Captain Obvious

Took me a page and a half of scribbled op-amp circuits to catch up to you (and I think there are some surmountable resistor value related errors in the design), but I got it. Neat use of active positive feedback. I won't guarantee that it would actually be as linear as expected without bread boarding it, but it certainly looks promising. Your kung-fu is strong. I reiterate however, that I think you're loony for even thinking about such ventures... The original Bosch design is a highly characterized black box of analog voodoo that cost probably hundreds of thousands of 1970's dollars to develop, took thousands of man hours, and several design iterations before they even had anything that would start and run under all input conditions. That said, I'll do whatever I can to help. Haha!

TomoHawk, Not sure what you're asking... What do you mean with the above? I'm probably just dense, but can you ask your question a different way?

Look up tables aren't analog.

The reason I brought up the integrating ADC is because it uses the concept of a linear ramp to a threshold and also uses analog switching to change around the input circuitry. I wasn't saying it would be a drop in for anything here, but a lot of what you suggested is "reminiscent". I didn't mean it was a solution, I just meant that it has a lot of the same trappings inside. As for your sketch... I don't see anything on there anywhere that would result in anything except steady state DC voltages. I think your little graph in the lower right that shows a linear ramping voltage is creative license that I don't think would occur. If you want a linear ramp generated from a DC voltage, you have to integrate the area under the DC line over time. You need an integrator and I don't see one anywhere. No bad vibes intended, but I think the output of every op-amp in that sketch would be flat-line. Yes, I went there. Boating, Miatas, football, Sandy Bottom Nature Park, Plum Tree Island Reserve.

I have no direct experience with the brake check valve, but there is a parameter of any check valve called "cracking pressure" and it's the differential pressure required to "crack" the valve open and allow flow. Because of stiction in the sealing surfaces inside, they are never completely smooth and that thump you feel and hear is probably the "crack". As for your calipers sticking... The check valve is a red herring. The brake booster will always have vacuum present in it even when the engine is off. I'm no expert, but I've heard it's a federal safety requirement to allow for continued brake power even in the event of a motor stall. You get like two good pushes before the vacuum in the booster is gone. So I don't know exactly how the check valve should sound, but I can tell you that it has nothing to do with your calipers sticking.

Not my fault....

Does anyone else have these sorts of troubled thoughts? Well I'm sure you're not surprised to hear that I do, but my advice to you would be... Think about something else. Maybe boating. What you described is reminiscent to an integrating A/D. You ever mess with one of them? It's similar except you're proposing a variable threshold instead of a fixed reference voltage. Something else... Maybe sports?

Yes. the stock 260 distributor has a vacuum controlled mechanical advance feature.

I'm there too. I don't know when I started paying attention to the details, but I see a lot more now than I used to. You'd have a field day with my car.

Me too!

Are you the older one or the younger one?

Namerow, Forgot to ask... Does this plug-n-play diagram agree with what you were intending to construct? Other than the early pigtails using a black wire between the main harness and the bulb prongs, does everything look right and make sense?

Yup. That's the same thing I've found as well. Thanks for checking. So somewhere along the way they changed some of the wire gauges sizes and the color of the common connection wire (from black to red), but I don't think the pigtails ever used "side specific" wiring colors.

Depends on the year of 280... 77/78 are different than previous years. An easy way to tell the difference is that the 77/78 have an angled front mount and flat rear mount while all the previous years had flat mounts on all four corners. I believe the change occurred at the same time as the different doors. They changed a lot of sheet metal at that time and I believe it was all part of the same upgrade. So I believe the bottom line is that you could use 280 mounts in your 240 or 260 as long as they are from 1975 or 76.

Excellent. Thanks for the pic and the tip to that one on Amazon.

TomoHawk, Thanks for the wiring diagram. If you get a chance to look at your pigtails, let us know. Namerow, That's another change they made in later years. The 77/78 connectors between the engine bay harness and the pigtails is different than previous years and not all of the contacts are the same size. At the bulb end, mine are all the same size, but at the harness end, the R/W (high beam) is larger than the other two. Doesn't really make electrical sense and I would have told them there's no benefit, but I wasn't there when they designed it.

The 77/78 pigtails kept the same wire gauges all the way to the bulbs which makes more sense electrically. In theory, they could cut the gauges on the pigtails some because each side only carries current from one bulb instead of two, but they kept them all the same. I've seen that printing on the back of the headlight connectors as well. Makes me think that at one point the plan was to run the headlights with the common connection to ground. I doubt Nissan molded their own connector shells, but the people who made them were thinking that common to ground was the intent.

Hardway, Have you got a link to the template you used to make your timing chain wedge? I looked for Californiaparts.net and came up blank. Better yet, have you got a copy of the drawing template you used that you could post here?

I just took a look at the wiring diagrams. The pigtail connectors didn't show up at all until 74 and the colors of the pigtails were never listed.

Take a look when you get the chance. I'd be surprised, but it would be good to know for sure. The connectors and short pigtail lengths didn't even show up on the earliest wiring diagrams, and then in the later diagrams, the connectors and pigtails made it to the wiring diagrams but the wire colors aren't noted on the pigtail. The engine bay harness has R and R/Y, but the pigtail colors aren't labeled.

TomoHawk, It's more complicated than that... In 77 and 78 they used the same short headlight pigtail on both sides from the bulb back to the engine bay harness. So while my 77 has a Red coming out of the harness on the pass side and a Red/Yellow on the driver's side, both sides are the same color (Red) after they pass through the three position connector to the short pigtail length to the bulb. In other words, the colors on my diagram above are correct. At least for 77 and 78. I don't know about the other years, but since there really isn't any difference in the pigtail for either side, I would be surprised to hear Datsun actually assembled different ones for each side in any year. Just no good reason to spend the extra money to build, stock, and use two different versions. Are the short pigtail wire colors different on each side of your car?

Thanks for the additional info on the MPV relay block. Those relays are a very common form factor and can be found pretty much everywhere. In fact, I think those are interchangeable with the Honda relays that I used when I did my upgrade. The one you pictured is SPST, but there's also an SPDT version in the same form factor (with the addition of one more pin on the bottom). The headlights only require SPST, but keep in mind for other stuff that you can get SPDT as well if necessary. Don't know if the MPV block has provisions for the additional pin, but just thought I would mention it. As for the starter relay... Do I think you really need a relay to operate a relay? The starter solenoid wart sitting on top of the starter draws more current than the ignition switch can handle forever. Eventually the contacts inside the ignition switch will burn up and you'll get intermittent starter operation. It's not absolutely necessary, but you'll eventually be replacing the ignition switch if you don't put in a starter relay. Maybe you and I will be dust by the time that happens to your car, or maybe it'll happen tomorrow (and I hope I'm not dust by then). I had already had my contacts burn up in my ignition switch once and didn't want to subject my new switch to the same eventual doom. I was in there messing around with wires and stuff already and just bit the bullet and did it all at the same time. Those are my thoughts. Hope that helps?

Just in time. Here's a redrawn version of the 4-relay option with emphasis on making it as reversible as possible. And in fact, it should be completely plug-n-play for your early 240Z. This scheme would work in the later cars as well, but it wouldn't be quite plug-n-play because you would need to do the under dash changes to make the fuses hot at all times and give the HI/LO switch the three states required. But since your early 240 is already wired like that you're ahead of the game! Who knew? So for an early 240, this should be plug-n-play, and "almost plug-n-play" for everything else: The only thing that makes it a little more complicated than the tradidtional 2-relay version is that you need to make connection to the driver's side headlight connector off the harness to pick up the R/Y wire. The traditional 2-relay version does not require any connections to the engine bay harness on that side of the car because it powers both relays off the right headlight side. I don't see it as a hardship though. You always have to run wires over there anyway to get to the headlight pigtail. It's one more connector and an additional wire. IMHO, I think that's a small price to pay for the benefits of fault tolerance and reduced voltage drops.

Sounds like a plan. One of the things that I like about having the fuses always hot and doing all the relay switching on the low side is that you need to bring one less wire to the relay block. You just connect one side of the relay coil to one side of the contacts. You can just daisy chain the R (and R/Y) wires to two connections on the same relay which results in less wires to the rest of the car. I like that relay block from the MPV. In another thread, there was some discussion of pre-existing relay/fuse blocks that could be harvested from other cars, but that one didn't come up. So the MPV block has spaces for six relays, all the same style? Any fuses in the block, or just relays? I would use one of the other relay positions for a starter relay to take the load off your ignition switch. If you're doing (or have done) the internal regulator upgrade, it's a convenient time to do the starter relay because the internal regulator leaves you with a couple unused signals that are needed to do the starter relay. Namely, hot at all times, and ground. You can re-purpose those two connections for the starter instead of the external regulator.

Great. And thanks for the early wiring diagram trivia. Earliest year I've ever personally taken a wrench to is a 74 but I like that trivia stuff anyway regardless of the year. So before you go cutting any wires... I still believe it should be possible to do a four relay option without cutting anything by plugging into the stock connectors. Especially if your car is already setup with fuses that are hot at all times and a beam select switch that has three states,: Hi to ground Low to ground No connect I know I said I would look into that a while ago (and didn't), but give me another day or so before you start cutting into your harness. I might be able to come up with something more plug-n-play.