deebee

I got the fluid in my rear end changed. 1996 Z28 a4.

I took it to a GM dealer. Lube guy said it was pretty dirty. Understandable. 1st time it was changed in 20 years.

But, the work order shows they only put in rear end fluid and not the additive that comes in the little bottle. I figure they have to account for everything they use as far as supplies and he didn't put the rear end additive on the work order.

I am going to assume the worst and say they didn't add it. Would it hurt for me to add a bottle of it? As in...if they actually did add it and I add another bottle is that too much?

Injuneer

Why not ask them why they didn't add it?

94Z28LS1toLT1

That's what I would do,I like wat Fred and Rob always said n i learned from them,it's better to just do the work yourself n learn about the cars/lt1,I did my rear end fluid change myself,dealer just will screw up the order or job n don't trust anyone touching my beast

deebee

I know if I ask them they will say they added it. But it isn't on the work order.

And I can't do it myself as I have underground parking and we are not allowed to do mechanical work down there, or I would. I live in a condo, not a house.

I was just wondering if I added as a precaution and they actually in fact did add it if too much would cause a problem. I am thinking of adding the additive just in case, but if it is going to cause damage I won't.

Injuneer

Is there a part number on the work order or invoice for the gear lube? If so, look up the part number and see if it might already have the LSD additive.

Failing that, take it out in an open parking lot and do some aggressive figure-8's. If it chatters, you need additive. If it doesn't chatter, leave is alone.

Too much additive may reduce the friction and degrade limited slip performance..

BandDirector Blk98ZM6

I had my pinion seal changed several times under warranty on my '98 Z28 with the Auburn rearend. I once got in an argument with the tech doing the work because the additive wasn't on the paperwork either. He insisted it wasn't needed since my rearend uses the synthetic fluid. I told him the manual calls for it even with the synthetic fluid and then stood there watching while he drained a little fluid out and add the additive. He wasn't too happy with me, but I didn't care, it wasn't his car, it was mine.

Over the years, I've tried RedLine synthetic rearend fluid as well as Mobil 1, all with the GM additive and my rearend always seems to "howl" with anything that isn't the high dollar GM synthetic fluid. That's all I'll use now and I do make sure I use the additive. I never had a chattering rear end, but the thing will howl at highway cruising speeds without it. If you have the howl or chatter, I'd definitely add a bottle!

deebee

Guys, I dug up the work order and this is what it says:

REAR DIFFERENTIAL SERVICE - SYNTHETIC
2 89021678 GEAR LUBR
1 RDS55072 REAR DIFF GASKET
111992 REAR DIFF SERVICE DONE BY TECH 206. GASKET WAS REPLACED AND 1.8L OF 75W90 WAS USED.

No mention of the additive. I was actually wondering if maybe it is in the fluid now. But I will do that figure 8 thing and see what it does.

I am hoping they did it right. It is a Chev dealer and they sell a lot of Corvette's and Camaro's so I am assuming (hoping?) they service them as well and do it properly.

Injuneer

Amazing how hard it was to search on part #89021678. What I eventually found was an indication that is a Canadian GM P/N, and the universal P/N is 89021677. Summit sells that P/N, and the online listing indicates it is a synthetic GL5 that meets the performance requirements.... including limited slip.

If you used a dealer with a lot of Corvette experience, they would be more likely to be relatively sensitive to the gear lube requirements, since there have been some major recall issues related the the gears lubes that were factory installed.

I'm betting you are fine. Still be worth the figure-8 test. And I don't think you need to be aggressive as I suggested earlier. The problem should be more apparent at lower loads.

deebee

Thanks everyone! I am going to do some figure 8's and if it is quiet leave it as is.

Apologies for the part # confusion. I should have made it more clear I am in Canada. I didn't realize that the part numbers would be different.

Injuneer

My "You Need A Signature" sticky explains why it's a good idea to use the "Location" field in your profile, so it appears under your screen name in each post . I think my surprise was that GM had a separate part number for Canada. I didn't know they did that. Knowing your location wouldn't have overcome my lack of knowledge. No big deal.

Fatdog2

Auburn says do not use synthetic's in their rear end.Too slippery for the clutches.(Hench the no limited slip additive needed.)Do a search here for examples from years ago.Any commercial place you go to will use synthetics like aamco ect.The rear ends were changed in later years so the syns may be ok.Just do what your manual says to do.Hope this helps.

wjogert

Unlike the days when the additive was most popular, most differential fluids used by shops today (including dealerships) have slip additive already in them. So they would only add more if there was an issue with your tires chirping around corners.

Honestly, I've always preferred to get a few tire chirps and know that my clutches are always working their best on launches