too slippery" for the Auburn cone clutches such that engagement is more difficult. Wouldn't the LSD additive only make it more slippery? But, the Auburn site doesn't mention that....just that "clutch chatter" could result. I went with the majority opinion on what I've researched and stuck with non-synthetic + additive. In the 1999 owner's manual they changed the requirements to "synthetic." Apparently, they were adjusting for the change from Auburns in 1998 to Torsens in 1999....and leaving out those owners who ordered Auburns via SLP.
....I really wish the service manual didn't say to use synthetic - then I'd have a good case to take it back and make the shop fix it
That service manual excerpt is apparently incorrect. The 1998 Camaro should be with the top grouping (pre-1998 cars and 1999 Corvette). And for 1999-2002 Camaro SS's and Firehawks that got the Auburns from SLP, that table is also incorrect. Your 1998 owner's manual would have been correct. One would think that a seasoned repair shop would know that there's a different recommended fluid with the use of differentials using cone or clutch type units (ie Auburns, Eatons, etc.). These types of posi's may be more common on the road than the gear/spool type units. An experienced shop should have familiarity with all the major differentials and how to service them. Isn't "Alldata" just some on line intermediary between the customer and the manufacturer? Is it the actual reproduced, original service manual for each year/model?
I agree the chart isn't right based on what everyone says. It's a transmission rebuild shop, could be some kid did it - maybe looking at the same chart.
Alldata does seem to basically be a digital version of official gm service manual. They say 80,000 shops are using it on their web site.
Do you think using a hand pump to get most of it out and refilling should be okay? Need to do it on the cheap
Do you think using a hand pump to get most of it out and refilling should be okay? Need to do it on the cheap
Yes, you will be FINE with getting as much out as you can with one of those cheap, Harbor Freight, or Wal Mart hand pumps (or one of those Lincoln suction guns if you already have one), and then putting in as much of a quality, mineral based, 80W/90 gear oil (like Valvoline, Castrol, Pennzoil, etc.) as you can with 4-6 ounces of a good (I use the stinky, but excellent Motorcraft/Ford Racing XL-3 stuff) limited slip friction modifier.
One more question - went to get the oil today, only real name brand I could find was valvoline, and it says it already has the limited slip additive in it. Should I use the GM additive anyway (already on it's way), skip it, or use store brand stuff?
The one you linked is for Valvoline 85W-140. Nothing there that says it comes with the LS additive. Not being a lubricants engineer I don't know how that stacks up against the recommended 80W-90.
One more question - went to get the oil today, only real name brand I could find was valvoline, and it says it already has the limited slip additive in it. Should I use the GM additive anyway (already on it's way), skip it, or use store brand stuff?
Usually, I have to add at least 4 ounces to gear oil which already claims to have the friction modifier in it, but then I have an Eaton Posi, and I will burn up the carbon clutch pack if it binds/chatters too much (even though some don't care about this and run it without the additive for that 'locker-like' instant lockup).
I don't know how the factory Auburns react in this respect as I've never had one, but my best guess is that it too would need at least the 4 ounces of additive, given that Auburn states to use 6 ounces of the additive.
What you could do is; install the almost 2 quarts of gear oil, put the fill plug in, and then drive it around to find an empty, cop-less, parking lot, and do about 10 tight figure 8s to work the fluid in.
IF, after the above, it still creaks/moans/groans/pops when turning into tight spots, or around 90* corners, then add the GM l.s. additive, and repeat the figure 8 process above.
06-22-2015, 07:10 PM
Shop used 80/90 lube synthetic in 98? 
