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OBX Differential Inspection and Installation

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Oh man. Totally missing a few key points. Go back to the first post, and click on the links Trumpet posted in the original post.

 

You DO NOT want the washer stack getting slammed into under acceleration. The differential motion happens EITHER WAY.

 

The Subaru front diff is located beneath the initial gearset. It is not attached to the gearset. The front axles have to turn a certain way to propel the car forward, obviously.

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Oh man. Totally missing a few key points. Go back to the first post, and click on the links Trumpet posted in the original post.

 

You DO NOT want the washer stack getting slammed into under acceleration. The differential motion happens EITHER WAY.

 

The Subaru front diff is located beneath the initial gearset. It is not attached to the gearset. The front axles have to turn a certain way to propel the car forward, obviously.

 

Yes, I was very confused.

 

I understand what you are saying now, but it still isn't clear to me which way my gears should go in.

 

Also, setting the backlash correctly has me a little scared to attempt te swap on my own. I don't want to ruin my transmission.

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I understand what you are saying now, but it still isn't clear to me which way my gears should go in.

 

The front diff's ring gear is facing the same direction [and has the same gear cut] as both the Subie and Datsun rear diffs.

 

The front and rear diffs in a Subaru are going to have the same forces [directionally] on the carrier under acceleration. This means you need to flip the gears like we do for our RWD Z cars. take a look at all of the pictures again, and it should make sense.

Edited by flatblack280

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Woah... Sorry guys. I guess I didn't realize I had killed the thread, but don't you think this could be used as a good resource for athoer people who want to swap in OBX diffs to their cars?

 

Subaru front differentials not apply :D

 

Okay, I dropped my spare 3.54 R200 and modified OBX carrier off at a machine shop this morning, with the ring gear bolt "sleeves" and these torque specs [From the 78 FSM, page PD-25]:

 

Ring gear to drive pinion backlash: 0.13-0.18 (mm) [0.0051-0.0071 inches]

 

Ring gear bolt [use locktite]: 6.0-7.0 (kg-m) [43-51 ft-lbs]

 

Carrier bearing cap bolt: 9.0-10.0 (kg-m) [65-72 ft-lbs]

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So does anyone have finished picture with the obx installed and/or videos of the obx installed(like a burnout)?

 

Um. It'll just look like an R200?

 

I have a picture of my car with a snapped U-Joint when i took it to the track after installing the OBX. Can't find it at the moment though.

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Just finished installing the OBX unit on my R200, torqued everything to spec and now backlash is .002 only. It turns smootly but i'm concerned about the smaller lash. Is it ok to run it like that or do i have to adjust it? If so how do i know what size spacer to use to adjust it? Thanks

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Just finished installing the OBX unit on my R200, torqued everything to spec and now backlash is .002 only. It turns smootly but i'm concerned about the smaller lash. Is it ok to run it like that or do i have to adjust it? If so how do i know what size spacer to use to adjust it? Thanks

 

I had mine adjusted at a shop, unfortunately I don't know what to tell you.

 

Here is a fantastic write-up by a Dirty Impreza member [who also owns an S30] about the defects/manufacturing defects that are so common in our OBS units.

 

http://www.dirtyimpreza.com/forums/showthread.php?p=231318#post231318

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.002 is not enough lash. You'll need to reshim the ring gear to the left to open it up. Take some shims to your local gear shop and see if there is anything close in outer diameter, then buy a shim kit for that model car.

 

While you're at it, you can shim in some more preload on the carrier bearings. Get the backlash correct and then add some shims equally to each side so that the carrier doesn't just fall into the housing. The tighter the carrier is the better, because that preload on those bearings keeps the ring gear in alignment with the pinion.

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Thank you for the help. I think my carrier bearing well preloaded since it was a pretty snug fit to get the OBX unit in. I was just wondering if i just take measurements of the stock shims and the go purchase the next step up from that measurement on the left shim. Will the differance between the two move it just that much to the left? Say mine is .255 and the next one up is .260, will that open the backlash .005? Thanks again, you guys are great help! ;)

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Iinstalled an OBX into my Datsun R200 diff. The washers failed after only 4 hours of track testing. They were essentially flattened. We were not aware of the reversed gear trick (just found this thread today), and replaced the washers with a heavy coil spring. We have only driven it on the street a few kilometres since, but it seems to work. Will see if it lasts any longer than the original washers...

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All,

 

I just wanted to add a note that I have been shipping kits with two different diameter washers for a few months now with very good success.

 

The big problem I have had with the R200 OBX LSD was that there is a large space between the center washer retainers which can allow for the washers to slip outside of it and then misalign.

 

Picture this: [)()()()(] If the () washers in the center aren't surrounded by the edges of the retainer and there is space for them to move then they will....

 

The solution is this:

 

[)()()(]

 

 

I ship 4 larger washers that go in the center so that they keep everything aligned. The larger washers are actually retained by the diff case its self instead of the washer retainers. They also cup around the smaller washers so that they hold the smaller washers in place. I took care to make sure that they are very close to the same spring rate as the smaller washers. (because they are larger they have to be thicker too)

 

I have been shipping 4 larger washers and 7 smaller washers. This is because the machining hasn't been that consistent and some of the LSDs require more washers. I don't expect people to require all of the washers and in most cases only 2 of the larger ones will be needed but on some of the newer units they seem to be a deeper pocket where all 4 larger washers can be used. Originally the first R200 diffs only needed about a 14mm stack of washers and I have recently heard of them being ~20mm (based on customer feedback) so that is the reason that I can't just give people a one size fits all configuration. :(

 

 

The larger center washers should only be used if they are sufficiently spaced by the outside washers to where they won't ever touch the normal washer retainers. If they compress and touch the retainers then the small washers will be loose, rattle, and not do their job.

 

If anyone has feedback on the latest kits it would be great to hear it here. I am also interested to see some pictures of your installs.

 

Thanks,

 

Rich

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I just installed the updated version of rbryant's kit and here are some pics. The gears have been reversed.

Hardware on the top is what came in the unit, hardware on the bottom is the rbryant bolt/washer kit.

 

post-4314-013276200 1291083503_thumb.jpg

 

What I found is that if I install the "new" stack )()()(, the larger washer rest on the retainer, so I stacked them like this )(()())(.

 

post-4314-067480500 1291085023_thumb.jpg

 

You can see how far the retainer sticks up with this configuration before I put the cap on. Does it look acceptable?

 

post-4314-098434400 1291085253_thumb.jpg

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So I just took the Z out for a nice Sunday morning run and heard some bad noises. I installed obx unit described above in a rebuilt r200 3.9. Upon acceleration, everything is good, but when I let off the gas I hear some nasty grinding/rattling noises coming from the differential. Ideas? Help?!

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Anyone consider just putting a solid thick spacer in there to take up the slack? Lots of other helicals aren't preloaded at all and taking the slack out would probably eliminate all the cracking/popping noises under decel. It sounds like once the springs wear down you don't have any preload anyway.

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So I just took the Z out for a nice Sunday morning run and heard some bad noises. I installed obx unit described above in a rebuilt r200 3.9. Upon acceleration, everything is good, but when I let off the gas I hear some nasty grinding/rattling noises coming from the differential. Ideas? Help?!

 

I'm using a different LSD unit in my car but I had a very similar symptom. I had a shop install my LSD and it turned out to that the pinion nut was not torqued tight enough. This allowed the flange bolted to the driveshaft to spin at a different rate from the differential on decell and ended up grinding the splines on the flange off quite a bit before I made it back home. Pinion gear splines were still fine, but had to replace the flange. Not a hard fix, but definitely not fun.

Edited by h4nsm0l3m4n

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I'm using a different LSD unit in my car but I had a very similar symptom. I had a shop install my LSD and it turned out to that the pinion nut was not torqued tight enough. This allowed the flange bolted to the driveshaft to spin at a different rate from the differential on decell and ended up grinding the splines on the flange off quite a bit before I made it back home. Pinion gear splines were still fine, but had to replace the flange. Not a hard fix, but definitely not fun.

 

I dropped the diff out today and nothing is obvious, the pinion flange seems to be good and tight. When I look through the center of the diff, the washers still look ok. Not sure what's going on, so I am going to run it by East Coast Gear Supply in Raleigh to see what they say. I'm also going to see if they have a solution to the washers, as in a solid spacer what JMortensen is talking about.

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