As the title says, I'm wondering if the GSL disc brake rear end is wider than a drum brake rearend.
The reason I ask, I installed an 84 GSL rear end in my 83 GS, and I seem to have tire clearance issues now. The car has a set of older ST springs (blue, if that tells you how old they are) and Ronal 15x7 +15 offset wheels, with 205/50-15 Kumho Ecsta SPT tires.
I had an issue of the rear bumpstops getting too much use, so I cut them down about 1-1/4". This induced some minor tire rub on the rear. Rolled the fender lips, and all was well.
Now that I installed the disc rear axle, the rub is back. Both rear tires rub, so it's not that the axle is sitting off-center.
I have a feeling the axle is wider, though barely, than the drum brake unit. It may only be by a few MM, but that's all it took to bring back my tire rub issue.
Am I right?

 

There were no issues when I switched from a GS to a GSL rearend back in the days.Since the drum and disc cars all use the same 13", "plus" wheels and the same chassis,I would think both axles would be the same width.
The GSL-SE rearend is wider due to its axle flanges,thus the lack of any dish on the stock 14" SE wheels.

 

I rolled the fender lips the minimum amout needed to prevent the rubbing a while back, so a difference of even 5mm would be enough to bring back the rubbing.
I don't know if this could be from something as simple as the 84/85 large axles having an extra 2mm (or so) thickness at the wheel mounting surface vs the small axles, or the rotors having a slightly thicker center. I did go from a small axle drum unit, to the large axle disc.
Trust me, somehow, somewhere, there has to be ~5mm difference. Normally, this could not be noticed, but my car is far from normal......
I have 2 options. Rolling the fenders, again. Or, shimming the bumpstops.

 

Can anyone comfirm my theory that the S3 rearend is slightly wider than the S1/S2?
Last month, I autocrossed the car with the S2 drum axle under it, and had no tire rub issues with more weight inside the rear of the car (on the way to/from). This weekend, I autocrossed it with the S3 disc axle, and even with less stuff in the back of the car, I had tire rub issues (on the way to/from).
Nothing else changed. Same tires/wheels/springs/shocks. Heck, I never even drove the car between the events, as I killed an axle bearing in the drum axle at the last event, thereby motivating me to make the upgrade. VERY worthwhile upgrade, I might add.

 

I have an 83 lsd unit and it's 56-1/2", hub to hub w/o the discs. Also, the lower control arms on the S3 units are longer than earlier models. Did you change those and are the rub spots in the same spot as before?

 

I left the original arms on the car. The lower arms were still on the axle, but my bushings looked better, little did I know just how much better. The rear bushing sleeves had fused to the bolts, so out came the hot wrench. Apparently, the same method was required for the front bolts, as those bushings had burn marks, but I didn't see them till after the rear was cut loose.
The rub spots are the same as before, just getting the last ~3/8" of sidewall, where the tread pattern ends. Other that making lots of noise, there's really nothing for me to worry about, it's not cutting the tires, just leaving them a little scuffed.
Hmmm, 56-1/2" axle flange to axle flange, anyone have an S3 rearend without drums/rotors to measure?
My old drum unit was deffinately the small axle unit. I found a fast/easy way to determine, without even pulling a drum. Measure the distance between the top 2 backing plate bolts. Less than 3" is small axle, more than 3" is large axle. (The distance between the top and bottom bolts is too close tell with a tape measure.) I had to rob an axle out of a spare 85 drum rearend to go into the disc unit.....