Question for JJ

chefdab · **Posted:** Thu Jan 11, 2007 7:14 pm

Hey JJ, you're the resident oil expert here and I need some advice. I am putting some Rockcrusher diff covers on my LJ. The owners manual says to use 80W90 gear oil for both diffs, 75W140 for towing applications. Unfortunately, I didn't realize this until I had finished up the front diff with some Mobil 1 in a 75W90 weight. Before I crack open the rear (or redo the front), is there any significant difference between the two weights of oil? I would really hate to have to reopen the front now that it's done. Can I use the 75W90 without causing any issues to the drivetrain?

On a side note, I also may have overfilled the front since I was going by the fill hole which is located higher on the new cover. Will this do any damage? I tried to remove some with a cheapo turkey baster but couldn't reach much because of the angle. If I really need to, I guess I could get a suction gun from the parts store, but I'm trying not to spend anymore than is absolutely necessary. Does anyone have any suggestions?

JJsTJ · **Posted:** Thu Jan 11, 2007 8:26 pm

chefdab wrote:

Hey JJ, you're the resident oil expert here and I need some advice. I am putting some Rockcrusher diff covers on my LJ. The owners manual says to use 80W90 gear oil for both diffs, 75W140 for towing applications. Unfortunately, I didn't realize this until I had finished up the front diff with some Mobil 1 in a 75W90 weight. Before I crack open the rear (or redo the front), is there any significant difference between the two weights of oil? I would really hate to have to reopen the front now that it's done. Can I use the 75W90 without causing any issues to the drivetrain?

On a side note, I also may have overfilled the front since I was going by the fill hole which is located higher on the new cover. Will this do any damage? I tried to remove some with a cheapo turkey baster but couldn't reach much because of the angle. If I really need to, I guess I could get a suction gun from the parts store, but I'm trying not to spend anymore than is absolutely necessary. Does anyone have any suggestions?

Well, I don't consider myself an expert, maybe one in training though. :wink:

I don't think it will be a big deal on the weight difference but I would suggest changing it sooner than you usually do. Running a little more because of a higher fill plug isn't a huge deal either. If anything, a little more capacity is better.

DarbyWalters · **Posted:** Thu Jan 11, 2007 8:29 pm

Amsoil Severe Gear 75W-90 is a good replacement for standard 80W-90W so you should be fine (Mobil Syn 75W-90W should work too). Your fill level it most likely fine too.

chefdab · **Posted:** Thu Jan 11, 2007 8:53 pm

The reason I am worried about the fill level is because it was suggested on another forum that overfilling could lead to failure of the axle seals due to the increased pressure. I definitely can't afford to replace axle seals right now and due to my overfilling, it certainly wouldn't be covered under warranty.

jcphoto20 · **Joined:** Sun Nov 19, 2006 1:36 am **Posts:** 507

why does everyone recommend red RTV? whats wrong with black? when i was buying it, seemed like it was more suitable than all the others, but perhaps i missed something on the label.

i have mobil 1 75/90 in the front and mobil 1 75/140 in the back, both have lucas oil syn oil stabilizer

Cacher123 · **Posted:** Sat Jan 13, 2007 12:43 am

Was reading an article in a 4x mag and they suggested that after putting on the RTV, to tighten the cover just enough to let the RTV begin to squeeze out then stop and let it cure for 24 hrs. Then tighten the cover down fully. Evidently this makes a better gasket than just squishing it down to begin with. Of course, u have to wait the 24 hrs for the RTV to cure but it seems to make sense.

chefdab · **Posted:** Sat Jan 13, 2007 6:48 pm

Well to be safe, I haven't driven the jeep since Tuesday. I just finished the rear yesterday, and I'll probably drive it to work tomorrow evening. The front has had like 3 days to cure while the rear will have had about 36 hours by the time I go out tomorrow.

Quote:

why does everyone recommend red RTV? whats wrong with black?

I just used the black that came with the covers.

unixxx · **Posted:** Sat Jan 13, 2007 6:52 pm

I always hear people recommending Permatex Ultra Grey, Ultra Black, or the Right Stuff.

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