Recently my mechanic ripped a rear end out of an 89 firebird formula, it was the 305 TPI motor with a Five speed Transmission.

Would the rear end gearing be the same as the IROC-Z that came with the five speed? which in 89 was 3.45 for the 305

 

If it was a G92 car.

If it wasn't, it probably would have come with a 3.27.

It should be a 9-bolt with PBR brakes.

 

how can i tell if they are PBR brakes? It does have disc brakes also.

 

in 1989 3.08 gears in a 10 bolt were standard equipment for 305 tpi 5 speed cars. the 3.45s were optional and were in a 9 bolt rearend.

ur mechanic should easily be able to tell what you have just buy counting the number of bolts that hold the differential cover on nd buy either counting the teeth on the ring and pinion gears or looking for the stamping on the ring gear that says what ratio it is.

 

for 89-92 all rear disc brake equiped F bodys had the PBR style rear brakes (single piston aluminum calipers with 11.625" rotors)

 

but he said 305 tpi 5-speed (3.45 was very common on those) I guess your rpo build sheet will tell you what it had from day 1

 

3.08s were standard and 3.45s were optional

 

Check the following link for pics of PBR's:

https://www.thirdgen.org/techbb2/sho...hreadid=249098

JamesC