Clunk elimination has begun, with pics

[Zedyone_kenobi]

Just an update...

Today after I spent hours mending a fence to serviceable conditions, I decided to take a stab at more clunk diagnosing.

I pulled the yoke out of the old diff and put it in the new one with the bolt just finger tight. I could still move it up radially just as much as I could with the old diff, which leads me to believe that my old diff may be okay, still hard to measure clearances just eyeballing it. I did find a local diff guy that would rebuild it for 250 plus parts. May be worth doing, we will see. It may be perfectly fine.

I removed my mustache bar and wanted to look at the bushings inside those. Well it unbolted rather easily, not lose mind you, just not stuck bolts. When I looked at the rubber inside it, it looked fine. No cracks, it was still supple actually. So far the investigation has been just mechanics eyeball for now, but heres the score.

half shaft u-joints feel tight as can be... no detectable slop found

Front Diff mount appears to be in good shape, with the rubber not showing any cracks or damage or give

Mustache bar bushings look to be rather new, not really in need of replacement

I may need to turn my attention to the transmission if I cannot find anything of substance. The back end is not giving me any smoking guns.

[Poindexter]

Glad to hear that everybody is well, not counting the trees.

A small thing that comes to mind, if you indeed have to do some diff rebuilding- what about adding a limited slip WYAAI? It's high on *my* list, as every time I punch it as I'm turning, especially at slower speeds, like when pulling out onto a highway from a parking lot, something feels...lacking. I'd like to be able to put the power down more consistently, from both sides. Plus there always seems to be patches of sand or small gravel accumulating right at these curb cuts too, reducing the available traction.

Just thinkin'...

Edited September 17, 2008 by Poindexter

[Zedyone_kenobi]

Thats good advice, but I would need to start looking for a R200 then right? I am not sure I really need a LSD with my stock L24. Sticky tires and throttle modulation will work fine for now, but if I can find a good posi unit to put in it, I most certainly would not thumb my nose at it. At the moment, I would not even know where to look.

[Diseazd]

Zedyone.......I think you may be going in the wrong direction with your diff replacement. Check out what Yellow Jedi said....It wasn't his u-joints or diff mount...he replaced those twice....when he finally replaced all rear bushings the clunk disappeared! My guess is his problem was the four rear control arm bushings...remember the u-joints, driveshaft and diff mount aren't the only areas under stress in the rear. The wheels and tires are trying to twist the control arms apart! If the four large bushings aren't installed correctly or have been worn from high torque runs over the years, you can have metal to metal contact or severe movement on either side of the bushings. However like previosly mentioned in this thread, they must be installed properly. Loosen the large bolts on the forward and rearward side of the bushings then take the caps off (2 small bolts on rearward cap, diff bracket capping forward bushings) When finishing the job, tighten the large 4 bolts only when rear wheels are under weight of the car. Clunk elimination is part of Z ownership.....good luck!

[Zedyone_kenobi]

I was strongly considering ordering new inboard rear control arm bushings. I mean I am practically there already with the front diff mount off the car, the rears are just 4 small bolts. I think I will do this. Heres the reason why.

As mentioned, my rear diff feels exaclty like the diff I ordered. Now there is no guaranty that the one I ordered is any good either, but the chances of them both being bad in exactly the same way, (or rather what I perceived as bad) is extremely slim. So since I found no smoking gun, I am left scratching my head what to look for next. I will take a look at the inboard rear control arm bushings. Pics to follow.

[jmortensen]

Thats good advice, but I would need to start looking for a R200 then right? I am not sure I really need a LSD with my stock L24. Sticky tires and throttle modulation will work fine for now, but if I can find a good posi unit to put in it, I most certainly would not thumb my nose at it. At the moment, I would not even know where to look.

You can get several different LSD's for the R180. Nissan Comp had one, Quaife, and a company in Australia which was similar to a Quaife with helical gears. I wouldn't be surprised if there were others too. The issue is that the ring gear ID changed in the mid 70's. So you can get a new R180 to go with your new posi, or you can try to find an old LSD to go with the original gearset.

[Diseazd]

Just fixed my clunk! Jack up the car and in order 1) Check for loose nuts on all halfshafts and driveshaft 2) Grab and shake halfshaft u-joints and drive shaft u-joints 3) retorque 2 nuts on backside of mustache bar and 2 nuts holding mustache bar to frame 4) check front diff mount rubber bushing for deteriation 5) check play in diff front yoke ( 1/4" back and forth is absolutely normal ). I did 1-5 with no culprits! 6) Replace control arm bushings ( mine were the culprit) I replaced with new Motorsport teflon and the annoying clunk is totally gone! It was clunking on acceleration and release and now it's like brand new! The 4 large bolts on the front and rear of the control arms had come loose and the control arm had shifted over one of the bushings causing a shift in the control arm on acceleration and release. I had always suspected all the previous culprits but didn't think of the control arm bushings, and they are pretty easy to replace without removing the diff! Give it a try.

[Zedyone_kenobi]

UPDATE:

Possible smoking gun. I took my half shafts to a driveshaft shop in town. Seems three of my ujoints had a little slop, so I went ahead and replaced all 4. Apparently there is a technique to feeling the Ujoint out. So that will be done next week. But the real story is when I climbed under my car to clean some parts.

When I looked at the transmission mount I found out that I can pick up on the tail of the tranny an easy 1/4 inch while the mount stays motionless. I think this may be the culprit I have been searching for. If its this easy for me to push on the transmission and do this, I would wager that torque from the engine can do much more. It also explains why it sounded like my clunk was coming more from the middle of the car than the back.

I will order these parts today along with some steering rack bushings, why rack bushings?

I don't see any way to remove the steering coupler without moving the rack forward to gain some room to slide it off. I was going to do an easy steering coupler swapout with the urethane bushing I bought, or so I thought!!! But the job will take more than the 45 minutes I thought it would. now we are moving the whole rack forward. Nothing is every black and white! Are we having fun yet! I know I am! This is why I wanted a project car.

Also, when its said and done, I will be able throw my ITG's on there once I find a way to get all the stock vacuum plumbing figured out.

Seems even the smallest job grows on this car, but I think I have at last found what I was looking for. The tranny bushing seems easy as pie, so when I get all that done, I will post some pics of the painted parts and the install.

Oh, what the heck. EUREKA!!! Just felt like screaming that.

Edited September 27, 2008 by Zedyone_kenobi

[grantf]

on my $300 280z I have had a rear end clunk, first noticed a BADLY worn half shaft u-joint, took about 40 min to replace.

test drove the car and the clunk was better but not gone, so I inspected the drive shaft and there seemed to be some play in it.

I was wrong (a good thing), the play seemed to originate from the other half-shaft when I removed it I felt for play and there was but really minimal.

After replacing the two u-joints on the second one the clunk is 90% cured.

I might replace the last one and see what improvements I get, but now I'm thinking about looking at my transmission mount also!

[trykflyr]

Dude, I have garage envy. Track lighting???? What ever happened to a bare bulb on the end of an extension cord wrapped in duct tape?

My driveline and rear end are down to individual molecules. I'll be following along as well from the frozen freakin north!

[Zedyone_kenobi]

I guess I should not mention my elevator! haha

[biggun_1953]

I have worked on a few 280Zs with rearend knocks over the last 14 years. As you know, these cars are known for their knocks and there are lots of places (both drivetrain and suspension) that can have slop which will cause knocking. Some not often discussed are the rear shock insulators. While these can look solid, they may partially separate. A couple weeks ago, both the left and right insulators on my '76 280s completely separated (incredibly within 2 days of each other while the car was on jack stands) and the wheels slumped down. I had inspected the insulators carefully when I replaced the shock struts. I have now replaced the insulators with used ones, as new are not available, in the hopes that they are sufficiently solid.

I will make an entry after I drive the vehicle which will be a few months away. My post is for those who have tried everything else. Good luck to all!