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OBX Differential Inspection and Installation


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Were the heads of the bolts hitting the diff on accel or decel? If accel, then your gears are backwards. The side gears should move out under accel pushing the CV's away from the housing.

 

Jon, neither/both. I was getting static interference with the diff case while coasting. Was unable to spin the wheel by hand, because the bolt heads were contacting the side of the diff in their static position until I pried the flange out a bit...but I doubt that the circlip is properly engaged now.

 

That stub needs to be clipped in. If it's not it could slide out a bit and strip the splines off. Saw a pic of that from an EVO just recently.

 

What if that stub was never engaged even before I started this project? Maybe they're already stripped and that's why I have the slop? Why would I be able to feel slop on driver's side but not the passenger side? I know you said this not a good test, so you're saying it's normal to be able to feel the slop I'm describing on one side but not the other...? I guess I'm just missing something about how these gears engage, sorry.

 

Is there a stub axle maybe from a different car with the same (or slightly different but worn) spline count that would slip into the driver's side of an R200 but is slightly too short (groove cut 1/8" too close to the flange) to clip in without interfering with the case??

 

I really don't think this is an issue with the OBX unit itself (guess I should've started a new thread?), because it feels like I'm discovering a pre-existing issue that I didn't know was a problem. The only way the OBX could be at fault is if I got the preload way wrong, and therefore the washer stack isn't spreading the sun gears apart enough to locate the stub axles correctly...

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Jon, neither/both. I was getting static interference with the diff case while coasting. Was unable to spin the wheel by hand, because the bolt heads were contacting the side of the diff in their static position until I pried the flange out a bit...but I doubt that the circlip is properly engaged now.

If you can't properly install the axles without them hitting the case, I would consider that a manufacturing defect.

 

What if that stub was never engaged even before I started this project? Maybe they're already stripped and that's why I have the slop?

Stripped splines means that the splines are gone. You would know if this was the case.

 

Why would I be able to feel slop on driver's side but not the passenger side? I know you said this not a good test, so you're saying it's normal to be able to feel the slop I'm describing on one side but not the other...? I guess I'm just missing something about how these gears engage, sorry.

 

Is there a stub axle maybe from a different car with the same (or slightly different but worn) spline count that would slip into the driver's side of an R200 but is slightly too short (groove cut 1/8" too close to the flange) to clip in without interfering with the case??

 

I really don't think this is an issue with the OBX unit itself (guess I should've started a new thread?), because it feels like I'm discovering a pre-existing issue that I didn't know was a problem. The only way the OBX could be at fault is if I got the preload way wrong, and therefore the washer stack isn't spreading the sun gears apart enough to locate the stub axles correctly...

If you jack up one side in the rear and move the tire back and forth, you're potentially feeling any slack in the splines on the stub axle to companion flange that you're moving, wheel bearings, u-joints or cv joint slop before you even get to the diff. Once inside the diff you've got the splines on the stub shaft to the side gears, the side gears which move in and out normally as a regular function of this kind of diff, and all the lash between the side gears and the helicals, the helicals on one side and the other, the helicals from the opposite side and its side gear, the side gear to the splines on the stub shaft, the u-joints or cv joints, the splines to the companion flange and the wheel bearings on the far side. Because rocking the wheel back and forth will allow you to feel play in any of these parts, it's not a good test. When you jack up the opposite side, you're feeling the same thing from the other wheel, so you should get the same result. Maybe you have a brake dragging or something that makes it not move, but this test should feel the same from either side.

 

I think you're barking up the wrong tree with the "side shafts too short" idea. Much more likely that the OBX has the grooves for the circlips machined in the wrong place.

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  • 2 weeks later...

Just an update on my problem:

 

My mechanic removed the differential again and opened the OBX to find some shiny spots on the helical gears inside, but no damage. (Good thing I was clutching it on decel to prevent the grinding noise of the sun gears collapsing against each other.) Apparently when I rebuilt the OBX, I didn't put enough washers between the gears, so there was enough play inside the center to prevent the driver's side stub axle from engaging without the bolts interfering with the case (big gears could move 1/8-1/4"). When they had it on the lift, turning the driveshaft moved the axles visually moved in and out of the case!

 

Originally, I'd used the count the number of turns to fully clamped down, taking it apart over and over again to add/remove from the washer stack. I think what fouled me up was that the machining tolerances on the OBX were so loose. I couldn't really tell whether I had the correct preload, because the case didn't sit flush UNTIL I started clamping it down with the bolts which screwed up my count. I recommend a vise to anyone else who might have a similar experience with their OBX, because it needs to be fairly tight. (I wish I knew how to calculate the size of Jon's spacer idea to hold the gears apart enough not to grind on decel, but not large enough to keep the diff always locked up...and this spacer would be a different size for each OBX due to lack of uniform quality control.) Anyway, I had finally opted to leave out the two bigger washers and thought I finally got it right...but i was wrong. My mechanic added all but two washers (5 total, I think, including the two big washers in the center) and now I have no problems at all!

 

The diff is quiet and operates great: both wheels lock under straight line acceleration and no more burnouts when taking a turn; it just hooks! Also my driveline clunk is gone thanks to the R/T mount and poly mustache bar bushings I installed at the same time. Love it! I'll be testing the new LSD more thoroughly at "Icebreaker" Oregon's earliest autocross tomorrow afternoon (supposed to be nice and sunny). Even though I doubled the cost of OBX due to having to pay labor, I still spent less than a Quaife!

 

Thanks everyone for all your help!

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  • 2 weeks later...

Interesting observation. I have my car apart for various reasons so I measured the depth of the retainer ring inside both sides of the R200 with the OBX in it. I measured the depth from the outer oil seal to the snap-ring down inside the OBX splines. Amazingly, both sides are the same depth, and apparently at the proper depth for the longer of the two CV shafts! My side gears are still preloaded (no crushed washers) and are pushed against the outside of the case in their resting position, as they were when I built it a couple of years ago.

 

Now I don't quite understand how the "short" and "long" 280ZX CV halfshafts were both able to snap in and not grind anywhere?  It looks lke there are two shine rings on the shorter CV shaft where the oil seal rides.  One  probably  from when they were in a stock R200 and one from being in the OBX.  They are about 1/4" apart.  Incidentally it seems that most of the drive train slop is coming from the AXIAL and RADIAL play of the CV shafts when they are in the differential.    More investigation to follow.  

Edited by cygnusx1
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  • 3 weeks later...

240SX CVs [this is in my S14]

 

Go here:

 

http://rbryant.freeshell.org/obx_washers.htm

 

And scroll down to the "R200 Differential Only" section. It's a good write-up.

 

 

I have the rbryant kit installed in mine, I'm just running into some rubbing issues with the passenger side stub/pumpkin. I am going to take it out and fab a solid spacer for mine instead of washers.

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Problem with a spacer is that you can't really have any pre-load. Not a terrible thing. Alternatively, I was thinking about some sort of heavy duty coil spring...and I mean heavy.

 

If anyone can measure the "space" where the bellville washers sit (length and diameter of the pocket), I can look up a heavy duty die coil spring that might work.

Edited by cygnusx1
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Problem with a spacer is that you can't really have any pre-load. Not a terrible thing. Alternatively, I was thinking about some sort of heavy duty coil spring...and I mean heavy.

 

If anyone can measure the "space" where the bellville washers sit (length and diameter of the pocket), I can look up a heavy duty die coil spring that might work.

 

Mine is apart, I'll try to get some measurements when the new washers come in.

 

I'm assuming you want the length of the retainer set with the washer stack installed?

Edited by FlatBlack
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 Ideally, the size of the available space where the washers normally house.  With the dimensions, I can calculate the spring that would fit in there with the right amount of preload when compressed during the assembly.  There may not be enough room.  By knowing the space I can work with, I could explore the options.  Belleville washers are the natural choice for a tight space with little movement, but maybe we can get something else in there. 

Edited by cygnusx1
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Measured the washers and washer stacks with some Mitutoyo calipers this morning.

 

Let me know if you need any other dimensions, I'm going to measure the casing, planetaries, and sun gears later this morning.

 

**All sizes are "flat height" unless called out as 'ID' [inside Diameter] or 'OD' [Outside Diameter]**

 

Rbryant Washers: | Orientation | Size

Small ) 0.0865

Large ) 0.1125

Small/Small () 0.1720

Large/Large )( 0.2240

Small/Large () 0.1935

Full Rbryant Stack )()()()()( 0.8875

Full OBX Stack )()()()( 0.8840

Washer retainer 1 = 0.3975

Washer retainer 2 = 0.3925

ID Washer Retainer O 1.2620

ID Retainer "Lip" o 1.1390

OD Rbryant Small o 1.2375

OD Rbryant Large O 1.3935

 

OBX Washers:

Small ) 0.1080

Small/Small () 0.2240

Small/Small )( 0.2205

 

fff. Formatting fail. Here's a screencap of my excel file.

 

Washersizes.jpg

Edited by FlatBlack
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I need to dig through my photos to get a mental cutaway diagram. I can't remember what the center "star" looked like. I refer to the small splined part that sits with the Belleville washers, in between the two side gears.

 

 

 

 

EDIT: here it was

 

IMG_0216.jpg

 

 

 

 

I would need to know:

 

1) The "assembled length" in between the flats of those two "stars" when the diff is assembled.

 

2) The "ID" of the lip inside the "stars" that would dictate the maximum diameter of the possible spring.

Edited by cygnusx1
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I took pictures of all the measurements I took, I'll try to get them up today, but all the info you need is in that spreadsheet:

 

I would need to know:

 

1) The "assembled length" in between the flats of those two "stars" when the diff is assembled.

 

I measured the height of the stacks:

 

Full Rbryant Stack )()()()()( 0.8875

Full OBX Stack )()()()( 0.8840

 

2) The "ID" of the lip inside the "stars" that would dictate the maximum diameter of the possible spring.

 

Largest Diameter:

 

ID Washer Retainer O 1.2620

 

Smallest Diameter:

 

ID Retainer "Lip" o 1.1390

 

**edit for pictures:**

 

RBryant stack:

 

IMG_20120410_074309.jpg

 

OBX Stack:

 

IMG_20120410_075219.jpg

 

Greater ID of washer retainer [or star piece as you call it]

 

IMG_20120411_073653.jpg

 

Notice the variation from my measurement yesterday - I'd try to get something that would be right in the middle of the range between the greater ID and the lesser ID. [Maybe somewhere around 1.200?]

 

Also, JMort suggested leaving a washer in there to act as a secondary retainer for the spring if you went that route, I'm assuming to prevent the spring from accidentally coming off that retainer 'seat.'

Edited by FlatBlack
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My "Gen 2" RBRyant stack ended up looking like this:

 

()()()()

 

With a stack height of 0.7240"

 

The bolts had about 0.75-1.0 turns to full tight.

 

My threads were SUPER buggered on the lower case - I had to go buy some 50mm bolts after spending ~2 hours yesterday tapping out the holes.

 

Stock are 45mm M8x1.25, the RBryant bolts are 60mm M8x1.25. I ended up with 50mm bolts, which added 5 threads into the case. I'm using blue locktite as well.

Edited by FlatBlack
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  • 2 months later...

So I'm revisiting this whole circlip issue, since on decel even after upgrading to the latest Rbryant washer stack I still get grinding on decel, and the occasional clunk. In this case, I think my slack is resolved, but my passenger side-stub is rubbing on the diff.

 

I see above that Cygnus says the circlip locations are both the same depth, so I'm thinking I might try getting another set of stub axles and running two long ones. Anybody have a donor set I could purchase?

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  • 3 months later...

I'm looking into getting one of the obx units the only problem I'm having is I cant find the unit part number #10528. If someone could point me in the direction of who to buy from or where people are getting them I would be much abliged.

 

on Ebay motors, you get some choice !

 

http://motors.shop.ebay.com/i.html?_nkw=obx%20lsd&_dmpt=Motors_Car_Truck_Parts_Accessories&_fln=1&_fpos=Zip%20Code&_fspt=1&_sadis=2000&_ssov=1&_trksid=p4506.c0.m282&Make=Nissan

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