I am looking into buying a LS or Posi Rear end ( and of course gears). But I am not sure which one it had 26 or 28....i have head both and was looking for another 89 firebird or camaro that could shed some light on this subject

 

89 is the ABSOLUTELY WORST YEAR for asking that question about.

From posts on here, it looks like about 80-85% got 26 splines; but toward the end oif the year, a few 28s started creeping in.

Bottom line, the only way to know for sure what you've got, is to take off the cover and look. Or, don't worry about what's there now, buy upgraded axles of the size you want (28 no doubt) to go along with your other parts.

 

grrrr

 

Another variable for you, if its a 9-bolt forget about find ing a limited slip. And I bet you have a 28 spline 9-bolt if it a Formula 350.

 

is there a way i can check that without looking at it? (calling dealer and such?)

 

Look at the rear cover. A 10 bolt will have a smooth cover and 10 bolts. A 9 bolt will have a rubber fill plug and 9 bolts.

Other than that, the only way to know the spline count if it's a 10 bolt is to pull the axles. Chances are if you have a 10 bolt, you have 26 spline axles.