ok i'm looking to put a axle from an 87 formula onto an 84 monte both axles are posi and have drum brakes does anyone see a problem with fitting or anything else. thanks

 

the spline ought to be the same on both, 26, better check the length to see if ti's the same.

 

Not quite sure of your question, are you looking to swap the axles individually, or are you looking to swap the whole rear end assembly? From the way you said the axle was posi, I gather you want to swap the whole rear.

The F-body rear is a three link, a lower control arm at each end and a panhard bar to locate the side to side. Your Monte Carlo rear is a four link, two lower control arms and two upper.

You would have to weld upper control arm mounts to the Formula rear, and I am not so sure the housings are the same width, or the lower control arm mounts are in the same location.

NOW, if both rears are 7.5" ten bolt GM rears and the axle spline count is the same, you could swap the carrier and gear set into the Monte Carlo housing, BUT you have to set the pinion backlash and ring gear clearance just like a rear end overhaul to get it right.
Either way, it's not that simple of a bolt in. You may want to find a Monte Carlo (Cutlass, Regal, Gran Prix) rear with the ratio you need in a junkyard as it would be a lot less hassle.

Eric

 

yeah i'm looking to swap the whole rear end. looking at them they look a lot alike i still have to measure them up. the biggest difference i can see is a few extra mounting locations on the formula's (for the track bar etc...) i'll post back when i found out more
later

 

They're not at all compatible...even if the width is correct (probably not), there is no provision for a torque arm or panhard rod, the LCA brackets aren't in the right place, and you'd have to cut off the upper control arm brackets. itd really be a lot easier to find a G-body rear. Besides, some of them (incl TType/GN, 442, etc) have 8.5 inch 10 bolts, far superior to the 7 5/8 junk they put in F-bodies, and they'll bolt right in to your car.