Rear diff fluid - now I hear something

[triplexbullies]

I may have made a real bonehead move.. I just did my rear diff fluid because it was leaking just a little bit. The fluid looked fine. I got on here and I found the fluid that my 2003 GMC Z71 needed. NO Limited Slip additive. Well I wanted Royal Purple, so I got one and then a Mobile 1 and the guy said mixing the two would be fine. Well I JUST realized that it says LS on it... I've driven about 1500 miles since I added it. I went on vacation and drove about 1300 from that. On the way back I started hearing a noise. It's something down there. I am now assuming that the LS is limited slip and I messed up.. The rattle isn't terrible... Have I messed it up completely? Is that really what the LS stands for? Can I recover???

 

I realize I probably made a mistake... I was looking for LIMITED SLIP, no LS.. So let's try to be helpful.

[triplexbullies]

I was very certain not to do that. The magnet wasn't that secure to the side of the cover. It came right off, I cleaned it, cleaned the inside of the cover and placed it back in the place where I took it off. Should it have been secured down with some kind of adhesive??

[triplexbullies]

As far as other things. I just replaced both of the u joints on the rear driveshaft and the right front hub. The driver hub seemed fine when I had my wheels off last time. I just got a new AC compressor and the other parts that go with it. That was done the day before I left for vacation.

[triplexbullies]

It only started making noise about 250 miles ago. It started about 200 miles away from home on the way back from vacation. I had the front passenger hub replaced right after I got home. I knew the hub was busted but it turns out that's not where the sound was coming from. Now I think it's probably the rear diff... especially after seeing the LS.

[triplexbullies]

LS definitely means it has the friction modifiers. Yes... I am an idiot. So I guess step one is change the fluid again and don't be a bonehead??

[brainpause]

Yeah, that magnet might be the problem. Me and a buddy were changing his fluids. We couldnt decide on epoxy'ing it or not. Found some pictures somewhere of someone securing it with adhesive of some sort, so we did epoxy. He hasn't had any trouble. We let the epoxy and magnet sit overnight prior to filling the diff, so the epoxy would cure.

 

It seemed to both of us that the magnet didn't have much affinity for the diff cover.

[txab]

Sound like you're not sure where the sound is coming from. Find out for sure where the noise is coming from. Plenty of things underneath to make noises. The Mobil1 LS is not the problem. Plenty of people on this site have used and are using Mobil1 in their G80swith no problems. I personally wouldn't have mixed the two brands. Should have gone 100% Mobil1 or 100% RP

 

Did you get it re-filled to the proper level?

[triplexbullies]

I could tell it wasn't terribly attracted to the cover, but it definitely stuck a little bit. At this point though, it probably would have done the damage if that was it, right?

[triplexbullies]

I had it on a slight decline when I dropped the cover so it didn't all come out. I put two full quarts in it. Mine refills near the yoke and I wasn't sure how to check it, but knew it had right about 2.1qts in it.

 

I recently replaced both of the u-joints on the driveshaft.

 

The noise is more apparent over 40mph and seems louder when I let off the gas and let it coast. I was trying to troubleshoot before I paid for it.. Since I've recently put about $1200 in it...

[brainpause]

I don't know. You'd think so.

[triplexbullies]

I'm going to take a closer look at the rear u-joints tonight. I didn't notice anything when I droppped the drive shart the other night but I didn't pay that close of attention to it. I guess I need to check the front drive shaft also. Anything other ideas of what I should take a look at?

 

I can hear the noise at low speeds. I don't think it's worse but I can hear it, it's just pretty quiet at lower speeds.

[Z45]

You are confusing gear lube with a specialized additive. Its the additive not to use, not the gear lube. Just because it says it will work in a LS differential DOES NOT mean is has the additive in it.

 

I would not be mixing the lubes, pick one and use that. When you mix brands of lubes you are playing chemist. Using a gear lube suitable for use in limited slip is not going to cause any problems. Do they say do not use a gear lube suitable for use in limited slip differentials? No, its the additive that should not be used.

[triplexbullies]

Ah... So should I go ahead and flush it out and replace with just one? Could that be causing the issue?

[Z45]

Its hard to say but I doubt the noise has anything to do with the differential. Over 18-20 mph the rear locking differntial will not even engage so I fail to see how it could make noise from lube. Unless...........you left something inside the rear end?