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My 1971 521


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Hi, new to the forum and new to buying a 521 but long time fan looking for one.  


Anyways I looked at one today that was in good shape, drove and stopped very well, little rust, interior was solid, bed was solid, couple dents but all in all a good truck. Seller told me the oil sending unit was replaced recently but looking under the truck there was oil and sludge all around the sending unit, dipstick and drain plug.  I wasn't sure why that was and I would have thought that would have been cleaned up when they replaced the sending unit or its leaking somewhere else.  Also the rear end was leaking.  I am wondering whether either of these I should be concerned about?  Tried to post pics but keep saying "you are not allowed to use that image extension on this community."


Link here:  https://goo.gl/photos/xR7EuBaFtwJ6td4w6



EDIT:  Bought it.



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(picture of differential)


Normal. If front at the driveshaft is wet the pinion seal may need replacing. In any case if you buy be sure to empty and replace the differential oil with GL-5 80w90. There's no telling when it was replaced last. Should be checked every 15K and changed every 30K miles.


(picture of front trans and engine oil pan)


Looks like caked on dirt not wet with oil. This will power wash off. If there were fresh drips I would be more concerned.



(picture of transmission underside)


Bottom transmission pan is clean and any oil has transferred back from the engine by the wind. Again replace the transmission oil with GL-4 80w90 NOT GL-5. Check every 15K and change every 30K miles.



(picture of valve cover and starter)


Hard to tell. If dipstick has lost the rubber seal blow-by will wet the block nearby. Oil senders can sometimes weep oil. The fuel pump should have two gaskets and a plastic spacer between them. These can leak and also the pivot pin on the pump body. Best to power wash and de-grease with brake cleaner and watch for wetness... then fix. 


Over all I would just replace the valve cover gasket the biggest and most likely cause of an oil leak.


Last is the crank pulley seal. These get old and drip and the fan and normal air blowing past spreads it over the engine. Check behind the crank pulley for wetness or a drip. But do the valve cover first as oil flows down hill.

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Datsun L-engine use British pipe threads on pipe fittings on the engine.  They are different from the threads used on domestic engines.  NPT will start to thread in to the engine but not seal.

Go to a Nissan dealer, and get an oil pressure switch with the proper threads.

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When u did comression was engine warmed up and throttle wide open and did u use screw type of tester.

Nah, seller did it and told me the results.  Like I said the truck started and drove without issue so I took his word for it.   The only thing I noticed was a slight hesitation around 65MPH on the freeway but cruising around it was fine. 

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Bought it and I am pumped!  Guess this truck was on here in a past life, owned by Patd: http://community.ratsun.net/user/4071-patd/  , sold to dubdlux and now owned by me.  What goes around comes around I guess.  


Some questions..

1. If I re-index do I need blocks in the rear too?

2. 6 chevy blazer rally wheels fit on a 521?  15x8 but no idea on the offsets.  

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Bought this from BAT, was owned a long time ago by @patd who sold it to dubdlux who then put it on BAT.     


Got it home today, ran damn well, some slight vibration at speed on the freeway but it hummed along at 65-70 although the speed said I was going 80.  In attempt to get the hub caps off I nearly broke my finger, seems like they have been on there a long time.  Previous owner did a fair amount of maintenance with very little miles over the past 6 years.


  1. New water pump, thermostat, and heater hoses (2010)
  2. New seals including rear main, timing cover, valve cover, valve stem, and oil pan (2010)
  3. New clutch with resurfaced flywheel (2010)
  4. New muffler and tailpipe (2010)
  5. New brake shoes all around, drums, wheel cylinders, return springs, and hoses (2011)
  6. New battery (2015)
  7. New oil pressure switch (2016)
  8. New spark plugs (2016)
  9. New front main seal (2016)


Short list of stuff I would like to do

  1. Get cigarette lighter working, its disconnected not sure why.  There is black wire w/plastic sleeve hanging behind it but no Lg/r wire that I can see.  
  2. Fuse for dash lights needs to be reset (taken out and put back in) once they stop working.  Not sure why that is?
  3. Dome light doesn't work
  4. Radio doesn't work
  5. Lower it
  6. Get some rally wheels pc'd white
  7. Yellow fogs film/tint on high beams
  8. Fix vibration on freeway
  9. Replace rear view mirror
  10. Line-x bed



Pics for clicks






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A few useful diagrams for you.  First a general wiring diagram.


Here is a lights only diagram.



What year is the build date on your 521?   Some electrical system changes were made from the early 521 trucks, to the later ones.

all 521 trucks I have seen had a six fuse fuse block.  Earlier 521 trucks had three always hot fuses, later ones had four always hot fuses.  The other fuses got power through the ignition switch.  Three hot fuse trucks had headlights, tail lights, and all other lights on one fuse.  Four always hot fuse trucks separated out the headlights on their own fuse.  Dash board, or instrument panel lights are on the same fuse as the tail lights.


There are four wires under the ashtray, there wires are for the stock radio.  I think the cigarette lighter wire comes out of the wiring harness near there, also.  The cigarette lighter wire is always hot.


The dome light wire is always hot.  The switch on the dome light grounds the light, making it come on.


The stock fuse box is barely adequate for a stock 521, with no added electrical accessories.  Use an added fuse block for anything else, including the fog lights.


A simple modification you can do to ease the electrical load on the stock fuse is to add an extra cube relay by the stock headlight relay.  You use the red with a yellow stripe wire to trigger the coil on the added relay.  The added relay gets fused headlight power directly from the battery.

Pin 86 on new relay, gets the red with a yellow stripe wire from the stock headlight relay.

Pin 85 on the new relay gets grounded.

Pin 30 on the new relay gets fused battery power.  Use at least 12 gauge wire for this.

Pin 87 on the new relay goes to the pin you pulled the red with a yellow stripe wire off the original headlight relay.  12 gauge wire here also.

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Bought it and I am pumped!  Guess this truck was on here in a past life, owned by Patd: http://community.ratsun.net/user/4071-patd/  , sold to dubdlux and now owned by me.  What goes around comes around I guess.  


Some questions..

1. If I re-index do I need blocks in the rear too?

2. 6 chevy blazer rally wheels fit on a 521?  15x8 but no idea on the offsets.  


I assume that you want the truck to sit level? If the front goes down the back should try to match it. You only need to index the torsion bars if you run out of adjustment. You will be setting the height you want so set the front and figure out how much to lower the rear and add blocks. Unlikely it will be exactly level the way you want it so adjust the front to match. Take note that extreme lowering will put the rear frame down on the axle and fuck the ride. Same with the front.


Six bolt chevy rims have the same bolt pattern. If raising the ride I'd say go for it. Lowering you'd better make sure the rims are inside the fenders.

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Thanks dubdlux, I used a pry bar to get them off but still managed to jam the shit out of my index finger.  


I don't know the build date, where can I find that? Got a link to the cube relay?  I can do that no problem just need to know what to buy.


I really want to get that cigarette lighter working and whats odd is that the black wire in the picture below is hanging down from dash in my truck, its not connected to the back of the lighter like the picture shows.    






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