Hello, I'm speaking for my friend with a Slash 4x4. There's something odd happening suddenly. If you take apart the rear assembly(as in all you have is the whole front assembly, slipper clutch assembly, and rear diff assembly). They each work perfectly on their own. But once you put them all back together, the rear slipper/diff area aren't getting along very well. Once you install the rear diff assembly with the slipper clutch, the clutch seems to 'push' the pinion in the diff too much and cause a tight mesh between the ring and pinion gears. It's a harsh, rough, highly-resistant feeling when you roll or spin the clutch when it's with the rear diff assembly. I tore down the clutch assembly, and of course the whole rear diff assembly, nothing seems to be out of the ordinary. All bearings are in top shape. There is evidence inside the rear skidplate that the spur gear and clutch backplate is rubbing it. The diff gears are perfect too, hence it rolls fine on their own. I've heard of diff housings being warped and worn to the fact that the gears don't have that perfect mesh anymore, but I can't tell of anything of the sort.
If anyone can help or has had this experience, please pitch in. He is now considering selling his S4 and moving on to a Pede 4x4. He's had many problems with his S4, but they are mainly annoying problems, not so much expensive problems. It's the reoccurring problems that are getting to him I believe, and I understand, but I've been in this hobby for awhile now, so I've grown very patient and observant with anything that doesn't perform right. I try to convince him that it's nothing bad and it normally isn't. But in this case, I'm pretty much stumped, been spending a couple hours just analyzing it as one whole truck and in sections. Have gotten no knowledge of anything causing the problem.