Wrong Fluid!

[gtmud]

I have an 89 XJ with the NP242 Select-trac "2-P/T 4-F/T4- N-4LOW". Went to change the fluid (149+) and found that it had gear lube in it. I refilled it with 75-140w synthic for now to get home. SHould this be drained and flushed then refilled with mercron, or would it be better to leave it alone. No noises heard from T-case.

[MagicRat]

A Jeep specialty shop did the same to me a few years ago.

They claim the gear oil is better for the case, especially if it gets lots of heavy duty off road use in low range.

I was concerned the ATF fluid (as specified by the manufacturer) is much thinner and can lube the tight clearance bearings better, especially at highway speed.

IMO if you use the Jeep mostly for on-road use, drain the gear oil and put in ATF. I do not think a 'flush' is necessary.
I did this drain and fill to mine with no problems.

[thundergod1320]

The actual "w" numbers for synthetic products far exceed the designations
I use Amsoil synthetics in all my vehicles and although I was an "unbeliever" in anything other than real oil (which has more additive packages in it than oil).
Some years ago I was involved in a top fuel dragster operation... At 7000hp, engine bearings would come out black after a few runs (if we didn't blow it up) I began running synthetics and NEVER had black death on a bearing ever again. The synthetic lube you had in your transfer case is slick enough to get into even the closest fit components. A synthetic is more molecularly stable than conventional oil and will not "shear" (destruction at a molecular level which causes loss of lubricity) A synthetic will also "stick" to parts and not drain off, offering cold run protection. I use a 0W 50 oil in my engines... It pours like hot coffee even at below 0 temps, yet protects like a 50 weight oil even above the boiling point of conventional oils. If you took the synthetic out, no problem. The residue mixes with any oil. If it's still in, leave it there.

[citizen@large]

Well damnit thunder.. Do tell...

That's interesting info coming from a first hand user. Wanna give the details to the dragster or your part in the fun?

[thundergod1320]

Well, a long long time ago, when dinosaurs roamed the earth (or so my nephew tells me) I was involved with a couple of race mobiles... The "fun one" was an experimental top fuel/sometimes alcohol dragster. (except for compression ratios and camshaft) both are pretty much the same motors with different tuning) 'Wasn't owned by anyone famous, but it ran pretty good and made it into some good shows (like Summernationals & Indy. Back then the record was in the high 5's and our car ran low 6's which was pretty good at the time. It wasn't so much for the pride of it as much as in the satisfaction of trying new stuff and making it work. Most people don't realize the amount of research that goes into what you see on the track.
Now, I'm semi-retired and still do some wrench turning whan I feel like it but stay away from racing (it gets in your blood and makes you crazy)
The one thing I miss though is having a shop and lots of contacts. I can't find answers to the stuff I don't know and "manuals" somehow come just short of the info I need, generally saying that you need to bring the vehicle to a dealer for that because it's complicated.(BS)
Anyhow, the stuff I said about synthetics is valid... My last two vehicles finally died at well over 375,000 miles. That's not too shabby! and, both weren't fatally broken, just tired. I ran synthetic in both.

[gtmud]

THanks for the info I have since drained the gear oil out and filled with the AFT3. So far no problems, or noises. I have remedied one problem with the switch in lubercant, the t-case falls into the 4 modes faster, no lag time.