I changed my dirve shaft yesterday for my 99 sc400 and replaced it with a low miles DS. The car rides much smoother and there is no vibration from the area like I had before. However, I can still a low grade humming sound above 65mph when I'm on the accelerator. I went up to 110 several times and got off the accelerator and the slight low humming stopped. The new DS supposedly has 80K miles. Anyone had the problem, how did you solve it.

 

I would say it's one of two things assuming the humming is actually coming from the trans or driveshaft:

1. Transmission mount is old/cracked/even sagging, but still looks good.
2. Driveshaft phasing issue. This can be complex and maybe I got lucky, but the triangular ds mounting ends need to be 180 deg out of phase (based on the white/yellow mark) with the trans output or diff input. The reason I said OR is because I'm not entirely sure. The details are in the propeller shaft section of the SC manual. I am not an expert at this, but I would say the vibes/humming should be correctable with one of these two issues.

 

thanks, I'll try to find that info. I do have a new trans mount I'll install Saturday. Your build looks good, I'm building up the guts to do this my self.

 

Finally fixed, I changed my transmission mount..No more humming. The car is soooo smooth and quiet. I recently got new tires, changed driveshaft for low miles DS and the TM. My accelleration and ride qualitu is 100 times better. I'm working on replacing LC arm bushings. Finished the drive side, cann't wait to feel test them.