I recently got my Rx-7 out for the first time in a while because of the bad weather, and while driving was reminded that I have a gs model with the open differential. This makes for unimpressive launches and horrible traction when it is wet or the roads are slick. I was wondering if finding the LSD rearend with disk brakes is worth the trouble, and what I should expect to pay for one in good shape. Also, if someone coould inform me on exactly how the LSD rearend works as opposed to my open differential, I would greatly appreciate it. I was under the impression that an LSD rearend sends power to both wheels during launches and driving in a straight line, then in a corner stops sending power to the outside wheel so the car does not understeer like a go kart or something. Please let me know if I am wrong. I have heard some people of questionable intelligence tell me LSD rearends only spin one wheel at a time, but those people also told me I should get a "Posi" rearend. I tried to tell them Posi was a brand name used on Pontiacs or something and probably is not made for my car and will not let the car handle well. Sometimes I worry about these people. Thanks for any and all advice. By the way, I have those new 15x7 konigs on the car now, and tried to post pictures but they were too big I guess. I am working on that.

 

http://auto.howstuffworks.com/differential.htm

 

You are correct, Positraction was a GM marketing name, but so many people think LSD == Positraction that sometimes it is easier to just call it that depending on who you are talking to.

 

An LSD tries its best to keep power to both wheels all the time.

 

definatly worth it

 

I checked out the howstuffworks article, very interesting. The torsen rearend seems really cool, but I'm not sure if it woud be as beneficial as an LSD rearend. How much can I expect to pay for a good LSD rearend and have any of you noticed much understeer as opposed to the open diff? I am more interested in handling well than going fast in a straight line, there are a lot of good backroads around here.

 

Going rates seem to be running up to 250 for the entire rearend, should include brakes and the 2 rear brake cables needed. You can simply switch out the diff, but make sure the seller does not remove or loosen the pinion nut, otherwise you will need a new crush sleeve and the lash set. Also make sure you get the year that is compatable with your car and the diff flange matches up.

 

I have seen other post where a 95-99 miata diff was installed. mod were needed to clear the Watts link.

 

I guess I had better start looking now. Thanks for the advice guys, I do not think I will go with the miata diff, I want the gsl disc brakes too.

 

just make sure the calipers are'nt siezed because they arent cheap just a little advice.

 

understeer can be reduced by stiffening up the rear. The LSD will make the car more predictable through the twisties because you'll have two wheels working through the turns at all times.

The FB LSD uses clutches to keep both wheels spinning instead of gears, so just make sure the one you buy isn't worn too badly, and the correct oil is used.

 

Worn 1st gen LSD rears are pretty much the norm these days.They are just getting old and tired.You can try to get the best one possible,but I wouldnt neccesarily pass one up,just because the wheels turned easily and the LSD preload was weak.

Thankfully,the stock LSD is an "active" type of unit,very similar to the famed Spicer Power-lock LSD.It takes torque input and uses it to compress the clutchpacks and hold the two axles together.The more torque you feed it,the tighter it grips.Even if the clutches and springs are tired,you can still get some measure of action from the unit,unlike passive/preloaded clutch LSD's which simply stop working altogether when the discs and springs get thin.
Granted,N/A rotaries dont make a ton of torque,but in 1st gear,when you are most likely the spin a tire,the tranny will multiply the engines torque the most and get the LSD working.