I'm lost as hell here
I have a 87 sport with a 5spd

when I pulled the old driveshaft out it was a good 4 inches or so diam
this new driveshaft I bought slides in just fine as far as the splines go and almost looks like it lines up I just can't tell yet being the bolts I have the threads slip through just fine at least for one of them but the smooth part of the bolt is too fat to fit.

another thing is this new driveshaft is only maybe 2 inches if even in diam

my mesurements might be off but the thickness difference between the two is HUGE
both slide in the thick one work fine but u joints are going
there is a sticker on it something like m60 I think though on the new one

any idea why the driveshaft I pulled out is huge. the new one is small and the bolts don't fit perfect right now?

 

Only M60 I'm aware of is a BMW engine.

 

some n/a rx7's had really thick d-shafts, some were really thin.....i've personally had both (ive had 6 rx7s) ...... but the bolt difference baffles me! my advice... junkyard.... get the bolts off of another one and try them! or go to a hardware store and pick up some grade 8 bolts that fit

 

sorry it was m060 was the sticker on the replacement driveshaft.
ended up fixing it with a hammer, socket, and some nice beating and twisting... it seem to fit fine after that
the bolt holes seemed a tad too small but where able to fit. think I just freaked out being I had stuff I needed to get done right after this and just had that ah **** feeling


this is my third driveshaft in this car
the first one was tiny. the second one was HUGE and this new one is tiny also
didn't really notice how much bigger the second one was being I took the first one out and and let it sit for almost 4-5 months till I was able to get a new tranny and driveshaft. driveshaft blew spun around and beat the tranny causing internal damage.


but is there going to be any strength difference between the two cause if so and this thicker driveshaft is fixable by replacing the u joints I might just try to get it put back in there

 

strength differences? heh better believe it. I'd start to question an n/a "tiny" driveshaft around 200 hp.

That thicker driveshaft sounds like a mazdatrix or custom fab. The normal FC3S ujoints are not replaceable at all, at least not without raping the **** out of it using parts that were never meant for an FC3S driveshaft.

 

there is a place here that will tink with them and somehow fit replaceable ujoints in the driveshaft
only thing I would be worried about is I had to drive it around on a bad u join for a while and don't know how much damage that has caused

this thicker driveshaft how strong would you take that to be?


though as far as the tiny driveshaft had a friend running over 350hp on drag radials using the N/A rear from his GXL and the auto driveshaft.
he busted rear axle first not the driveshaft

 

Thicker driveshafts? I dunno, I'm sure there are some 500hp TIIs running around with stock TII driveshafts somewhere. I'd imagine much past that, and they'd have to get some beefy (thinking truck beef) aftermarket driveshaft though. But like with your friend with 350 on the n/a driveshaft, you might be damn suprised.