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Old 03-29-2017, 12:52 PM   #1
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Default 940 Rear (LSD) options

I recently posted about finding an LSD diff for a 240 I was going to get. Plans changed and I am now picking up a 940 (1991). I'm aware some of these came with a G80 locker, and while it's better than open, it won't suffice for the torque I'll be twisting through it.

So...again...what are my options here? I'd love an assembly that would just bolt-in, but if I have to get custom, so be it. Tall ratio is still a must. That 4.88 setup in the other thread would be extremely useless in my configuration.
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Old 03-29-2017, 12:54 PM   #2
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what are you planning on doing with the car? there's a dana 30 lsd that you can buy in terms of that.
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Old 03-29-2017, 01:06 PM   #3
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what are you planning on doing with the car? there's a dana 30 lsd that you can buy in terms of that.
It will see the dragstrip a couple times, but mostly be driven on the street with the occasional highway romping. About 500-550 ftlbs torque at the wheels.
My 2JZ / CD009 will be getting swapped in.
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Old 03-29-2017, 01:13 PM   #4
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Old 03-29-2017, 01:13 PM   #5
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eh. g80 is fine with that, just not really consistent enough usually. as far as final drive ratios, they go as high a 3.31 if you shop it out a little.
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Old 03-29-2017, 01:46 PM   #6
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eh. g80 is fine with that, just not really consistent enough usually. as far as final drive ratios, they go as high a 3.31 if you shop it out a little.
Consistency is fairly important. So I take it no bolt-up assemblies to use? I see the Eaton Truetrac is favored by some, and saw a few links that people say "may" fit. I've never done any diff work, but as an engineer, I'm not afraid to dig into anything.
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Old 03-29-2017, 01:55 PM   #7
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trutrac fits. you won't have much luck digging up just a ring and pinion, so you'll be picking up a whole different axle assembly
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Old 03-29-2017, 01:58 PM   #8
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trutrac fits. you won't have much luck digging up just a ring and pinion, so you'll be picking up a whole different axle assembly
But people are just putting the truetrac in the stock housing without any issues?
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Old 03-29-2017, 02:57 PM   #9
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yeah
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Old 03-31-2017, 03:21 AM   #10
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eh. g80 is fine with that, just not really consistent enough usually. as far as final drive ratios, they go as high a 3.31 if you shop it out a little.
3.15 in Turbodiesel AW-55 3-speed auto '83 760, but pretty rare.
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Old 03-31-2017, 06:50 AM   #11
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OP, where are you located? I've got a 1041 rear end housing with 3.31 installed..... just getting ready to disassemble, but you should save yourself a lot of work and buy one factory fitted, then fit the TrueTrac. Case spreaders are recommended by the factory to open it .006" to properly preload your carrier bearings. Regardless, if the 3.31 is what you are after, you must find a factory 5 speed donor.
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Old 04-14-2017, 06:46 AM   #12
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I'm in southeast PA.

So a 5-speed rear is what I'm after? What kind of power levels can the housing and axles handle, safely?
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Old 04-14-2017, 08:40 AM   #13
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WELL, my 3.31 R&P has been purchased, and the housing will soon be headed to China/Korea. Do some research..... the Dana 30 will take some fairly high torque levels (these are listed in the Greenbook). In my experience it depends on your intentions..... auto cars won't shock those rear internals like the gear-bangin' stick shifts will. I can tell you that the axles have good size, and the spline count is similar to many V8 cars. The R&P bolt circle likewise has good size (1031 and 1041.... not the 1030). So the fuses are likely the (1) pinion area crush sleeve/bearings and (2) the LSD. Lots of users of the TrueTrac from Eaton.... I've not heard of anyone breaking one yet. See what the JEEP guys are doing to shore up their pinion bearings/crush sleeve and you should be able to put down some power.

Suggest you speak further with the drag guys here on their experience.... BABBs and LINUXMAN. They've likely broken all these parts and can give you more suggestions.
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Old 04-14-2017, 10:14 AM   #14
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I'm with ^^^^ about the TruTrac. Drop-in, actually designed for our diff's if you get the 912A588. Don't need a spreader, you can figure out the pre-load without it without much trouble. I've done it both ways with no issues. Got a 1041 in mine now with a TT, going on around 80k on it with a daily diet of 275ft.lbs at the ground, hasn't batted an eye, but I know there's many others with far more going thru them.
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Old 03-17-2018, 05:30 PM   #15
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Well, the 2JZ is finally in. I got a bug up my butt last week to resume on this project. Had to make some custom mounts which turned out well. Had to make a new trans mount and modify the shifter, but all done and engine is installed. I have to get my driveshaft ordered and looks like I'll need a 2-piece shaft like the OEM unit because of the bend and the frame support, but that's OK. I have tons of wiring to do, but I'd like to get a jump on the rear diff. I'll probably order the 912A588 like you guys recommend, but where can I get a ring/pinion set so I can change the ratio to something more suitable for this application? I'll need something around 3.08 but it sounds like 3.31 may be my only option.

Last edited by phuz; 03-17-2018 at 05:38 PM..
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Old 03-17-2018, 08:41 PM   #16
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I sold my 3.31 R&P to a TBer up in Quebec, but others are probably available if you are patient. Perhaps you can run a taller tire that the stock sizes to make the final gearing closer to your desired ratio. Will you have a manual gearbox ahead of the 1041? If you are going to shock load that rear suspension, you will definitely need to reinforce your rear subframe and perhaps the torque reaction "doggones" as well. I've got pics in my build thread showing the beefed up subframe using the Yoshifab kit.
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Old 03-18-2018, 12:53 PM   #17
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I sold my 3.31 R&P to a TBer up in Quebec, but others are probably available if you are patient. Perhaps you can run a taller tire that the stock sizes to make the final gearing closer to your desired ratio. Will you have a manual gearbox ahead of the 1041? If you are going to shock load that rear suspension, you will definitely need to reinforce your rear subframe and perhaps the torque reaction "doggones" as well. I've got pics in my build thread showing the beefed up subframe using the Yoshifab kit.
That's kind of why I'm trying to hunt this down now, so that it's not my last piece of the puzzle. Plenty of wiring, charge piping, exhaust, etc. to do in the meantime. Just don't want to let this part slip. I CAN run a slightly larger diameter tire, and plan to, but can't go as big as I did in the past. I'll need to roll the fenders, too. (never did that, so may have to pay someone to do it so I don't botch it)
My trans is a 6-spd manual from a 350Z (CD009), and I can't order my driveshaft until I have the new/modified rear 100% in place. I'll check out your thread for the subframe "beefing." I appreciate it.
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Old 03-20-2018, 04:27 PM   #18
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Found a 960 rear axle assembly about 2 hours away and picking it up Thursday AM. Ordered the 912A588 from Summit. FYI, they price match so I found one for < $500 and they matched it.
So now the hard part begins of getting the diff in the assembly because I have none of the special tools.
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Old 03-21-2018, 06:25 AM   #19
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Alternately, take the 588 and 960 rear end assy. to a rear end specialist. You won't like the price, but I guarantee you will enjoy the time saved! They know all the tricks, have the tools, and will complete quickly.

OR if bucks are tight, learn and enjoy the experience
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Old 03-21-2018, 06:34 AM   #20
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I've prided myself on doing all my own work on engines and electrical, but not sure I want to risk screwing this up. I guess I need to read more about how these things come apart and go back together before I decide.
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Old 03-21-2018, 10:05 AM   #21
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It's a little daunting until you do it the first time, then you realize how stupid simple it is. lol
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Old 03-24-2018, 09:23 AM   #22
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Got the rear end from the 960 and got the TrueTrac. I'll be dropping the 940 rear in a few hours and test fitting the new one so I can get an exact measurement for the new driveshaft. They'll probably need several weeks to get that done so I might as well get that started.

The dust shields on the donor are all bent so I want to swap my good ones over, and it looks like I have to remove the axles anyway for the diff swap, so is there a writeup floating around of how to remove the hubs/axles? I'm going through AllData (which uses the factory repair manuals) and the only thing I've found is a diagram saying to "remove axle shafts (use brake discs)" and I don't really see how that makes sense.
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Old 03-24-2018, 02:40 PM   #23
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With the 4 bolts which connect the cadmium steel plated retention plate & dust shields against axle end flange (bolts released thru the axle flange access hole), you simply turn the rotor around 180*. Loosely install 3 lug nuts.... then slide the rotor "slide hammer style" and the axles will come out. Old BrickBoard trick from BITD......

Host up pics of your TT installed in that 1041 with the 3.31 ratio.
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Old 03-24-2018, 02:49 PM   #24
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LOL, we're a bit aways from that. I actually figured out the trick to remove the axles about an hour ago. Got them out. Took the measurements I needed for the driveshaft and then removed the rear assembly again. I pulled the cover off and removed the bearing caps, but the diff seems like it doesn't want to move. Someone said I need a case spreader and someone said I didn't.
Is there another trick to get this beast out?
Can I re-use the shims and bearings or should these be replaced? (If so, source?)
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Old 03-25-2018, 08:10 AM   #25
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All of the diff. assemblies (G80 in your case with ring installed) are preloaded .006" to .008" by DANA. No doubt some bearing wear has loosened this preload, but some remains. Try putting a pair of levers on either side of the diff. and leverage it out of the axle housing..... some are really snug, others come out without much struggle.

You can start with the same shims, but I'd suggest new bearings ($30 on eBay). Have these pressed on and THEN the fun begins! If the assembly drops in, then too little shim..... if you can't drive it into place (plastic dead blow) with bearing cones lightly greased, too much!

Gary didn't need a case spreader, but I did for my LSD.....you can see the pics in my build thread. Either road, once you get it installed with the "proper preload" then torque your caps ~ 45 lb.ft. and read your indicator for the target backlash.

These installs are a "2 Equations, 2 unknowns" type problem..... you can read backlash until your preload is proper.... changing one affects the other.
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