So, to revive a year+ old thread, I started into my new rear-end this winter and thought that I would give my 2 cents worth to anyone who is considering this upgrade. There is lots of good info on this site, but there are still some details missing or deleted over the years. Who knows if I got them right, but here's my take on it. If this can help you, great, if not, no loss to you. (I'm not normally one to write on the internet in more than one sentence)
First off, any information listed is for reference only, and should not be assumed as accurate or correct. Please make your own measurements and judgments. Consult an expert if you are unsure; I am not one.
The stock Datsun rear-end is ~48.5" wide from the outside of each drum. I have a set of 14x7 +10 Panasports that I want to fit with lets say, wider than average tires on them. Based on test fits and a bunch of squinting, I figured if I made the new rear-end 3/4" narrower per side than the stock axle, with longer wheel studs, I could always space them back out, but it's harder to go the other way. So I settled on making it 47" wide.
The RX7 rear-end (1984 GSL-SE vented rotor version) measured up at 58.5" wide. Which means, lucky me, I get to end up with 11.5" of scrap steel.
It took me some time to track one of these rear-ends down, and the one I ended up with was a little worse for wear cosmetically, but was in good shape where it matters. I stripped it down and removed every bracket and widget on it with exception of the breather. I left the one mounting point on the middle-rear that you may see in the photos as I thought I may use it, but no, don't bother, cut 'er off too. Earlier on, I didn't take as may photos, so the timeline jumps around a bit, but here is what I started with, and then once stripped down (RX7 on top of the stock one).
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The calipers turned out to be in good shape once they were scrubbed up. They were rebuilt and powder coated with Hawk pads installed. Same with the backing plates & brackets.
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Narrowing the tube is fairly easy once you know how much you want to cut out. Grind the welds off the outer flanges, knock 'em off, mark the same distance from the end of the tube, cut, grind and hammer the flanges back on. Here you can see the welds missing, the tube already cut and smoothed out, and the flange hammered back on for mock up.
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So far, this is all quite ordinary, however, you may notice that my brake caliper orientation is not as "ordinary".
Cue taking an operational car and making it not so functional, but hey, it's winter.
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The spring perches sit 35" apart centre to centre.
The "up tilt" of the pinion angle is 5 degrees. You need to measure this for yourself to ensure it's right.
Once you're confident on the stock bracket locations, get out the grinder and do your worst. You'll need most of the brackets, and you've come this far, so take 'em all.
You'll have this pile left over when you're done.
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Next, we do the centre section. What I can say is that I did a bunch of research on this before I tore into it and low and behold, some information I got off the internet was wrong (gasp). Refer to the FSM and don't trust all the self-described "experts" on the RX7 forums. However, once I opened it up it was pretty obvious that the RX7-keyboard-warrior was lost in left field.
I debated going torsion Miata, but my wallet won on this account. I'm not racing, and I've put 800kms on the car so far, so I don't think I'll wear the RX7 LSD out. I don't know the mileage of the car it came out of, but for how crusty it was on the outside, it was wonderful on the inside. I will vouch for the people that say these things last. Like lots of other accounts, my LSD shims measured like new.
The factory break-away torque is supposed to be around 35ftlbs, and when I checked mine, I was at 33. Not bad for being 35 years old.
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