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Subie R180 input flange swap


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Hi all, long time lurker, first time poster here.


Quick intro:

My name is Dirk, I have a '73 240Z and '70 510. The 510 is the car I've learned to wrench on since I got it a few years ago. The Z has become my rolling project and daily driver since I bought it about half a year ago. Powertrains are stock-ish on both but I'm planning an L28 NA build for the Z. I'm fairly mechanically inclined and have completed a bunch of moderately challenging projects on both cars, but I'm entirely self-taught and far from an expert.


My questions:

I'm getting ready to swap a Subie R180 Torsen diff from an '08 STi into the Z, a fairly fresh used diff and the betamotorsport stub axles are on their way to my home, as well as a Ron Tyler mount while I'm in there, and I've done a bunch of research on the swap so far.


This is the best illustrated how-to I could find on the swap: http://inzane240.blogspot.com/2014/01/subie-r180-install.html


At this point, everything but swapping the input flange seems really straightforward to me. The best thread I could find on that topic was this one: http://forums.hybridz.org/topic/90321-r200-clsd-mounting/

But since that thread is about a different diff than the one I'm going to use, I'm not sure if the same tolerances and advice apply. I'm asking specifically for advice on how to retighten the flange nut in the best possible way so I end up with a safe, reliable set-up.
What I believe so far is:
  • The flanges should swap straight between my stock open R180 and the Subie R180
  • I can remove the nuts for the flanges on both diffs with an impact
  • I might need a puller to get one of the flanges off, but probably won't
  • When putting the Datsun flange on the Subie diff, I should put red loctite on the nut and tighten it to around 137 ft-lb
  • The Subie diff doesn't use a crush washer for preload of the bearing or anything complicated like that, so no to count rotations of the nut when coming of, or to measure flange thickness. I can just tighten to spec, and then just check that the diff still rotates freely.

If you see any errors in the above, please let me know.


Now the next steps are where I'm getting a little lost and this is where my lack of expertise as a mechanic shows:


When tightening the nut with an impact, it's really easy to overdo it. But when trying to using a torque wrench the diff will spin before tightening that nut. I see a few possible options to do this, and would like to hear your recommendations (or if you know of an alternate approach that I've overlooked, even better):

  1. Put the diff on a bench, put the flange in a vice. This allows me to tighten the nut with a torque wrench without spinning the input shaft. (seems like the best option. only worry: damaging the flange with the vice).
  2. Assemble input flange but don't fully tighten it, install the diff in the car, connect half-shafts to it but before connecting drive-shaft, put on the parking brake, raise car again, and tighten the input flange nut to spec while on the car. (seems like the surest option as long as I don't forget to tighten the nut. worry: seems like a hassle and means that if anything binds internally after tightening – e.g. seal against flange – I have to remove the diff again)
  3. Just jam the nut on there with my impact driver (I have an electric one that's capable of delivering somewhere between 150 and 250 ftlb of torque), even if that over-tightens the nut. (quick and dirty, worry: damaging something by over-tightening)

Approach 3 is what Jon Mortensen recommends in the above-mentioned thread, just get it RFT. But since that's about a different type of differential than the one I'm working with, I didn't want to assume the same advice works equally well for the Subie diff.


I'm leaning toward option 1, since it seems the most straightforward way to get to spec. Option 3 also makes sense to me because I'm probably going to use a similar approach to tighten all the other nuts to spec (half shaft to stub axle, drive shaft to input flange).


Any advice or recommendations appreciated, thanks!

Edited by rundwark
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Regarding torquing of the pinion flange nut, you could try a hybrid of your methods 1 and 2.


1: Assemble the subaru diff with datsun pinion flange

2: While the differential is on the workbench, lock a pry bar between the bolts on the differential stub (output) shaft flanges. If you need something to keep it still, consider using a piece of scrap flat-bar with holes drilled to keep it from falling out.

3: The pry bar interference with the workbench should keep the differential from rotating while torquing.

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I've done this swap and can confirm all the points you've already made.  The flanges are a direct swap.  I didn't need a puller on the Z flange, I was able to slowly tap it out by working my way around it.  I also used the same appoach Jthom mentioned, leveraging the workbench and the stub axles to lock it down.  Good luck, and happy future 2-wheel driving!  :wink:

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I brought both diffs to a diff shop, the guy had a bench setup with and adjustable mount for the pinion flange (sort of like an engine stand, but with a hold in the middle) and he used an air gun to get it off and put on the datsun flange. Took 15 min total and wasn't charged for it. 

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The clack noise is coming from the front of the diff, I believe either from where the pinion and crown gears connect or the pinion bearing. And the light creaking noise that goes along with it isn't coming from the diff, but from the material it's resting on on top of my workbench.

I just got my dial gauge and backlash on the crown gear (holding pinion still, moving crown gear by hand; pic attached to show how I measured) is somewhere between 0.009"—0.011". Spec is 0.004"—0.008". Also measured crown gear runout and that's right around 0.002", which is barely within spec.

What do you think, adjust it first, or close enough to use as is?


Edited by rundwark
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  • 1 month later...

You don't need to lock tite the pinion nut and you don't need to torque it specifically. Just put it on and hit it a couple quick times with the impact. Keep your impact on the low setting and just do a quick "braap, braap.". There's no real load on that nut other than the weight of the driveshaft. The rotational torque from the engine is applied to the splines. The driveshaft keeps the nut from falling off if it were ever able to back off any. It won't.

Edited by RebekahsZ
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  • 4 weeks later...

I have all the parts and tools scraped together and am going to do the swap today.


Planning to use an iron angle bar with some holes drilled in it to bolt the pinion flange to temporarily for torquing that nut. Even if it's only to verify that I put it on tight enough with the impact.


pics coming up, wish me luck :)

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  • 1 month later...

Better late than never :) – here's a write-up in the hope it'll help the next person researching a diff swap.

The install went well, it only took me twice as long as I planned. About 8 hours of work, plus a 2-hour "break" looking everywhere to try to find a missing bolt. If you're a not-so-experienced mechanic just like me, you can do this job in a day, by yourself, if you have access to a lift and a trolley jack.
Trickiest parts of the job
  1. Getting the old driveshaft and half-shafts hardware loose. It's a pretty tight fit to get your tools in there, and it helps to have a two regular-size and one thin set of metric wrenches. A lot of times you'll need two 12mm wrenches to twist both sides against each other.
  2. Getting the new diff's input flange loose required extreme amounts of violence. Let's just say I was glad I had my biggest hammer with me.
Parts used
General notes


I didn't end up fabricating a special tool to hold the input flange and torque the pinion nut to exact spec. After several hours of work, I was running a bit low on patience and ended up doing something very similar to what RebekahsZ suggested: take my electric impact to it until it was pretty damn tight. I did put some red loctite on there though.


The backlash on the diff, which was slightly out of spec (see my video a few posts up) is not noticable when driving the car. My old diff clunked a lot when transitioning on and off throttle, this one is tight.


Filling up the diff through one of the axle holes (per http://inzane240.blogspot.com/2014/01/subie-r180-install.html ) sucks. The oil is so viscous that it didn't go down into the diff easily. I had to fill it bit by bit, stirring in between to make the oil sink. I wish I'd just put the diff level and used the intended fill hole instead. Might not have been any faster or less of a hassle, but at least I would've known for sure I ended up with the right level of oil in there now, instead of my approximation of 1L, what looked like pretty much completely full of oil.


I put about 1000 miles on the car since the install. The new diff definitely makes more noise than the old one. It's mostly a high-pitched whine and it's loudest at highway speeds. Not loud enough to bother me but noticeable for sure.


It's really nice to have two-wheel drive, and to not have to worry about breaking anything inside the diff in a one-wheel spin – which is what I think happened to my open diff. My car doesn't develop a lot of power (stock L24) but it does put down what it has a lot better now, there may be some confirmation bias here, but I can definitely feel a difference in how well it corners.

Pics and more detailed notes
Pic from a week earlier, trying to get a sense of how everything was layed out
Old diff out of the car
Car minus diff, note that I didn't drop the exhaust. I originally planned to but discovered that the rear-most exhaust hanger was welded on both sides. So instead, I just removed all other hangers from the exaust, disconnected it at the front, behind the collecter and reattached it loosely to the bottom-most mounting hole with a long, thin bolt so I could push it out of the way a bit. You can see how it's hanging from the picture.
I wouldn't recommend leaving the exhaust on the car unless you have access to a lift and a good trolley jack. To clear the exhaust with the front diff mount (see pic above, it comes out together with the diff) required rolling the diff clockwise about 30 degrees – far enough to feek like it would almost drop of the trolley, and yawing to the right while slowly lowering the trolley jack. And then to do the same in the inverse when installing the other diff. I put a piece of wood between the trolley jack and the diff to prevent it from sliding around to much or getting damaged.
Before removing the diff, I made a loop out of duct tape and used it to hang the drive shaft from the e-brake cable mount – I really didn't want to remove it from the car, and deal with the transmission oil coming out. After taking this pic I redid it a bit tighter. I put the loop through the U-joint at the tail end of the driveshaft to make sure it couldn't slide backwards and drop out of the tranny.
This worked really well and I'm pretty sure this approach is faster than removing the driveshaft for this job. You have to slide the diff forward to get the studs on the read cover to pop out of the rear diff mount, so the driveshaft is in the way for that, but there's plenty of room to pull the driveshaft up further and to push it to the side a bit, making this a non-issue. I even installed the new diff once with the much longer Subaru rear cover studs on it by accident and there was still enough room.
Also, the u-joints easily slide forward and out of the way and are resting on the control arms here. I was worried that they'd get in the way of the diff, but that wasn't a problem at all.
Shiny new diff waiting in a box
Old diff minus input flange
Input flange
I lost one of these half shaft bolts – I can still remember ordering exactly 8 and stopping myself from ordering any spare ones because they're pretty expensive. Next time, I'll order 9. 
Thankfully the shop has a hydraulic press, so I was able to use that to get one of the old bolts out of the old diff's stub axles and use that. It ain't pretty but it'll work.
New diff installed:
It was dark when I was done, but the Z drove home under its own power :)
Edited by rundwark
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  • 5 years later...

Old post but since someone just reached out over PM to ask me for advice about this very swap, I'll post here what I wrote them for others who find this post through search:



I ended up installing the Datsun flange on the Subaru diff with an impact, just ratcheted it on. Bad idea. You need to find a better way to do it so you don't end up screwing up the input bearing on your diff. Mine started whining more and more after a while, and while I can't be sure that the way I installed the input flange is the cause, it is the most likely cause. I would take the extra time to do it right next time.


How I would do this next time: get a long piece of L-channel steel from the hardware store, and drill two holes in it so you can bolt it to the input flange and hold it in place. With the diff on the ground and the L-channel bar as a means to stop the flange from spinning, use your torque wrench to tighten the nut to the exact torque spec (136 lb/ft).


You can probably make this easiest for yourself if you lay the diff on the ground with the front support, and putting the L-channel piece to your right when looking at the diff. Now all you need to do to stop the flange from spinning while tightening the nut is hold the diff on the ground (perhaps get a buddy to hold it down).

Edited by rundwark
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