1 hour ago, Patcon said:

Crenelated as in the style on the studs or the style on the string?

Studs

my 7/71 had the flat style.

Nissan seem to have had lots of complaints about rear-end noise for the early cars.  The text in the Mar-71 TSB bears this out to some extent, although it implies that the problem showed up only in cars with the automatic transmission.   The (expensive) change in the entire diff mounting scheme that occurred in 71-06 is a better indication that the issue was significant (at least, as far as customers were concerned) and affected both the manual and automatic-equipped cars.

According to the online 'Car Parts Manual' reference, the factory made a change to these 'castellated' rubber washers as of 71-04 (roughly the same time that it changed the diff mount design so as to straighten out the halfshafts).  There's anecdotal evidence to suggest that the change amounted to making the 'fingers' longer.  That would make them more compliant (which would help cut down on the transmission of gear whine noise into the rear cabin area).  If somebody has a picture showing a set of NOS early washers in their factory packaging (PN 55474-21000 or 55475-21000), we'll know for sure.

Unless you're dead-set on originality, it may be better to go with the long-finger versions (the ones shown mounted on the studs in your picture), working on the theory that 'original' isn't always 'best'.

Also:  Given that there are two different PN's for these castellated washers (irrespective of vehicle manufacture date), can someone comment on whether this means that there's an 'upper' and 'lower' washer?  If there is, what's the difference and how do you tell which one is which?

1 hour ago, Namerow said:

Also:  Given that there are two different PN's for these castellated washers (irrespective of vehicle manufacture date), can someone comment on whether this means that there's an 'upper' and 'lower' washer?  If there is, what's the difference and how do you tell which one is which?

Yes they are different. The upper washer has a larger hole because the chassis stud has a larger diameter as you get closer to the car floor. Also the lower washer with the smaller hole has a recess sort of like the tension rod washers to accept a washer and nut I assume.

On 3/10/2018 at 6:19 PM, Patcon said:

So the car had a turbo engine in it when I got it. I don't know if it ran. This is the fuel tank that was in it.

The tanks are a lot thicker than they look. I tried the slide hammer to pull the dents, not happening!. I have another tool to try. I may put a 240z tank in it, since I don't need any of the EFI ports, baffles or sizing.

What is the stock feed supply size?? this tank has a 1/2" feed port...

Stripped with some airplane stripper

plug all the holes except 1, and apply some air pressure. for the most part, the dents will disappear

10 minutes ago, sweatybetty said:

plug all the holes except 1, and apply some air pressure. for the most part, the dents will disappear

Even on an efi tank? There are a lot more structures internally; it's pretty stout

It will expand wherever the air has the most leverage.  The broad dent across the flat bottom will probably pop up, but the corner dents, not so much.  Might be possible to overblow it then beat/finesse the overexpanded parts back down to where they're supposed to be.  Then there's work-hardening, which makes dent removal even harder.  Some kinks will probably never come out.

With a pressure regulator you might be able to get it to start to correct and with some well placed blows on the corner high spots get it to a serviceable level.

 

IIRC, there's a CZCC thread from about two years ago in which the poster illustrated a tank repair where he split the tank along the join seam.  An option worth considering? Another option, of course, is to just find a replacement tank that's in better shape.

I have 3 different tanks here but it would be nice to salvage this tank too. I may not use it in this build but I would still like to try to get it reasonably shaped. I am sure I could cut the tank and split it but am not sure I am a good enough welder to seam it up again

I have a number of studs welded to it right now and the slide hammer wont even budge it. That makes me wonder if air pressure would even do it.  I guess if the pressure is high enough. The small holes wouldn't be an issue to cap but the large ones might be if I needed fairly high pressures...?

 As long as the studs are in place and the interior is clean, try more heat, Propane torch might be enough for sheet metal, oxy-acetylene would be quicker. If you get it hot enough, it will move.

Ok, so I worked on one of the other tanks I have. This is a 240z tank. there is an amazing difference in weight between the 240z and the 280z tank. The 240z tank is maybe half the weight and noticeably thinner.

A little aircraft stripper...

Great stuff but don't get it on you!!

Several large dents on the bottom

A few studs going on

This tool is really cool. It was $100-120 but when trying to pull larger dents works well. When you pull too hard on a single stud you can get a raised dimple or even tear the stud off. When you get 4 or 5 studs on you can really pull on them with out the raised areas

We were banging on this with a 16# or 20# slide hammer. Had to stand over it on the table to do it.

I took a piece of rebar and tried to make an extended dolly. It helps some but was hard to position and keep pressure on. If the holes into the tank were only slightly larger I could get my hand in there.

This is sort of where I stopped. Not perfect but I will probably skim a few of these areas to satisfy my OCD then shoot some black on it

This is a 100+ studs later...