• COMMON ZCAR PROBLEMS

    1970-78

  • 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.

    ONE 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 under the wiper motor 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 get blocked with old dirt and let water pool around the center wiper motor area(!)


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

    This standing water will rust the seam between the firewall and the front of the cowl. So when there is a heavy rain the cowl will fill up and 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 next to the wiper motor on 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.


    AIL-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 over a year, what a sneaky, frustrating cause. @#$%*.

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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 + wire will get 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.

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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.

 

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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 26+ 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 easist solution.

NOTE: the bearing that holds the distributor shaft wears too. You can tell wear by lightly moving the rotor 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 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. 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. The problem is that if you tighten things in one spot it seems to immediately shows up in another: these cars will find any slack in a heartbeat. If there is one thing that Datsun should have designed differently it's the rear end on these cars.

If you hear it thumping the floor behind your seat it's a broken/stretched differential mount...the rear driveshaft flange can actually jump up far enough to strike the handbrake linkage. This sounds like a ratcheting sound on hard acceleration. If you hear it farther back its likely one of the causes below:

  • - 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
  • - driveshaft bolts loose
  • - worn out mustache bar bushings (replace with urethane)
  • - 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

    Even after you try all these you may still have a clunk. The only solution then is learn to shift more smoothly.

ENGINE FAN CLUTCH IS LOUD
This is when you car sounds like a hovercraft when accelerating...the cause is that the finned viscous fan clutch on the front of the motor 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 clutch 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.

Don't worry, it's not full of exploding springs, its 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.

GROWLING FROM REAR AROUND 70 MPH
This is usually due to a worn out rear joint on the driveshaft. Go under and twist the driveshaft 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 the circips and joints. 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 and made me a custom driveshaft which was very high quality.

EXHAUST/GAS FUMES EVERYWHERE
Beautiful car, but with terrible aerodynamics on the rear. The shape sucks up and billows exhaust around the back. Opening the windows causes low pressure in the car and sucks it in. These fumes are insidious and will find the smallest opening to exploit. Check these several areas:

  • - 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 to find gaps.
  • - 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 fumes into the engine compartment.
  • - Secure and seal the vinyl panel on the inside of the hatch. If you have a 1970 with rear vents they will pour in fumes if the panel is loose. If you have missing emblems the holes in the hatch can leak.
  • - check the firewall for missing throttle boots, gaps around heater hoses, speedometer cable. I had leaks around my A/C hoses which I found were pouring in air.
  • - while driving in colder weather open the driver window slightly and run your hand across the bottom of the door sill. There is a hidden rubber seal on the bottom of the door itself which could be leaky, you can tell as you will feel cold air leaking in.
  • - 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 and behind the vinyl 'dogleg' trim panels behind the doors.
  • - The left rear fender on 280Zs has a rubber plug on the bottom edge which can also leak air in. You can see it by looking underneath next to the muffler.

  • On early 240Z rear decks look behind the plastic side panels closest to the hatch. On my 1970 there was a precise 1/16" gap where the deck and fender meet. Not a stress gap or rust hole, Datsun didn't appear to have welded them at the factory...I could actually see light from below. So I used seam sealer on them. If you have an early 240Z check yours.

  • 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. I also experienced a leaking exhaust gasket on one joint.

    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 rubber heater hose, gas eats right through it.

SUSPENSION CLUNKING ON BUMPS
I have had this happen to mine twice. I would get a strange "clunk" from the rear when I hit a bump but couldn't track it down. It sounded like the spare tire was loose, weird. It turns out the "gland nut" or cap holding the strut insert in on one strut was loose. It was letting the insert clunk up and down in the strut housing. If you live in an area with rough roads this can happen more easily than you think. Just slip a pair of thin channel-lock pliers between the coils and tighten the cap back down.

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 35 years.

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. I suspect these "jolts" you see are the regulator hiccupping if you have a 240Z. If you have a 280Z then it's likely the alternator which has the regulator built in

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 likely the black plastic ignition switch behind the key lock. It's held by two small screws, easily replaced with a screwdriver. About $25 and still sold.

FUSES KEEP MELTING (240Z)
Plagued by melting fuse wires, redhot fuses? Well, the 240 fusebox uses simple rivets and crimped wires to hold the fuse-clips together. These contact areas oxidize over 3 decades and increase the resistance in the connections. Through such marginal connections, current draw goes way up and so does the temperature.

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 and 280ZX)
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.

Don't use duct tape to seal these crack, it looks cruddy and leaks. If you can't find a new boot spend some time using black silicone to seal them properly. The bellows may have to be removed to see the cracks. The rubber is 25+ years old after all.

 

STEERING WHEEL VIBRATES EVEN WITH BALANCED TIRES

BEFORE GETTING UPSET, DO THESE FIRST IN ORDER OF IMPORTANCE

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



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