How to tell between S2 and S3 disk rear?
 

There is a 7 at the local junkyard that has been modified. It has disk brakes in the rear and an s3 dash, but the junkyard is claiming it is an 83. IIRC, the s2 had smaller axles.

What I want to do is swap the rear into my 85 GS. Is there an easy way to tell the difference between the s2 and s3 disk rears?

81-83 all had smaller axles.
84-85 had larger axles.
Up to Early 83 had the small driveshaft flange
After that point they had the larger driveshaft flanges.
If the driveshaft flange is the same as yours then it is the later models.

Does anyone have the measurements of the flanges so I can quickly measure them?

Large flange mounting surface is 3 1/4, bolts center to center are 2 5/8.

Thanks. I assume that the small flange is significantly smaller?

if the holes in the flange are threaded its a small flange

If they are vented they are '84-'85 GSL-SE.

Correct. Threaded holes = small flange. Non threaded holes = large flange. Also, the threaded holes are not in a true square pattern, they are rectangle, while the non threaded holes are square.

Archive and FAQ nomination.

Be aware some 83 GSLs had the bigger axles and bearings per the 84/85 GSL, all calipers/rotors for GSL rear discs are the same

So I got a threaded flange with the large measurements, and two small flange rear ends. what gives?

I have never come across the later 83 models having the larger axles. The only thing that I have encountered is the larger flanged diffs.

Have you personally come across this?

Are you measuring the bolt holes straight across or diagonally?

straight across...

pull an axle, its not hard

S2 has solid brake discs
S3 has ventilated discs

^ not here at least. Only the GSL-SE has vented, the others are solid disc in the rear