Hey CF. I recently bought a '98. 4.0, AX15, NP231, Dana 30, Chrysler 8 1/4. 179,000 miles. I'd like to do a complete tune up. I just have some questions... Which is the best fluid to use in the transmission, transfer case and differentials?

Here's the Tune Up list:
Oil Change (Rotella 6)
Coolant Flush
Transmission Fluid Change
Differentials Fluid Change
Transfer Case Fluid Change
Power Steering Fluid Change
New Plugs, Wires, Cap & Rotor
Upgrading Fuel Injectors w/ 4 Port Injectors
Air Filter Change

I'm going to change the brake fluid when I install the new Rotors, Calipers, Hub Assembly's, Drums and Pads. Control arms will be done at that time as well.

Am I missing anything else?

Thanks & KCCO

DexMerc in the Transmission and Transfer Case.

80W-90 dino will be fine in the differentials unless you plan on doing a lot of towing, then you will want something like 85W-140

Make sure you use either champion copper or NGK copper plugs for the tune up. 4.0 doesn't run all that great with the newer fancy schmancy plugs.

Chive on!

Don't forget a good oil filter too. Such as Mopar, Napa Gold or a Wix filter. Star away from fram or any other crappy filters like that.

On the trans I would either have it flush and filled or if DIY, several changes over the next few thousand miles. remember you are only changing 1/3 of the fluid in a drain and fill. If it were me I would at least check the waterpump and fan clutch and change the rad cap and T-stat. I would do all new heavier gauge battery cabling and freshen the grounds.

I'll look around at home much it'll cost to have the transmission flushed and whatnot. I may have the coolant system steam cleaned and then filled. I think it could definitely benefit from that. New battery cables are gonna happen when I get the new battery, next month.

i would use 75/90 GL3 in your trans, not automatic transmission fluid. I used synthetic 75/90 in the difs and atf dex/merc in the xfer case.

Yes, the AX-15 runs 75w90 GL3 gear oil. There's no flushing. It does not use ATF.

GL3 has been pretty much discontinued as newer transmissions use different lubes, and GL5 is better for axles (hypoid gears). Unfortunately GL5 is corrosive to the AX-15.

At the parts store look for a lube specifically labelled as for synchronized transmissions and/or yellow metal safe. "API GL4/5" alone is not good enough. Qualifying oils include "Synchromesh" oils from Castrol, Pennzoil, AC Delco; Royal Purple Synchromax; Redline MTL and MT-90. MT-90 is my favourite - and a lot of others' favourite - meets all of the original specs and is on the shelf at my local NAPA.

Any old ATF is good for the transfer case. Synthetic lasts longer in it on account of vaporization.

OE friction material is ceramic. Semi-metallic and organic are a waste of time.

While you're in the tuneup zone, consider that a 16 year old computer-controller vehicle may be starting to show wear in the engine management department. Sensors get old and dirty. If you have the means to, either an OBD-II scanner or multimeter, check that the Intake Air Temperature and Engine Coolant Temperature are accurate. The Throttle Position Sensor should be tested as well as the entire throttle body cleaned. The O2 sensors are rated for about 100k miles and are probaby original.

Good Catch. Sorry I didn't even look to see what trans the OP had. Just assumed AW4.

You know what happens when you assume...

dont flush the trans. could cause premature failure if that trans has not had it regular flushes. just drain, and refill.

also I am running the bosch iridum(spelling?) spark plugs and picked up an amazing 5mpg seriously.

also you could reset the PCM.

I recommend cleaning the trottle body as well. and get some diletric grease and hit every plug you can find.

adjust trans kick down cable. over time they can get out of whack.

when it comes to tuning up a 15 year plus old vehicle the sky is the limit really...

Picked up some stuff at the auto parts store. Still have to get some gasket maker and new radiator hoses. I had to work with what they had locally.

Hope you got more atf fluid than 3 quarts. Btw you know that you will not be able to get all the old fluid out of the trans. Most of the fluid is stored in the torque converter. You will need prolly 4 to 5 quarts just for a drain and refill. And again. You will be mixing that sythetic with non most likely. Unless its already running syntheic which I doubt.

That would probably make sense if he had a torque converter

And I would take the Synchromesh back, and go for some Redline MT-90. My AX15 feels buttery smooth for how old it is (180k miles just like yours.)
When I get a second, I'll post my maintenance history since I bought my heep 6 months ago.

<3 my MT-90

At any rate I only see two bottles of Synchromesh. Whatever you use you're going to need two more.

I have 4 of the Synchromesh. 4 Diff Oil. Pep Boys, Advanced or Autozone don't sell the Mt-90 here. Gonna have to go online.

Ah okay only saw two in the pic. Just run the Synchronesh for now and change if you need it. Don't spend your life hoarding things and not drivin the Jeep lol.

No NAPA in your town? They have Redline on the shelf here.