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OBX Differential Inspection and Installation

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cnunes    11

Sorry to resurrect this old thread, but I'm having some issues installing the OBX LSD into my '75 280z's stock open R200.

 

I rebuilt the OBX using the instructions posted here with rbryant's deluxe kit. I did not have to swap gears but I did flip over the top gear to ensure BOTH c-clip grooves were toward the center/inside of the case. Sent it with my R200 diff to a reputable shop that even specializes in Z cars. The owner has installed many other carriers including Quaifes but not the OBX. He installed fresh carrier bearings and c-clips from Nissan, but he tells me that although one of my stock stub axles snaps into the OBX just fine, the other side was too short to engage, but the 300zxt CV shaft snaps right in.

 

First of all, I've searched and searched but I've never heard of the stock 280z stub axles not fitting the OBX. Secondly, both sun gears should be identical so I couldn't have them reversed. Thirdly, why do 300zx CV shafts fit fine? I thought they had similar tolerances, but is the c-clip groove on those closer to the tip??

 

I was prepared for the easy task of rebuilding the OBX, but I wasn't prepared for this complication...anybody got any ideas? I feel like my mechanic and I may be missing something simple...and the first autocross of the season is coming up in less than 30 days! Please help!

 

-Chris

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Tank    11

Just to rule out the obvious, I would double check the part number of the OBX unit to make sure it is correct. This is the first I have heard of this problem, I know mine lock in tight with the stock 280zx stubs. But with the halfshafts bolted to them, it scrapes the housing upon deceleration because of the play in the worm gears. The sun gears are identical but have to be oriented opposite of each other for the c clip grooves which it sounds like you did. Does you mechanic accidentally have the stubs mixed up? Is the groove clear and straight on the stock 280z stubs? I know these are obvious questions but possibly overlooked?

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cnunes    11

Tank, I searched by part number before ordering and I *think* I recall verifying the part number on the box when it arrived, but I'll have to wait 'til Monday to check the part number on the actual unit itself to be sure...

 

And Jon, I was not aware of that slight 3/8" difference in length of the stub axles. I knew the halfshaft lengths were different, but I personally thought the stubs were symmetrical. Not sure if my mechanic is aware of this difference, but I think that might explain our problem. I'll be crossing my fingers until Monday!

 

I really appreciate both of you for chiming in; I've been wracking my head trying to figure this out!

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Leon    35
And Jon, I was not aware of that slight 3/8" difference in length of the stub axles. I knew the halfshaft lengths were different, but I personally thought the stubs were symmetrical. Not sure if my mechanic is aware of this difference, but I think that might explain our problem. I'll be crossing my fingers until Monday!

 

You've got it backwards, all half-shafts are equal-lengths. It's the stubs which snap into the differential that are different lengths. Did this solve the issue?

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John Scott    0

Image of the stubs easy to see the difference

OBX008.jpg

For what ever its worth my 2009 OBX install, after correcting the gear direction, crappy fasteners, using McMaster washers etc is still quieter than the stock diff ( no thumps, bumps, or gear noise) no flaws or failures to date.

Edited by John Scott

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cnunes    11

Swapping the stubs did the trick...well, sort of. It solved the passenger side issue (shop was saying stub was too short to reach the circlip groove in the diff) but now the driver's side stub (shorter one) is engaged way too far into the diff (opposite problem).

 

Test drive was cut short by loud clunking as the heads of the halfshaft flange bolts contacted the differential case. I pried the flange out a bit and it popped into what looks like the correct position with plenty of clearance between the flange and the diff, but I don't think it's engaged with the circlip anymore, because when we noticed this problem before installation, popping that stub out to where we thought it should be left it loose enough to easily withdraw by hand.

 

I don't think this is a problem with the OBX itself, because I seem to recall a bit of play on that side as we were removing that halfshaft and I didn't check the stub for looseness after disassembly, because I thought the play might've been in the U-joints on that side...but they're solid so now I'm wondering if this was a pre-existing problem.

 

Furthermore, after popping that stub away from the diff, I now get no catch when turning the wheel by hand, BUT while doing so, I noticed some rotational play coming from WITHIN the diff; I can hear the gears clunk as I rotate the wheel forward and back as if there's play in the splines (always felt this clunk while letting off clutch before the LSD install)...is it possible the driver's side stub was replaced with the wrong part long ago and has been wrong all along!? This would explain both issues...

 

I can't even test the OBX, because I'm afraid to drive the car hard with all these potential issues...I was so excited for donuts.

 

Anyone have a hypothesis? This install isn't supposed to be this complicated!

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JMortensen    235

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.

 

I really think someone needs to make some solid spacers for these things. Seems like you guys are having a ***** of a time with the washers (compressing washers on decel is what allows the stub to move inwards).

 

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.

 

Don't attempt to figure out slop in the diff issues by turning the wheels. Not an accurate test of anything. There is slop between the side gear and all of the helicals that has to be there, and even if everything is perfect there will be a good amount of lash in there.

Edited by JMortensen

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cnunes    11
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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JMortensen    235

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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cnunes    11

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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cygnusx1    12

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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Tank    11

At it again...

 

Took it apart today, and flipped the gears. Just waiting on the RBryant kit to get here, then I can ditch the stupid welded R200.

 

Oh, and one of the bolt came pre-stripped :unamused:

 

IMG_20120403_175859.jpg

 

IMG_20120403_175910.jpg

 

 

What axles are you using? Also, will you post your washer stack orientation? Thanks.

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Tank    11

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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cygnusx1    12

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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FlatBlack    17

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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cygnusx1    12

 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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FlatBlack    17

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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cygnusx1    12

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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