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Deep into yet another rear end clunk


wheelerz31

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Hello everyone, just wanted to start off by saying thank you to all who contribute to these posts. Your experience and advice have been very helpful in the past.

 

So I have done my research and homework on this so far and I know there are more than enough posts on this issue out there, but I have replaced/refurbished just about all of the usual suspects up to this point. I'm hoping to get some more ideas to help resolve this for myself and hopefully offer some help to anyone else who is in a similar situation. Basically the problem is similar to what many others have described as a clunk whenever I get on or off the throttle in any gear and more significant whenever I engage the clutch from a stand still. It is particularly noticeable when going from reverse to drive.

Here are the details and list of work done...

 

'87 300zx Turbo 5spd (w/LSD) 190k

Purchased about a year ago from a guy who owned it since 89. It had this clunk when I bought it.

Since then I have done the following:

-Replaced subframe bushings and mounting brackets

-replaced rear shocks with KYB

-replaced rear upper and lower spring insulators

-all polyurethane control arm and sway bar bushings

-new OEM diff mount

-PO had the prop shaft replaced about 5yrs ago (less than 20k miles on it)

- trans mount was replaced at the same time

-lastly, I had the diff rebuilt with all new bearings and seals. (front seal was shot, also had a distinct whine while coasting)

 

So I have a couple videos I took that show the amount of play in the rotation of the propshaft from the transmission side and the diff side before the car starts to move. Also, I don't think it's the ring and pinion backlash, because I asked the guy after he rebuilt it and he said it was fine, I think I remember him saying 0.007, which I know is on the high end of the spec, but its still far less than what I'm seeing in the driveshaft rotation.

https://www.youtube.com/watch?v=dIAvunygQwg

https://www.youtube.com/watch?v=BMs-a2yyK1g

https://www.youtube.com/watch?v=74b1X_2XtbY

 

I have seen other posts suggesting that there is the potential for slack in the spider gears or the cross pin shaft. I have to admit my understanding of the internal workings of a differential is limited so this is where I could really use some help from someone with more experience. From what I understand its normal for the spider gears to have some play in them, but I have also seen someone suggest that the gears can get worn on the outside of the carrier? The FSM has a spec and thrust washers to adjust the clearance between the "side gear" and diff case, but I'm not sure if that is the same thing and I also don't see where the LSD uses thrust washers at all or even shares the same spec. So again, I am a little outside of my knowledge base here.

 

One last thing just to put all the info on the table, after I got the car I topped off the diff fluid (because of the front seal it was about a half quart low) and after doing this I noticed a chatter when turning hard like into a parking space. To be honest it sounded more like it was coming from the tires, but the FSM says some chattering can be expected after a fluid change so I didn't think much of it and also knew I would be getting it rebuilt soon as well.

 

So that’s where I am, I know there are many possible causes of the clunk, but hopefully someone can offer some direction here and maybe this will also help others who have the same issue narrow it down for themselves.

 

Thanks again for all your help!

 

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How do the insides look?  New bearings and seals won't fix differential wear.  Maybe it's just worn out.  

 

A better gauge of "play" might be to have both wheels locked with the parking brake, and turning the propeller shaft by hand, with the transmission in neutral.  Your videos show movement, but don't show that the other stuff isn't moving.  When you turn the wheel, the propeller shaft could also be taking up play in the transmission, for example.

 

This is a 300ZX right?  So the typical S30 diff mount and/or loose strut mount issues won't apply.

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What the pinion does when you rock the car back and forth has very little to do with the backlash. LSDs will perform worse on your clutch test than open diffs as well. You haven't really tested anything with what you've done. Not that familiar with the Z31 so don't have any great ideas of what to check next, but I can tell you that your videos don't show you anything useful.

 

If you haven't already seen it, here is a write up I did on S30s with clunks:

http://forums.hybridz.org/topic/105207-the-dreaded-diff-clunk/

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Thanks for your replies,

yes I do realize the r200 tends to be a bit loose normally, but I still cringe when I let off the clutch too quick. Its just not a very pleasant driving experience. And yes I realize the vids dont provide any accurate test results, but they were really just to try and show visually what I am able to hear and feel. Additionally, at the very least I thought it would help show that the various U-Joints appear to still be tight.

 

Also, I probably should clarify on the videos:

Trans was in 1st, brake off, I was under the car rocking it. If you listen closely you can hear a clank as the car rocks forward and catches as the prop shaft twitches slightly.

 

Here I was shifting back and forth between 1st and reverse, engaging the clutch on and off. If anything I was just trying to show that the issue was not inside the transmission or front U-joints as you can see the prop shaft rotate before moving the car.

 

I took this one a while back, before the diff rebuild. I can't remember if the trans was in gear or not.

 

Jon:

I did read your post, multiple times, on the typical s30 issues, but unfortunately many of the issues you identified are not applicable or the equivalent parts were already replaced in my case. Like you said, im "into the weird stuff." I'm glad you chimed in though because I really thought the information you provided was very insightful. Outside of anything specific to the z31, is there anything you can suggest related just to the r200 LSD? At this point it seems like the LSD assembly is where I need to be focusing. I would like to say its more likely related to excessive wear due to low fluid than hard driving given what I know about the car's history, but I'm purely speculating.

 

 

 

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The lsd acts by moving the crosspin to squeeze the clutch packs. So it might move nearly as much as that totally screwed open diff that Miles posted and be totally fine. You can pull it apart and look for worn parts if you want, but the only real weak part of the 300ZXT diff is the clutches. If you upgraded the clutches with Savage42's parts, then I really doubt the LSD is to blame.

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How do the insides look?  New bearings and seals won't fix differential wear.  Maybe it's just worn out.  

 

This is the only look inside I got. This was after the rebuild. I didn't get to see it after it was taken apart.

 

https://onedrive.live.com/redir?resid=64A59902FF9B0098!1330&authkey=!AE69ytawVUj_SiE&ithint=folder%2c

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The lsd acts by moving the crosspin to squeeze the clutch packs. So it might move nearly as much as that totally screwed open diff that Miles posted and be totally fine. You can pull it apart and look for worn parts if you want, but the only real weak part of the 300ZXT diff is the clutches. If you upgraded the clutches with Savage42's parts, then I really doubt the LSD is to blame.

 

Would I be able to see that movement all the same if I removed the rear cover and repeated the tests from my video(s)? I have the FSM spec for wear limit on the friction components, but other than that I don't really know what to "look" for unless its as obvious as the video which your saying could be considered normal for an LSD. And I have not yet done the Savage42 upgrade to the clutches, although I have read about it. Looking at his latest post he says he still has some, would you recommend I contact him to purchase a set and see if that fixes it? Or if the cross pins themselves have worn away or the pressure ring has worn, that i assume is not fixable at this point without available parts.

One last thing to ask, the LSD should have a brekaway torque of (minimum) 18 ft-lbs so shouldnt there be at least that much pressure holding the cross pins against their respective pressure components? I suppose I should probably check that spec before jumping to any conclusions.

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It is cheapest and easiest to drive it till it breaks then replace it. You may be surprised at how long it lasts. I've owned a Datsun for 24 years and Ive had a rear end clunk for 24 years. Still haven't broken a diff. If it whines, tell your buddies you have a dog box and keep driving it.

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Don't forget the two "CV" joints (tripod-tripod or double  offset-birfield, whichever, the joints in the two back driveshafts), and the splines in the diff that couple to those shafts.  If you add up all of the movable joints and couplings on the way from transmission to wheel it's easy to see why everybody has some degree of clunk

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Would I be able to see that movement all the same if I removed the rear cover and repeated the tests from my video(s)? I have the FSM spec for wear limit on the friction components, but other than that I don't really know what to "look" for unless its as obvious as the video which your saying could be considered normal for an LSD. And I have not yet done the Savage42 upgrade to the clutches, although I have read about it. Looking at his latest post he says he still has some, would you recommend I contact him to purchase a set and see if that fixes it? Or if the cross pins themselves have worn away or the pressure ring has worn, that i assume is not fixable at this point without available parts.

One last thing to ask, the LSD should have a brekaway torque of (minimum) 18 ft-lbs so shouldnt there be at least that much pressure holding the cross pins against their respective pressure components? I suppose I should probably check that spec before jumping to any conclusions.

I would get the clutches. I think it's worth doing. Never seen or heard or worn xpins or pressure rings in a Nissan LSD. I bought mine with 200K on it and those parts weren't worn at all. The 18 ft lbs is just the breakaway pressure with no spreading of the pressure rings. What happens in that test is that you're forcing the xpins up the ramps, spreading the pressure rings against the clutch packs, so breakaway pressure when under load is comparatively huge.

 

If I had to guess, I'd say look at the transmission, but that really is a guess.

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It is cheapest and easiest to drive it till it breaks then replace it. You may be surprised at how long it lasts. I've owned a Datsun for 24 years and Ive had a rear end clunk for 24 years. Still haven't broken a diff. If it whines, tell your buddies you have a dog box and keep driving it.

 

Dog box huh? So I'm supposed to be ok with just having a Limited Slip Dachshund instead of a proper LSD?

Ok, sorry thats enough of that :)

 

 

Don't forget the two "CV" joints (tripod-tripod or double  offset-birfield, whichever, the joints in the two back driveshafts), and the splines in the diff that couple to those shafts.  If you add up all of the movable joints and couplings on the way from transmission to wheel it's easy to see why everybody has some degree of clunk

 

They are double offset-birfield in my case, and yes I do realize there will be some play there as well. I know the vids aren't an accurate way to test them, but you can see the half shafts rotate at the same rate as the tires. The splines inside the diff on the other hand could still be an issue as I cannot see inside while they rotate.

 

I'd be fine with some play, but its like getting hit with a sledge hammer when I take off sometimes. And there are pleanty of s30 owners at least who were able to fix their clunk by taking care of the mounting related issues, so some people obviously have a clunk-less diff. So it seems to me we should be able to do something to correct this or at the very least lessen the severity of the clunk.

 

So if I have rulled out anything external to the diff then that should just leave:

-cross pins or the pressure rings they press against

-clutch components

-output splines

-something between the spider gears and side gears?

 

Unless someone who has delt with this before can tell me which component to replace then it looks like I may have to just take the diff back to get dissasembled further to figure it out. I just would prefer if I had some more knowledge going in.

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I would get the clutches. I think it's worth doing. Never seen or heard or worn xpins or pressure rings in a Nissan LSD. I bought mine with 200K on it and those parts weren't worn at all. The 18 ft lbs is just the breakaway pressure with no spreading of the pressure rings. What happens in that test is that you're forcing the xpins up the ramps, spreading the pressure rings against the clutch packs, so breakaway pressure when under load is comparatively huge.

 

If I had to guess, I'd say look at the transmission, but that really is a guess.

 

Thanks for the advice, I guess I'll go ahead and get the clutches. At least that will give me a better excuse to have to take it appart again.

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Quick question on the clutches after reading the various posts on the subject.

Should I get 4 just to replace the spacers and just add shims to rebuild back to spec if necessary?

or

Shoud I get 6 and just assume I will need to replace the 2 existing disks as well?

 

And one other theory that crossed my mind as I was thinking thru this, what about the spring plates? Would it be possible that they might have fatigued due to excessive heat? Say, I don't know, as a result of low fluid level?

 

Thanks for your continued support!

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I hate to differ from Jon, but when I did my CLSD clutch upgrade, I wound up with too much preload mixing old and new clutches. When i bolted it all up with mixed clutches, the diff was a spool. Savage42's clutches are just a touch thinner than the original and I wound up with 45# preload just by installing 6 new clutches without any shims. I built one before with shims to preload to 65#; I wouldn't run that much preload again-that diff was to TIGHT and really "bang-bang"-ed on low speed turns. No more shims for me!

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I hate to differ from Jon, but when I did my CLSD clutch upgrade, I wound up with too much preload mixing old and new clutches. When i bolted it all up with mixed clutches, the diff was a spool. Savage42's clutches are just a touch thinner than the original and I wound up with 45# preload just by installing 6 new clutches without any shims. I built one before with shims to preload to 65#; I wouldn't run that much preload again-that diff was to TIGHT and really "bang-bang"-ed on low speed turns. No more shims for me!

 

Thanks for the reference, but just to clairify...

your saying you REPLACED the original 2 clutches with 6 new ones got 45# preload without shims? But the first time you tried just adding 4 new clutches WITH the originals and ended up with even more preload?

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