Grinding in Neutral After Changing Outer CV Joint

Question

2010 Fiat Ducato x250 Multijet 120 2.3L with 6 speed manual

Summary: I replaced the outer CV joint on the driver's side and now there is a grinding noise in neutral that goes away when I press in the clutch, and I can't put the vehicle in gear at all. It drove fine for about 20 feet before this started. Now for the details.

So I removed the driver's side drive shaft to replace the outer CV joint. Wasn't sure how to remove the gear oil drain plug, but quite a bit of oil came out the driveshaft hole. Refitted the drive shaft, but wasn't sure where to refill the oil. Removed the battery box looking for refill / breather hole but only saw what looked like shifter linkages? Finally found it on top of the gear next to what I assume is the transmission speed sensor and engine mount. Manual calls for 2.7 liters 75-w85 GL-4 oil when fully drained. Everything I read said 75w-90 could be used safely. Filled with 2.5 liters ( since I figured there would be residual oil ) of Castrol Syntrax Universal Plus 75w-90 rated GL-4 / GL-5 / MT-1 supposedly safe for gears requiring GL-4:

Castrol Syntrax Universal Plus 75W-90 is a full synthetic multipurpose manual transmission and final drive lubricant. It
may be used in synchronised manual transmssions and final drives/differentials of a wide range of vehicles
(commercial vehicle, construction equipment, passenger cars) where API GL-4 or API GL-5 fluids are required and it
carries a number of approvals.

I replaced the battery box, started the vehicle, put it in reverse and drove about 15 feet. Then drove forward about 5 feet, put it back in reverse and then started hearing the grinding, and it wouldn't go into gear. Stopped the engine figured I didn't put enough oil in and added another 350 ml about. Restarted and noticed it was giving that mild grinding noise even though it was in neutral. Stopped engine, played with the shifter a little and after restarting no noise. But when I tried to put it in gear again the mild grinding started again, even in neutral, but goes away when I press down the clutch.

So I'm a bit confounded here. I can think of two possibilities, but no idea which might actually be right:

1. It drove 20 feet because the old oil was still stuck to everything but once the new oil started circulating the synchronizes stopped working properly because it's the wrong oil. Not sure why that would cause grinding in neutral.
2. Drive shaft wasn't quite in all the way and somehow popped out of place inside the gear . Why then no oil leaking from shaft hole? Why would that cause grinding in neutral?

The grinding in neutral is really weird. I assume it's constant mesh and so everything is rotating even in neutral but what could be grinding?

EDIT

Here's a picture of the inner joint where it enters the gear box:

Question is how do I get it the rest of the way in if that's the problem...

EDIT Additional Tests and Videos

So I jacked up the truck and the first thing I'll note for clarity, the side with the wheel off ( the driver's side ) is the side I did the work on. During all these tests, only the driver's side spun, the passenger side never showed any movement.

So first of all this first video kind of shows the problem, with me letting off the clutch and you can hear the grinding:

Grinding in Neutral

Then I unscrew the driveshaft / axle nut and give it a few good wacks to try and push the shaft in a bit. I'd note there is no noticable change in how far in the shaft is, yet after this the drive's side shaft starts turning smoothly in neutral, first and reverse:

Shaft Moving OK after Getting Wacked

I'll note again that only the driver's side axle moves, the passenger side axle never moves. Then I did the test again and it started grinding when I put it in reverse:

Grinding in Reverse

In general, I found unscrewing the nut and smacking the shaft in about 10 times would temporarily make the driver's side shaft respond properly while at the same time the passenger side shaft wouldn't turn at all. There is no visible change I can noticed in how far in the shaft is after I smack it.

I'm not sure if this makes things more or less confusing...

Answer 1

The grinding is likely coming from the splines on the driveshaft. Either it is not fully engaged in the differential or the splines have become damaged.

In neutral, if there is no resistance to movement, the shafts that the gears are located on will still rotate due to the viscosity of the oil. If your driveshaft is not fully home, the differential will be allowing the gearbox shafts to rotate. Pressing the clutch disengages the drive to the gearbox, hence the grinding stops.

Presumably the car won’t move under its own power now, since one of the differential outputs is not connected to a wheel, so no torque will be getting passed to the other wheel either.

Answer 2

I remove the axle and notice the new outer CV joint seems oddly loose, play with it a little and realize it's almost completely off the axle! How can that be? I open the boot up, the joint slides right off as only the tip of the axle is in the joint and I see the Circlip is missing! I stick my finger up into the CV joint and find the clip is shoved up into the joint!

I took apart the joint and the circlip wasn't just shoved up in there, it was completely shattered.

Got the cv joint cleaned and reassembled and inserted the shaft and --- it was just barely able to rotate. The splines in the joint and on the shaft are just fine, the cv joint is just about 2mm diameter too big. Apparently it felt snug when I assembled it because of the circlip, but once I started driving the circlip must have sheared off which let the shaft rotate in the joint which was the grinding I was hearing. I was up in the cab, so when I heard the grinding my mind immediately jumped to the worst conclusion and I assumed it was coming from the gear. I think when I wacked it all I was doing was getting the shaft deep into the joint and maybe the splines where catching on the broken circlip inside...

Take a look and you can see what I'm talking about:

CV Joint Too Big

POSTSCRIPT

After speaking with the parts guy and giving him the VIN of my vehicle he double checked and said he was sure the CV Joint he gave me was the correct part and to check the history of the vehicle to see if the entire axle was ever changed in the past. I checked and in 2018 the driver's side axle was changed with a second hand part from a junk yard - which apparently fit but wasn't actually the correct part.

Apparently, the Ducato Short and Ducato Maxi use the same axle except one difference - the Maxi has slightly larger heavy duty splines on the shaft that inserts into the CV joint and tripod joint but other than that they are identical.