Need R200 Differential Advice

[inline6]

I damaged an R180 differential years ago, and it had the same symptoms you are describing.  When I would try to turn it from the front flange, it was harder to get turning initially than my good R180.  And, I could feel the "bumpiness" as I rotated it, though it was slight.  It would lessen if I rotated it quickly.  Rotate slow, and it would be very noticeable and even hang up a bit.  This behavior wasn't present on the good diff.  

If I recall correctly, I damaged it by replacing the front seal (behind the front flange) and then torqueing the pinion nut to what felt like 100+ ft lbs... because I didn't have a torque wrench, or some other stupid reason.  I knew nothing about the importance of setting the correct preload on the pinion bearings.  It's been many years now, so I don't recall how long it took before the noise showed up and I pulled the diff out to examine.  It exhibited very much what you describe.  I ended up selling it the way it was - it had value because of the unique 3.7 ratio that it was.  

At any time in your possession, did the front pinion nut come off and get put back on?

[Patcon]

I understand.

The three shops I recommended have very good reputations

[ckurtz2]

@inline6Oh boy, what a mistake to make! But that's why I want to save this one, the CLSD combined with the 3.7 is just a solid setup. Especially because I have it matched with the 280zx close ratio 5 speed. It's fun in the twisties haha.

Anyway, measured ring gear run out because I can with nothing apart. The manual provided says less than 002 in. Mine measures exactly at 002 from the lowest point. Maybe even possibly a quarter of a thou more. My gauge setup though was only around $45 so I can't imagine its that accurate. What did ur runout measure?

Ok so I rotated it slowly. I truly can not make out any noticeable bumpiness, it does seem pretty smooth. However, about 4/5 of the rotation is free and smooth and about 1/5 is noticeably harder to spin. I did it over multiple times and kept finding that small binding point. So, another clue! 

 

[ckurtz2]

Pulled the ring and carrier. both side bearings rolled smoothly and seemed to be in perfect condition. The races looked shiny and felt buttery smooth. Rotated pinion and it felt smooth with no clicking or other oddities besides that slight binding point. Looked closer and the idler/pilot bearing @inline6 mentioned indeed is defective. About 1/3 of the rollers on that bearing were not spinning/rolling but just sliding across the bearing surface. I still can't justify why backlash went to zero from this...

Bit the bullet and called a very well-known differential shop in PHX. They said they could take care of it and would look it over and give me a quote. Judging by the problems some forum members have been having rebuilding diffs, I decided I don't think I want to go that route. If I had more time, I would as it does look like a great learning experience. I will let you all know what I am quoted, and what the failure actually was. 

[inline6]

When the pilot bearing goes, the preload on the other bearings is no longer what it should be.  Things are no longer locked in place. 

Note that the sleeve in this picture seats against the back of the pilot bearing:

If the pilot bearing goes bad, I believe it introduces looseness, or another way of saying it: the bearing allows longitudinal movement after it is damaged.  That longitudinal movement causes the rest of the stack of components on the pinion shaft to no longer be locked in place.  Think of it this way: the pinion gear/shaft is engaging with the crown gear, which resists rotation because of tires on the ground.  I think that when the stack of parts bearings and spacers become no longer "locked" in place because of the looseness introduced by the bad pilot bearing, the pinion gear can literally pull itself closer toward the crown gear.  

When everything is locked in place with tight bearings and correct torque on the pinion nut, the pinion gear is locked in position.  It can't move forward or backward longitudinally.  When the pilot bearing fails, the the pilot bearing inner race which is up against the sleeve in the picture above is no longer locked in place.  It can shift longitudinally.  This introduces looseness in the rest of the stack of components on the pinion gear. 

Then the pinion gear, acting on the crown gear, because of the way it is cut, literally pulls itself toward the crown gear due to the force coming from the engine/driveline.  The looseness in the "stack" allows the pinion/shaft to pull itself - to slide within the front and rear pinion bearings (these are only a press fit).  After the pinion gear/shaft has moved, then the pinion to crown gear relationship has gone all to hell vs. what it should be.  And lots of noise ensues.

Anyway, that is my attempt to describe what I think can happen.  

I am hopeful that replacing the pinion bearing and setting preload properly is all you will have to do to fix your issue.

Edited January 25 by inline6

[AK260]

So very sorry to hear this happened! It’s a shame about the garage not thinking but nothing can reverse that now.

When reading this thread my immediate thought was: under prolonged hard acceleration, what little oil there was sloshed to the back of the diff and starved the pilot bearing / pinion shaft.

I have to say what Mr @inline6 is saying is the most likely cause IMHO! Good luck and keep us posted. I do hope it’s just as simple as the bearings - nothing else in your photos seems to be obviously damaged and these diffs are pretty hardy / well engineered.

[ckurtz2]

     Amazing description @inline6. Makes absolute sense to me, I bet you nailed it right on the money then. Everything carrier/ring gear side looked super solid to me, I couldn't even find a micro scratch scratch on any of the bearing surfaces. Yes, definitely an oil starvation issue. Hopefully the few miles I had to drive with no backlash and loud wine didn't ruin my gears! @AK260 I agree! I kinda am sad I am not doing this job by myself, but I could use the time saved. I will be checking the gear contact pattern myself though before sealing the cover, so as not to get jipped by another shop:). 

[ckurtz2]

Shop fixed the differential. The pinion bearings failed as suspected. Shop told me gears were unfortunately toast too (something about overheating, as well as too worn). So they put new bearings/seals/ring and pinion in and repainted the housing. Does anyone have a 3.7 or 3.9 differential they are willing to part with? Unfortunately, they couldn't find the correct gear set and installed the regular 3.545 ratio. They said if I find the proper set they would replace it for free though. I really would like the 3.7 or 3.9 ratio, as that was my bread and butter behind the differential. Please let me know, maybe a deal could be made.

[inline6]

17 hours ago, ckurtz2 said:

Shop fixed the differential. The pinion bearings failed as suspected. Shop told me gears were unfortunately toast too (something about overheating, as well as too worn). So they put new bearings/seals/ring and pinion in and repainted the housing. Does anyone have a 3.7 or 3.9 differential they are willing to part with? Unfortunately, they couldn't find the correct gear set and installed the regular 3.545 ratio. They said if I find the proper set they would replace it for free though. I really would like the 3.7 or 3.9 ratio, as that was my bread and butter behind the differential. Please let me know, maybe a deal could be made.

Did they swap to the 3.545 and tell you after the fact when the payment was due?  I would be upset if that happened.  I would have liked to attempt to source a gear set before having them assemble it.

[Zed Head]

Search your local Craigslist and Facebook Marketplace.  Probably have to buy a complete used diff.  Maybe even a beat up parts car.

[ckurtz2]

@inline6 no they did not. I was very frustrated with it and talked with the owner. Honestly, doing that was my plan B, so its not a huge issue if I can find the proper gears for plan A. 

@Zed Head I have come to that conclusion too. I have found several 3.7 R200 open diffs online. The problem is that some ring gear bolts in the 300zx had 12mm bolts, and some had 10mm. I need the 12mm. I can't come to any conclusion online as to which year and trim had the 12mm ones. Unfortunately, all of the eBay differentials are sealed, so they can't check for me either.

[Zed Head]

The bolt size problem is well-discussed on other forums.  In principle, the clamping force of the bolts does not depend on the space around them, and the ring gear should never move on the carrier once clamped down.  But people still use sleeves to take up the extra space.

I can't remember which has which but it sounds like you're saying that your carrier has 12mm holes.  By the words in the various discussions you should be able to use a ring gear with 10mm bolts.

Put these words in to Google and a bunch of Hybridz threads will come up.  You'll find links to sleeves/spacers if you want to go that route.  The diff shop might have some opinions too, I'd guess.

site:hybridz.org 10mm 12mm differential carrier