The Camaro Club (UK)

My 1997 3.8 V6 auto (bought in May) is about to go in for its first service in my ownership at 88,000 km (55,000 miles). I occasionally experience a groaning noise from the diff, particularly when in stop/start traffic. It also happens in reverse gear. My suspicion is that the diff has either been filled with the wrong oil, or that the oil needs replacing. Has anyone come across anything similar? And what is the correct oil to use, and how much?

Thanks, Cosmic

From what you describe, I would not suspect the diff itself but would look to the mounting rubbers in control arms etc that locate the axle. The reason I say this is that stop/start and reverse involve low overall gearing, which maximises torque at the axle. This is turn puts strain on mountings. I could be wrong, but then it's always difficult to diagnose noise related problems via the written word! HTH
Cheers, Martin

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Thanks, Martin, we'll get it up on the ramp and have a look. I take your point about diagnosing odd noises; sometimes it groans, at other times it clicks. In the cabin, it feels like plates are rubbing against each other. Am I right in thinking even the smallblock has a limited slip diff? Could it be slipping when it shouldn't, or not slipping when it should?

Cheers, Cosmic

if you have a limited slip from factory your door jam will have a G80 code.

If not it may have beeen fitted after. If you had an LSD the clunking would be prominent under turning more than straight line. Check diff oil level too while its in, some decent 75w90 is reccomended I believe

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'99 Z28 A4, 253 LS2 heads, 228R TSP cam, Patriol Dual Springs, Double roller timing chain, LS6 ported oil pump, OBX LTs, 3" True Duals, LS6 intake, 42lb/hr injectors, SLP lid + bellow, EFIlive COS 3 Speed Denisty Tune (self tuned), 3200 Circle D stall, CAI mod, KYB AGXs, Eibach Pro Front Springs, UMI panhard, LCA + Brackets, Strut Brace, Custom Subframe connectors, WS6 axle with 3.42s, 18" American Racing Rebels, US mirrors, 93 tail lights, 3.5 inch custom cowl hood. Mickey T's Street DRs on Vette-ZR1 wheels for the strip !
Best ET: 12.0 @ 116 mph (on a 0-60ft of 1.8 s)

Thanks for that. There's a G80 code on the doorframe, so it has got a LSD (I'm pretty sure all fourth generation cars have). I've talked it over with the guy who's going to service it, and we both think that it's unlikely that the oil in the diff has ever been changed, so he's going to drain and refill with the correct viscosity. There's also an additive he's going to put in which apparently works wonders.

Now, next question: there's a grainy deposit in the coolant header tank, which I assume is Dex-Cool breaking down, so I've suggested we do a coolant system flush. Is there any flushing agent which is specifically for use with Dex-Cool?

I just removed the coolant overflow bottle under the battery and cleaned it all out, popped off radiator hoses and wahed through with a hose pipe and clean water till clear was coming out. I'm not sure on the whole flush solution tbh. Refilled via top of radiator

With your car being a 97, this is an overlap time when they changed from Auburn clutch type LSD to Zexel Torson torque biasing helical gear Posi traction LSDs. Both do same job essentially. Anyway, without getting super technical the auburn MUST have friction modifier in otherwise clutches have too much friction and diff clunks, click and locks up all the time. The Zexel doesnt require the aditive to function as it uses gears, not slipping cones or clutches. HOWEVER, Gm noticed that in cases with the Zexel diff there were some clicking/ticking noises (called rusty nail problem) and they found a small amount of friction modifier solved this issue.

As a first try I would refil the diff. I used redline 75W90, nearly 2 quarts goes in (a bottle is one hence yank units). I got one bottle of 'standard' oil with no friction modifier pre mixed and one bottle with friction modifier pre mixed. Try get a hold of the bottle to read exactly what the oil has in before using. If you have the Auburn LSD with the springs inside when diff cover is pulled, I'd try get some actual GM stuff or something your mechanic trusts (hope he is good, I service and work on mine myself, cant really trust some garages these days with 'performance cars', they all charge you more because it is american, yet an oil change is and oil change, parts cost same and uses only 5.2l oil (in V8) plus last gent who had it before me had full service and he took his own parts and they changed only 4 spark plugs cause the other 4 take longer, ie a reason GM give the job about 2-3 hours,not kwit fit 30 -60 min jobby). I had some incorrect oil (correct spec and with additive) that wreaked my auburn LSD, so back to zexel now

hope this helps

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'99 Z28 A4, 253 LS2 heads, 228R TSP cam, Patriol Dual Springs, Double roller timing chain, LS6 ported oil pump, OBX LTs, 3" True Duals, LS6 intake, 42lb/hr injectors, SLP lid + bellow, EFIlive COS 3 Speed Denisty Tune (self tuned), 3200 Circle D stall, CAI mod, KYB AGXs, Eibach Pro Front Springs, UMI panhard, LCA + Brackets, Strut Brace, Custom Subframe connectors, WS6 axle with 3.42s, 18" American Racing Rebels, US mirrors, 93 tail lights, 3.5 inch custom cowl hood. Mickey T's Street DRs on Vette-ZR1 wheels for the strip !
Best ET: 12.0 @ 116 mph (on a 0-60ft of 1.8 s)

That's really helpful, thanks. I've printed it off and will give it to the garage (who are pretty good). It's going in next week, so I'll post the results when the diff's been treated. Hopefully 2012 will be quieter than 2011! Cheers.