2006 Pajero 3.2 GLS (Gen3) knocking noise when central diff lock is engaged

[noggin]

Hi Guys. This forum is always a great source of valuable information, but I couldn't find any related threads to the noise I am experiencing.

The vehicle:
2006 (Gen 3) Pajero 3.2 DiD (4m41) SWB GLS with autobox and central diff lock. Mileage: 192000km. I bought the vehicle with full service history at 120000km, and have maintained it myself with the help of this forum and the Heynes Pajero Maintenance Manual (https://haynes.com/en-au/mitsubishi/pajero/1997-2014) and some other resources made available through these forums.

The issue:
Actually, since I bought the car, this issue has persisted, but it's never given me a headache and I'd like to put my mind at ease with the help from some gurus here.

When I am driving in sand and need to use 4HLC or 4LLC, I experience a single clunk / knock when transitioning between forward and reverse. It only happens once per cycle. For example, if I am in forward, and need to reverse under strain / load, then the vehicle emits a single clunk when I initially start reversing. It reverses fine, and I do believe that the central diff lock is engaged (due to the fact that it helps and I get out of sticky situations, but I can't actually confirm this). and there is no persistent clunking or knocking noise. When I then go forward again, under load, there's another single clunk / knock, and the vehicle moves forward with no persistent knock / clunk. If I were to reverse again, the knock comes back, once, and so on. This happens in both 4HLC and 4LLC.

All oil levels and grades are correct (front diff, rear diff, transfer case, autobox, engine) as far as I know.

I have thought of the following, but I'm looking for someone to shed some light.

1. A loose mounting bolt or worn mounting bush somewhere, but it could be anywhere (engine, autobox, ?). I have not done a thorough investigation, and I'm hesitant to say this is a probable cause, because I would expect it to happen in 4H also?
2. A problem in the transfer case. Hopefully this is not the issue because I don't want to have to open her up like that. If it is a problem in the transfer case, what is the likely cause? Backlash due to wear doesn't seem likely as I wouldn't expect such a sudden, loud knock from that. The knock seems more likely to be the result of something in the drivechain suddenly slipping due to excess load, not some clearance being gradually taken up until meshing / contact occurs.
3. A problem in the front wheel drivechain, but who knows where. I'm thinking worn CV joint (inner or outer), U-joint, front differential, or where the drive axles or front driveshaft meet their mating flanges. I don't know, and it doesn't make sense to me that it only happens in 4HLC and 4LLC and not 4H.

If anyone has any ideas or has experienced anything similar, please assist. I don't think it's a critical issue, but I don't want to be in a sticky situation that then results in me destroying my transfer case somewhere deep in the bush...

Looking forward to the guru responses!

[RoelfleRoux]

Is the single knock there everytime you switch forward to rearward (with CD locked)? If not, will you please explain the conditions.

My opinion: a locked CD will in most conditions cause some wind-up. The switch of front to back releases that strain - clunk!

Very few 4x4's behave like Limousines when the front and rear shafts are locked by unforgiving metal.

If it hasn't changed over the last 70k km, then if it was my car, I wouldn't scratch too hard.

Please keep us updated, and I'm sure the real clever guys will be along soon.


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[noggin]

Thanks for the reply!

To answer your question, it happens under load only. If I'm on a flat gravel road and switch from F to R to F to R etc with the central diff lock engaged, then there is no knock when trying to move in opposing directions... If I apply the brake to create an artificial load, then the knock happens every time I change direction. Also if I am under a real road such as thick sand, then the single knock is present when altering direction.

I'm also not too stressed about it, but I don't think it's normal. I want to find out how far from normal it is, and how difficult it may be to rectify.

Cheers for now.

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[RoelfleRoux]

Thanks for the feedback.
Let's see what the gurus have to say.

Sent from my SM-G955F using Tapatalk

[PhilipM]

This is a wild guess, but the description of the clunk / cling-sound points maybe to the prop shaft. Maybe check for play on the universals or the bolts connecting the prop shaft and the rear diff. Put your vehicle on a lift, turn (by hand) the prop shaft backward and forward to see if you can not replicate the sound. If there is no result, while still on the lift, ask somebody to do the gear shifting for you under the hand brake strain to try and locate the origin of the sound and take it from there.