03 Montero front diff noise deceleration
 

Hi All,

New member, first post, bought an 03 Montero limited in Sept 2018 with 110k miles on it. It has been expensive to get it running the way it should, but now is a pleasure to drive. I bought it to do long highway trips, drive on the beach, drive in the mountains and snow, and to camp in.

About a month after I got it, I was driving down the highway in 4H at about 60mph and started noticing a faint high-pitched whine on deceleration only. I changed the front diff gear oil, no real difference, maybe a little quieter. No metal in the old gear oil. The noise is only present in modes that use the front diff (4h, 4hlc, 4llc) and not in 2h. It is louder when decelerating from a higher speed but slightly audible even around town. Only happens when decelerating, goes away as soon as I get back on the gas. Overall it's faint and not a "bad" noise (not a grinding, just a light whirring or whine).

I have lubed the front diff freewheel clutch actuator rod and replaced the freewheel clutch actuator solenoids. I have no blinking lights on the 4wd display.

Everything I read, including the service manual, say the first thing to do is check the turning torque on the pinion nut and tighten the nut if the preload is too low. However, no shop I've taken it to seems to want to do that. They all basically say it's not serviceable and I just need to rebuild/replace the diff.

Questions:
1. Why won't the shops check the turning torque? Do they just want to do the bigger job (rebuild), or are they afraid to overtighten the crush washer etc?
2. Could it be something else besides the diff? Sure sounds/acts like the diff as far as I can tell, but I'm no expert. It seems to shift in and out of 4H smoothly now (it used to hang up a little and there would be a delay between moving the lever to 4h and it actually getting engaged, but that's better now).
3. If it's not an issue with the pinon preload needing to be tightened, should I buy a used, guaranteed one? A new OEM one? Have them rebuild it with OEM parts? Please school me on my options. If I don't do anything, will it keep getting worse?

Thanks for your help!!!

running 4H on pavement.....you are destroying the front diff 2H for pavement 4H on slipery surface did you not read the manual ?

Sorry, but you are completely wrong on this one. In full size Montero Limited, 4H is the All-Wheel Drive mode (center differential is unlocked). You are 100% fine driving in this mode on dry pavement. This mode engages both front and rear axles, but leaves them spinning independently, so no stress is added to any components when you turn. In fact, that is the mode I leave my Montero in for the whole winter. Plus, the manual states that if you are pulling a trailer (regardless of road conditions) you should have your transfer case in 4H mode.

You WILL however damage your transfer case or differentials if you are running on dry pavement in 4HLC. This is where the center differential is locked and both axles are forced to turn at the same ratio. This mode is only for mud, ice or snowy conditions.

Coming back to the original post:
the reason shops may not want to check the pinion torque is because it is way too much work. I think you have to completely disassemble the differential (take all the guts out, except the pinion set), then check pinion torque. Than you have to put it back together and check that all the gears mesh properly. If not, disassemble again and adjust washers on the pinion set and re-torque everything again... Not many people know how to do this any more (it's more complicated than an oil change...). If the noise is not horrible, scary grinding kind, and you had no metal debris in the front diff oil - leave it be. Run it, be aware of it and note if the noise suddenly get's worse. No reason to replace differential right now. One thing to check is the front wheel hub bearings. When they go out, they start making an intermittent semi-quiet whining noise. You might hear them on deceleration only or at other times. I've noticed it more at lower speeds though. You might get slightly more noise from the front if you are turning left or right (depending on which side is going out).

Thank you HunterD! I really appreciate your answer to my question and the thorough explanation you gave. I didn't realize that the turning torque couldn't be checked on-vehicle (just unbolting the front driveshaft from the front diff with the diff disengaged / in 2H ).

A mechanic also told me the same about just running it as long as it's not getting worse and no metal in the oil (which there's not).

I will check to see if it worsens when turning either way to see if it's a wheel bearing by chance. I haven't really noticed that so far, but I'll keep an ear out.

Thanks again,

Matt