I replaced the rear end fluid in a 8.25 rear end. I read you needed 4oz of the friction modifier, I bought one bottle (4oz) at the dealer. After reinstalling the diff cover, I added the modifier and used Lucas SAE 80w-90 gear oil. The oil IS NOT a synthetic. After a week or so of driving I noticed a sort of grinding noise coming for the rear, when turning. 95% of the time it happens when I'm at a complete stop, accelerate and turn. I noticed that the bottle states, "Excellent for use in limited slip differentials. No special additive needed." After reading "you need the modifier unless stated on the gear oil bottle 'with friction modifier'" many many times, i felt the 4oz was nessecary. May jeep NEVER did this before the change of oil. Now I'm wondering if the modifier was too much? I'm hoping someone reads this that was had the similar problem I'm having, and hopefully with the same product.

Also, my rear drive shaft has a slightly worn u joint at the axle. It's so minimal that it would be hard to believe that's making such a ruckus.

 

first of all what does the title have to do with the post? your clutch packs are in your transmission (automatic) and you're taling about the rear diff...... as far as the rear end...ive never used any modifiers when changing out the fluid

 

Do you have a LSD in that 8.25?

 

there are clutch packs in Limited slip differentials..
Cameron

 

Thank you for clearing that up.

Yes my 8.25 has LSD. Like I said the grinding really only occurs when I'm at a stop, then resume acceleration WITH a right or left turn. Usually when I start the turn and hear the noise, I let off the gas and let it coast then resume and the noise is gone.

 

Adding too much of the additive won't hurt anything mechanically, it will just allow the unit to slip a bit more. That's all the additive does- allows the clutch disks to slip a bit to reduce noise and shudder. It's sort of a trade off between how much lockup you want and how much noise/vibration you are willing to tolerate.
Non-synth Lucas 80/90 is fine to use, BTW. Not to be obvious, but it is filled to the correct level, no?
Go find a parking lot and do about 10 figure-8's and report back.

 

Sorry for high jacking this but since its on the same ish subject, if I wanted to get more "lock up" could I change my oil out and add regular oil and maybe 2 oz or none at all of the additive? Or will that destroy my clutch packs?

 

sorry, wasnt thinking about it being an LSD

 

There are clutch packs in the rear end, which can go out and exhibit this very problem when they do. I have a Mercury Mountaineer that began exhibiting the same symptoms a few months back.

 

Yes the level is good, I checked it when the noise started. I'll try the figure 8's when I get the chance but not sure if the noise will happen. Definitely going to do the rear drive drive shaft u joints soon though.

Not sure, but I read too much friction modifier can be bad for the clutch discs. That it can allow them to slip too much and wear faster then normal.

 

Yes, and yes. You can get more lock with less additive but it'll come at the expense of considerably shorter life and more noise and chatter.

 

Do the figure 8s. About 10 of them. That will get the lube all over the clutch packs.

 

Oh, ok that makes sense now haha. Didn't think of that when Radi said so. I'll do that when i get the chance and post the results.

 

Thanks for the advice about the figure 8s, but unfortunately they didn't help any. I don't get it. I'm wondering if I should have used 75w-140. My manual says to use that if equipped with class lll hitch. I've read you don't need 75-140 unless you trailer alot, but..... I don't know..... Im going to replace u joints and go from there.

 

The gear oil you used should be fine. Are you sure the noise is coming from the diff and not a rear brake or something similar? I got some scraping/grinding on turns when my rear brake hardware let loose (rust)