i have an 86 FC and i dont think it has lsd , i also have an extra rear end out on an 88 n/a(does it come with lsd either?)

 

LSDs are a trim level option. Check the faq if your cars trim level includes it. Other than that, someone could have swapped one in. Check for an lsd tag on the filler bolt or you can try lifting the car in the air and spinning one wheel while in neutral. If the other wheel spins in the same direction, chances are good you have a LSD. But this technique is not definite, a worn out lsd can act like an open diff. For the one you have laying about, do the same thing, spin one flange and see if the other spins the same way

 

what if they spin in oposite directions, would that be and open diff?

 

no 86 models came with lsd, and the if the 88 n/a was a gxl then yes, any other modle besides turbo2 and gxl in 88 had open diff, yes if you spin the yoke (where the driveshaft would connect to) and both axles turned the same way then it is lsd, although some s4 lsd's could be wore out as they were clutch type lsd's unlike s5's wich were hellical gear type lsd's. anyway if you spin the yoke and each axle turns opposite directions then its open diff. pretty much. but this could all be affected if the ring and pinion is fucked up or the clutch type lsd is worn out