AW4 Noise Issues

[willcomsto]

Hey all, long time reader, first time poster!

I posted this in NAXJA too, I would like to figure this out before my Trans explodes on my next business trip!

I have been reading through this forum, as well as a dozen other jeep sites, and haven't been able to find a thread that specifically targets my issue. I just purchased my second XJ, a 1992 Laredo with about 220k on the clock. I took it on a 4 hour round trip, with varying speeds from 60-75 mph, and I started hearing a noise.

Between 50 and 60 mph, I hear a faint whining noise regardless of throttle position. No real vibration, but a definite noise, and it sounds like it's coming from the trans tunnel.

After 60mph, the only time I hear it is on deceleration (foot not completely off the throttle, but not pushing it either, think maintaining speed downhill on the interstate). If I let off the throttle, it goes away, and if I press the throttle, it goes away, and if I change nothing with the throttle pedal, and shift it into neutral, it goes away.

I have read other threads regarding axle noise, and varying trans noises, but nothing seemed to fit this bill.

Thanks a ton in advance for the help!

[4.3LXJ]

Am I to assume you have no lift or CV joints in the rear drive line?

[willcomsto]

I have a mild lift (springs and add-a-leaf to about 2.5") but nothing that would require CV joints or SYE.

[NW99XJ]

i'm gonna go thru the redundant stuff first, and ask if you've checked all your fluids for both proper level as well as whether its burnt or spent in some way.
I'd also look at the trans mount. A worn mount can cause all kinds of weird issues. This COULD be related to the transfer case, so I would really look at the fluid level there, and suggest that there's a "chance" that the chain could be stretched. A stretched/worn t-case chain (in its early stages) could potentially cause some of these symptoms. If you want to do some "exploratory surgery" on the jeep, you could open the transfer case on the jeep... just drop the drive line, and start splitting the case. I know it sounds horrible, but its not all that bad of a job. That way you'd know for sure what that chain looks like. All you're invested in for this kind of job is the time, some fluid, and some RTV for re-sealing the case.
The AW4 is one of the strongest most resilient auto trannys on the planet. even with high miles, they will still pull strong. It may just simply be time for a service, or at worst case, a rebuild. but if you're not feeling any surging, slipping, or vibration....then i'd start looking at some of the other things first. The driveline joints may be another thing to consider. They're cheap, and easy to replace, and will give you peace of mind. I dont usually suggest throwing parts at a problem unless you know for sure what it is... but in this case things like fluid checking or fluid/filter swaps and a few u-joints, isnt all that big of a deal, and will further help isolate whats going on.
Good luck, I hope this helps.

[willcomsto]

That does help, thanks. Would it be a bad idea to have the AW4 flushed and filled with full synthetic, or would that make things worse with such a high mile trans?

[Mudderoy]

That does help, thanks. Would it be a bad idea to have the AW4 flushed and filled with full synthetic, or would that make things worse with such a high mile trans?

I would never have a AW4 flushed. Also keep in mind that high mileage transmissions may only be working because of the band debris that is floating the fluid.

Check your fluid first and see what it looks like, what Josh said. Then you might want to do a 50/50 fluid change. Where you use half new fluid and half old fluid. If everything still works, you can do this again after a few weeks. Eventually you'll have mostly new fluid in.

You guys jump in with your thoughts on this. I'm just repeating what my mechanic did on my first transmission fluid change at 100k miles. :D

[NW99XJ]

Yup, good advice.
The 50/50 drain/add is common practice, and has proven good results method for the AW4....
IF it comes down to that, this would be the thing to do.
I have to ask... Do you know what you're looking for in checking fluid levels in the tranny and t-case?

[willcomsto]

Can you do the 50/50 add with synthetic, or is there a specific fluid that will help my trans more than hurt it?

As for the trans, yes I do know what I am looking for. T-case, not so much. Same goes for the diffs. I should probably do a driveline fluids change this weekend, on everything... ANy idea how much time that would take, and if it'd be worth it?

[NW99XJ]

i *THINK* (if I remember correctly) its a Dextron III blend... unless you're 100% sure that its already filled with synthetic, then I would not mix the two. Really there is no MASSIVE benefit to running a synthetic auto trans fluid. Honestly, you'll gain much more benefit from installing a trans cooler. The AW4's only weak point is its susceptibility to heat damage (usually only happens when towing heavy loads, or serious offroad use in 100° plus temperatures)

[Mudderoy]

I would only run the DexIII/Merc fluid.

[willcomsto]

Yeah, so I think I am going to spend the weekend cleaning and freshening the fluid in the front and rear differentials, the transfer case, and the trans. I think I am going to go ahead and do the engine oil too while Im at it.

Anybody know of a good (cheap) way to upgrade to an automatic electric fan? Off subject, I know, but my xj started pissing coolant this morning, so I am going to take the opportunity to upgrade the cooling system.

[4.3LXJ]

Define upgrade. Are we talking manual switch or pulling more air?

[NW99XJ]

There's always the Taurus Fan mod....
Basically installing an electric fan from a Ford Taurus.
You can use a thermostatic controller or hook it up to a switch.
Popular mod, very effective, and relatively cheap.

[willcomsto]

Yeah, I was looking at that, but most every person I see doing that mod had manual cab switches for the different speeds of the fan. I really dont want to be zoning out on the way home in traffic, and not see the engine overheating, Id like it to moderate itself. I have the mech fan on there now, but this is all moot as the leak was from a loose hose clamp, and convincing the boss that I needed a cooling system overhaul immediately faded into the mist.

I think when Im ready, Im going to do the Dirtboundoffroad fan kit, as well as high flow components from hesco. Overkill for a dedicated daily driver? Maybe, but I like wrenching.

[4.3LXJ]

Ya gotta take these XJs seriously when it comes to cooling. They were under designed anyway