Captain Obvious

Not to worry. The Sentra throttle body has not only the same mounting bolt hole locations as the original, but also has the identical throttle plate diameter. So no performance upgrade to "worry" about there. So... Since the throat bore and throttle plate is the same as stock, then one might ask "So why would you go through all that trouble to switch?" Valid question. Answer - Because it has roller bearings and built in vacuum seals on the throttle shaft. Smooth as silk and absolutely no leaks. That's why!

The throttle body I've been working with is (basically) from a 96-98 Sentra. There are some differences between the beginning and end of that range. Most noticeably the inclusion or lack of a vacuum port for the distributor advance. The earlier ones (96) have the port, but they stopped using the port in 97. Presumably digitally controlled instead of vacuum starting in 97. It's not a direct drop-in swap, but it's manageable. I had to make some customizations, but here's a teaser: One thing to note on the above pic is the green spring in the lower left of the Sentra throttle body. That spring is part of a system that boosts the idle when cold by acting on the throttle linkage. It's essentially the same function performed by the AAR system on the 280Z. Using the throttle body above allowed me to completely remove the AAR system and all it's associated plumbing while still having a boosted idle when the engine was cold. The tradeoff is that you have to plumb the new throttle body with coolant to heat up the built-in thermostat. If you don't mind keeping the original AAR idle boosting system, then here's another option... I didn't buy one and dissect it in my shop, but just from analyzing at the yard, I believe the throttle body from an earlier Sentra would be a pretty easy adaption as well. This is from 94, but I don't know the year range. It's simpler than the 96-98 version as it does not have the temperature controlled idle boost incorporated into the linkage. I chose the 96-98 version because the temperature controlled idle boost allowed me to get rid of the whole AAR system and still have a boosted cold idle. Note that this one has the vacuum port connection for the distributor:

Kats, I haven't been able to follow the part numbers, but all three of these caps appear to have the check valve which allows coolant to flow back into the radiator from the overflow can when the engine cools off and draws a vacuum. I'm not sure it will add anything to the discussion, but I did a little radiator cap repair work on my 280. Here's a pic of the cap disassembled. The inside (usually hidden side) if the check valve is in the upper left corner:

If they won't hold vacuum (even with the M/C hole sealed off), then there is probably an internal leak. Hole in the diaphragm or the poppet valve seal is leaking. If that's the case, when you try to draw a vacuum on it (or in your case... pull air through it), you should be able to hear air entering in the assy at the pedal push rod. Through the little felt filter thingie. Other possibility of not being able to hold a vacuum is that it's leaking at the seam between the two sections of the clamshell where the diaphragm is pinched, but you don't hear much about that happening. it's usually something internal. Please make sure you let us know what you turn up for rebuild options and/or parts!

The FSMs says the following for the 280Z (75 - 78): Front springs for 75-78 two seater - 1.84 kg/mm or 103.0 lb/in Front springs for 75-78 2+2 - 2.06 kg/mm or 115.4 lb/in Rear springs for 75-78 (both 2 seater and 2+2) - 2.28 kg/mm or 127.7 lb/in So it appears there is a difference between front and rear as the rears are about 25% stiffer. Of course I've never measured any of that for confirmation or accuracy, but that's what the documentation indicates.

I connected mine up to my vacuum pump. Used a little valve cracked a little as a regulator so I didn't suck the booster down to absolute zero. You don't have to blank off the master cylinder port. The rubber vacuum seal on the output shaft should keep the vacuum in the clamshell.

Yup. All at the same time. Plug everything you really don't need and try to isolate the issue.

I'm in agreement with the theory of vacuum leak(s). Your vacuum at idle should be well into the double digits. Hopefully 15 in Hg or higher. I'm also in agreement that simplifying the system to try to isolate the leak is a good idea. Pull and plug the brake booster. Pull and plug the EGR system. Pull and plug the HVAC system. Pull and plug the carbon canister system. Carefully inspect the PCV tube on the underside of the intake manifold.

I've got a couple steering shafts around here from different years. I never looked for numbers on them, but will do so when I get the chance. Maybe a couple more data points for a shaky theory.

I took a look a one year further back in the manuals, and the spring numbers are all over the place. The 74 manual even seems to indicate that the front left and front right springs were different. Do people really believe that to truly to be the case? The fische has all sorts of numbers and left and right are different! All I can say is that I'm glad they got that all sorted out by the time they got to the 280!

I couldn't get the video to load. Can you put it on youtube?

Without having the parts here to inspect, I'm kinda at a loss to come up with ideas. If everything measures properly and everything is seated properly, then it should work, right? I modified a pair of calipers so I could make a direct measurement on the distance between the two bearing seating surfaces. Here's a pic showing that direct measurement: And here's a pic of some distortion that can cause problems. This is what happens when you try to press a bearing in at an angle. You can see the semi-circular mark on the far side where they gouged the cylinder wall that is supposed to locate the bearing. That raised bump was pushing the bearing to one side and not letting it seat square:

I fought a sticky throttle body causing a handing idle for quite some time. Here's some of my (mis)adventures: https://www.classiczcars.com/forums/topic/45152-sticky-throttle-body-hanging-idle/ I even modified my throttle body to include delrin bushings instead of the original worn steel bushings" https://www.classiczcars.com/forums/topic/57126-sticky-throttle-body-fix-delrin-bushings/ None of that worked. In fact, my Delrin bushings were even grabbier than the stock steel and made matters worse. Worked fine when cold, but caused significant troubles once everything got hot and expanded. That project was a complete failure. I finally gave up and switched over to a completely different throttle body from another car, and it's awesome. I've been meaning to post up details. but haven't had the chance. I will do that soon.

It's obviously making the data fit the theory, but if forced, I could still believe they are date codes... Reversing the numbers and reading from bottom to top: 7047 could be 7/4/77 6212 could be 6/21/72 491 could be 4/9/71 Like I said, probably making the data fit a theory, but that's all I got.

I'm no bearing expert, but I don't believe you should have to beat on anything to get this stuff to fit together correctly. @Jason240z, are you positive sure you weren't rubbing against the inboard grease seal? You could try putting everything together and leave that grease seal out completely to see what happens. It's easy to take that nut back off and install the seal later after you have confirmed that everything else fits correctly. Also, you said you measured the distance piece and found the marking "B" stamp on the hubs. But did you actually measure the hubs to double check the dimensions?

Looks great! You didn't blast the body shell yourself, did you? You took that to someone else, right?

Seemed odd to me that the front and rears would be so wildly different, so I took a look at a couple years of the FSM... I haven't dug deep into it, but there's definitely a typo in there somewhere. You're right that the FSM (for 1976) lists the rear spring rate at 2.28 kg/mm or 197.7 lb/in. But the problem is that 2.28 kg/mm does not convert to 197.7 ln/inch. If you do the conversion manually, you'll find that 2.28 kg/mm is in fact 127.7 lb/in. So my suspicion is that they typo'd a number and that 197.7 should be 127.7. As further supporting evidence, the 1977 FSM lists the fronts as 103, but the rears are listed as 128 lb. (not 198). So it seems they realized the mistake and fixed the typo in 77 moving forward.

Yeah, Madkaw, I'm hoping everything goes great with your neck as well. No more boxing or drag racing for you. Safe travels to everyone, and hopefully I'll be able to check in while I'm away. Depends on the internet access availability. That and how much beer is between me and my keyboard.

Hi Kats, Thank you so much. I'm humbled and honored and I'm just trying to help out where I can.

Well I wasn't there at the factory when they were swaging those bushing, but I suspect they did it in just one step. Keep in mind, however, that they have access to machines and processes that I don't. I'm also sure they heat treated their dies, and I did not. I started with a mid-hard heat treatable steel that I could heat treat to a very suitable hardness, but I figured I'm only going to be doing this a couple times, and even without the heat treat, my dies should outlast me. So IMHO the bottom line is that I think it's possible to do it in just one operation, but I wouldn't recommend it unless you really know what you're doing (and I do not). However... After going through this, I believe that I can simplify the die design. You see... The first flaring die did such a fantastic job of tapering the material outward that the curved section of the second did never even made contact with the bushing wall until the flange was pressed completely flat. In other words... The complicated portion of the second die (the carefully radiused and polished center section) is pretty much unnecessary and that second die could look just like a donut with a hole in the middle. That raised portion isn't even necessary. In fact, I believe I could have simply flipped my tapered first die over and used the flat side to press the flange to it's final position. I think that if designed properly, you could get two forming operations from two different sides of the same die. So, if you're looking to minimize the cost of having dies made, I would try that. Here's a pic at the very start of the first tapering operation: And here's how it looks fully tapered with just the first die. You can see that the material is "rolled outward" so far already that it never even contacts the curved portion of the second die: If I had known that a the beginning, I may not have even made two dies. I may have made one "reversible" die instead and saved myself that polishing time.

Haha!! I looked for the MRI on this computer and it's not on here. I've got the disk somewhere and I'll see what I can do. I'm travelling for a week starting tomorrow, so I'm likely to disappear for a couple days off the forum, but when I get a chance I'll look for the disk.

The old single flange design would be a lot easier to replace (because you just press the old one out and press the new one in. The later two flanged design is a little more involved. This is what I did. First, I cut a bunch of slots in one of the flange ends with a thin cutting disk: Then, using a couple punches and a hammer, I peeled up the "petals" of the flanged lip. Worked my way around the bushing: Once those petals were peeled up, you can push the old bushing out of the bar and press the new bushing into place. No pics should be required for those two steps. In order to form the second retaining flange on the new bushing, I made a pair of press forming dies for the hydraulic press. Here's a pic of a new bushing and the dies I made. I made two dies to form the flange in two steps. First flaring step is a simple taper (on the left), and second step flattens the lip after the taper die has bottomed out: Here's another view of the dies. Preliminary taper form on the left, final form on the right.: Once the new bushing is pressed in place, I used the preliminary form to flare the metal outward: And then once the flare was formed, I switched to the final form die: And finished the flare flat into the retaining flange:

So that is "What are you doing to get ready for ZCON 2018??" Woof. That's no fun. Mine are screwed up too. Should I bring my films to compare?

Ztherapy is on the web here >> http://www.ztherapy.com/ I'm sure you can buy the SU video from them. If you hit the "customer support" link, and then hit the "video" link, there's some talk about costs and stuff. But best to call them and order it over the phone. I'm assuming this is the clear tube measurement you mentioned with the coat hanger? So you're on Marco? My neighbor just got back from there. Her was there for two weeks for vacation. Told me it was fantastic!

Yeah, I'm no expert on the bushing lineage, but I'm not so sure about that either. Have you seen a picture of that kind of bushing?