Any one know what this is or how strong it is? It is supposidly out of a '78 Trans-am and is an 8 3/4" 10 bolt. I thought 8.5" was the size, not 8 3/4". I'll be putting maybe 350-400 hp. thru it. Whatayathink?

Hi do you have a ID code on it, 8.5 not 8 3/4 l'm sure it is a locking rearend, here goes the codes(PS 2.41) (PT 2.56) (PW 3.08) (PX 2.73) (PP 3.23) they are the codes for 78 pontiac firebird,T/A's as far as HP, 350 should be fine but 400 you might want to go threw it to check it out TROY

Troy,

I have not seen the unit yet, but I will put new gears and bearings in it. Am I correct that it is 8.5"? Can it be 8 3/4"? I think it has 3.08:1 in it now. Can I put 3.42:1 gears in?

Thanks

if it is 8.5 you can't change them around with other 8.5, they didn't but a 8 3/4 in any of them cars! TROY

A 78 T/A should have an 8.5" posi rear standard (a base firebird will have an 8.5" open rear standard.)
gear ratio is 2.56 to 3.42 (probably 3.08:1)
it will handle 350-400Hp no problem if it's in good shape.

if you have 3.08 gears, you can swap 3.42 gears in to the rear- both use "3 series" carrier, which is 2.73 up to (I think 3.73 or 3.9?)