ok, just for the hell of it, i tried a burnout on a back road, with no one around.

afterwards i expected to see two long tire tracks. i didint i saw one. i thought this car had a posi rear? i guess not. is it possibel to stick a posi bar on a 1975 280?

What is a posi bar? To get both wheel to spin you have to modify the diff internally.

What is a posi bar? To get both wheel to spin you have to modify the diff internally.

Spinning wheels indicates a lack of traction, not good.

No, Nissan never offered limited slip diffs in the 240/260/280Z's. (Posi-traction is GM-speak for limited slip.)

I've read that some Subaru diffs with limited slip can be made to fit, but know nothing about what might be needed to do this, or what gearing choices are available.

Arne is correct about the Subaru differentials. Some Subaru models use an R180 differential with a clutch type limited-slip differential. They should bolt right into the Datsun R180 differentials.

A limited-slip differential is a great performance addition to the Z, especially if you like to participate in drag racing, autoX, road racing, or just having fun on your favorite twisty back road. It will make exiting right hand corners as effective as the left hand corners.....no more right rear lightup on the right hand corner exits. Also, the posi carriers usually have a four pinion spider assembly as opposed to the two pinion spider on an open unit, and contribute greatly to the strength of the differential.

umm... my 75 280 2+2 leaves two marks, I thought they were posi too.

If not then why does mine leave two marks?

Yours leaves to marks because you have equal traction on both sides. An open differential will work like a "posi" in a straight line provided you don't have a traction differential. The limited slipp will keep the power drom going to the wheel with the least resistance (less traction). Just because you leave two marks doesn't mean you have "posi". It means that you had equal traction on both sides so there was no path of least resistance for the power to flow out of. Therefore it went to both wheels.

o I see thanks.

Spinning wheels indicates a lack of traction, not good.

Let me reword that. To hook up both wheels you need.......

Sometimes a lack of traction is loads of fun.

ok, so has anyone added the subaru limited slip parts? and bolt in where, inside the diff? or just use the entire subaru diff?

GREAT LSD info: http://www.gordon-glasgow.org/lsd1.asp

If you want to buy a NEW LSD, http://www.reiderracing.com/home.htm has the R180 and R200 "Power Brute" for ~$500. The Power Brute is a rebadged Nissan LSD. Both the R180 and R200 sold by reider racing the much stronger 4 pinion units.

If you want a Subaru diff, the mid 80's XT Turbo came with a 3.7 R160 with LSD. It was the same clutch type LSD, and the manufacturer that makes them for Subaru is the same one that makes them for Nissan, Fuji Heavy Industries (parent company for Subaru too, IIRC).

There's also the Quaife gear type LSD that runs ~$1500 and is way overpriced IMO. I guess Australia has some gear driven units for under $1000 (not sure if that is AUD or USD) but that would be a better deal than Quaife, personally from what I've learned about them I prefer the clutch type.

Info about shimming the LSD tighter for anyone interested: http://forums.hybridz.org/showthread.php?t=92629