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nmehdikh

New diff. New Ujoints. New bushings. Rear end clunks. Oh joy.

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I have gone down the rabit hole of rebuilding my suspension and driveline. Car did not have any noises like this before I started. I installed a Subaru R180 out of a 2011 STI, with torsen LSD. Sitting on jackstands, going through the gears, there was massive clunking and banging coming from the rear end. Very apparent when going on and off the clutch. Checked to make sure everything was tight, no luck. Removed the differential, and took it to a specialty shop to check it out. The differential has a clean bill of health. If you hold the differential input, and try to turn the output, there is a bit of play. Differential guys said this is normal.

Put the differential back in, hooked up the driveshaft only, no axles. Sitting on jack stands, going through the gears, clunking noises GREATLY reduced. Like down to 5% what it was before. You really have to listen for it. Hooked up passenger side, clunk is immediately back. Wheel off, clunk is gone. Wheel on, clunk is there. Wheel is not loose and has no play. Got annoyed and didn't bother testing the drivers side just yet.

Things I've done before the clunk appeared:
1) While welding on coilovers to the rear spindles, I noticed the stub axle had some play back and forth. Further examination lead me to fine the peened nut had come loose. I replaced both sides with a new locknut from MSA, torqued the spec (close to 200 ftlbs) and the play was completely gone. Did not remove the stub axle or mess with the bearings in this process. Just took the nut off and put a new one on.

2) All 4 rear axle u-joints were replaced about a year ago. Car hasn't gotten many miles on it since, but they don't have any play.

3) New T3 suspension installed, including new mustache bar and drop mounts. I've also installed a Ron Tyler diff mount about 2 years ago on my old R180. The diff is in there solid, and there isn't any play when hearing the noise. I've tried jacking up the diff at different points and it doesn't budge.

Thoughts / Ideas
1) I'm leaning towards maybe a driveshaft u-joint. With just the driveshaft hooked up, the noise is faintly there. With the added rotational mass of the wheel, it might be exasperating the problem.

2) My dad is convinced its a rear wheel bearing issue. I'm not buying it as I'd expect a consistent grinding/whirring noise. Not sudden chassis shaking rumbles.

3) Poorly fit splines somewhere:

    a) Differential input : factory subaru piece, just drilled to match the 240z driveshaft. Splines went it tight with no slop.
    b) Differetnail output : got output flanges from silverminemotors , they went in tight with a rubber mallet. Didn't appear to have any play
    c) Stub axles spines are worn out. I can't feel any play moving the two flanges relative to each other, but maybe the force from the engine is enough to cause some play.

Any ideas on what the hell I'm chasing down here? 

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Were the jack stands under the suspension or under the body?  Were the wheels hanging?  Might be that you just had too much angle on the u-joints and they were binding.  Put the stands under the control arms so the suspensions is at ride height distance and try again.

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The jackstands are under the body, not on the suspension. Before I had the differential out to take to the shop, I put the car down and went up and down the driveway. Still clunked hard. Also, if they were binding, I'd feel it while rotating the wheel by hand correct? I've rotated the wheels multiple times and there is no obvious spot its hitting/binding either. The clunk can instantly be reproduced by engaging the clutch, it doesn't even have to go a full revolution.

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Not clear if  you're getting clunks when you shift gears or when you apply power or just when the transmission is turning.  Add some detail to what the "clunk" is and when, exactly, it happens.

 

The simple test is to grab each side of the possible clunking parts and look for play.  The wheel flanges, the pinion shaft and output flanges, the driveshaft in the transmission, etc.  

 

If you apply the parking brake you can load the drivetrain with the wheels hanging.  Might make any play easier to see.   I'd still move the stands under the control arms.

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People have found clunks from odd things like loose studs in the diff cover.  And when you apply power the diff twists and the mustache bar ends, out away from the diff, can move if they're loose.  Other stuff to check.  

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On the topic of ujoint binding, how much angle is too much angle? Now that I think about it, the coilovers haven't been adjusted yet, so the car is sitting relatively high (probably 2-3 inches higher than stock). So even when the car was on the ground and rolling, maybe that was still too much angle for the ujoints causing it to bind?

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What side axles are you using with the STi R180; and are you sure they're properly seated in the LSD?

 

Also, it sounds as though you've driven at least a few miles on the rebuilt half-shafts...so you're reasonably sure you can rule them out as source of the noise?

 

I had an issue with worn inner bushings on my rear LCAs causing a rattle/clunk; but that was only under heavy load.  Sounds like your issue is happening under any loading condition.  It still may be worth checking if you haven't already done so.

 

Finally, if your car is sitting 2-3" higher than stock, that's really high.  Definitely worth lowering it closer to your intended ride height and see if the problem persists.

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Posted (edited)

1) I'm using silverminemotors side axles. I'm not sure how to check if they are properly seated in the LSD. I tapped them in with a rubber mallet until they didn't seem like they were going in any further. I'll get photos in the next couple days

https://www.silverminemotors.com/datsun/datsun-240z/drivetrain-26/lsd-r180-sti-out-output-flange-conversion-stub-axels

Not the best photo, but its what I have on my phone off hand. Looks like the side axle is all the way in to me.
image.png.b18022afdc895e4317129027828e256f.png

Compared to what "moelk" posted on classiczcars a couple years back:
Bad
IMG_9708.JPG
Good
IMG_9709.JPG

2) yes, halfshafts have been driven on, which is why I'm ruling them out. 

3) LCAs were swaped with T3 arms and have new bushings. Along with the rest of the suspension (new coilovers etc)

4) I plan on lowering it for the next set of testing.

Edited by nmehdikh

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Posted (edited)
1 hour ago, nmehdikh said:

1) I'm using silverminemotors side axles. I'm not sure how to check if they are properly seated in the LSD. I tapped them in with a rubber mallet until they didn't seem like they were going in any further.

 

If they are seated you won't be able to get them out without a prying tool.  If they're not seated they'll pull out by hand.  Did you use/place/set the circlip in the LSD?  It fits down the hole and locks in to the groove on the axle when you tap the axle in to the hole.

 

 

image.png.37dca26f4e6adbde75a276db4833cffa.png

Edited by NewZed

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I didn't place in a circlip, there was already one in there. However, the axle did not slide in very easily, so I wouldn't expect to slide them out by hand, even if they weren't seated. I had to use a rubber mallet to get them in, and I don't know if I get them all the way in. I can try prying them out and see if I get any movement. Or trying to hit them in further.

Do we have a measurements of how far the flange should be from the diff body? I could measure it fairly easily.

If they weren't fully seated, do you think they would be causing the source of the noise? Looking at pictures of the LSD taken apart, looks like the axles play no part in the diff's operation. Like you'd be able spin the diff without any axles installed and it should operate normally

image.png.c1deec051bdc0b283f39350c1a377a2d.png

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Posted (edited)

Can't really say.  Most of us have spent time under our cars twisting the flanges and the driveshaft and lifting at various points.  If you get the halfshafts off lay under the diff and grab both flanges.  Twist them back and forth and see if you have play.  Do the same with the driveshaft and a halfshaft.

 

Most of these problems end with an ahah moment where you find the moving part.  But there are a lot possible clunk sources.  I just solved a clunk problem in my truck.  It was a large piece of metal, a shackle, that I had stored behind the seat.  Every time I went over a left hand turn with a  bump it sounded like I had a loose shock absorber or a broken spring.  I spent weeks looking underneath for the loose part but the problem was inside.  I just had to wrap the chunk of steel in a towel to fix the problem.

 

People with Z's often find their clunk in the storage bins behind the seats.

Edited by NewZed

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