Any iX owners here? Whit?

[SRR2]

I'm still looking into the gas mileage issue with this car. The parking brakes are troublesome, but even though they're not working very well, they don't seem to be dragging. However, there's a LOT of rolling resistance in the rear axle. With the trans in gear, it's very difficult to turn either of the rear wheels. I know that's supposed to be a LS diff of some sort, so that might account for it, but I don't know. I haven't been able to test it from the drive shaft because I haven't yet had all four wheels off the ground at the same time. The fluid was replaced in this diff with Redline synthetic about 20K ago. (I may drain that and refill with the Mobil 1 75W-90 with friction modifiers for LSDs.)

The other thing that struck me as odd was that the rear wheels turned in opposite directions when turning one of them. Other LSDs I have experience with have always caused the wheels to turn in the same direction. But then I don't know what kind of LSD is in this car, and all of this might be normal.

For reference, it takes around 70 lb-ft of torque to turn either wheel with the drive shaft held still. That seems like an awful lot to me. In contrast, I can turn either rear wheel of my 540 (non-LSD though) easily with one hand. Same thing with the '89 535 that did have an LSD. Turn with one hand, rotate in same direction.

[Rigmaster]

If you don't have all 4 wheels off the ground, you are working against the LSD unit in the transfer case that goes to the front wheels. (unless I am REALLY misunderstanding what you're doing.........)


No fair comparing an open (Non-LSD) diff to LSD.


Bret.

[SRR2]

Wellllll.... I could raise the drive wheels of the 535 w/LSD off the ground and turn them easily, with the trans in gear. They'd turn in the same direction, as you'd expect them to. The wheels on the 540, without LSD, also turn easily, but in opposite direction, also as you'd expect. On the iX, with an LSD (albeit an unusual one, and that may be at the root of this issue) the wheels not only turn very hard under the same circumstances, but in opposite directions. Unfortunately, I couldn't just put the trans in neutral to unload the drive shaft, since the front wheels were on ramps. However, in neither of the other two cases I've mentioned did the drive shaft turn. So what it boils down to is how the heck does that differential in the iX work, and is the resistance I'm seeing something you'd expect.

[Rigmaster]

Well, the only thing I know about the iX diff is that it uses a viscous type LSD unit vs. most BMW diffs which use a clutch pack type. They way I understand it, the viscous fluid in the LSD unit limits the amount of slip from one rear wheel to the other (exactly how this works is sort of foggy to me). AFAIK, the center diff (transfer case) also has a limited slip function, but I'm not sure if it's clutch pack, viscous, or something else....

In my experience, in a RWD BMW with LSD, if you jack up both rear wheels and turn one of them, the other turns the same direction (as you mentioned) AND the driveshaft turns as well- so I don't know what was going on with your 535 when you did this, unless the LSD clutch pack was completely shot- but then I would expect only one wheel to turn..... ??


Bret

[SRR2]

The transfer case has the same kind of silicone-filled viscous coupling as the diff has. There seems to be few complaints about them, even in high-mileage cars.

The more I think about this the more it makes sense that the drive shaft has to be free to turn with the iX diff. I'm going to have it in the air sometime this weekend and can test this theory. I can't believe that the differential could function with the levels of resistance to turning that I'm seeing.

[SRR2]

OK, I've researched this stupid differential. You are right that the drive shaft has to be free to turn. When you try to turn either of the wheels with the trans in gear, you fight the viscous coupling. That it's so daggone hard to turn leads me to believe that the coupling is doing what it's supposed to do.

The construction is fairly simple it turns out. Take a standard open diff and stick the viscous pack between the two drive shafts. That's all there is to it. When the ring gear can't turn, all rotation of one axle shaft is reflected to the other in the opposite direction through the crowns and pinions. If the drive shaft could turn, the wheels would rotate in the same direction because the viscous pack essentially locks the axles together.

Thanks for the sanity check!

Now, do you have any good ideas on how to get those rotors off? 8-)