Distributor Vacuum Advance Diaphragm Failed

[Zed Head]

I feel like I should thread this for future problem solvers.  It actually happens.  My engine was running weirdly, with a very light constant on-off surging at highway cruising speeds, and adjusting fuel mix with my coolant circuit potentiometer didn't have any effect.  So I took the distributor out to see if I might have a broken spring letting timing fluctuate.  Also checked the vacuum diaphragm and found it was blown.  Not completely but enough that you could blow some air through it.  The cam, weights, and springs were fine.  I'd guess that the vacuum would pull the diaphragm, advancing timing, then the hole would open and it would lose it.  Or something like that.  Put a another distributor in (I like to test my spare parts when I get a chance) with a good diaphragm and it's super smooth now.

 

I pressed on the lever to the diaphragm after I pulled it off and must have destroyed the remainder,  It made a crunchy noise and resistance to breath disappeared.

 

Just one of my recent odd old 280Z problems.  Along with EFI relay solenoid going bad, and battery crapping out, even though it shows a full charge.

[SteveJ]

A bad cell in a battery can be a PITA to diagnose. I had that one time. The multimeter said 12 VDC, but when I turned the key, voltage dropped to 0.

[Zed Head]

Here's some pictures.  You can see the threaded base on the rod that stops travel of the breaker plate actuating arm.  How people adjust maximum advance if they remove the epoxy plug on the canister.

[Namerow]

Interesting photos.  Never seen one of these dissected before.  How did you get it apart?

[SteveJ]

He has hands like Andre the Giant. The vacuum advance didn't stand a chance.

[Zed Head]

A bad cell in a battery can be a PITA to diagnose. I had that one time. The multimeter said 12 VDC, but when I turned the key, voltage dropped to 0.

I got lucky and it died in my driveway.  It would crank the engine fine for a few turns but not start then slow down then make that noise like it's about to give up.  Let it sit a few seconds and I could do it again.  I put a meter on the battery and it was 12.7, 11, 11, 9, 9, 9, 9, 9, 6, 6, stop.  Cleaned the battery terminals, cables are new, same thing every time. One side benefit though was I thought it might be my starter so I installed a gear reduction starter that I had as a spare.  It just gave more 9's but now I get the airplane engine sound when starting.  Problem wasn't solved until I installed my spare battery.  Which is old and will probably die soon also.

 

I think this might have been the actual problem that caused me to replace my EFI relay.  Although the EFI relay still tests bad, and I did get a week or two more before the battery gave out.  Weird how problems happen in bunches.

[Zed Head]

Interesting photos.  Never seen one of these dissected before.  How did you get it apart?

I mounted the piece in a vise and used a hack saw.  Cut, cut, rotate.

[Patcon]

Zed,

I don't know, that part doesn't look that bad...  I know, duct tape!!!