igotatruck

Welp, got it bolted back up. Drove it to the autozone to get a better clamp and a bit peed out in the parking lot there but, nothing when I got home so I suspect it was just a little excess working its way out. Sounds a bit better, temp gauge works fine, no steam or anything still. Ill report back after a few days of driving.

Thanks! Thanks also, off to buy new hoses!

I was able to remove the shroud and the radiator at the same time, had my friend lift/hold it while I massaged it around the fan. It was indeed a M/Fer. Here is a pic of the shroud; As you can see there is this metal clip that goes around the back but the main thing is solid the way around https://drive.google.com/file/d/0B1clQg_QvWC9OEdQOUNieUNjMzQ/view?usp=sharing Here is a comparison of old and new pumps: https://drive.google.com/file/d/0B1clQg_QvWC9eDlfd1hrZkFTTDg/view?usp=sharing The old pump has a little play in the gears but nothing crazy. It doesn't spin "easily" but it isn't grinding or anything. Also I see what you mean, the new pump is generally crappier. The cavity where the old pump was, rusty! https://drive.google.com/file/d/0B1clQg_QvWC9YkZpX0N6WENqUkU/view?usp=sharing The way it dripped out when I removed the pump was really similar to how it looked when it was leaking, so I really think it was the gasket/pump. It was also still wet directly underneath the pump before I removed it. Can anyone tell me what this little black tank is for? https://drive.google.com/file/d/0B1clQg_QvWC9RVU0em9EX0s2Nm8/view?usp=sharing

It does have a metal collar that goes around under the fan and clips in, but it is a solid piece of plastic that goes all the way around. I can see how it might be thin enough to slip around the fan on the bottom, but then it has lips that fit under the rad so you can't pull it close enough to slip under. I am just gonna pull the rad in the morning, since I am in there I might as well clean it out real good.

Will do, thanks. Am I correct in thinking the shroud only comes out after removing the rad? The Chiltons I have just says "remove the shroud" but it seems like it surrounds the fan and wont come out on its own.

I am not sure if the hoses are tight. I am trying to get in there for a closer look, currently stuck on getting the fan shroud out...

Ok, found the drain cock. I am guessing I should use a pump to drain it rather than just letting it spooge all over the bottom of the bay as it drips out? The leak sure looks like it is coming from under the bottom of the water pump. I tried the little mirror trick but couldnt see much, but I do see drops landing around the front under the pump and nowhere else on the engine. It also doesnt stink like I would imagine, if it was running over any of the engines hot bits. What would be a better part to replace it with? The belt driving the thing also got some coolant on it, probably should replace that too?

Also where are the plugs to drain the coolant?

So I realized I had coolant dripping. Did a litttle checking and found that it inly leaks when its been running a bit, no smoke or anything from the radiator, it runs fine, the oil does not look milky in any way. So I doubt it is a blown head gasket. I am suspecting the water pump because I do not see any leaks in the radiator. Plus the area it is leaking makes me think the gasket on it has worn out. It sounds really loud too and I doubt it has ever replaced I have ordered this one from AZ and I will be replacing it tonight: http://m.autozone.com/cooling-heating-and-climate-control/water-pump/duralast-new-water-pump/233999_381126_0 Anyone have any wisdom, things to check for while I am in there? Thanks

Hey I just went through this in my truck. How are you measuring things? Look for the mentioned 2.2k resistor by the coils. It will be in a thumb-sized black rubber connector on the wire. If you pull it you can check the continuity between the resistor, coil and the tach connector without worrying about wire colors. Since you have 12V, it seems like your fuse is fine. Make sure you have ground on one of the other pins (not both) and the third will be the signal to the gauge. If you have access to an oscilloscope you can check to see if the connector in the dash is getting any kind of signal. A cheap DMM might also be able to register some kind of AC response. Also, you can measure the tach meter. If you remove the gauge from the cluster, you should see some tiny, silver wires connecting the control circuit to the little springs that move the needle. If you measure these VERY CAREFULLY you should get a resistance of some kind, probably around ~100Ω, mine was 70Ω. The bad one died as 'open circuit' if I remember correctly, and the small voltage from my cheap DMM was enough to nudge the working needle. Check this: http://community.ratsun.net/topic/71865-84-datsun-720-gauge-hackery/

Happy Tacho Tuesday everyone. I am pleased to report that the new Tach works like a dream. When I got it I measured the resistance across the spring/coils that move the needle and got a healthy 70ohms, which means it's not burned out like my old one. So if your Tacho craps out, you can test it with the ole' DMM.

Just replaced the fuel filter in my 720 KC. It made a world of difference for the $5 and 10min I put into it. The old filter was so clogged I thought my clutch was still slipping. Better accel, engine runs much smoother.

Yes it was, then I pulled just the Tach from the cluster and plugged it back in, by its self outside of the cluster housing. I was measuring the voltages from the front of the little gauge circuit board so I know it was getting to the board. I am 90% sure that the gauge is toast, and I have a new one on order, I will post an update once it arrives. Now onto replacing the stereo!

Also feel free to send me any questions.

Hey, its been a few weeks but I have done a bit more work on the gauges. As of now, all gauges are working except the Tach. I pulled the tach from the cluster and plugged it back in so I could rule out connection problems. The wiring is all good from the ignition coil to the Tach Resistor and then to the Tach Gauge. I have ground and +12V in the connector as specified, and I am getting an interesting signal on the final connection. The signal coming out is a gnarly square/sine wave that goes up in frequency as I rev up. The voltmeter says its ~24Vp-p but my scope cant wrangle it into anything it can measure, as it 'clips out' wildly. This leads me to believe that my coil is somehow messed up and putting out a signal that is too ugly, OR The coil is putting out the correct pulse and my gauge is hecked. I wish I had a real function generator I could hit the gauge with to test it, but that will have to wait till I can get back in the shop. Anyone got any thoughts? UPDATE: I am measuring the spring/coil on the gauge as being an 'open circuit', meaning it's probably cooked, it should be a few ohms at least. Ordered a replacement from ebay, should be here next week. I payed $45 for the replacement if anyone was curious.

That sounds awesome, do you have a thread going on that? I might be able to help, I specialize in audio gear and I have done quite a few arduino projects.

I will check the Tach wiring after work tonight, it has a much more robust three prong connector on the back so I am less suspicious of that connector. Spent my lunch break scraping a little replacement for the Voltage Regulator. I made it using an LD1117 variable regulator with a trim pot so I could dial in a range between 7-9Vdc and kinda tune the gauges to the sensors. Picture of the replacement regulator: https://goo.gl/photos/G3U3PLKcJmZwPHnn7

On the ride to work today I found that the Temp gauge was now working also, gonna chalk it up to loose connections to the cluster. https://goo.gl/photos/L1tJQZnqX7rL9LAF6 Tonight I will try injecting some voltage into the tach meter to test if it works.

Greetings Rat-Monkies! First of all, thanks to everyone for your previous posts, they have been very helpful. I recently purchased an 84 Datsun 720 King Cab in need of some TLC. One (of the many) things that needs attention is the Panel Gauge Cluster. The fuel gauge, water temperature, and tachometer were not functioning properly. I do remember that the gas gauge was working when I picked it up. I have been lurking the forum for the last few weeks trying to sort this out and made a little progress tonight. I had little success finding an auto electrician who would touch it and since I do electronics for a living, this was personal. So I tried every little test, fuse, relay and connection I could find before yanking the cluster module out to test it. I hooked up a DC power supply to the Fuel and Temperature gauges to see if they worked, and they both worked fine. In another post around here I was reading datzenmike saying the voltage regulator keep them at 8V but they worked with 12. It does seem like the internal voltage regulator is busted, and though this seems to be more a matter of calibration/consistency than function, I will put a small replacement together tomorrow and post my findings. Here is a link to the pic of my disassembled fuel level gauge, responding to the DC power supply. I cant seem to get the Ratsun forum to show it, sorry. https://goo.gl/photos/R2qqggYTkdK3ux9V7 Other associated pics: https://goo.gl/photos/atPymVYiPeUWstfG9 I cleaned/reseated all of the connections on the plastic flexy circuit board and put it back into the dash (I need it to drive to work tomorrow), only to find that the fuel gauge was now working! Hopefully it just had a loose connection in the dash and wont turn up again. I also have yet to see if the Temp gauge works. More on the Tachometer later; I do know that its little resistor module measured at 2.2kOhms the other day (sounds okay to me). When I hooked my meter to the tach connections, I seemed to find: a chassis ground, +12Vdc and a third voltage around +12V that would drop (~0.5V) when I revved it. Hoping this is the correct control scheme for the tach, and I dont have to undo any wire wrap. If anyone has any ideas or anything please let me know, hoping this might help someone else out there. Thanks again!