Z problems plaguing many 1970-1983 ZCARS
Keep in mind that Zcars do not have magic engines or engineering that resists breakdowns. They did have very well built engines and were simply laid out. But the age-gremlins that plague other cars also live here. And despite their performance, a great many moving parts in the engine, suspension and drivetrain are getting pretty tired. Here are some quirks and fixes that seem to plague many 1970-83 Zcars.
When I started buying distributors at the junkyard, I started noticing a disturbing trend concerning the advance mechanism inside. This breaker plate is in all distributors and rotates the whole works in response to the vacuum solenoid. On Z's it's the large round plate you see directly beneath the rotor that holds all the "bits". The point is that it has a round plastic cage sandwiched into it which holds several little ball bearings, so it can rotate smoothly.
Well in every single distributor I've seen,
this little cage is broken/crumbled/dried out, due I guess to engine heat, old
age, and general use. This means the advance mechanism is either frozen, or
badly off kilter. These were in cars ranging from well maintained models to
beaters, but it was consistent.
In
other words, I would suspect that after 20 years, most distributors in street
cars are not functioning well and may be ruining performance.
If your oil
gauge starts reading zero at idle, don't freak and start tearing into the motor.
It's almost always the oil pressure sensor on the right side of the block.
Nissan makes great motors but can't manufacture these, they seem to fail every
few months. About $20 to replace. There are 2 types though: bullet lug connector
(early Z) and spade connector (late Z). Everyone always wants to blame the
oil pump, but I've never heard of one wearing out on a Z. Keep in mind the cheap
sensor from the auto parts store may not be accurate either.
CLUNKING REAR END
This is the bane of all Zcars, it's almost impossible to
completely fix. It can have many causes, but is almost never caused by the
internals of the differential, especially if it's an R-200.
The following are all the places the clunking can
exist:
This is when you car sounds like a hovercraft when
accelerating. The round, finned visous fan clutch is seized.
But
rather than spend bucks on a new or rebuilt one,
fix it yourself. Simply take the fan and clutch off the car, unbolt the two
halves, tap them apart, spray it out with brake cleaner, and refill the deeper
half with 90 weight gear oil. The original oil dries/leaks out over the
years.
But don't worry, it's not full of
springs or anything, it a simple design and bolts back up easily. Did it on mine
and it went from almost seized to spinning freely. A better fix is to simply
take the whole assembly completely off. You can then add electric fans on the
radiator. This will free up a couple of horsepower, and make the engine rev much
more quietly.
This could be caused by a leaky heater core, but
mainly is caused by rain water. The rain gutter channels it down the front of
the door sill (check the condition of your door edge gasket), or it also drips
from the bottom corner of the windshield. What I can't figure out is how it does
it so invisibly, and ends up pooled under the mat.
Worse, the brown jute padding that Datsun used
holds water like a sponge. No wonder so many Z floors have completely rusted
through.
I think this probably the worst Z problem.
Everyone blames road salt for rusted floorboards, but this does it faster. What
makes it worse it that it's preventable. #@!&%! I have to dry my floor out
every time it rains!
GROWLING FROM REAR AROUND 70
MPH
This is usually due to a
worn out rear joint on the driveshaft. Go under and twist the joint where it
bolts to the differential. There should be NO slight clicking or play, but after
20+ years it's gotta go sometime. Unfortunately, the joints on 280X/ZX
differentials aren't replaceble. Nissan made them cheaply by stamping the joints
in, so there's no way to remove and replace them.
The junkyard is a good
place to get a replacement, but you're still stuck with a used part (possibly
very used).
The solution is to have a custom driveshaft made, about $250 dollars. Either look in the yellow pages and find a driveshaft fabrication shop, or contact Powertrain Industries. These guys are Nissan specialists and can make anything.
Beautiful car, but with terrible aerodynamics on the rear. The shape basically sucks up and billows exhaust around the back. Opening the windows causes low pressure in the car and sucks it in.
Aside from checking all the seals around the hatch, check these:
I read about this in the Z newsgroup and found it to be true. I would get a strange "clunk" from the rear when I hit a bump. It sounded like the spare tire was loose, but I couldn't track it down. It turns out the "gland nut" or cap holding the strut inserts in was several turns loose. It was letting the insert clunk up and down in the strut housing. This can happen at all 4-corners, a pair of large pliers slipped between the coils makes this a quick fix.
These little fellows have spinning gears just like an old mantle clock. You can open it up and carefully clean the gear and lube it up. It's pretty old though, might be better for cosmetics than time...
Does anything need to be said?
POR-15 is a great
product. Do a search on it....
TACH "JUMPS" OCCASIONALLY (280Z/ZX)
I though this was the coil, but I think I found the real cause. Note that the only thing that makes the tach needle move at all, is a pulse to the tach sensor wire. 260/280 tach sensors are connected directly to the negative terminal on the coil, while 240 tachs are isolated and use an odd inductive wire loop which triggers the tach. So for the tach to jump, something has to be affecting the pulse.
Now on '75-78's, the - coil terminal sends 14v impulses out, which triggers the tach.
And at one point, my 240s regulator failed and started
putting out spikes of 17-19 volts. And when my ammeter needle jumped, so did the
tach. That's when I realized that any excess voltage in the tach sensor wire
causes it to jump.
So apparently
these "jolts" you see sometimes are the regulator hiccuping.
TIP: if your 240 tach is getting old, you can easily
upgrade to a '75-78 tach. All you have to do is remove the 280 "works", and
transplant them into a 240 metal housing and plastic front. The faceplate can be
swapped to keep the redline stock. Make sure you run a separate wire with the
resistor directly to the coil's - terminal. Note that the + and - power leads on
the tach are reversed. Easy and accurate.
KEY STARTS ERRATICALLY
This is when the key has to be clicked several times to
get the starter to turn, etc. It could be the starter solonoid, but if changing
the starter is doesn't work, it's probably the black plastic ignition switch
behind it the key lock. It's held by two small screws, easily replaced with a
screwdriver. $15 last time I checked.
Plagued by melting fuse wires, redhot fuses? Well, the
240 fusebox uses simple rivets and crimped wires to hold the clip-plates
together. These contact areas oxidize over the years and increase resistance in
the connections.
Through such a marginal
connection, current draw goes way up and so does the
temperature.
Adding to the problem is the
fact that the entire alternator output circulates through the right side of the
fusebox (in one 10 gauge white wire and out the other). With all this current
running through poor connections...you get the picture.
The two 10 gauge spades that connect the box to the car harness can also oxidize. Mine actually went "poooofff" and sprayed smoke as they melted the wiring one day. Remember, that's the alternator feed.
So if your fuses can burn your fingertips, replacing the
box is the solution. A cheaper fix is to take out the box, and use a hot solder
gun to resolder all the rivets and wire crimps. It only partially worked for me,
so I went a step further and soldered a single bare wire across the wires where
they entered the "crimps".
NOTE: only solder
a wire down the passenger side of the box, doing one on the driver side too
defeats the fuses!
This seemed to work much better. All cool now.
VERY POOR IDLE BUT REVS FINE (280Z, overlooked problem)
I saw this problem on several when I was autocrossing,
including mine. The bellows between the throttle body and the air box develops
holes deep within the "folds". This leaking air screws up the mixture after it's
metered by the air box, but on heavier throttle is insignificant. The bellows
may have to be removed to see the cracks, seal them with black silicone. The
rubber is 20 years old after all.
Remember that steel wheels are notorious for being out of
round/balance. And note that few tires are completely round either, due to
normal "high-spots" in the belts or tread. Even if in perfect balance, a tire
with a high-spot will slightly "hop" on every revolution as it hits the road.
This a very overlooked balance problem that affects many tires.
I also suspect that the front end is simply resonating
due to age and the unibody design.
So resign yourself to the fact that you may never get
all the shake out.