NewZed

I'd get a video of the front mount and diff nose, just to know all of the facts. If the axle axes are static (which they seem to be in the video) and the back of the diff is dropping, then the front of the diff has to be rising. Just saying, that's the way it has to be. Might just be taking up the elasticity of the front urethane or there's more flexing happening. This is different from what I first proposed. The short nose diff has a lot of leverage on those two arms used to make the front mount.

Apply the thumb.

I remember that one. Good to see you're still back in action. In your video it's hard to see what the front of the diff is doing. But you have elastic mounts up there also, it's probably twisting up and back, not too solid as I proposed earlier. And the leverage problem that everyone has who uses a short nose diff with the original holes for the strap mount. The nose of the diff is pressing upon a fairly long lever arm against the screws in the body. You might even be flexing those two arms also. I think that the front is moving allowing the back twist downward. The whole diff is twisting around the axles. And the tube you used for the rear bar seems to be flexing. The guys that run the Q45 diff have the same leverage problem on the front. The suggestions in your other thread about mounting directly above the diff nose probably still are worth considering. Just opinions...

You were on here before, right, a short while ago? A whole discussion about PCV systems and vacuum leaks? Hard to keep track of who does these things. Did you block the PCV valve on the bottom of the manifold? If not, the big hole in the valve cover will be a problem. Stick your thumb over it while the engine's running and see if anything changes.

Well then, carry on with the clutch control system, from pedal to fork. If it worked before you should be able to make it work again.

What does that mean? "Back".

Regardless, without ECU controlled idle speed, he needs a throttle body or blade bypass. The 280Z's had the bypass in the TB, the ZX's went to a hose bypass with an inline valve. Hard to get a good vacuum reading if the engine is about to die. He needs idle speed control. Set the idle speed then tune the engine.

What kind of throttle body (TB) is that? The 76 TB has a screw to adjust idle RPM,letting air past the TB. You might need to add a ZX TB bypass hose/valve setup.

Did you do these two things at the same time? That would change everything.

Here's a collection of information. Low impedance is old technology though so the choices are limited. If you're using dropping resistors you could remove them and go with high impedance. Some people use high impedance with the dropping resistors anyway, even with the stock 280Z EFI system. I have. It ran fine but I think I may have had current issues during starting (wouldn't start on cold days, but my battery is weak also) so I removed the resistors. Do you know the specs on the Adaptronic system? Maybe you don't need low impedance. http://users.erols.com/srweiss/tableifc.htm

What kind of diff? The single bolt on the back mount looks unfamiliar. What's the front mount look like? The Arizona Z Car mount has brackets on the control arm pivots, yours doesn't seem to have those. Not really clear what you're working with. Looks interesting though. Did you build it or buy it? If you want to confirm that the bar is bending/flexing you could run a tight string across the top of the bar, from mount to mount, as a reference line. Distortion from the camera lens might be making the bar look like it's bending. If it's camera the string will look like it's bending also. All you can really say from the video is that the back of the diff moves away from the car body. But, if you look at how far the back of the diff moves and compare it to how far the bushing flexes, you can see that the back of the diff drops much farther than the bushing flexes. That's a long lever arm from the end where the mount is to the diff. Also, the hangers for the suspension brackets are tied directly to the body. So the "dogbone" is a reference point also. The back of the diff is definitely dropping and it can't do that unless the bar bends. Even if it twists on the bushings it still has to flex/bend also.

My mistake. Paint is plastic. Chemically and often physically. It's squishy.

I see flexing of the bar and the bushings. The back of the diff is pulling down. Usually the nose pulls up but the rotational force is pushing down on the back at the same time. So the front is very strong now and the back is the weak link. Stiffer bushings without a stiffer bar might transmit more twisting to the studs. Fatigue could be a new problem.

The system worked. Could be the seller got caught with poor heat treatment like a couple of the guys on this forum did when they had stub axles made. The concepts are simple but getting things executed correctly seems to be difficult. Are you going to share the seller's ebay name so others don't get trapped? CFJ im[plied that Silvermine sells them but they seem to have a decent reputation for quality. They've been besmirched, indirectly, Make sure you get the clips installed and seated.

Looked like the bar was bending then springing back, kind of like the original bar was designed to, although it may bend much more with more torque. The mounting area, the studs, didn't seem to move. You didn't give any details at all about how the mount is made or what material it's made from.

You implied that you had the wheel mounted on top of the paint on the brake drums. Generally, mounting surfaces should be clean flat metal. Burrs, dirt, grease, grime, paint should all be removed. I've been surprised that Nissan paints the flanges of the u-joint halfshafts. I scrape it all off if any is chipped. Tried to find a general internet reference and this popped up. Copied an excerpt. Lots of good stuff in the whole document, actually, even though it says it's for trucks and motorhomes. Load is load, a high performance Z probably hits motorhome loads.. https://www.alcoa.com/alcoawheels/catalog/pdf/ServiceManual-English.pdf

The 78 and on starters are gear driven, with an offset drive motor. They seem to be reduction starters, but I've never actually seen the gears or a description of their ratios so can't say for sure. They're not direct though, and it would be kind of pointless to offset them without taking advantage. It should lessen the voltage drop allowing more juice for spark and other electronics, as noted above. Never heard of the turbo car gear reduction starters, and the 78 + starters weigh less than the big motor direct drive pre-78 starters. So it looks like three different types are out there. At least one manufacturer describes them as gear reduction, for what it's worth. Picture from Rockauto site. Just a few more factoids.

The likes are that much more valuable. Who to bestow your like upon at the end of every day.

Soft plastic paint on a metal mating surface isn't really a good idea. It will creep and compress over time.

You don't seem to be measuring anything. There's no numbers. One thing that many people do when they swap parts is to compare the old to the new. You could have, and still could, compare(d) the old MC to the new one. Sometimes people have to swap the rods to get the new ones to work. Added a picture. With the pedal in the proper position, one way to get really close on the MC rod length is to adjust it until the clevis pin drops in to the hole easily. And a typical test for air in the system is to pump it up. If the system pumps up, in other words works better after pumping the pedal quickly, then there's air. The pumping compresses the bubble with new fluid. Anyway, good luck. Take some time and look at each piece and what it does. It really is a very simple system. A collection of simple concepts.

Those hose clamps look scary. You can get CV boot clamps, and a $10 tool to fit them. https://www.summitracing.com/parts/oes-25326?seid=srese1&cm_mmc=pla-google-_-shopping-_-srese1-_-oem-specialty-tools&gclid=CMOxnZi35M0CFQeTfgodfqoH7g https://www.summitracing.com/parts/cwa-5013626aa?seid=srese1&cm_mmc=pla-google-_-shopping-_-srese1-_-crown-automotive&gclid=CN7XiqS35M0CFZNhfgodlFQK3w

Spray some WD-40 or PB Blaster on first to help. They rust. Found a picture of the back on the inter-tubes - http://www.ebay.com/itm/Used-70-78-DATSUN-240Z-260Z-280Z-QUARTER-PANEL-EMBLEMS-PAIR-/262514806476?hash=item3d1f1a0ecc:g:G4kAAOSwmtJXVdBb&vxp=mtr

They're just a press fit, with spring clips. Pry up the edges and they'll pop out. Don't know how fragile they are so use a wide blade and work slow.

See if you can get a decent picture of the inside of the cylinder. That's where the corrosion/crud that damages the seal or gets stuck under its edges lives.