Transfer case on AWD models: was it meant to be reliable ?

[killinghall]

The question remains. How many AWD owners have had defective transfer cases and what contributed to their demise?

 

[dgorbenko]

I bet it broke in the same place in all the waves - the lowest or highest point (depending on how you look at it) of each bend

you are right, I've noticed it also.

 

[oddball]

So if you pulled the AWD Fuse is there a risk of damaging the transfer case as there isnt any active lubrication due to the pump not running?

Or (excluding the input shaft and output shaft to the rear) because the piston isnt apply pressure almost nothing is moving in the transfer case to the risk is negligible?

That's an excellent question. I would certainly be concerned about it and wouldn't want to run in that configuration for extended periods of time. A few runs on the dyno would be fine, but a bunch of track time probably wouldn't.
It also depends on how much splash lubrication happens. It's hard for me to tell where the fluid collects and returns to the pump. So if the front output gear is actually sitting in fluid and constantly splashing it back upwards then that would help. But, wet clutches need constant lubrication (when disengaged) or they can glaze or burn.

This also assumes that fuse just controls the positive side of the pump and the ECU/TCU controls the negative side via a PWM control. That's the simplest way to do this kind of thing, so seems most likely.

 

[mfc1337]

I experienced transfer case failure on my first Stinger (see my previous thread history). I ended up returning the car so I don't know exactly what the root cause was, but I also had that same knocking sound.

 

[G70LEbyAdoom]

That's an excellent question. I would certainly be concerned about it and wouldn't want to run in that configuration for extended periods of time. A few runs on the dyno would be fine, but a bunch of track time probably wouldn't.
It also depends on how much splash lubrication happens. It's hard for me to tell where the fluid collects and returns to the pump. So if the front output gear is actually sitting in fluid and constantly splashing it back upwards then that would help. But, wet clutches need constant lubrication (when disengaged) or they can glaze or burn.

This also assumes that fuse just controls the positive side of the pump and the ECU/TCU controls the negative side via a PWM control. That's the simplest way to do this kind of thing, so seems most likely.

While reading this has been a blast and incredibly informative, currently, I know of an AWD GT line that runs all the time in RWD, from 100 miles or so to about 30K now, that has had 0 issues with it. we don't know how the internals look of his specific unit obviously but he has no issues so far, which makes me think that maybe the pump still provides oil to allow lubrication even if the clutches don't engage, and that the AWD fuse is a circuit specifically for the clutches? Just a thought though.

 

[oddball]

While reading this has been a blast and incredibly informative, currently, I know of an AWD GT line that runs all the time in RWD, from 100 miles or so to about 30K now, that has had 0 issues with it. we don't know how the internals look of his specific unit obviously but he has no issues so far, which makes me think that maybe the pump still provides oil to allow lubrication even if the clutches don't engage, and that the AWD fuse is a circuit specifically for the clutches? Just a thought though.

Well, if he runs *all the time* without the fuse, then he'll never know unless one of the bearings actually fails. The clutches might be toast which means they won't engage properly, which means that case might never engage AWD again. A lot of "might"s in there.
I agree that not running the pump probably won't cause a critical failure that stops the car from driving. It will probably damage the transfer case which will stop it from working properly.

Although, the gear attached to the basket must ride on needles. Could be a bushing, but given what we've seen and what's typically used in a manual trans, I expect a cage with needles. Those are more tolerant of limited lubrication than a bushing, but it certainly could overheat and fail.

 

[G70LEbyAdoom]

Well, if he runs *all the time* without the fuse, then he'll never know unless one of the bearings actually fails. The clutches might be toast which means they won't engage properly, which means that case might never engage AWD again. A lot of "might"s in there.
I agree that not running the pump probably won't cause a critical failure that stops the car from driving. It will probably damage the transfer case which will stop it from working properly.

Although, the gear attached to the basket must ride on needles. Could be a bushing, but given what we've seen and what's typically used in a manual trans, I expect a cage with needles. Those are more tolerant of limited lubrication than a bushing, but it certainly could overheat and fail.

Should I tell him to pop the AWD fuse in for a week and see if the car acts up at all then? hes a stock Gt line so its not like the dude is pushing any kind of power lol

 

[oddball]

Should I tell him to pop the AWD fuse in for a week and see if the car acts up at all then? hes a stock Gt line so its not like the dude is pushing any kind of power lol

¯\_(ツ)_/¯
We all make choices in life. It'll probably just be an adventure for the next owner. Especially if it's some poor soul who ends up in a snowy/icy climate.

 

[G70LEbyAdoom]

¯\_(ツ)_/¯
We all make choices in life. It'll probably just be an adventure for the next owner. Especially if it's some poor soul who ends up in a snowy/icy climate.

the way the dude drives it, their wont be a next owner.

 

[G70LEbyAdoom]

welp, as if the timing gods have blessed us, he is having it towed to a dealer because he got locked into 5th gear last night and apparently has had something whining fairly loudly for the last month. He has neglected to tell me that though or I would have told him to go to the dealer ASAP. Im just glad its not my car.

 

[dgorbenko]

yes, on my case I still have some knocking sounds coming underneath while driving.
in short: my assumption was for transfer case, and indeed, it had broken spring flaying around clutch basket, I replaced it, took all clutch packed, put the transfer back, and still have some sounds... maybe the same I had before, maybe different, have no idea, it's hard to judge.

 

[Avant]

Should I tell him to pop the AWD fuse in for a week and see if the car acts up at all then? hes a stock Gt line so its not like the dude is pushing any kind of power lol

Front wheels will still turn the transfer case internally so that wont help. When pulling the fuse it just doesn't send power to the front wheels.

 

[oddball]

yes, on my case I still have some knocking sounds coming underneath while driving.
in short: my assumption was for transfer case, and indeed, it had broken spring flaying around clutch basket, I replaced it, took all clutch packed, put the transfer back, and still have some sounds... maybe the same I had before, maybe different, have no idea, it's hard to judge.

Check the u-joints on all the drive shafts for play. There's also a guibo (flex joint) in the middle of the driveshaft going to the rear differential - make sure that's still in good shape. Also check the engine and transmission mounts for excessive movement.
It's also possible that the bushings that hold the yokes on the transfer case got damaged and are letting the yokes wobble. It can be difficult to tell unless you're used to what's "enough" and what's "too much" play for any specific unit.

 

[dgorbenko]

I checked drive shafts, flex point, mounts, they seems good.
Also I measured frequency of the knocking sound, and it's two times more than the frequency of wheel rotation.
In other words, while the wheel makes one rotation I can hear 2 knocks. And it's true for wide range of speeds, from 10 miles up to 50 (then it's hard to heard the knocks due to noise from the driving).
So, two impulses per one rotation...
And if I put transmission into neutral gear while driving and the engine would drop its RPM, the knocking does not change.

But you may be right, and it's just transfer case producing that noise.

 

[dgorbenko]

And ever more: I have another car, Mazda CX-5, and it makes 1 knock per wheel revolution It started out of the blue.
It is my wife's car.

 

[oddball]

I checked drive shafts, flex point, mounts, they seems good.
Also I measured frequency of the knocking sound, and it's two times more than the frequency of wheel rotation.
In other words, while the wheel makes one rotation I can hear 2 knocks. And it's true for wide range of speeds, from 10 miles up to 50 (then it's hard to heard the knocks due to noise from the driving).
So, two impulses per one rotation...
And if I put transmission into neutral gear while driving and the engine would drop its RPM, the knocking does not change.

But you may be right, and it's just transfer case producing that noise.

That sure sounds like a u-joint to me. But I haven't examined the driveshaft in my car and certainly haven't taken it out. Taking a look at the line drawing it appears they actually use CV joints on the driveshafts? That's nicely complicated. You would need to actually remove the shafts (or fully disconnect them) and check all the articulation to see if one ball has failed or trash has gotten into the boot in one space.

It would be useful to see if you put the car in the air and manually turn the tires if you can feel the thunk. Then start removing shafts to see if it can be isolated.

 

[dgorbenko]

I did it, i put it in the air, turned wheels, started car, run it in the air, and this is how we found the knocking sound coming from the transfer case.
need to do it again after I move my mazda out of the garage.

I checked U joins on drive shaft, seems OK, maybe I'm missing some, but the noise was coming from transfer case, so axles and driveshaft are out of my focus.

 

[oddball]

Very interesting. From the video it seemed like all the teeth on the gears were good. I assume all the bearings were good. Did the transfer gear spin easily on the input shaft? I'm talking about the gear that engages the basket. Delicate little needle bearings between that gear and the input shaft.
A bushing for one of the yokes could have gotten damaged, but I wouldn't expect a real "thunk" from that.

 

[dgorbenko]

yeah, it could be, you are right.
I just busy with other car in my garage and can't put the kia in the air, run it and find where the noise is coming from this time. Could be the transfer case again.
Seems like I just need to buy a new one

 

[oddball]

For anyone still around, Precision Transmission just did a teardown on a transfer case that's a very interesting comparison.

This one has a low range engaged by the planetary on the input shaft. The sliding gear that transfers power to the output shaft can engage either directly with the inside of the input stub or engage with the planet carrier.

But the 4WD section is interesting. It uses an automotive style clutch, but mechanically engages it by forcing the fork towards the back of the case.
So in this instance, the only purpose of the pump is to circulate oil, and we can see the damage done when that wasn't happening. Of course, in this case, it was running without fluid at all due to the hole cut in the side of the case.