jhm

Yes, your battery should read 14+ volts when running, if the charge system is functioning properly. Have you measured resistance from the alternator to the battery, as suggested by Newzed? That could help you track down where the losses are occurring. Also, how long is "a while", that the car continues to run after turning the key off? Finally, it seems you believe that a PO has modified the wiring to your tee connector; but have you traced the wiring from end to end? That's really the only way you'll know for sure if they mucked something up when they rewired it.

I would check your shocks as well. Good chance that they're worn out, unless you know for sure when they were last replaced (and with what kind of replacement units). KYB are pretty popular replacement shocks and very affordable. Konis are the bomb, but pricey. Several threads here discuss the many available shock and spring options you can choose from. Obviously, check your brake function too, for driveabilility and safety. Many owners go for long times between pad replacement, brake fluid flush and bleed. Congratulations on your acquisition. Do you know the car's history? If it's like 90% of the used S30's up for sale, it will need a solid going-through to ensure it's road-worthy.

To answer your first question....yes, the stock half-shafts are actually quite stout and often used in applications with similar hp numbers as yours. And half-shafts are very readily available used from any of the Z car forums and FB pages....no need to buy new, unless you just want new parts. Converting back to half-shafts from your current CVs might be a bit tricky. You will need the correct side axle (also sometimes called stub axle, but I believe side axle is the more correct nomenclature) to clip into the Quaife LSD that you could bolt the half-shafts to. If the Quaife internals are the same as the original R200 (spine count and diameter), you should be good to go. If not, I honestly don't know if there's anything commercially available for that. One of the more common LSD swaps uses a Subaru LSD diff, and there are a couple vendors that produce conversion stub axles to mate the OEM half-shafts with the Subaru LSD internals. Have you tried playing with different length sway bar end links? You can easily swap the middle spacer to shorten or lengthen the overall end link. (Sounds like yours might need to be shorter than they currently are.) Sometimes that's all that's needed to give sufficient clearance between the sway bar and the axles. EDITED: Forgot to mention that the half-shafts will typically have more driveline vibration and noise than the CV axles; which you may find undesirable or even unacceptable.

BUMP.

I've read your post a couple of times, and still not sure what you're looking for. If you're seeking an original replacement relay, maybe post on the "Parts wanted" sub-forum? Lots of guys keep a stock of old electrical components. Also, I didn't see where you specified what year and model your car is. The electrical systems varied widely from year to year in these cars. Finally, your post discusses the "combination switch" and "turn signal switch", but it turns out that you're really asking about a specific relay 'under the seat'. (Which seat, BTW?). Maybe that's why Miles posted the full FSM.

As NewZed pointed out, the reason one puts a little oil inside the strut tube is to prevent corrosion and assist with heat dissipation when the shock body heats up during heavy use. I've been doing this for years with all brands of shocks, both gas-charged and non-gas, and have never had a problem. You really only need a little to do the job -- enough to cover roughly the lower half of the shock body once inserted into the strut tube is what I shoot for.

Are they gas shocks? If so, they should still hold their gas charge and not be leaking oil, if they're ok. If not gas-charged, they'll still be leaking oil at the shaft seal and you should be able to visibly see the oil discharge. If they had blown due to excessive oil or pressure, the seals on the shaft would be leaking (possibly quite a lot). Is there any visible oil on the shaft or in that area? If not, good chance that they're still fine. You'll know for sure when you remove them and refill....they'll feel firm on the compression and extension strokes (moreso during extension).

Those appear to be the stock calipers; but if they were, the correct part numbered speed bleeder should've worked for you.

I can't imagine there being any damage to the shocks after three strokes of compression. I would remove and refill per the manufacturers directions. Just curious....why pick Gabriel for shocks? That's not a common choice for the Z, but I hope they work well for your application.

Pretty much everyone here has suggested trying a larger MC. You have discs in the rear, and apparently, some non-stock calipers in the front. It's very possible that the stock 7/8 MC will not handle your current setup.

IIRC, I relocated the long rod for the door lock knob on one of my cars...in order to use the different door panel in its original form. A simple job just cutting a new notch to coincide with the hole on the door panel. I seem to recall it was a difference of only a couple inches?

The correct Russell P.N. for the fronts is #639560. I have them in my car and they work fine. Do you recall what part number yours are? IIRC, the MC uses the same size as the stock rear drums.

If you replace all the stock bleed valves with speed bleeders, it's super easy to bleed the entire system yourself.

For starters, it sounds as though your reaction disk has fallen out of position in the brake booster. Search here for reaction disk repair...it's an easy fix, if that's what's happened. Next, did you go with a bigger MC when you installed the rear discs? I think most people choose a 1" MC when doing rear disc conversion....that might possibly be the cause of weak rear pressure. (You may also find that you need an adjustable rear proportioning valve, once the swap is completed.) Finally, if you still have the stock tee connector for the rear brake hard lines in the system, I would bleed the left rear first...then right rear. The stock tee connector is on the passenger side of the car, which actually results in the left rear having the longest run of brake line of the four wheels. Good luck with it.

Sounds like the engine is mounted in a JTR position, which locates the engine lower and more to the rear than other mounting positions. It also usually results in the best balance between front/rear weighting. You can google "Jags that run" to get more info on the JTR swap. Glad you're having fun with it.

Did you also post on FB? (There's someone there also looking for same years tank). I saw one recently for sale on my local CL: https://norfolk.craigslist.org/pts/d/newport-news-datsun-280z-gas-tank/6862346333.html. Good luck with it.

Can't say that I've ever seen any off-the-shelf options; but it certainly wouldn't be hard to fabricate your own custom-shaped pedal.

If the car doesn't already have one, an inertial cutoff switch is a good idea. I have both a manual switch and an automatic inertial cutoff switch in my fuel pump circuitry.

I bought this MC from Amazon, and was completely expecting a piece of junk due to the low price tag. Turns out I was completely wrong, and very pleasantly surprised by the quality of manufacture and materials. All the threads were clean and well-cut. The plastic reservoirs were plenty thick. Installed it with zero leaks on the first try. If you don't like the black plastic caps, you can substitute your own original metal reservoir caps. Haven't had it on the car all that long yet, but it worked great during one very long day of testing at the track. Highly recommend! https://www.amazon.com/gp/aw/d/B001PBHLCI?psc=1&ref=ppx_pop_mob_b_asin_title

I'm running both in my mild SBC. The stock mech pump is fine for street use, but I need the electric pump for any kind of track use. I'm using an Edelbrock pump, 38 gph, 4-7 psi.

Something like a black plastic 55 gal barrel, or one of those big black plastic drums that trees are potted in for sale....anything with at least a 3-4 ft diameter should have the right curvature.

If you're ok with aftermarket, Skillard makes them: https://skillard.com/products/280z-door-cards

FWIW, I've seen people make their own DIY liners from plastic barrels. Done carefully, they work as well as the stock pieces.

Glad you got it worked out. Is the car on a lift, that you need a transmission jack? If the car's on the ground, a car jack will work fine to lift the differential....just use ratchet straps to hold the diff in place while you're jacking it.