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Discussion Starter · #1 ·
Hello SF.
A few months ago, I picked up a used LSD differential from a 1991 Supra Turbo and finally have some time to get it installed into my 87 NA. This is my first time doing this and my concern is I'll be bolting up the driveshaft and cv axles to diff in a random manner. I've made marks on the driveshaft, trans and diff before when I replaced my center bearing carrier but when installing this "new" diff, I won't have marks to align with.
My search on TSRM, sf and net didn't give me any clues; so please let me know if this is a concern or if there's a method I should follow.
Thanks.
 

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It does not matter. The pinion flange is square, 60x60mm pattern.
Side shafts are not clocked either to a specific orientation.
Just make sure you torque all bolts to the correct ft/lbs as in the TSRM.

If you separate the 2 part driveshaft, that is the critical part to put back together the same way again.
The diff, does not matter.
 

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One additional tip if you assemble and get a vibration you're sure came from the diff. Mark the way it's connected with the vibration, flip it 180 out of phase and see how that goes. You'll have 4 ways it can bolt, and sometimes you can find the smoothest but the key is marking it so you don't lose track of which positions you've tried. I've owned a Syncro Vanagon and for some reason those things take every trick in the book to eliminate drivetrain vibrations and that one worked for me from a guy much smarter than I.
 

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Hello SF.
A few months ago, I picked up a used LSD differential from a 1991 Supra Turbo and finally have some time to get it installed into my 87 NA. This is my first time doing this and my concern is I'll be bolting up the driveshaft and cv axles to diff in a random manner. I've made marks on the driveshaft, trans and diff before when I replaced my center bearing carrier but when installing this "new" diff, I won't have marks to align with.
My search on TSRM, sf and net didn't give me any clues; so please let me know if this is a concern or if there's a method I should follow.
Thanks.
Keep in mind that you'll be losing some acceleration and showing slower than actual speed with the gearing change from a 4.30:1 (MK3 NA) to a 3.73:1 (89-92 Turbo).

The old school way to fix this was with a speedo 'bug' that would step up or step down the gearing accordingly so the speedo cable would spin the right speed, but I suspect that's a lost art these days. You'll have to do the math and mentally adjust to know true MPH vs indicated MPH. This will also affect your odometer.
 
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Discussion Starter · #8 ·
Agreed, I'll have to mentally note true MPH while reading indicated MPH.
And since I won't be making adjustments to speedo cable and I'm not really good at math, I've searched and found a website that calculates MPH based on gearing (trans & final), RPM and tire size (and converter slip % if applicable).
 

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Discussion Starter · #9 ·
After removing the diff cover and wiping away the old oil, I noticed that the lock plate claw for ring gear bolt is only staking the flat surface of bolt head. The other claw looks folded into the bolt head protruding edge but not staked per TSRM? - this is what all the bolts look like to me.
Previous owner told me that the diff had around 120K miles on it so I'm assuming it might still be OEM. My preference is to stake that second claw per TSRM unless its just me and this look good to go?

259941
 

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Lock plate staking looks normal to me and likely original from the factory.
They are sometimes folded around the corner of the bolt head, not always.
You could give the edge on the counter clockwise side of the corner a ding to secure it as in the manual.
Not a huge deal.

The bolts were torqued properly from the factory anyway (unlike the head bolts), the plate is just a extra safety measure.

I use red Thread locker on those bolts when assembling a diff.
 

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Discussion Starter · #11 ·
Sounds good! I think I'll leave it as it is, since the bolts have been holding fine all this time. Thanks again.
 

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Great info here. I also have a ltd slip diff I got from a U pull. I was thinking of installing it after I open and refresh it. Didn't know about the ratio which may change things for me. Is there a good reference of the various factory USA rear diff ratios available? For context, I have a stock 1988 5 speed USA N/A. I don't recall anything about the car I pulled it from. TIA
 

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There is an axle code on the chassis plate. You can use that to figure it out, but all NAs were 4:30:1 from the factory.

All NA had 4.30
87-88 turbo had 3.91
89+ turbo had 3.73
There are some subtleties for the 89 model year but this is mostly correct.

G284 = 4.30:1 4-pinion 8.0" pre-89 N/A Diff (no-LSD, USA Only)
G282 = 4.30:1 2-pinion 8.0" 89+ N/A Diff (no-LSD, USA Only)
G285 = 4.30:1 4-pinion 8.0" N/A Diff (with-LSD)
G315 = 3.91:1 4-pinion 8.0" pre-89 Turbo Diff (with-LSD)
G305 = 3.73:1 4-pinion 8.0" 89+ Turbo Diff (with-LSD)


259953


259955
 

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So in the sample plate is the ratio 2.92:1? Or is there further code analysis needed once I look at mine? Also, are all USA limited slips 3.73:1? If I'm getting that correct, I'll know everything tomorrow.
 

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I added more info after you posted. For the example plate:

G292 is 8" 4.10:1 2 pinion open diff. (its a truck diff and was never on a supra from the factory)
 

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Discussion Starter · #16 · (Edited)
So in the sample plate is the ratio 2.92:1? Or is there further code analysis needed once I look at mine? Also, are all USA limited slips 3.73:1? If I'm getting that correct, I'll know everything tomorrow.
I think the 89+ Turbo has 3.73:1 LSD; and the pre-89 Turbo has 3.91:1 LSD.

edit: see post #13 lol
 

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Ah - missed that was not a Supra plate. The word "truck" and numbers like 5350lbs should have clued me in (!). So, still a mystery on my end in one respect. I don't have the plate from the Supra I pulled the diff from. So, is there any way to verify with a diff case marking or serial number which ratio I have? I could count turns, but if the knowledge is out there, I'd love to have it. Tx.
 

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Counting turns or reading the stamped 2 digit code on the ring gear.
 

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OK, thank you. On the resistance, I am pretty sure it has a tag or "LSD" stamped on it, which is why I snagged it for $12 dollars - heh! I always bring my battery powered impact gun to the U pull and leave it in the car so if I find a gem I can get it off easily. It's actually super useful for rusty exhaust bolts where it simply snaps everything off in a couple seconds and then a few kicks and the entire system falls to the ground so you can access other things. Same with exhaust mans - another hard to get bit. Either the bolt or stud comes off, or you snap them and walk away with the manifold. I don't feel bad because usually the car will go to the crusher in mere weeks around here.
 
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