I've been searching and got a little frustrated so I'm going to ask directly. I am still a little new to S-30 ownership -sorry. I am planning to rebuild my differential. The bearings are very noisy and I have it out so now's a good time. I thought that it was an R-180 but I have confirmed that it is an R-200. Would you expect to see that on a '76 280 with a 4spd?

The R200, with 3.54 ratio, is the only differential used for the 1975 to 1978 280Z's. It's shown in the Service Manual. They're hard to rebuild right, from what I've read. They seem to be a noisy design in general, but much of the noise can be isolated with the right bushings, and a little sound deadening material in the back of the car. You might do a little more reading, there are more frustration stories than success, from what I've seen.

Are you sure it's the bearings that are making the noise, and have you checked to see if the diff was full of fluid? After 36 years much of it will have escaped through the breather.

I agree with Zed. Rebuilding a diff is not to be taken lightly. Ive mostly played with Ford 9" and salsbury diffs. Just understanding the geometry and the paterns on the crown takes years of experience. A lot of diffs will run with the alignment a little off, but they wont run quietly. You could make it worse by changing the bearings and making it whine through crown/pinion alignment issues.

Are you sure its bearings and not a gear noise?

You could try changing the oil can reduce the noise. Another option would be to pick up another diff.

Chas