Captain Obvious

I don't know the current temps in IA, but here's something to try... Disconnect the electrical connector from your cold start valve. You might be flooding your engine while cranking which might be making it hard to start. And since it's temperature dependent, the times it starts OK might be a degree or two warmer. Warm enough to disable the cold start valve? If your start stumble goes away with the CSV disconnected, that might be a clue. Or, on the other hand, if it now does it ALL the time, that might be a clue as well. I know it's the shotgun approach, but it's free, easy and reversible.

Gotcha. So Rockauto has phantom stock. Well I don't know what's wrong with your existing wheel cylinders, but I think they're all the same internal bore (7/8 inch). If your external dust boots are OK and the problem is the internal piston seal, maybe the piston seal from the newer 72-76 rebuild kits would still work for your older cylinder? There really isn't much else in the kits beyond the seal, dust boot, and bleed nipple cap, right? Is the rubber boot to the backing plate included and is it the same one for both first and second designs?

Mario, Yes, the wire colors came from the wiring diagram in the FSM. And remember that it's just a theory. I'd be happy to be proven wrong. I'd also be interested to hear if any other 78 owners have seen similar behavior. I guess unless they had a pressure gauge installed, they may never know. After watching your last video, I don't see anything wrong with either the fuel pump or the fuel pressure regulator. They both appear to be working fine. Yes. there is a check valve back at the fuel pump, but that's not what is causing your starting issues. It might be what is causing your eventual loss of fuel line pressure, but you showed that your starting stumble occurs even after you have primed the fuel lines. Your start stumble is not caused by low fuel pressure. So while it might be a good idea to chase your fuel line leak down at some point in the future, I don't think you need to do that now. It's not that big of an issue.

I have a theory about the short "priming" pulse to the fuel pump in the 78 Z... When you start turning the key to start the car and you get to ACC position, the wires to the fuel pump control relay have the following voltages on them: Black/Yel - No connection to anything. (Will go hot in START, but we haven't gotten to START yet.) Yellow/Blk - Connected to ground through the oil pressure sender. Should have been that way since before you put the key in the ignition. Blue - Connected to +12 through the CHG lamp and the coil of the brake warning relay. White/Blk (input side) - No connection to anything. White/Blk (output side) - Connected to the White/Blk input side wire, but since that's not connected to anything, the output side doesn't get any power. The instant you turn the key to ON, the wires to the fuel pump control relay have the following voltages on them: Black/Yel - Still no connection to anything. (Will go hot in START, but we haven't gotten to START yet.) Yellow/Blk - Connected to ground through the oil pressure sender. Should have been that way since before you put the key in the ignition. Blue - Pulled low through the alternator to essentially ground. White/Blk (input side) - Connected to +12 through the ignition relay. White/black (output side) - Now here's where it get's tricky... The two relays built into the fuel pump control relay will change positions, but that doesn't happen instantaneously. Before the key is turned to ON, the relay is in such a position that the input WHT/BLK is connected to the output WHT/BLK. And when the key hits the ON position and the ignition relay pulls in, and for a brief time the output WHT/BLK will still be connected to the input WHT/BLK and it could temporarily energize the fuel pump relay sending power to the fuel pump. So when the key hits the ON position, the alternator controlled side of the fuel pump control relay will pull in. When this side pulls in, it makes the connection that pulls in the OTHER side of the fuel pump control relay. The pulling in of those two relays takes a little time and maybe that's the brief instant the fuel pump gets a short shot of power. It's not supposed to happen, but I can definitely see it happening in reality. Especially if the contacts in the oil pressure switch are starting to get a little dirty and don't provide as strong of a connection to ground as it should. That could delay the pull in of the second side of the fuel pump control relay causing a longer pulse to the fuel pump.

I'm a little confused as to what it is that you're looking to buy. I assume the answers are obvious, but it's my job... If you're looking for rebuild kits for your 70-71 cylinders Rockauto lists two options. Rockauto, however, does not list replacement wheel cylinders for 70-71. But your original post makes it sound like you're wanting to rebuild your original cylinders, not replace. And for the 72-76 cylinders, Rockauto lists both replacement cylinders AND rebuild kits. So exactly what is it that you're looking for?

I got some pics of my 77 style brake warning relay. Four position connector, three populated positions. Here it is in it's natural habitat: I took it out of the car and discovered that I had left myself a note from the last time I was in there: Pull the guts out of the metal case. Note the black crispy areas on the coil windings: Looking it over, I was actually able to see the break in the coil wire: Also, being the curious type, I measured the resistance of (what is left of) the coil and I got 10 Ohms, which is way too low. It does, however explain the balled up melted blobs of copper on the ends of the magnet wires where the wire melted back... Tells me that it didn't go peacefully. When this thing went open circuit, it went with gusto! So with all the above info, here's my forensic analysis... The coil ran hot from day one and eventually degraded the varnish insulation between coil windings until it shorted internally somewhere. It may have gone from it's original starting resistance is to the current level of 10 Ohms in one shot, or it may have shorted out just a couple turns initially which would reduce the coil resistance, draw more current, and get even hotter (avalanching to it's ultimate death). In any event, eventually one coil turn shorted to another and greatly reduced the coil resistance to the current 10 Ohms. For a short bright instant, the coil drew over an amp until POP, the wire acted like a fuse and vaporized a quarter inch of copper. I'm comfortable not using it at all. I use my parking brake religiously and it also lights the brake lamp on the dash. In other words, my brake bulb gets tested even though I don't have the relay installed.

Sampler flights!! I'm in!

I'm always grabbing stuff I shouldn't be....

Thanks for the additional info. I haven't looked at the MSDS sheets for any of those products, but I would have expected them to be more nebulous. I would have expected the usual "proprietary blend of petroleum distillates". Some of them get away with that and some don't.

And one more thing... At 100 Ohms coil resistance, that wrecking yard relay will draw less than half what your original is pulling. A little over 1 Watt being dissipated inside the case of that one compared to close to 4 W for your original. I know 4 Watts doesn't sound like a lot, but put an empty soup can over a 4 W nightlight plugged into the wall for an hour. Then pull the can off and grab ahold of the bulb.

Oh yeah, I forgot to talk about your current relay. It certainly looks like a water line on the relay, but what has me confused is that it doesn't look level. So unless the car was parked on a very steep slope or the relay wasn't bolted into position and was hanging at some off angle by the wires, it may not be a water line? Is that simply a trick of the surrounding reference points and the rust line IS actually level? And I don't think that submerging it would really prevent it from working. The resistance of water is way higher than copper and the vast majority of the currents down there would still go where they were supposed to even while submerged. Not to say I would recommend it, but just saying I don't think that would kill it right away. I think a mechanical failure would occur before an electrical one. In other words, I think the internals would rust up solid before the coil would fail. That's definitely gruesome though. Thanks for sharing!

djwarner, I've heard that kind of thing about acetone before, but I've never been able to verify the reliability of the info. Can you personally substantiate that info about adding acetone to increase octane? Have you worked at a refinery at which they did that? Have you got the credentials to back that up? Chemist or Petrochemical Engineer perhaps? Please note that I'm not attacking here, I'm just trying to establish the credibility of that info. I'd love to be able to purchase lower grade gas and convert it to higher octane by adding a cheap compound to it, but I'd also like to be positive sure my info comes from a reliable source. On one hand, it seems too good to be true, but on the other hand, I have absolutely no experience in that field.

"Have I wrecked this?" Yes. Sorry.

Yup. You're reading it right. There are both NO and NC contacts in the 76 relay, but only the NC contacts are used. With the way you have your relay connected, you could replace it using the NC contacts inside pretty much any SPDT relay that is designed to run on 12V. In 77 they used the exact same normally closed scheme, but they changed the relay. The way I know that is the number of contacts in the connector going to the relay. Your 76 has six positions. Five of which are populated on the relay side and three that are populated on the harness side. The 77 has four positions in the connector with three populated on both sides. And I wouldn't worry to much about your fuel pump relay, even if you are overdriving the brake check relay some, I bet the fuel pump still draws way more than the relay. In other words, I bet the fuel pump draws the lion's share of the current and the brake check relay is a drop in the bucket compared to the total. I also wouldn't worry too much about the brake check relay either. If it eventually decides it doesn't like the current any more, it will just go open circuit on the coil side. You'll know it has happened because your brake warning lamp will stay lit and won't go out like it's supposed to. At that point, reach under the seat and pull the connector off the brake relay and the lamp should go out.

Oh, and by the way... I keep referring to the "N" terminal out of the alternator as the "Neutral". I kinda made that up as I've never seen it referenced that way in any of the literature. I can tell you, however, that the "N" connection IS a neutral connection out of a three phase generating system, but for all I know the "N" stands for some Japanese word that has nothing to do with "Neutral". Myself? I'm going to continue to refer to it as the neutral connection until someone shows me literature to the contrary.

Nope. Everything on the entire car is driven from the "Line to Line" output on the alternator except for the charge relay inside the mechanical voltage regulator and the brake warning relay. Those two things (charge relay and brake relay) are the only two things driven from the "Line to Neutral" output from the alternator. And because of the three phase nature of the alternator, the line to line is SQRT(3) times the line to neutral. In other words, everything on the entire car runs on normal alternator output of 12 to 14 Volts EXCEPT those two relays which run on alternator output divided by SQRT(3) or about 8 Volts. Now, of course, all relays have a range over which their coils will pull in and they are constructed and spec'ed such that they are guaranteed to have pulled in above a certain voltage, but Datsun designed the voltage regulator relay to be guaranteed to pull in at a voltage well below full output, and it's my belief (assumption?) they did the same with the brake relay. There is a bunch of discussion about the charge relay portion of the voltage regulator on pages EE-23 and EE-24 (76 FSM). And in that area it talks about the voltage expected to be seen on the "N" terminal. Also the chart on EE-24 indicates the relay is designed to pull in between 4.2 and 5.2 volts (Guaranteed to be pulled in by 5.2 volts). I haven't found that level of detail about the brake warning relay, but I would expect it to be the same?

And it looks to me like one of the holes is marked, but not drilled? Is that your sync pulse?

I bet you say that to all the Z's.

Zed Head, Water mark on the outside of the relay body? Nice! That's an interesting story if it could tell it, huh? So if you measured 0.3A to the relay, then you're dissipating between 3 and 4 Watts inside that tiny little box. It's gonna get hot in there. For both you guys, next chance I get, I'll take some pics of my 77 relay with the cover off. Mine went intermittent after being on and baking for however many hours it took to accumulate just under 100K miles on my car. IIRC, it's crispy...

According to the wiring diagrams, both 76 and 77 used the same "always powered" relay coil, but the internals of the 76 brake warning relay was different than the internals of the 77. Implication being, they used a different relay between the two years and maybe the relays they used in 76 are more robust than the ones used in 77? I don't know for sure, but you might not suffer the same hot coil crispy fate with your 76 relay style. Does remind me about another point about the relay and the alternator upgrade though... The brake warning relays used in 76 and 77 are designed to actuate (pull in) at a coil voltage less than the full alternator output. If you've done the internally regulated alternator and rewired your brake warning relay as a result of that upgrade, you're probably applying more voltage to the relay than it was designed to handle and might have inadvertently accelerated the hot crispy coil burnout. The relays are originally driven by the "N" output of the alternator which is actually the "Neutral" output from a three phase generator system. The voltage at this neutral connection is full output divided by the square root of three. Because of this, the brake relays are designed to pull in at about 60% of the alternator output voltage, or about 7 Volts. If you've reconnected that relay coil to full alternator output voltage as part of the alternator upgrade, you're overdriving the relay. Zed Head, How did you reconfigure your relay when you did the upgrade to make the light go out?

That car ad showed up in my area as well. I bet the guy at the other end of that phone number isn't very happy right about now...

Glad to help. I'm sure you've mentioned it in the past, but out of curiousity, what year Z are you working with? Because if it's not a 78, I think it's just a matter of time before your brake warning relay goes belly up. In the original configuration, they are energized any time the engine is running and the heat eventually takes it's toll.

I doubt the dielectric grease will melt. I was going to suggest RTV instead of the grease though. I mean, how many times do you think you'll be in there changing bulbs? Hopefully never. I don't think you need a hi-temp RTV grade either. I'm sure it doesn't get hot enough to warrant that. I just worry about the duct tape adhesive though. I've seen it get gummy slidey when used on a hot car surface in the sun. Then after a couple months, it dries out and doesn't stick anymore. Adhesive turns to powder. My first thought would be to use some of the non-permanent peelable RTV that they sell for temporary winterizing of your windows.

Hmmm... How hot do you think the bulbs get?

Maybe the two of you used different Hella versions? (Are there different Hella versions?)