I had the same issues others have mentioned. Felt like what can be described as a kicking or yanking or jolting. It's been something that has happened for years but I've never been able to figure out a way to reproduce since it wasn't very often. I remember it happening under warranty, but because it was so rare (once or twice a year) I doubt the dealership would have found anything. I'll also have to assume they checked the coupler during inspections for leaks and found none. So with that being said I think in my case this part failed very slowly, over the course of 4 or 5 years when I first remember a weird kick/yank/jolt.
I really started to notice it when I was traveling in an area with lots of hills last year. But shrugged it off as it went away when I came home. Then it started happening much more frequently, even in flat areas. It got to the point where it was always doing it when I was on a slight incline and making a left or right turn. Doing a three point turn always made it jump. Now that I could reproduce it whenever I wanted I decided to look into it because it was only getting worse. I was afraid it was the transmission failing, thankfully it was the coupler.
Now if you start researching this you will find tons of information from Russia. There are videos, forum posts and webpages dedicated to fixing this coupler. There seems to be a lot of different outcomes after fixing it unfortunately. Some people said the fix lasted a month, some a year, some a few years, and some even do preventive maintenance on it by refilling it every 2 years.
The common theme is that you will have little to no fluid in the coupler. When I opened mine, it had none. It wasn't bone dry, there was just a slight coating of fluid but that's it. After I removed the drive shaft to pull the coupler off it started leaking a black fluid immediately. I thought the rear diff seal was shot but it was only about 20ml and smelled like transmission fluid. Once I got the coupler removed I knew the fluid came from it.
Basically every Russian post I saw talked about replacing the oil seal on the coupler (Corteco 19026317B). I few people also replaced the bearing and seal on the part that connects to the drive shaft if it was making a noise. I had bought the parts to do this just in case, but my bearing was completely silent, had no play, and spun around fine so I left it alone. I didn't even need to take the coupler apart as I only removed the one oil seal. The south main auto video you find is about that bearing at the front being shot, it has nothing to do with the kicking or jolting. But it's possible to have both issues. The rear diff seal can also be leaking, but that was very rare from my searching.
Things I would have done differently.
Removed the drive shaft right away. I was really trying to avoid disconnecting the whole thing but I ended up wasting an hour. There isn't enough room to pull the coupler out without taking the drive shaft off. So that's 3 bolts on the coupler, 4 at the front, and 2 hanger bolts. I had two jack stands hold it up as I took it off. I also had the front end on jacks so I could put the car in neutral and park when turning the drive shaft.
I should have looked up a video on how to remove an oil seal, youtube it, you punch on hole, put a screw in the hole and simply pry it out. I was trying to be so careful with it and broke a couple tools not realizing how pressed it was into that hole.
Technically you can remove just the oil seal and refill it through the bearing, but there is a risk. You don't know how much old fluid is left in your coupler. I've read about people refilling from the bearing and the repair worked for a few weeks and others years. It's also very difficult to know when it's full, you are supposed to fill it, let it sit for a few hours and fill again. I honestly don't know, some fluid is better then none I guess. I decided I would just do it the way I saw in some of the videos and not fill it this way. Also some people were adamant failure was a result of not emptying out all the old fluid, depending how much old fluid was left, I don't think anyone really knew for sure.
To get access to the clutch plates you sort of have to pull the top part off with pliers or I even saw people tap screws into the three recessed holes. Since I removed the oil seal I didn't have a vacuum effect and I think it made it easier for me to pull it apart. The moment you remove the ring holding it down and flip it over, you are pretty much committed to opening it and reassembling it since the bearings will pop out of place.
How much fluid to add? I saw 150ml ATF everywhere, but I also saw a video of a guy filling up just past the plates. I probably did 160ml to 170ml as a medium. I'm not sure anyone knows what the true value and everyone gets it close enough. I used Valvoline MaxLife full synthetic ATF. I had some left over from when I did my transmission a few years ago. But people said any modern ATF would be fine.
What caused all the fluid to escape in the first place? This question has really bothered me, I know for a fact from my coupler the fluid escaped from the socket where the wires connect. But how is that possible, the fluid would have to travel vertically against gravity. Comparing the two oil seals I would say the new one was much more supple and the old one which was much harder. I think it's a safe assumption to say the oil seal eventually fails, this allows the fluid to then escape. I'm not sure the mechanism of the failure, maybe its a combination of the fluid becoming old, heat and the seal degrading. But I'm also guessing that if this has something to do with pressure/heat/boiling points maybe sometimes instead of venting out the electrical connection it finds a path through the rear diff and destroys your rear diff seal.
After refilling mine and replacing the seal I no longer have any kicking or yanking. Drives great, nice and smooth, I tested it for a good 30 min trying everything I knew that would cause it to kick or jump. How long will this repair last, I have no idea. From what I read it's dependent on lots of things driving style, hilly area, snow/ice, have the clutch plates been damaged too much being used without sufficient fluid, is the magnet also damaged. It's just a big question mark that will be different for everyone.
The only good news I will say is, before my parts came in I disconnected the coupler by simply pulling its electrical connector. This completely disables the magnet in coupler and got rid of the kicking and yanking. I drove around like this for a few weeks and didn't have a single issue and it drove beautifully. I would not hesitate to drive with it disconnected again. The bad news is you get "ESC off" and I think it was the drive train light flashing. Somewhere I saw someone get the ohms for the magnet, I wonder if sticking a resistor with this same value could trick the ecu into thinking it was still there to get rid of the annoying warning lights. I guess you could also simply remove the drive shaft making it a FWD vehicle, then you could leave the broken coupler plugged in so you don't get the warning lights.
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