Big_Taxi

Hi, all

I recently received some serious help on this forum regarding and engine hiccup and now I'm back. I have an '00 XJ 4.0 with an automatic transmission. I have acquired a couple of things, some of which might have been there for months but I was so focused on my hiccup that I couldnt think of anything else.

When idling (1/3 of the time, mostly when colder) there's a vibration trending to a rumble that happens down the spine of the car, beneath the center console. Literally the moment I put some gas on it disappears, only to be replaced with a "howl" (although "drone" would also be accurate) starting at around 20 mph and increasing in volume up to 60. I've looked into quite a few threads but my problem is it's hard to relay a sound and a feeling over the internet. Is there anywhere I can start? I think I can knock off fluid levels, I recently added some Dex VI (please tell me that's OK), but I don't know about rear diff.

Potential culprits based on what I've seen:
Engine mounts
Rear diff bolts/gaskets (?)
Pinion joint bearings (is this a thing?)
Wheel bearings (for sound at speed)
Misaligned drive shaft

Thank you all for your help in advance.

Big_Taxi

Naturally more suggestions came up after this, and after skimming through some I thought i might add some things:
No vibrations coming from the wheels or when moving, even 40+
Maybe a slight grinding sound between 0-20 mph but I'm not really sure
nothing smells, no sound from the rear of the vehicle.

Big_Taxi

I put the back seat down to see if I could hear more clearly, and I was mistaken, there’s definitely a light rumble/rattle from the back end when idling. Putting it in neutral at stops eliminates the sound... so that’s probably a good clue.

Big_Taxi

Did some more research. If I'm at a stop in D, then nothing is moving and it's engine/transmission that's causing the vibration. Can anyone verify this? This would indicate engine mount/trans mount. Can I replace these things by myself?

The howl/drone is another story and much harder to pin down. The problem is that I don't have vibration when moving, the sensation is more like something is winding up and then not loosening when at 45+.

dave1123

Check the tailpipe where it passes the fuel tank. I had the same thing happen when my tailpipe hanger bracket was broken, except mine was rubbing on the trailer hitch. Another thing might be the transmission mount allowing the exhaust pipe to rub on the crossmember. OR both these things.

Big_Taxi

Good idea, and if that works then it'll just be my mysterious front-end sound.

Did your sound go away when you applied gas?

dave1123

Ha ha! Crossing posts. Check the trans mount as well.

PatHenry

You absolutely CAN do the motor and transmission mounts by yourself if you have a half-way decent floor jack, some jack stands, regular hand tools and the desire to do it.

The transmission mount should be replaced with an OEM or Napa brand. Do NOT use Anchor or a cheapo part - these parts will not keep the exhaust off the crossmember, which is very likely part of your problem.

Changing the tranny and motor mounts is primarily just taking the weight off the location, undoing the hardware and swapping the part out. Lots of excellent tutorials online. If Matt at Bleepin' Jeep has a video on this, I'd start there.

Since you have to loosen up the tranny mount before doing the engine mounts, you aught to do all of them at once if you're going to be doing both motor and tranny mounts.

gat

I'd just do the transmission separately from the engine. I'm not sure whether you meant unbolt the supports for the engine and transmission simultaneously or you meant swap for the transmission then for the motor one after the other.

PatHenry

What I mean is that when you do the engine mounts, you'll want to loosen up the tranny mount bolts (so you're not twisting on it when aligning the motor to each mount).. and if you're going to loosen them, you might as well throw the new tranny mount on there when the motor mounts are done. That is, if you're doing all the mounts.

ForrestLee

I've got a similar problem with an 04 larado.
I noticed the fan blades slowed down, its a clutch fan.
So i thought maybe the water pump or fan were going bad but the water pump works fine, and the fan seems to be doing its job.
Just because I've had a similar rumble issue with a hemi, I replaced the tensioner pulley, and idler pulley. Those didnt fix it on this jeep... but I was replacing the serpentine belt anyway so those are all new now.

Whats weird is I first noticed it rumbling when I had the ODBII scan tool hooked up, checking codes.
It was idling at 2800rpm! And it would start a rumble and shake the whole vehicle. Teeth chatter vibration, sitting in park with an extremely high idle.

Now, when I drive it, it starts around 35mph. And its really bad at 46mph. That's the worst speed, up hill, down hill, or level... 46mph is horrible rumble. Then it gets better until you get to 59mph...

I can't pinpoint it. I down shifted to see if it would change it, but its still there in 2nd, or Drive.
Its a 4x4 always on.
Anybody figure out what was causing the rumble?
I too have thought trans mount, or maybe torq converter bolts.
I may have a couple separate issues. But that rumble is really bad. It feels like a harmonic balancer is coming apart. And it comes in waves.
Anyway it would be best to do just the trans mount... then the engine mount so you can determine the actual problem. If you do both, how would you know which one caused it?

Big_Taxi

I only have a rumble/chatter at idle, and I think it's likely that it's a bracket or something similar that's just rattling, as Dave1123 mentioned.

My sound is from under the hood, and it's a drone or howl but the car runs totally fine (maybe revving a little too high/feeling tight when coasting or on a downhill). I might get the belts checked and still mgiht do a transmission mount swap, but I guess at this point I'm OK with how it drives.

ForrestLee

I just replaced the belt and idler and tensioner pulleys.
It actually sounds like the fan clutch bearings are going out... as weird as that is. Watch the fan as it idles and see if it slows down as the rumble starts... maybe Im seeing things but I swear thats happening.