Zed Head

But was he running old bushings? I'm suggesting that he replaced old worn bushings with new and it changed the geometry.

New bushings could have moved the wheel forward. As the bushings compress and shrink the suspension components move backward since braking is the dominant force. Control arm (transverse link) and T/C rod both. You might gain a mm or two back once you start driving it.

It might be that the missing return spring caused lower travel at the fork, but who knows. A smaller bore on the slave/operator cylinder will give more travel at the fork. I'd take a look at your pressure plate if you can and see if you have 1972 parts or newer parts. Looks like the master cylinder bore stayed the same but Nissan changed the slave cylinder bore over the years. Probably to match pressure plate changes. If you decide to get an aftermarket slave cylinder make sure you take it apart and clean it before installation. Some of use have found machining grit inside that will damage the seals.

What the hell is happening! My world makes no sense! We might have discovered the source of decades of clutch problems. New sizes.

It gets weirder. 1970. 5/8". 0.625". Matching master and operator.

Looking further I think that you asked a good question. I'd never really thought of it before, and even now assumed that you would just want to match the master and slave bore sizes, that they would be the same. But that is not the case, see specs below for 1976. Add on to that that the 240Z's had a taller pressure plate and maybe it is important to match the specs on all of those components. Pressure plate, master, and slave. Many people put later model pressure plates on their L24's. It deserves some study. Notice that image I pasted above has the 1976 style slave cylinder non-adjustable rod. Not the same! -

Actually, there is some weirdness out there. 3/4" does not equal 0.690". Not sure if the 3/4 molded in to the cylinder is its size or something else.

The seller didn't say, and nobody asked. Probably works just fine. He didn't get his price. He was hoping for 20, only bid up to $13,750.

11/16" = 0.6875 inches = 17.5 mm. I think that that's all that's out there. The self-adjusting slave cylinders have a spring inside. No need for the external spring. Nissan improved the system. Maybe a PO already used a newer cylinder. You'll need to swap rods like site said though, unless you change the clutch fork. https://www.rockauto.com/en/catalog/nissan,1971,240z,2.4l+l6,1209158,transmission-manual,clutch+slave+cylinder,2044 p.s. if you put your car info in the signature box and save it it will show up under each of your posts. It's under Account Settings. https://www.classiczcars.com/settings/signature/

Here's an interesting 75. Has had the EFI system swapped for a 1983 system. I wonder if it works well without an O2 sensor. Maybe @cgsheen1 knows. Looks like they did all of the parts, from AFM to ECU to ignition module/distributor. I'd comment on BAT but don't want to mess with the auction. https://bringatrailer.com/listing/1975-datsun-280z-66/

Automatics kill (value). $5,000 for a running, driving, passed-emissions-in-CA 280Z. https://bringatrailer.com/listing/1978-datsun-280z-193/

No reserve 240Z project with Stromberg carbs. Non-running for 20 years. Oak Harbor, Washington. @Terrapin Z https://bringatrailer.com/listing/1973-datsun-240z-313/

Loose mustache bar diff nuts is not an uncommon cause of a clunk.

I hate to say it but I don't think that you can trust most aftermarket parts today. Everybody is buying from Asia and they probably don't want to get tied to a specification. The primary spec. on the only part that had a spec. was huge. It was 1978 when Nissan created their 0.84 - 1.02 spec. About a 17% range. The Wells coil today, above, is 0.7 - 1.4. 50%. Not even close to the Nissan spec but they're selling it as a replacement. https://www.made-in-china.com/quality-china-product/ignition_coil-4.html Four E's VietnamFour E's VietnamDecade-long expertise in manufacturing premium Aftermarket Ignition Coils

I think it's just where the internet is going. I did go to the NGKSparkPlugs site and look and nothing came up. I also searched for a coil for my truck and it did come up. The database for 1978 280Z was just empty. There's probably an old NGK catalog in the back of somebody's parts store that has the listing. We might have to go back to paper. https://ngksparkplugs.com/en/part-finder But wait! I tried NGK.com (which oddly says that it is not associated with NGK Spark Plugs...so confusing.) and found it. But..it's Not Available. From them anyway. Watch out for counterfeits. Okay, I'll stop now. https://www.ngk.com/application/search

In case anyone is wondering - Here's 1976 - Here's 1978 -

Bollocks!

Nope, now it's a Reddit post - https://www.reddit.com/r/Datsun/comments/1atbwl8/do_i_have_the_wrong_ignition_coil/

BUT. Now it's back, halfway, but with a +2. I wonder is CZCC is one of the +2. Searching... -

Found another example of the sad state of the AI "boom". The AI overview uses two single word references to write two full paragraphs, from one single Ratsun thread. BUT, even scarier, as soon as I copied that Ratsun link in to my other post AI stopped using it. I think that AI is watching posts in real time and adjusting replies. https://www.google.com/search?q=ngk+U1099 Before - After. It's gone. No more Ratsun reference -

The number does look familiar. But, unfortunately, when you search it, not much shows up. It's something that I've noticed recently, that many of the old sources that I was sure are out there on the web, seem to be missing. I think it might have something to do with the monetizing of the internet. On top of that, the genius AI chatbots and their "overviews" cite posts from Reddit or forums like Ratsun as authoritative references. They just steal from the single source and post it as their own creation. The internet is getting really weird. https://www.google.com/search?q=ngk+U1099 https://ratsun.net/topic/83046-1977-620-l20b-no-spark-condition-on-fuel-injection-conversion/

How do you know it's the correct coil? RockAuto doesn't show it as a choice. https://www.rockauto.com/en/catalog/nissan,1978,280z,2.8l+l6,1209260,ignition,ignition+coil,7060

Actually, some specs are there, I missed them. Pretty wide range. Looks like RockAuto is confused though on the ballast reistor. They list one for use with the "external resistor" even though, as CO pointed out, 1978 doesn't use it. It has the module with current limiting capability. I'd just go down to Oreilly Auto with my meter and see what they're selling. (Edit - actually I'd probably just go to the wrecking yard with my meter. Coils are spendy at the parts stores!) https://www.rockauto.com/en/moreinfo.php?pk=940830&cc=1209260&pt=7060&jsn=448 (what's a 200 scale?)

Rockauto has a selection of coils. Probably meet spec. although they don't show them. You might start planning for the ignition module to fail though. It's what they do.

How about the voltage regulator? It has moving points that could get stuck. Maybe it's backfeeding in to the ignition system. The brake light in the dash should light when the key is on, engine not running, but go off when the engine is running. I think that that is also controlled through the VR. Should start and run with it unplugged. Maybe you'll get lucky. Edit - actually I'm not sure what it will do if you unplug it. Have to study the wiring diagram. If you have a spare it might be worthwhile to swap it.