C4inLA

If I remove the center diff slave(Longitude lock) and want to check the slave for proper mechanical function, what would be the process?

FeralComprehension

Pressurize/depressurize the system and ensure that the actuator rod extends/retracts as normal and verify that it doesn't squirt brake fluid everywhere?

C4inLA

Thanks for the idea.

I noticed also in the diag tool I have the ability to run a test, one pulse at a time.
So, to be clear on these two locks, I can keep all lines attached and remove mounting screws, pull away and with it pointing away from my face, have a buddy run various pressure tests, lock, unlock, pulse test, as I observe? If I wanted to go a lot further, remove to bench, remove retaining clip, pull guts, check seals, etc. ?

The Clutch slave cannot be tested in such fashion, i.e. the clutch pedal pressed, correct?

Goughary

I haven't tried that. But, the system is under huge pressure when it pressurizes...so I would be concerned that the circlip will fail and the rod will come out like a bullet. So unless someone can tell you how much pressure the tester will be using and that you won't destroy the diff lock, I wouldn't do that.

So be careful.

C4inLA

Point taken. If my "grunch" is isolated to torque transfer box, i'd sure hate to think not checking for proper functioning of a frick'in slave cylinder, ends up setting a bomb off in my gearbox.....

Probably makes sense to just pull slave cylinder to work bench and pull apart, then reassemble ... Learn something.... I have new seals from 9M for future, but current locks not leaking externally. For those wondering why I'm focused on the slave lock;

Excerpt from 2005 post where Adrian was speaking with a chap Bill Wagner;

"The other issue mentioned about the planetary gears.
This is a failure of the differential lock.
The differential planetary and sun gears are forced into gear with each other by the clutch plate assembly which is operated by the slave cylinder. Their job is to lock the front and rear drive shafts together.
The failure occurs when the gears come together in a manner, which results in teeth hitting teeth instead of teeth meshing with teeth.
I have seen it a couple of times myself. Usually caused by severe treatment. Excessive torque on the gearing. Regular attempts at spinning of the rear wheels when exiting corners is one way. Doing burn outs in shopping centre car parks another.
People cannot imagine the torque these relatively small gears absorb when the lock is engaged. The engine is now driving through this tiny little plantetary and sun gear assembly.
Mind you such failures are still quite rare.
Ciao,
Adrian."

Thanks again Adrian for sharing your thoughts with us ....

alexjc4

Adrian has a fundemental misunderstanding about how planetary gearsets work. The planetary gears are in constant mesh. The clutch pack locks the planet, ring and sun gears together so they rotate as one. I've never seen a pic of the planetary gears broken, only broken planet gear carriers and the consequent breakage of the ring gear. This failure happens when the shafts that the planet gears spin on binds to the planet and walks out of the bridge at one end. Small sustained difference in wheelspeed front and rear is often the cause, as you get with incorrect tyre size. Gross wheel speed differences, as per wheelspin/donuts, should lock up the diff protecting the planet gears (as they stop turning). Another cause would be poor lubrication. Another failure mode is where the centre diff actuator is stuck with the clutch pack engaged, this can wind the bolt of the end of the shaft holdint the ring gear cage to the end of the output shaft, and bad things ensue.

Goughary

You beat me to it. Adrian is wrong. Granted, he also said that years ago, and since then we've seen the majority of planetary breaks are as Alex stated above.

C4inLA

Need you chaps to dumb it down to my level and answer this question;

Can the center diff slave if piston not working freely, gunked, not engaging or more importantly unlocking, say unlocking half way? Or locking half way? Cause problems in torque transfer box? What would be scenario of grind grunch in torque box when wheels are fully turned in slow circle? Shouldn't be subject to left/right load for center diff, correct?

Goughary

Crunch will be either bad cv joints, or if the crunch is coming from the middle of your car, the likelihood is a bad planetary gear.

The rod in the diff slave is literally in there free to move back and forth. If you take the diff slave out and press the rod in and it springs back, then it is working and it's fine (apart from leaks). It's a very simple device. And further issue with it engaging or not is a problem elsewhere. The pressure valves that you see attached to the hardlines behind the right rear wheel, or in the system in the frunk....but non of that would cause a clunck, chunck or otherwise...

Also, don't engauge your PDAs on dry pavement and ask about clunks...cuz you will find them. If it's doing it in the rain or snow, you likely have a problem, like I said, in a cv joint or planetary gear. Pray to the heavens above, below, or sideways, that it's not a planetary gear...if it is...don't do any further work to the car. Park it and just look at it every so often with fond memories....(kidding)- it's just an expensive fix.