Differential on it's way out??

[jmortensen]

Regarding the U joints, there's a GSP (Chinese) CV half shaft available for this car from Advance. I'm not thrilled about Chinese manufacture, but it carries a lifetime warranty and costs only $70 per side. Hopefully that would be a cure for the common clunk. Any thoughts?

I wouldn't go buying $140 worth of halfshafts right off the bat. I'd take them out and feel the U-joints first. There are only 8 bolts on each halfshaft, and 4 on the driveshaft. Some people can check the U-joints with the shaft installed, I never could. With them out though you just grab the shaft in the middle and the flange on the far end of the U/J and wiggle them back and forth and feel for slop. Any slop = bad U/J. Factory Nissan joints seem to be better than the replacements you can buy, so if you don't need them I wouldn't buy them.

My first suspect for a clunk would be front diff mount/strap. The stock mount goes underneath the diff so when the nose lifts it tries to pull the mount apart, which is a really bad idea. I think this is possibly the worst aspect of the Z's design (could be a tie with the way the back of the rear suspension is hung from the two uprights back there). There are many different solutions to a bad front mount from replacing the mount and strap with factory new parts to making your own mount. I like Ron Tyler's mount, which I think can still be purchased from Roostmonkey on hybridz.org. http://forums.hybridz.org/showthread.php?t=127993 It goes over the diff, so when the front of the diff lifts up it compresses into the mount. There is also the "clamshell" design which can be fabricated quite easily with some materials from the hardware store: http://album.hybridz.org/showphoto.php?photo=2501

Second suspect would be mustache bar bushings. Third I'd probably go u/joints, 4th might be worn splines on the stub axles, which I think is more common than people realize. I think there are more possibilities than that, but those are the ones coming to me right off the top of my head.

Edited August 25, 2009 by jmortensen

[FastWoman]

Mitchell, I went with the specification the auto parts store looked up -- pretty sure it was 75/90.

Jon, I had the car's back wheels parked on ramps while I was working in the fuel pump area -- not jack stands, but ramps, with the weight of the car supported via the tires. I reached up, grabbed the half shafts, and wiggled. I didn't measure the play, but I'm guessing there might have been even 1/4 of slop when twisting back and forth -- at least 1/8", I'd say. I'm sure much of it was from the U-joints, but also the splines -- and probably even some in the differential. I probably should have taken more time seeing what slop came from where, but I was being attacked by a squadron of mosquitos and was in a big hurry to get the car done. Anyway, I'm pretty confident the half shafts need replacing. I don't know about the bushings.

I remember looking at the strap over the front differential mount and thinking, "how odd." Nothing seemed out of place, though. The bushings on the moustache bar looked fine. I should have spent more time diagnosing but didn't. Probably next weekend's job.

[jmortensen]

Jon, I had the car's back wheels parked on ramps while I was working in the fuel pump area -- not jack stands, but ramps, with the weight of the car supported via the tires. I reached up, grabbed the half shafts, and wiggled. I didn't measure the play, but I'm guessing there might have been even 1/4 of slop when twisting back and forth -- at least 1/8", I'd say. I'm sure much of it was from the U-joints, but also the splines -- and probably even some in the differential. I probably should have taken more time seeing what slop came from where, but I was being attacked by a squadron of mosquitos and was in a big hurry to get the car done. Anyway, I'm pretty confident the half shafts need replacing. I don't know about the bushings.

I think you're feeling the slop in the spider gears, not the joints, and this is totally normal. This is a really common pitfall where people misdiagnose joints. The other one that catches people out is when they crawl underneath and turn the driveshaft and are amazed that the driveshaft turns 1/4" before the gears lock up inside, so they think that the gear backspacing is off on the ring and pinion. Not so, it's just that measuring the backspacing off of the pinion is not easy to do and the measurement at the pinion is much larger than the measurement at the ring gear.

Again, I'd suggest you take the shaft out and test it out of the car, otherwise you'll probably spend money that doesn't need spending.

[ezzzzzzz]

Sarah, you should drop by Tidewater Z. Todd can put the car up on a lift and give it a good visual. The play you indicated in the halfshafts could be attributed directly to lash in the diff as well as u-joints/spline wear. Either way, you'll know for sure. Since everyone is confident there is no diff issues I'll just side with them for now. I had a lot of play in my axles which was all due to excessive wear in the diff. Plus I've never had a diff or tranny with 3/16 long metal shavings that didn't have some sort of wear issues. That's my story and I'm sticking to it.

[jmortensen]

Your LSD is not really comparable to the stock open diff. The side gears move laterally in your LSD, and when the clutches wear that allows for a lot more movement. If you were to take the clutches out of an LSD and put the gears back in, they'd probably move 1/2" per side. This movement would allow the cross pin to move diagonally in between the two pressure rings. Basically worn clutches, especially in a 2 pinion LSD, allows for all kinds of motion you can't get in a regular diff. In an open differential, the only movement that should be available to the side gears is dictated by the slop in the spider gears and the case and the tiny amount of clearance between the gear and the cross pin shaft it rides in. Probably 1/8" total slop or so.

If you jack up the back end of the car and twist one wheel on an open diff the spider gears will twist but nothing will happen to the ring and pinion, so she won't be feeling backlash in the diff at all. She's just feeling u/joints, splines for the stub shafts, and the play in the spider gears. To even feel the backlash on an open diffyou would have to move both shafts at the same time, or hold one still. To measure backlash really requires using a dial indicator on the ring gear, as previously measured trying to measure through the pinion is pretty much futile. Doing so by twisting the halfshafts or stub shafts is also a bad idea because it's so easy to introduce the slop from the spiders into what you think is the backlash.

Having worked as a mechanic and done more than my share of diff oil changes, I've seen chunks of metal as big as those described in her original post with no ill effects in the diff. I'm not saying her diff isn't damaged, I'm just saying that her description doesn't have me worried. Maybe if she drove for 1000 miles and drained it again and it was full of metal I'd be concerned, but these diffs are just noisy IME and the clunks are usually from something else other than the gears in the diff.

Edited August 25, 2009 by jmortensen

[FastWoman]

Thanks again, guys.

Ezzzz, I'll eventually get around to dropping in on Tidewater Z. However, I'm still in DIY mode. There are a lot of items that definitely need addressing on my car that aren't over my head, so I'm going to keep chipping away at them as free time presents itself. Then after I've fixed what I can fix, and after I've blown out enough cobwebs that I have a more or less normally running/operating car, that's the time to explore the issues that are beyond my expertise. Anyway, Todd is definitely on my "to do" list.

Jon, I think you misunderstood about my U-joint diagnosis. The weight of the vehicle was on the tires/wheels, which weren't turning even a micron. So if I was able to twist my half shafts back and forth that much, then there was definitely play in the half shafts. There may be more play elsewhere (probably is), but I think it's reasonable to conclude my half shafts are in need of retirement. After some much needed rest and relaxation in a scenic scrap yard resort, they will go to scrap metal heaven and then on to their next lives as cheap chassis for Chinese consumer cr@p. To deny them this transition would be to interfere with the natural ebb and flow of the universe -- very bad karma.

Speaking of Chinese products, any opinion on the Chinese lifetime-warranted CV shafts?

BTW, you refer to my "LSD," but I had assumed my R200 was only a conventional differential. Were they installing limited slip units in 1978? Maybe you're confusing my differential with ezzzzz's quaife-equipped differential? (I confess I don't know what a quaife is, but I'm guessing it's something to do with an LSD.) Were all the R200s LSDs, or just some -- or is that just a mod, like ezzzz's?

Edited August 26, 2009 by FastWoman

[jmortensen]

I drove my 240Z with the R180 singing an increasing whine for a couple of years until that and the 'clunking' became a real nuisance. The mounts and halfshafts were tight so I knew it wasn't the culprit. An inspection proved the NiSMO LSD was completely worn out after 38 years of service (I've only owned the car for about 6 years).

ezzzzz was talking about his LSD from back in the day, and how it went bad and caused all kinds of slop in the differential. Then he was advising you based on that experience. That experience doesn't relate to your open differential very well.

I'm still not 100% convinced you've done your U/Joint check correctly. I worked as a mechanic for probably 10 years and there was no way I could test them accurately in a Z without taking them out of the car, unless they were obviously broken. Worst thing that happens is you don't need U/Joints and you waste some money, so do what you have to do.

The part of your diagnosis that doesn't make sense is that you tested the U-joints with both wheels on the ground and the halfshaft moved. If the halfshaft moved at all the wheel MUST have moved too, since they're bolted together. The only way I can see this happening is if the stub axles are destroyed and the diff is destroyed. I don't think that is the case since the car drives with only a whine in the diff. EDIT--Actually in thinking about this if the outside u/joint was bad it might allow just a bit of movement, but it would typically be just a tiny bit, and it would in my experience usually require more than a jiggle to get it to move. Maybe the outside joint is bad... I suppose we'll see.

As far as the Chinese u/joints go, if you're not drag racing or drifting I doubt you'll have trouble, but if you are then I think you'll likely be using that warranty. Again, I think the Nissan u/joints were particularly strong.

Edited August 26, 2009 by jmortensen

[FastWoman]

I might not have been using the right terms. My understanding is that "half shaft" refers to the entire assembly, from U-joint to U-joint. What I grabbed, according to my FSM, was the sleeve yoke. I gave that a light twist back and forth and felt the play I described. For me to be able to rotate the sleeve yoke with the wheel stationary, I would have had to have slop in the outer U-joint and/or the spline at the very least. The slop on the other side would have to be collectively just as much, combined between the inner U-joint, the differential, and the U-joints and spline on the other side.

Anyway, I agree that there's no harm in removing the shafts and examining them for wear before buying the replacement shafts. No worries about drag racing!! I'm not a particularly fast driver -- much too old for that.

[doradox]

As far as the Chinese u/joints go, if you're not drag racing or drifting I doubt you'll have trouble, but if you are then I think you'll likely be using that warranty. Again, I think the Nissan u/joints were particularly strong.

U-joints serve as a kind of driveline "fuse", so stronger isn't always better. But more than likely the Nissan U-joints are Goldilocks strong. Just right.

Steve

[Travel'n Man]

I like Ron Tyler's mount, which I think can still be purchased from Roostmonkey on hybridz.org. http://forums.hybridz.org/showthread.php?t=127993 It goes over the diff, so when the front of the diff lifts up it compresses into the mount.

Not trying to steal the thread but I had to say "thanks" to Jon for the tip on the R/T Diff Mount. I ordered one today.............I'm real excited to see if it STOPS THE THUNK. I have already changed out all u-joints and replaced the diff mount........$62 bucks........I'll give it a shot to get rid of that THUNK

Again, didn't try to steak the thread but had to say thanks!

[FastWoman]

I wrote:

Regarding the U joints, there's a GSP (Chinese) CV half shaft available for this car from Advance. I'm not thrilled about Chinese manufacture, but it carries a lifetime warranty and costs only $70 per side. Hopefully that would be a cure for the common clunk. Any thoughts?

Just a follow-up on that one: I ordered a couple of these in. They definitely ordered in the "right" parts, in the sense that they were the ones listed for a '78 280Z. Unfortunately they look like something that would go on a large truck. Nothing about them would fit on a 280Z, by any stretch. Soooooo.... I guess I'll be getting in touch with Tidewater Z to see if they can rebuild my half-shafts or refer me to someone who can. (I've got some major wobbly U-joints.)

[bryand2]

can someone tell me were to find the drain and fill plug for the transmission and the drain/fill plug on the diferential on a 280z? i have the FSM but no where does it seem to say where these plugs are?