Hello everyone--

Maybe some of you can give me some clues as to what to look for. I have a 2001 4wd, automatic trans., ZR2, about 125,000 miles on it. I drove 600 miles from Western PA to Boston. Got there and found I have a rumbling sound coming from I'm not sure where (my hearing is not good). My first inclination was to reach over and down shift, but of course this is an automatic, but it feels like lugging. Got back from Boston fine. Noise hasn't gotten any louder.

--Transmission works fine. No fluid leaks. Fluid is clean and clear. Goes through gears smoothly. No codes that might indicate a transmission problem.

--U joints are fine. No play.

--Tires had uneven wear, so I switched them around. No change.

--I just installed new hub/bearing assemblies about 2 months ago. I've had bearings go bad and this isn't the sound I associate with them. But then maybe. . .

--I thought just maybe the air conditioning was doing something odd, but no. Same sound on or off.

--Doesn't happen when I'm coasting, only when I'm accelerating, at any speed.

Any suggestions where to look next? I'm thinking maybe engine mounts or maybe the bearing assemblies going bad fast.

 

Wow really hard to say. Can you take a ride with someone who hears a little better to try to get a location. My first thought would be transfer case switch going bad with front actuator trying to engage.

 

Thanks for the reply. Is this what my manual calls the "Transfer Case Control Module"? Looks easy as pie to replace, but a little pricey. Auto Zone wants $326 for it. Can I go at it with my electrical tester to verify?

I should point out that 4wd low has never worked in this vehicle. I'll press the button. It'll flash, then go out.

One more detail, which I don't think is relevant, but for the record. Just before I left for Boston, I discovered a fast drip coming from my water pump. I had no time to get in there and do anything, so I used cooling system stop leak. Didn't want to, but no option. Kid was starting college and HAD to be there. So I left the front underplate off the vehicle for the drive so I could watch for the leak. Not a drop the whole way. Water pump is even quieter, but could leaving the underplate off have exposed something to wear or damage?

Thanks again for the comments.

 

More Information for DORMAN 49315 Sorry to disappoint but I think it's about 17.00. Don't worry about the skid plate some people leave them off it just keeps things cleaner and a little protection off road.

 

Thanks for the link. I was going to ask. I googled up "transfer case switch" and got three things to choose from. I have no experience working with 4WD, so this is a little new. I like the description: "harsh conditions under my car." That's for sure! I live at the end of a 1/3 mile mud and gravel driveway. At the very end is a puddle that often turns into a pond that I have to drive through to get in or out. I've killed a couple of starters. They don't take to prolonged and continuous immersion well.

For $17.00 I can afford to replace it just to see.

Thanks again.

 

Just thought of something. If this switch is going bad, wouldn't I have trouble putting it in 4WD? It definitely goes into 4w, even low worked today for the first time. Could there be something out of balance?

 

Yes most likely. If you go to the BF homepage type in "acceleration rumble" in the goggle box there's a whole bunch of stuff to read. Something might sound familiar. That's really the best way to search on this forum. It will show all the threads tagged with those words. Good luck I'm sure it will be there. These trucks all have the same problems.

 

There are a few things happening when you put your truck into 4wd. What you are commenting on is just the engagement of the transfer case, not necessarily the engagement of the front axle. Take a read through the tech article section, specifically the thread entitled 4wd Front Axle Clicking When in 2HI - Goes Away when in 4HI/4LO.

 

I'll take a look at the info on 4WD. Would help if I understood the system better.

I did some looking around various threads here and I think I've got the problem narrowed down to transmission shudder. I decided to try a tube of Dr. Tranny's Instant Shudder fix and it reduced the problem dramatically, but it's still there, kicking it about about 40 mph and fading out at about 60-65. No shudder at all at low speed now. Could new transmission fluid make a difference, or could this be new transmission time? Other than the shudder, it runs great. Goes through gears smoothly, no slipping.