Keep in mind that Datsun Zcars do not have magic engines or engineering that resists a breakdown. The engines were very well built and the design was well 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 1970-78 Zcars.

WET FLOORS
Z cars have this mysterious ability to end up with water on the floor under the mats after a hard rain. Both my '70 and '76 had this problem and I could never track down the exact source. One day I decided to remove the fan under the dash to repaint the firewall. Guess what I found? It wasn't leaking from the windshield corner, it was coming from the body seam between the firewall and cowl. Late 1960s Ford Mustangs had this problem too.

THE CAUSE: Under the windshield-wiper cowl there are two very tiny drain holes under the crossbraces on each side which I never noticed before. Not the down spouts under the fenders, these drains are in front of the windshield. Well, rain water flows under these from the center out to the large drain tubes on the side of the fenders. These small holes were blocked with old dirt, there was actually standing water pooled around the center wiper motor area(!)

This standing water had rusted the seam between the firewall and the front of the cowl. So when there was heavy rain the cowl would fill up and the seam would leak down the firewall into the car. The solution is to take out the wiper motor and use rustproofer on all the seams in the cowl area. NOTE: There is a non-removable metal box in the passenger side of the cowl which is the fan inlet. You can't remove it, but you have to seal this all the way around. In the photo below the fan inlet rust is just cosmetic. The seam below it is the actual culprit.

Looking up at the underside of the dash with the glove compartment and main fan removed

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Worse, the brown jute padding that Datsun used on the floorboards holds water like a sponge. No wonder so many Z floors have completely rusted through. 

TAIL-LIGHT/DASH/SIDE MARKER FUSE KEEPS BLOWING (240Z)
This is when the 3rd fuse down on the right side of your fusebox keeps blowing (taillights, dash lights). Sometimes immediately, sometimes after 10 minutes. You've changed all the bulbs, cleaned all the connections, resoldered the fusebox, and replaced the headlight switch with no solution. My 240 had this problem for several years and I avoided driving at night. I just found the cause (!)

The insides of the the front turn-signal sockets are very cheaply made. A small fiber disc with poorly stripped connections pushes down on a spring to hold the bayonet bulb in. The bottom of this spring is perched on the metal socket inside...which just happens to be the ground. If the top of the spring touches the exposed hot wire next to it it blows the fuse. So I used liquid electrical tape on the wires and made sure the inbound ground wire was securely soldered to the metal socket body. My lighting is solid as a rock now and the fuse has not blown in 8 months, what a sneaky, frustrating cause. @#$%*.

NOTE: check all your signal/marker light sockets and make sure that the negative wire really is negative. If the socket wire base has rotated in the socket over the past few decades you could have reversed terminals. This will blow the fuse because the light housing is grounded to the body.

TWO ODDBALL IGNITION PROBLEMS
For a while I had been getting a strange stumble when accelerating from low revs or at odd places in the rev range. Also, my tach needle would jitter at PART throttle but not at full throttle. Weird. I checked all my grounds, rerouted all the wires from my MSD 6A ignition to prevent RFI, measured resistance on all plug wires, and rebuilt the distributor. I even got a new alternator, but no solution.

I finally discovered that my fairly new distributor cap (Borg-Warner, brass terminals) had a ring of brass powder running between the terminals...CROSSFIRING! I don't bame the cap, I suspect the shaft on my distributor was worn and rocking side to side. Interesting how the tracking seems to follow almost a magnetized path around the terminals.So I bought a new distributor and the engine is smooth as silk, startup instantaneous and tach perfect. An interesting lesson to be learned.

BURNT CENTER TERMINAL and ROTOR
On a completely separate occasion, I checked inside my cap one day and found the center terminal that touches the top of the rotor was badly melted, along with the rotor top. Amazingly the engine seemed to run fine. This meant the center terminal was having to arc 1/8" to reach the rotor top(!) I don't blame my MSD 6A ignition though...it was the fault of the distributor cap center terminal. If you pull it out the button you will find it only has a tiny spring behind it to make it contact the rotor. This very tiny spring carries the entire output from the coil and simply melted the cap.
MORAL: don't buy cheap parts or replace the spring with a heaver version.

DISTRIBUTOR BREAKER PLATE
When I used to buy distributors at the junkyard I noticed a trend concerning the breaker plate inside.This breaker plate sits beneath the rotor and rotates the whole works in response to the vacuum solenoid. The point is that it has a plastic cage sandwiched into it which holds several little ball bearings so it can rotate smoothly.

In every distributor I saw this little cage was broken/crumbled/rusted, due to engine heat, old age and general use. These were in cars ranging from well maintained models to beaters, but it was consistent. I would suspect that after 25+ years, many breaker plates in Z cars are not functioning well and hurting performance.

• the way to test yours is to take off the distributor cap, and while watching, suck hard on the vacuum hose leading to the dashpot on the side of the distributor. The plate should rotate clockwise smoothly about 1/2", and snap back when you release pressure. If you can hear your breath hissing from the distributor, the vacuum solenoid is leaking. If the plate crunches, sticks or moves poorly, the cage in it is probably bad.
• Even a good plate can be stiff: take the breaker plate out and look on the bottom and make sure the ball-bearings that rotate the plate haven't rusted. If they have, spray it out with WD40 and grease it up and you may be able to get the plate to rotate smoothy.

Nissan dealers carry them for about $80. Buying a new or rebuilt distributor today is probably the best solution.

NOTE: the bearing that holds the distributor shaft wears too. You can tell wear by lightly moving the top of the shaft side to side. Bad wear will throw off spark intensity, especially on point ignitions. A distributor shop can replace the bushing for you, a new distributor from Victoria British is an easier but more expensive route.

OIL PRESSURE GAUGE READS LOW AT IDLE
If your oil gauge starts reading zero at idle don't freak and start tearing into the motor. Everyone always wants to blame the oil pump, but I've never heard of one wearing out on a Z. It's nearly always the oil pressure sensor on the right side of the block. Nissan makes great motors but after 30 years these little sensors lose their abilities at low pressure. About $20 to replace. There are 2 types though: bullet lug connector (early Z) and spade connector (late Z). 

Also, if your engine has a lot of miles this can be caused by large bearing clearances due to wear. The pressure goes up while driving but will be very low at idle. Instead of rebuilding the motor, install a 1981-83 turbo 280ZX oil pump and pick up some pressure.

CLUNKING REAR END
This is the bane of all Zcars, it's almost impossible to completely fix. It can have many causes, but it's rarely caused by the internals of the differential, especially if it's an R-200. If you hear it thumping the floor behind your seat it's a broken differential mount. If it is farther back its likely one of the causes below:

• worn out mustache bar bushings (replace with urethane)
• u-joints on the halfshaft ends are loose and worn-out (common, replace the joints)
• tighten the bolts/nuts on both ends of the halfshafts
• front differential mount broken (try tightening the center nut in the bottom first)
• driveshaft bolts loose
• shocks bad or loose in strut
• replace the control arm spindle pins
• ball bearings/grooves in halfshaft body worn (replace halfshaft)
• tighten the two large nuts that hold the differential to the mustache bar
  
  Personally think most of the time it's caused by the mustache bar bushings. These thin rubber bushings rot and flex and let the bar clunk the floor on acceleration.
  

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 30+ years it's gotta go sometime. Unfortunately, the joints on 280Z/ZX driveshafts aren't replaceable. 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 very used part.

The solution is to have a custom driveshaft made, about $300 dollars. Either look in the yellow pages and  find a driveshaft fabrication shop, or contact Powertrain Industries. These guys are Nissan specialists made me a custom driveshaft which was very high quality.

• the gaskets around the taillights, seal with silicone rubber if needed.
• check the thick rubber gasket around the rear hatch: slam the hatch on a piece of printer paper in different spots and try pulling it out. You can find leaks this way.
• make sure the both PCV hoses are connected. If you have ring blowby which is common on an older motor using a tiny K&N filter on the valve cover will vent all the fumes into the engine compartment.
• check the firewall for missing throttle boots, gaps around heater hoses, etc. I had leaks around my A/C hoses which I found were pouring in air
• while driving in cold weather open the driver window slightly and run you hand across the bottom of the door sill. The rubber seal across the bottom of the door is notorious for leaking.
• Secure and seal the vinyl panel on the inside of the hatch. The emblem holes in the hatch can leak.
• If your rocker panels are rusted from behind, air can filter in through the "swiss cheese" holes stamped into the door sills under the carpet. The left rear fender on some Z's has a rubber plug on the bottom which can leak air in.
• On early 240Z rear decks look behind the plastic side panels, there can be a precise 1/16" gap where the deck and fender meet, Datsun didn't appear to have used seam sealer. Mine were not rusted but I could actually see light from below. I used silicone sealer to seal them.
• Sounds simple, but make sure the exhaust system from cylinder head to tailpipe isn't leaking. My header was cracked at the weld where it entered the exhaust pipe once.
  
  If you have gas smell, check these areas
  
• If you have a 240Z, check the gas vapor tank behind the panel in the right/rear fenderwell, spend an afternoon replacing all the hoses with new ones. Make sure that the vapor tank is not cracked anywhere.
• Drain and drop the gas tank and replace the 2 large vent hoses. But don't spend $$ for the old fashioned braided types from Nissan, just buy good quality gas hose from an auto store (if you can find the right width). DONT scrimp and use cheap heater hose, gas eats right through it.

CLOCK STOPS
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 after 30 years.

RUST
Does anything need to be said? POR-15 is a great product. Do a search on it.

280Z/ZXTACH "JUMPS" OCCASIONALLY\
I thought 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. 280 tach sensors are connected directly to the negative terminal on the coil. So for the tach to jump, something has to be affecting this pulse.

On day my voltage regulator starting acting up and began putting out spikes of 17-19 volts. And when my voltage 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 can be the regulator hiccupping.

KEY STARTS ERRATICALLY
This is when the key has to be clicked several times to get the starter to turn, etc. If you've ruled out the starter solenoid and changing the starter doesn't work, it's usually the black plastic ignition switch behind the key lock. It's held by two small screws, easily replaced with a screwdriver. $15 part last time I checked.

To make matters worse, if you look at the 240Z schematic the voltage feed from the alternator actually routes through one side of the fusebox and back out to the battery to charge it. The entire battery feed is relying on one little crimp(!) My fix was to run a new 12 gauge wire from the positive "A" terminal on the alternator directly to the + terminal on the battery to spare the strain on the fuse box.

Another partial fix is to take out the fusebox and use a hot solder gun to resolder all the rivets and wire crimps. You can also solder 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 defeats the fuses!

VERY POOR IDLE BUT REVS FINE (280Z-ZX, overlooked problem)
I have seen this on several motors including mine. The rubber boot between the throttle body and the air box develop rot-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 25+ years old after all.

STEERING WHEEL VIBRATES EVEN WITH BALANCED TIRES

• tighten/replace wheel bearings
• replace tie rods
• get the front end realigned
• replace steering rack bushings with urethane
• check for free play in the spider joints in the steering column
• replace TC bushings with urethane
• new shocks

I would recommend replacing your wheel bearings, ESPECIALLY if you don't know if they have ever been done. The auto store will have them for $15ea. Also 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. A tire with a high-spot will slightly "hop" on every revolution as it hits the road. It may just be that the Z front end shake 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.

© 2008
Z Garage Engineering LLC
Hamden, CT