drepamig
NAXJA Forum User
- Location
- Northern Michigan
Hello everyone. I've been a lurker on the forums for a while, since I got my Jeep in May. I must warn that this is going to be a hell of a long post. First off, the specs:
2001 Cherokee Sport w/ 138k miles
4.0L
AW4 transmission
NP231 TC
8.25" rear end
edit: I forgot to mention that the Jeep is bone stock save for larger tires (235/75 vs. the 215/75 that came stock, if memory serves)
Here's what's going on - Shortly after I bought my Jeep I noticed a slight whine from what sounded like the rear end at 45 mph during cruise. It was so quiet that I could only hear it with the radio turned off and the windows up. It would only be present at cruise and would change pitch with speed, though it was a small window where I could hear it. I changed the oil in the rear end (along with every other fluid in the truck) as part of making it mine. A few weeks later the whine started at about 35 mph and continued to about 50. A couple weeks later it had continued to about 60.
Eventually I had a friend of mine said there was something wrong with the rear axle, so I swapped in a used axle with 65k on it. Changed the gear oil out and put synthetic 75W140 (I was planning on doing some towing) and took it for a ride. Now the noise (which I thought was coming from the new axle, but I’ll cover that in a minute) has changed a bit – the whining is still there from 35 – 60 and has slowly gotten louder. In addition, there was now a howling/whirring noise during deceleration at any speed above 35 or so, changing pitch with speed. I couldn’t return the used axle so I lived with it for a while (about 2500 miles) and it never seemed to get any worse but it bugged the hell out of me.
I brought it to a trusted mechanic who thought it might be a pinion bearing because of how the sound came and went with coast but wasn’t sure. He opened up the axle, found some rust in the front pinion bearing and figured he’d found the problem. I had him replace all of the bearings (both pinion and both carrier bearings). He reset the gears and refilled the case, again with 75W140. I took it out for a spin and neither sound changed at all. They were both still there!
I brought the jeep back to the mechanic to try to find the noise again. He rechecked the rear end and said everything still looks good and that it’s in spec (he mentioned the gears looked fine, bearings are new and look fine, etc). He took it for several rides and was able to replicate the noise but it seems to change positions (from directly under the driver at low speeds to the rear end at higher speeds) and he couldn’t tell where it was coming from. He had 3 other mechanics look at it as well with no conclusion. Also, it apparently doesn’t make any strange noises while up on the rack no matter what speed.
The mechanic asked me to drive it for a while longer to see if the noise changes or if it gets louder. When/if it does, then bring it back to him and he’ll go for a ride with me to try to figure it out. The only suggestion he had is that it might be the transfer case, but he said that wasn’t much more than a shot in the dark (Side note: the transfer case seems somewhat noisy in 4HI… it kind of has a whir to it but doesn’t seem major. BUT, I have nothing to compare it to because I’ve only otherwise driven cars. Also, the fluid was dark red and seemingly clean when I changed it)
Cliff notes:
I’ve done a ton of searching but no conclusions. Could it be the transfer case? Transmission (which otherwise seems fine)? Please help! Thanks a lot!
2001 Cherokee Sport w/ 138k miles
4.0L
AW4 transmission
NP231 TC
8.25" rear end
edit: I forgot to mention that the Jeep is bone stock save for larger tires (235/75 vs. the 215/75 that came stock, if memory serves)
Here's what's going on - Shortly after I bought my Jeep I noticed a slight whine from what sounded like the rear end at 45 mph during cruise. It was so quiet that I could only hear it with the radio turned off and the windows up. It would only be present at cruise and would change pitch with speed, though it was a small window where I could hear it. I changed the oil in the rear end (along with every other fluid in the truck) as part of making it mine. A few weeks later the whine started at about 35 mph and continued to about 50. A couple weeks later it had continued to about 60.
Eventually I had a friend of mine said there was something wrong with the rear axle, so I swapped in a used axle with 65k on it. Changed the gear oil out and put synthetic 75W140 (I was planning on doing some towing) and took it for a ride. Now the noise (which I thought was coming from the new axle, but I’ll cover that in a minute) has changed a bit – the whining is still there from 35 – 60 and has slowly gotten louder. In addition, there was now a howling/whirring noise during deceleration at any speed above 35 or so, changing pitch with speed. I couldn’t return the used axle so I lived with it for a while (about 2500 miles) and it never seemed to get any worse but it bugged the hell out of me.
I brought it to a trusted mechanic who thought it might be a pinion bearing because of how the sound came and went with coast but wasn’t sure. He opened up the axle, found some rust in the front pinion bearing and figured he’d found the problem. I had him replace all of the bearings (both pinion and both carrier bearings). He reset the gears and refilled the case, again with 75W140. I took it out for a spin and neither sound changed at all. They were both still there!
I brought the jeep back to the mechanic to try to find the noise again. He rechecked the rear end and said everything still looks good and that it’s in spec (he mentioned the gears looked fine, bearings are new and look fine, etc). He took it for several rides and was able to replicate the noise but it seems to change positions (from directly under the driver at low speeds to the rear end at higher speeds) and he couldn’t tell where it was coming from. He had 3 other mechanics look at it as well with no conclusion. Also, it apparently doesn’t make any strange noises while up on the rack no matter what speed.
The mechanic asked me to drive it for a while longer to see if the noise changes or if it gets louder. When/if it does, then bring it back to him and he’ll go for a ride with me to try to figure it out. The only suggestion he had is that it might be the transfer case, but he said that wasn’t much more than a shot in the dark (Side note: the transfer case seems somewhat noisy in 4HI… it kind of has a whir to it but doesn’t seem major. BUT, I have nothing to compare it to because I’ve only otherwise driven cars. Also, the fluid was dark red and seemingly clean when I changed it)
Cliff notes:
- Whining noise at 35-60 during cruise/acceleration
- Whirring/howling noise while decelerating from speeds above 35 mph
- The whining noise has existed with 2 different rear axles
- The whirring/howling noise has only happened with the replacement axle BUT persisted AFTER a replacement of all of the bearings.
I’ve done a ton of searching but no conclusions. Could it be the transfer case? Transmission (which otherwise seems fine)? Please help! Thanks a lot!