[FiatPower]

Our new-to-us 2017 6spd will do this occasionally, although it is not that loud. It is always when I'm forced to putter long at a low steady speed in traffic. If I drive it at the speeds I normally would, running it up through the gears with load applied, then removed, then reapplied while shifting it does not do that. I suspect that engaging/disengaging the mechanism may need removal of load to fully operate, but with an auto that doesn't happen.

When it does it if I lock and unlock the 4WD it will go away.

 

[FiatPower]

Our Jeep continues to do this, although it's still not loud nor particularly objectionable. It's clearly only when the system fully opens up the wet clutch in the RDM.

I plan to change the RDM fluid shortly, although I had to search for a synthetic 75W-90 GL-5 gear oil without a limited slip modifier. They are not common anymore, and none on store shelves (at least ones that were clear about the modifier). Summit Racing has Mobil Delvac, so I will order that.

 

[FiatPower]

I tried to have this flash done at the local dealer but they claim it doesn't apply to my 2017 1.4L 6spd. Does anyone know if 08-027-21 is for the automatic only? The wording is unclear - it should not matter as the rear wet clutch is the same in both.

 

[FiatPower]

the tsb is for renegades with awd and an automatic transmission. It’sa flash for the drive train control module for an at+awd.

Shame - the manuals have the same issue with the rear diff, I wish they'd bring out an update for the those too.

 

[FiatPower]

I'm going to continue playing with rear diff fluid to see what difference that makes. I first replaced it with synthetic 75W-90 GL5 WITH the limited slip additive (because that's easier to find). Trying to decide what to try next:

1. Increase the amount of LS additive
2. Try oil without LS additive
3. Try heavier weight oil

So far I think this is a mechanical resonance that occurs when the front dog clutch is opened (around 37mph), as that is when there is there is a significant speed differential between the plates of the wet clutch. If the speed increases above ~50mph then the resonance seems to stop or drastically decrease.

Curious that turning off traction control stops it - I had not tried that. Still, it's probably just a programming change that prevents opening the front clutch at those speeds.

I want the front clutch to open for improved mileage, but I'm concerned that a mechanical resonance that strong may be creating parasitic friction/drag anyway - which might negate the benefits of disconnecting the driveshaft.

 

[FiatPower]

I tried it tonight and can confirm that turning off traction control stops the noise, which I find interesting. Apparently with traction control off they run the drive shaft instead of shutting it off - so you have more traction but less traction control!

 

[FiatPower]

I'm going to leave these links here:

Fiat 500X All Wheel Drive System Explored

The Fiat 500X uses an advanced all-wheel drive system that guarantees excellent traction in the worst slippery conditions. Here is how the system works.

www.fiat500usa.com

GKN Automotive | One AWD platform, two distinct driving experiences

GKN Automotive is the first tier one supplier to design, develop, manufacture and integrate a complete all-wheel drive system into a customer’s vehicle. The system that underpins FCA’s Jeep Renegade and Fiat 500X delivers specific brand characteristics based on GKN Automotive's tuning capabilities.

www.gknautomotive.com

Note that when the drive shaft is engaged it is the rear wet clutch that spins up the driveshaft first, then once it's up to speed the front dog clutch engages. I'm pondering what this means in terms of the noise. That happens when the driveshaft is stationary, but not sure where in the process.

My real concern is that it's a bearing problem in the rear diff. When the driveshaft is disengaged the entire hypoid drive gear is stationary, so there must be a bearing between that ring gear and the differential unit. That bearing would only operate when the driveshaft is disengaged, which is also when it's noisy.

Also, I've been trying to see if there is a difference in fuel mileage between running with traction control on or off, but I have not seen it yet. Maybe too many variables? Anyway, it should be better with it on and the driveshaft stationary.

Someday I will get one of these rear units out of the junkyard.

 

[FiatPower]

AWD is disabled above 50mph, which is why it goes away at 50mph.
The noise is dependent on the traction control programming, which is why it goes away when it is below 40F (It's really 37F I believe, which seems to be the industry standard bridges may be icy warning temp). Once it is cold enough it switches to a different TC algorithm when in auto mode for the 4wd. It should also greatly diminish in wet weather. In my experience the noise happens, but in a much narrower range of circumstances when it is very wet. (My daily commute from 2015 to 2019 had about 12 miles in the noise sweet spot, so I got to analyze it a lot in spring, summer, and fall).

As for it being a bearing problem, I don't think it is defective or worn bearings, and I don't think it wears out the bearings. Primarily because we haven't seen lots of complaints of failing RDUs. If your bearings are making noise, they tend to not last that long. I got a bum RDU with my 2015. It was only about 3000 miles before the 37mph grinding noise was WAY louder and happened from 10mph to 70mph.

The bearing fear was just a background concern, it really seems to be a mechanical resonance.

Mine does not really "go away" at higher speeds, rather it fades in amplitude. By 60 it's really hard to hear, but still there. So as speed increases you can hear it turn on at around 37 (as the clutches open), and then it's loud until maybe 50 or so, and decreases from there. At any time during this you can turn off the traction control, and there will be a bit of a clunk and the noise will stop instantly.

As long as the driveshaft is engaged then everything is turning at about the same speed and there is nothing to resonate.

 

[FiatPower]

The noise happens when the driveshaft is disengaged at both ends. At low speed the driveshaft is always driven from the front - probably with the traction control shut off too. I'd bet the the firmware update just keeps it spinning or changes the speed where it disengages.

 

[FiatPower]

If you look at this cutaway image of the rear diff, you'll see the multi plate wet clutch on the right. These are interleaved friction discs, where every other one is connected to the ring gear & input shaft (lower left), and the others are connected to the differential.

The only difference in this assembly when the grinding noise is heard is that the input shaft & ring gear are stationary, and therefore every other disc in the clutch pack is stationary. When the input shaft is spinning there is very little speed difference between the discs. The noise cannot come from the input shaft or ring gear, or their bearing, because it happens when they are stationary. Therefore the noise comes from the clutch pack.

I noticed the other day that when the grinding noise occurs the entire floor resonates like a sounding board, yet the entire rear diff and suspension is attached to the chassis with rubber isolators/bushings. Maybe the problem isn't that the diff is resonating/vibrating, but rather that the bushings have failed - just as the motor mounts fail and allow engine vibrations into the chassis. I'll be looking at those isolators on mine this weekend if I can spare the time.

Also, some are discussing a "clunk" - not sure what that is, but it sounds more like some transmission issue.

 

[FiatPower]

SOLVED! At least for mine. The problem is once again a floppy rubber isolator that has lost its support.

All of the rear subframe and diff support bushings seemed fine. That left the center driveshaft support to be examined, and it was a major suspect since it's connected to the rear diff input, and therefore to the clutch pack which must be the source of the vibration. Clearly there was also a mechanical resonance occurring. I noticed the drive shaft is light and that when shaken there was a rattle at the center support. If you gripped it solidly enough the rattle was damped out - but of course it must be able to spin. It was also really easy to move it around in the rubber bearing support, so I figured maybe if that rubber part were stiffer it would damp out that rattle.

I found that there is a fairly deep groove around the center bearing towards the rear, and I was able to cut a piece of 5/16" fuel line to an appropriate length, and pack it into that groove. Took it for a drive and the groaning/growling vibration is gone.

I have no doubt that the line I packed in there will fall out eventually, so when it is warmer I will glue it in with some urethane adhesive.

 

[FiatPower]

Minor correction - the groove I packed the tubing into faces the front, not the rear.

We drove it going out to dinner last night and it was so much nicer to drive. It was a bit warmer today, and I realized I had a can of rubber cement for tire patches and the like which had a brush in the lid. I brushed it all around the tubing in the hopes that it will hold it in place. There really isn't much force trying to push it out, it's just the the bottom of a vehicle is a nasty place......

 

[FiatPower]

The only problem with the rubber isolator theory is that this happened in vehicles from new. Mine did, and it did it after a rear drive unit replacement. If the bushings were beat, they wouldn't put them back. The point of the wet clutch is to have varying levels of slip/engagement by managing the clutch engagement. The operating theory for a long time is that it isn't as disengaged as it's supposed to be due to the traction control strategy. It'd just likely be even louder without the rubber isolators. It also isn't shocking that the vibration is transmitted through the drive shaft to an extent since it is mechanically coupled to the RDU.

You are confirming my theory. The bushing I'm discussing is the center support for the driveshaft and would not need to be removed or replaced to remove the RDU - and likely why replacing the RDU didn't fix yours. It still has the same center support isolator.

The vibration source must be the wet clutch itself - whether that's because it is not fully disengaging and is therefore dragging, or some other design issue I couldn't tell. However, that should not be causing the entire floor to vibrate strongly like mine did. While riding in the passenger seat I could feel it vibrating right below my feet - right about where the driveshaft center support is located. The driveshaft is clearly resonating, making the vibration much worse, overwhelming the center support isolator and transmitting that resonance to the floorpan. Ironically the center support isolator needs to be stiffer to prevent an undamped oscillation of the driveshaft.

We bought our Renegade used, so I have no idea if it did it from new, but I noticed it not long after we bought it. When I changed the fluid in the RDU it was quite clean, so I doubt it is a wear issue, and so I suspect it was always that way. Note that I was not really suggesting the isloator wore out, rather I think many of the rubber isolators (motor mounts, exhaust hangers, this driveshaft support) were poorly designed and simply don't work well.

 

[FiatPower]

I drove it to work today, about 60mi round trip. On the way home the noise came back, so I checked it when I got home. The tubing had worked out out of the groove somewhat. It has to be firmly seated, and most importantly it has to be snug against the inner rubber snout that holds the bearing.

I'll be working on a way to secure it in the groove, or perhaps a better tubing, but this is definitely the right track.

 

[FiatPower]

I think you may have multiple issues, and many others may too. But I've never mucked with that bearing or bushing, and mines essentially gone now. Also even when mine got BAD, you could never feel it in your feet anywhere and the noise was centered left to right in the cargo area just behind the rear seat back. Basically right above the RDU.

Like a lot of FSA stuff, the parts sourcing is probably bad and there's a lot more variance in the actual parts than the engineers designed for.

I suspect you are right that it is contributing to the how pronounced it is in your case (and likely others), but I'm pretty sure it won't make it go away, just make it less prominent for those with that flavor of the problem.

If you've ever experienced a bad motor mount (or a race car with solid mounts), you know how awful the vibration can be - and yeah, you can feel it too. Is the engine bad? Well no, they just vibrate a lot. I found that the noise was pretty well gone when the fuel line was packed in tight.

It's also quite reasonable to assume there is variation, both in the driving vibration in the clutch pack, as well as the resonance of the driveshaft and the characteristics of the center support bushing. As far as I know some vehicles don't do it at all. I've been dealing with manufacturing issues for over 30 years, and this stuff is typical.

 

[FiatPower]

So I took another shot at it today. I removed the tubing and noticed it had flattened somewhat, which is no surprise as it was not designed to hold shape in compression. I decided I should look for something to insert into the the tube to give it more strength, and found an old power cord that was just the right diameter. Once I had that together I put a layer of RTV (Permatex Ultra Gray) on the outer and inner walls of the bushing, and then pushed the tubing into the slot. Then I filled in more RTV on the surface. Note that the slot is towards the rear, I just kept remembering it wrong.

Anyway, I put a heater under it and let it set for a few hours, then took it for a drive. Big mistake! I made it way too stiff/rigid, and you could hear and feel everything going on down there, from engine vibrations coming down the driveshaft to the clutch opening up, and the clutch vibration that is the source of this whole problem. It didn't really resonate the way it had, just could feel and hear it. That was unacceptable so I pulled it apart again (the RTV was not totally set yet).

I put it back with a fresh piece of tubing with nothing in the center. I think it's an acceptable compromise. On occasion I can hear the vibration between 40 and 45mph, but it's much more damped and does not shake the floor. Most of the time you don't hear it at all. Not sure what the random element is - perhaps the position the draveshaft stops in? Anyway, it's one heck of a lot better than it was.

I have no doubt that this bushing/isolator could be tuned so that it never does it, but I don't have that kind of time to spend on it. Time will tell if the rubber tubing crushes down and stops damping out the driveshaft.

The fuel line I used is about 0.560" OD. I tried some 0.625" stuff, but that was too wide to go in.

 

[FiatPower]

Just going to throw this out there... Have you considered your bearing/bushing combo is beat and you just need a new one? There are even third party ones that look like they might have more shock absorbing material than the OEM version.

It's always possible the bushing is shot, although there are no obvious signs of damage. The bearing however cannot be a problem, as the noise happens when the shaft/bearing is not spinning. Do you have any links or info on 3rd party parts?

Overall I think the bushing was designed to filter out normal driveline noise, without consideration for the vibration from the rear diff clutch unit. Pretty sure that's not supposed to be there.

 

[FiatPower]

Here's an example. Different format than OEM that doesn't use the square housing.

Jeep Renegade / Fiat 500 Center Bearing 2014-2019

Jeep Renegade / Fiat 500 Center Bearing 2014-2019 552674310, 68246927AA, 4787671AA, 4787672AA

www.driveshaftparts.com

Also if you go digging far enough back, there was a run of bad drive shaft bearings in the past resulting in clunks accelerating and stopping IIRC.

Thanks - I'll look at those. I wish I had a FSM as I don't know how the driveshaft comes out or comes apart at this point.

 

[FiatPower]

Well, it's a mixed bag. It worked great when I first put it in, but over time the fuel line crushes at the bottom where it is loaded most. Now it is still much better that it was, but you can hear the vibration when it kicks in. You can also hear other driveline noises as the stiffer bushing/isolator lets more of that through into the chassis. It's far from obnoxious and I actually find I like it that way, but others might not. The difference is that the driveshaft is not able to go into a full resonant vibration, so it never get out of hand like it did before.

My previous attempt to fix the crushed line resulted in an isolator that let far too much high frequency stuff through. I'm sure that a properly designed bushing would fix the problem - as would a driveshaft with more mass.

I got a FSM on disk, and removing the driveshaft is more involved than I feel like dealing with. There is also no instruction for separating the driveshaft at the center support. Otherwise I might try replacing the center support with one of the aftermarket ones, but it's not broke now so I can't justify the effort.

 

[FiatPower]

Thanks friend. Wonder if putting a small section of power cord on the bottom would ad support without being too stiff. Maybe use it to join the ends of the fuel line.
I mentioned in my intro post today how Jeep said the bearing wasn't replaceable and a blown one necessitated an entire shaft replacement. Starts at $1,200.
Wish I could upload the 2-sec video clip of my driveshaft being yanked around inside the bearing. Pretty impressive.

Well they do sell the bearing/center support aftermarket. I have no doubt that I could get the driveshaft apart if I needed to, but I cannot justify the time and effort now. I rather like the slightly added sound/vibration I get now, so I'm just leaving it alone. I couldn't stand the severe resonance it had though.

I suspect that a small section of power cord in the bottom would act about like the full loop I tried, as most of the force is on the bottom section anyway. Still, you never know until you try it I guess.