I have an 88 fc with a welded diff that i just got running again about a month ago (was the fuel pump) anyway, im starting to daily her more and more and i need something that doesnt wear my tires so quickly. I found an 87 NA LSD rear end, will that bolt up and will the splines all match? I just need something good for daily that will still lock up good (when i need it). I have looked everywhere and no one really talks about how good an s4 na lsd works compared to open and compared to welded. Thanks for any help!

 

All FC NA rear ends are interchangeable.

 

As stated above all NA rears are interchangeable. S4 LSDs are mechanical. At this point chances are any that you find that have not had their clutch packs rebuilt will have little to no locking ability due to pack and spring wear. The forum rule of thumb is the factory clutch LSD's last at most 40k before they should be rebuilt. The S5 LSDs are viscous coupling. They use the differential oil to operate. These will not wear out (within reason) and may be a better solution for you for general street use. Another factory Mazda option is to track down a Torsen differential from a Miata. IIRC they only came on the Miatas optioned with the 6 spd transmission. These can be difficult to find due to limited number of cars that came with them originally and they are highly desired in both the Miata and RX7 communities.

P.S. - If you don't go the S4 LSD route would you mind passing on to me the sales info for it? I've been looking for one for my track car but have had little luck with pricing.

 

How do you like your welded diff? I'm thinking of doing that while I save up for a LSD

 

I love my welded diff and have never had any problems with it. I just need my car for daily driving now so i need my tires to be able to last...lol. I welded steel plates to mine though so yeah you may want to do the same..

 

Yeah i was thinking about getting a s5 lsd but I figured I don't daily it so I might as well just take it down to the shop and weld up the diff in it right now. Thanks for the advice!